Knucklehead Porting Aid

 

One of the things that will quickly jump out at anyone who sets out to port a set of knuckle heads is the chunk of casting that protrudes into the bowl of the intake port. That protruding section of the casting houses the threads for one of the head bolts, specifically the one that's between the two cylinders closest to the intake spigot. Unfortunately, it also happens to be in a key area which limits airflow. 

Arrow indicates the casting "lug" as found in a stock port

 When porting, generally speaking, the more of this chunk you can remove the more you can improve the airflow. However, grinding through into the threads is, . . . well, let's just say grinding through is problematic. If only there was a easy way to check how much material there is between the port and the heads if for no other reason just to cut down on the anxiety while you're grinding.

Well, as to happens there is one. Here's a little tool I rigged up that you're free to copy if it will help you out.

 The idea for this tool came from a You Tube video by legendary engine builder John Kasse. It's really just a scaled down version of a home-made tool he featured in one of his tech tips. This one is obviously modified to fit this specific task, but it's worth mentioning that the same concept could also be adapted for checking the thickness of cylinders that have been bored oversize multiple times which would be particularly useful on Knucklehead cylinders. Build it to the right dimensions and checking the thickness between the fins and the cylinder bore would be a snap rather than a guess.

The simple concept behind the tool is that as long as it's built symmetrically and with the pivot centered properly, the thickness of whatever the points on one end close down upon will give you a visual of that thickness on the other end.

                                   The tool in action on a dual carb OEM Knuck casting that has                                       already had a considerable amount of the lug removed

 For checking the Knuck head at this one particular spot, one of the straight arms has to be trimmed so it will slide into the head bolt hole (be sure to trim the "outside" edge and not the "measuring" edge) and also shortened just a bit so it can bottom out in the hole. One thing that you'll soon learn when using the tool is that as you grind material from the boss in the port, the material will get thinner at deepest part of the head bolt hole first. That's fortunate because it is the part of the hole that can most afford to be weakened and if you do grind through, it's still possible to repair the mistake.

And no, the picture is not of a Swastika.

Knuck Return Lines

Much as I love the fact that I am able to make a living (of sorts) working on Harley motors, in every profession there are inevitably some aspects of the job that we don't look forward to performing.  Sometimes there is not even a rational reason for the mild distaste that the prospect of performing the operation produces, which often leads to putting it off as long as practical.

Boring cylinders has long been one of those operations for me.  Totally irrational, I know; I have equipment that does an accurate job, and good measuring equipment that confirms that accuracy.  The fact is, my shop would probably do better financially if I spent all day, every day, boring and finish honing cylinders, yet I am thankful that the volume of cylinder boring that comes through my shop is not that high.

But then there is the other type of job that I enjoy even less.  The kind that is time consuming and difficult to produce good results, which in turn leads to being a losing proposition from a financial standpoint.  However, sometimes after years of "fighting" an operation which fits that description, you come up with a method that takes some of the pain out of it.  One of those dread jobs is what I'd like to present here.

If you've been around Knuckleheads for a reasonable length of time, you have probably noticed that some of the small oil lines on the heads which connect the lower spring covers to the back side of the rocker boxes, don't always age gracefully.  Oft times the flare that provides a seal to the rocker box is the first to cause problems, whether it be split from often over tightening, or a case of just one too many on/off repetitions.  Then there are those lines which have been in contact with parts they were not designed to share such close quarters with, resulting in spots nearly to the point of striking oil.  And lets not forget rust, because it never sleeps, and eventually that tenacity will likewise make a tube unfit for service.

A twofer: at the top center of pic you can see the tube is flattened out, and at bottom left the flare fitting has a previous emergency repair via a compression fitting

What to do?  Replace the whole assembly?  While that might be tempting, once you determine that these particular parts seem to only be sold in sets of four, and then price them out, ...ouch.  The logical thing, and what we were forced to do for many years when there were none being reproduced, is to replace just the tube.  Now, it may very well be that someone somewhere is reproducing and selling these tubes, but if they are I have not been made aware of the fact.  Instead, for as long as I can remember, I have had to fabricate my own replacement tubes to braze into the lower spring cover.  And it has always been one of those jobs that I dread, because replicating all of those complex bends never seems to go well.

For years I contemplated building a fixture for making all the appropriate bends, or rather four fixtures since each cover takes a different length and shape.  But each time I considered it, I concluded that I lacked the time to undertake such a project. Instead I would painstakingly bend each tube a little at a time trying to duplicate the original's shape.  If you have ever attempted it, you know how frustrating it can be.  The first bend was usually the only one that one could get right, from there it was a tale of bend, hold the new and the old side by side to see how well they matched, bend some more, match up, try to unbend that last one that didn't match up so well, and so on.

Here is a method that I have found to be much less frustrating, and best of all requires a minimal investment in time and money to get started.  First is the purchase of a brake and tube bending pliers.  The one pictured was under $20.  If you have previously had to fabricate your own line, you probably already own something similar.  The only other piece required is a piece of scrap aluminum thick enough to take 1/8 pipe threads and long enough to clamp into a vise.

A few tools that can help make a tough job a little easier

The fixture shown in the upper left is just a plate with two holes drilled and tapped for the same fitting as is used in the rear of the rocker box.  You want to put them as close together as possible while still allowing room to tighten the flare nuts.  Now, in the picture you may notice a couple of additional items that I fabbed up to make the process yet a little less painful.  They are merely a couple of clamps made from scrap aluminum plate by drilling two holes (the diameter of the tubing) which are the same distance center to center as fittings in the fixture.  Then cross drill a pilot hole which will be tapped on one side after you saw the plate through the center of the clamping holes.  The clamps are not essential, but I found them to be quite helpful.

To fabricate a new line, your first step is to cut a piece of tubing to a manageable length and then flare one end of it.  Note that these fittings take a single flare, not the double flare used in most brake line applications.  Once you have a nice flare on a new piece of tubing, mount it to the fixture with the original drain tube next to it, and with the fixture in a vise, commence the bending process.

With the lines side by side all that is required in your bending is to keep them running parallel

The additional clamps make it easier to keep the lines parallel to each other

Once you have duplicated the original line, all that is left is to braze it back into the lower spring cover.  It is a good idea to mock it up with the head and rocker box  in order to get just the right orientation.  Hope you haven't painted your heads yet!  One other quick tip before I go; the lower spring covers are very prone to cracking just below where the oil return line is attached as shown below:

The only thing worse than a cracked lower spring cover that goes unnoticed ...

... is four of them that slip by.

This last tip about the cracks seems obvious once it has been pointed out, but I can't tell you how many times I have had customers bring in nicely cleaned, straightened, and Parkerized covers that still had cracks that gone unobserved simply because they did not know to look for them.

Valve Stem Protrusion, Part 2: The Knucklehead

　
Now that you have been introduced to the basics of valve stem protrusion specification and how they pertain to Panheads and Shovelheads, let's go back to the beginning, so to speak, and look at what most would concede to be Harley's first modern OHV engine, the Knucklehead.

Time to "fess up." The question of the valve stem protrusion specification for a Knucklehead is one I have never been able to come up with a definitive answer to, and I have been pondering it for about 30 years. Apparently the factory did not feel it was important enough to publish (at least anywhere I have been able to find) or just overlooked it.

One of the figures I've seen offered (it was on the Internet, so it must be true!) is that the factory spec was 1.575-1.580" measuring from the shoulder on the guide to the tip of the valve. While this may be correct, no source was cited. Did it come from a factory drawing or was it info passed on from someone's step-uncle who once heard it from a guy who knew someone who worked on Harleys a lot under a shade tree in the back yard to supplement the income from his day job changing tires and doing oil changes at the local Texaco station?  Either way, this spec, to be accurate, would need to take into account the differences in the thickness between stock and reproduction gaskets that go under the lower spring cup. I cannot be sure what the OEM gasket thickness was, but from supplier to supplier I have seen as much as .030" difference in the thickness. Then if you use 2 gaskets under the intakes as the manual calls for, you have doubled any error. Incidentally, if the factory was able to hold a .005" tolerance on valve stem protrusion in the '30s and '40s, they were doing far better than what is seen from them today (admittedly a very real possibility).

Another of the "specs" I have seen given (also on the Internet, so it also must be true!) for Knuck stem protrusion is 15/16" above the top of the valve guide for the exhaust and 7/8" for the intake. Even if a source for that info was given, it would be meaningless without the dimensions of the OEM guide top.  The guides available today are not even the same shape as the originals above the flange, let alone the same height.  True as it may have been at one time, it is about as useful as giving directions to a stranger that include the phrase "turn left where farmer Smith's big red barn used to be."

One other "spec" I have seen published in a recent book, also without a source quoted, is intake 1.525" minimum/1.570" maximum and exhaust 1.575" minimum/1.620" maximum. That would also suffer from being at the mercy of gasket thickness.

I also tend to think that any stem protrusion "spec" that is given with intake and exhaust being different one from the other is probably suspect, because that would mean that without shimming, the spring installed height and seat pressure would be different intake to exhaust. I am quite sure valve spring shims were not factory installed.  My guess is that those "specs" were extrapolated due to the difference in overall valve length on Knuckles, intake verses exhaust.  Either that, or valve seat pressure difference intake to exhaust was considered acceptable by the factory.  The difference of .050" of installed height would work out to about 16 pounds more seat pressure on the intakes if KPMI's stock replacement springs are indeed made to exact OEM spec as advertised.  That is probably within the realm of possibility also, but again I would like to see a source.

And speaking of extrapolation, or my best guess if you prefer, here is my theory:

There is a chart on page 82 of the Panhead Service Manual 1948-1957 Rigid that lists specs for 18204-36 inner and 18203-36 outer OHV springs. Those would be the stock springs for a Knucklehead.  The chart lists a compressed length of 1.40625" for the outer spring under a column labeled "valve closed" along with a "valve open" length of 1.0625".  That leads me to believe that the 1.406 figure would be within the acceptable range for spring installed height. Adding the lift of a stock cam, which the same manual lists as .343" for a Knuckle on page 89, to the open height of 1.0625" gives 1.4055" which matches the 1.40625" after allowing for rounding up or down.  Now, the question becomes, does this spring installed height reflect a minimum or maximum valve stem protrusion, or is it somewhere in the middle?

Back to that table of specs.  According to it, the "Knuck" springs (we'll call them -36 springs from here on out) were used on all overhead valve engines (read: Knuck and Pan) except FLH (the higher compression 74"). That reveals a bit of a discrepancy hidden in the specifications.  Since the same valves, collars and keepers were used for both FL and FLH Panheads, it is safe to say that the -36 springs could safely be installed at the same height as the stronger FLH spring set, especially given the fact that there is no separate stem protrusion spec given for Panheads, FL versus FLH.  But the "valve closed" spring height for the FLH spring is 1.375 rather than the 1.406 of the -36 spring.  That would put the acceptable spring installed height of both spring sets somewhere between those two figures.

Interestingly, if we give the 1.375 figure a +/- tolerance of .005" we come up with exactly the 1.370" to 1.380" recommended installed height for KPMI's "stock replacement" Knucklehead spring sets, which are claimed to be "manufactured to exact O.E.M specifications."

Now it happens that I have measured enough Knuck valves, springs and collars over the years to confidently say that the spring installed height on a Knuckle will be .200" less than the valve stem protrusion measured from the tip to the top of the lip on the guide.  That .200" figure is valid when using stock spring collars and valves with stock keeper groove location.  It is also subject to the slight variation resulting from manufacturing tolerances.  That means if we were to take the 1.370" spring installed height and add .200" to it, we could safely extrapolate (there's that word again) a 1.570" minimum valve stem protrusion.  If we then want to take a stab at a maximum stem protrusion, I would suggest the same .045" spread that the Pans and Shovels use, resulting in a maximum spec of 1.615". 

But remember now, while that may provide a stock stem protrusion spec (depending on whether you buy into the multiple assumptions and extrapolations which I have made or not), this will only get you to the correct valve spring installed height.   One still needs to take into account the discrepancy in thickness of the gaskets under the spring cups if you are really concerned with getting the valve to exactly the same relationship to the head and rocker arms as when it left the factory.  Back here in the real world, though, the effects of the gasket thickness on rocker geometry are minimal.

In fact, I would go back to what I presented in the previous stem protrusion post about how changes in valve lift affect theoretically correct rocker arm geometry. If you are running a stock lift cam, then you are done. As I mentioned, according to the Harley's service manuals, the lift of a Knuckle cam is .343".  If anyone is wondering about this seemingly odd number, just convert that figure into a fraction and you will see it was quite obviously a rounding off of 11/32" - over the years Harley has been very comfortable with the use of fractions in their design parameters.   Incidentally, if you notice that I have been playing fast and loose with the terms cam lift/valve lift here when writing about Knuckles, its because the 1:1 rocker ratio actually makes those figures interchangeable, unlike other OHV Big Twins.

But if you simply read cam manufacturer's literature you might not realize that the stock lift was only .343".  The Andrews "S" grind, which is advertised as a stock replacement for restorations is .355" lift.  Lieneweber's mildest Knuck cam, the "0", is still a bolt-in but has .365" lift.  Back when Sifton was Sifton, their only Knuck grind came in at a whopping .450" lift.  Our friends in Viola seem to be the only manufacturer who makes a true stock replacement grind (even if it is listed as .346" lift). 

Using my "theoretically correct rocker geometry" method of adding 1/2 the increase in valve lift over stock to the minimum and maximum stem protrusion specs, one can see that even the mild bolt in cams add a little wiggle room.  The 110 Sifton on the other hand, coming in at .106" more lift than stock adds a full .053" to the specs.  In other words, if you accept my extrapolation (had to get that word in one more time) your stem protrusion specs would go from 1.570" minimum/1.615" maximum, all the way to 1.623" minimum/1.668" maximum.  That would, of course, create other issues that would need to be addressed, such as spring pressure and installed height, not to mention top collar to rocker arm and cover clearances.  But all of that will need to wait for another post.

One last point.  the figures I present here are my best estimate based on the numbers we do find in various factory service manuals.  I will be happy to print a correction if someone can provide their source material for conflicting numbers, or provide reasoning that improves on my own.  By no means do I mean any sort of insult to those who have presented different figures.  It is entirely possible that the whole concept of minimum and maximum stem protrusion specs was not even on the factory's radar before the printing of the Panhead service manual, and was merely left to the common sense and/or whims of the re-builder.

And in case anyone is not yet sure, the word of the day was, as you probably guessed, "extrapolation."

Valve Stem Protrusion; Knucks, Pans, and Shovels

Harleys are very rebuildable, and I would go so far as to venture that they may be among the most commonly rebuilt (using the term "rebuilt"somewhat loosely) of any engine family in existence. Such a supposition is somewhat bold, given the minuscule number of Harleys compared to the vast oceans of, say, small block Chevys. But face it, which engine is more likely to wind up in a scrap yard when it is in need of major repair?

Given that, along with the often less than spectacular life span of a top end rebuild on Knuckles, Pans, Shovels and Sportsters, many if not most have seen multiple valve jobs over the decades. Naturally with each valve job performed, the valves will seat a little deeper in the head. The method of gauging how much deeper is via the valve stem protrusion specification. Valve stem protrusion is one of those specs that is sometimes overlooked and to some extent misunderstood when dealing with Harley heads.

At issue are a several things. In no particular order; valve spring installed height, shrouding of the valve in the chamber, compression ratio, and finally rocker arm geometry. Having less than the minimum can lead to the devastating result of your valve springs reaching coil bind while your cam is still trying to lift the valves higher. Not a good situation and can usually be summed up as 'broken parts."  On the opposite end of the spectrum is the Panhead that looks as though the pan covers have been bashed out with a ball peen hammer (because they have indeed been bashed out with a ball peen hammer) so that the valve spring collars would not hit them.

Shrouding of the valve in the chamber from the valve being too deep is fairly easily remedied by a judicious modification of the chamber during the process of a valve job, though this too can overdone resulting in issues down the road when new seats are installed.  Along with deep valve seats comes a reduction in compression ratio (aggravated via de-shrouding) by making the chamber larger.  That may or may not be an issue depending on a number of factors.

Valve train geometry is also at issue, but I will attempt to address that later in the post.

To examine this subject I would like to start in the middle and work our way forward in time before going back to the beginning - that beginning being the Knucklehead.

On page 75 of the Harley Davidson Panhead Service Manual - 1948-1957 Rigid, we find what seems to be first official mention of the specification (at least that I can find).

The spec, which the drawing refers to as "Valve Seat Tolerance" is pretty self explanatory. It is the distance from the tip of the valve stem to top surface of the collar of the valve guide. The illustration also shows a gauge which was available for those lacking precise measuring tools or for quick checks. The gauge is simply a cylinder that straddles the guide. The "step" at the top of the gauge indicates minimum and maximum height; if the tip of the stem falls between the top and bottom of the notch, the stem protrusion is within spec.

The 1978-1/2 to 1984 FL/FX 1200/1340 4 Speed Service Manual (note the title may not be growing in length but it certainly is in use of numbers) shows the same illustration (page 3-18) for 1979 and earlier, but it might be worth noting that it offers a different illustration and spec for 1980 and later.

The difference, at least in part, is due to the changeover to valve guide seals. Earlier heads, both Pan and Shovel, only required a machined pad that was at least the diameter of the valve guide collar to locate the guide since the lower spring collar rested on the collar of the guide. The addition of seals made it necessary to rest the lower spring collar directly on the head to provide room for the seal, so the machined portion of the spring pocket was increased to the diameter of the lower spring collar.

Late vs Early

At first glance one might assume that the different spec is due to taking the measurement to a different surface, since it is now from the tip of the valve to the surface that the bottom of the guide collar seats against. And maybe that's the case, however, things don't seem to quite add up. If the collar on the guide is nominally .100" thick, then all is well. Add .100" to the early 1.500" to 1.545" spec and you come up with the '80 and later spec of 1.600 to 1.645". Ignoring the '80-'81 guides that used a .075" snap ring instead of having a guide with an integral collar, there is still the question of the gaskets that were under the guide collar on earlier motors. I had to look pretty close to even find the part number (18196-51) for this gasket in a Harley parts book since it does not appear in any later copies, though I have a small collection of them left over from top end kits. Measuring a random sample of these showed that they ranged in thickness from about .030" to .040". The James Gaskets catalog lists them as .031" thick with the application being 1951 to 1978.

Hmmm,... so with a window of only .045" in minimum and maximum stem protrusion, we find a variance of at least .030" just in whether or not a gasket was installed under the guide when rebuilding. And what about '48 to '50 Pans and '79 Shovels? Won't they show up as nearly at maximum protrusion right from the factory? And what does that mean when considering '80 and up which certainly never used the gasket? Now the .100" difference in stem protrusion spec doesn't add up so neatly because you have an "effective" guide collar thickness of .130" (collar + gasket) for many years.

Add all of this together and I think its safe to conclude that stem protrusion specification is probably not something will "make or break" your valve job unless you wander too far afield. My guess is that the spec was added after the fact as a guideline for mechanics rather than a part of the original design parameters of the Motor Company.

And if all doesn't throw enough margin of error into the equation, then consider this. If the Motor Company's stem protrusion specs theoretically provide correct valve train geometry (and that is a gigantic stretch given shops such as Baisley High Performance have presumably made a fair chunk of money over the years from their service of correcting Harley rocker arm geometry), then that still means that when you increase valve lift via a performance cam, you have also changed the stem protrusion numbers which should theoretically retain correct geometry.

Here is basically how it works. If you were to draw one imaginary line through your pushrod and another through the rocker arm's ball socket to the center of the rocker shaft, when your cam is at one half of its lift, the line should form a 90 degree angle. Likewise, an imaginary line from the center of the rocker shaft to the pad of the arm should also form a 90 degree angle with the centerline of the valve stem at that same half lift point. That way at zero lift the line through your rocker arm should be the same amount below 90 degrees as it is above 90 degrees at full lift. But that means that if you increase the lift of the valve with no other changes, then the angle with the valve closed will remain the same , but the 90 degree relationship between pushrod and rocker will no longer be at 1/2 lift. To get back to the theoretically correct valve train geometry you would need to lengthen the valve by an amount equal to 1/2 the increase in lift. Or, you could get the same effect by sinking the valve that amount. And guess which is easier and more cost effective, sinking the valve or having a custom valve manufactured?

All of that is to say that with a performance cam, the theoretically correct stem protrusion increases at a rate of half the increase in valve lift. In practice this also has the added benefit on a Harley of providing the increased valve to valve clearance during overlap (commonly referred to as Top Dead Center lift) which is needed for those performance cams.

Now, with all that to digest, I'll pause briefly before continuing with the question of valve stem protrusion on a Knucklehead.  Stay tuned.

Aftermarket Knuckle Heads

This is not the sort of post that I enjoy writing.  I would much prefer to write a glowing report on a good product.  On the other hand, these things are not cheap, so I do believe it is reasonable to sound a warning so that buyers can make an informed purchase. 

Reproduction Knuckle heads from V-Twin Manufacturing.  The "issues" I will list range from minor annoyances to full blown problems.

First let's look at the annoying things.  The black paint on the heads is thin to the point of being translucent in many places, except of course in the areas that have runs.  As it turns out the runs are just as annoying as the see though if you opt to blast it off for a full refinish since the runs do a pretty good job of resisting removal with glass beads.

Speaking of paint, the heads were obviously painted before machining operations were performed, leaving large areas of bare cast iron.  Notably missing paint are the large spark plug "wells" and the tops of the rocker box supports.  Perhaps for this reason the machined surfaces were not deburred leaving sharp edges, many of them sharp enough to cut you quite easily when handing.  As it turns out, that can be VERY annoying.

The set I purchased was the version without rocker boxes and shafts, so they came without the upper rocker cover tins installed, but gaskets for them were included.  Upon inspection, they found a new home in a trash can, since they were so dried out and brittle that clearly  any attempt at installation would have been an exercise in futility.

The spring cups, or lower covers as they may also be called, have a nice Parkerized finish, and seem to be fairly good stampings (better than those from the same vendor a number of years earlier).  The brazed in oil return lines, however, have a copper plating which does not "take" the Parkerizing.  That may be a good thing in some ways, since the color may discourage some from trying to pass them off as originals.

On to what I consider a little beyond annoyances.  The valve spring are green.  So, what do you have against St. Patty's day, you might ask.  Well, green is not my favorite color, but this goes a little past interior decorating choices.  The valve springs are painted green.  In fact they are thickly painted green, possibly with a brush from the look.  Thick to the point of chipping off.  I can't say just what chunks of this green paint would do to an engine, or where it would ultimately wind up, but its certainly not something I would want to take a chance on.

The heads come with plumber style intake nipples installed.  In fact, they are installed with a "stock style" rivet to keep them from turning.  And when I say "stock style rivet" it is because the rivet is of the 1/4" diameter oversize normally reserved for a damaged hole on a used and abused head.  Too bad about that too.  Once the oversize rivets were removed, the nipples could be removed easily enough, meaning they were not installed very tight to begin with.  That added to the fact that the nipples had been installed with no type of sealer, leads one to conclude that the possibility of intake air leaks would be somewhere between likely and inevitable.

Next up is the alignment of the spring cups.  Keep in mind that these are held in place by being sandwiched between the valve guide and the head, so they need to be in the right position before the guide is installed all the way.  I keep a spare set of rocker boxes (knuckles) with shafts (no arms) among my special tools for just this purpose.  That way, I can insure that the spring cups align properly with the holes for the rocker shafts and that the other end of the cover fits into the hole in the rocker box.  In the case of this set of heads, not only did the rocker box end of the spring cups not line up with the knuckles, there was a good sized gap between the cup and ear on the head where the rocker shaft  passes through it.  Any attempts to correct this without driving the valve guides partially out would result in bending the lower spring cups, possibly with further damage.





Hard to tell form the poor photo, but this shows daylight between the spring cup and the rocker support ear on head



Going a little deeper yet, I found that the I.D. of the valve guides to be abnormally rough; not necessarily a good thing for longevity.  But, as it turns out, that would not be a problem after all, since the valve to guide clearance was too tight, meaning that by the time you honed the guides for more clearance, they would likely have a smooth interior.  Measuring the valve to guide clearance with a dial ball gauge showed .0022 to .003" on the intakes and .0034 to .0055 on the exhausts.  However, the fool proof final check for guides (at least in my book) is checking with a plug gauge (also known as a go/no go gauge).  This takes into account a valve guide bore that is not straight, something the ball gauge will not tell you.  In this case, a plug gauge .001" larger than the valve stem diameter would make it through one intake and and .002" larger on the other intake.  On the exhaust side a plug gauge .002 larger would go through one and .0025 larger on the other.  Stock clearances for a Knuckle are .004 to .006" clearance on both intake and exhaust.  I cannot imagine that these heads would have lived at these clearances.

The next item is only a problem if you plan to use these on a 61 inch motor.  The counter bore for the fire ring in the head is a slight interference fit on an OEM 61 inch Knuck cylinder.  That doesn't affect you if you have a 74 inch since there is no fire ring on the larger cylinder. 

The last item on my list does not really fit into either the annoyance or the problem column, and so possibly not worthy of mention, but I won't let that stop me.  Both exhaust valves had been treated to an approximate 45 degree cut on the combustion chamber side of the O.D.  I have seen the claim in print that this enhances flow.  It does not.  My guess is that this is an old wives tale started because someone saw a set of high performance ported heads with this modification and assumed it was for better flow.  In actuality, this extra angle is a last resort option for valve to valve clearance during overlap.  If one had a finished set of ported and flowed heads with less than the minimum required valve to valve at TDC, one might cut an angle on the margin of the exhaust valve only (because the resulting flow loss would less costly there).  Many years ago I tested this on my flow bench, and the result was so profoundly bad that it made an impression.  The margin thickness on a valve can have a large effect on its flow characteristics.

That pretty well wraps up this product review.  As I stated at the beginning, I wish I had better things to say about these heads, but there is this:  I think we can all be thankful that V-Twin put these heads into production.  The supply of repairable original Knuck castings is fast dwindling.  I believe they would be a better value if they were available as bare castings, but still, better something to work with than nothing at all.

One More Thing for Us Knuckleheads to Worry About

Or, to be more accurate, one more thing for those of us who are Knucklehead aficionados to worry about; but that wouldn't have fit in the title box.

One of my long time customers who goes by the name "Tom" (and I suspect it may be his real name) has had the same Knuckle for as long as anyone around here can remember. Over the years, I have had my hands on and into most of the parts of his engine, but never all at once. You see, Tom is just one of many Knucklehead owners who like to do as much of their own work as possible. Back when many of us started riding Knuckles, this was often out of necessity as much as choice, paychecks being what they were.

In any case, somewhere between the turn of the century and 2005, Tom had me order up a set of new reproduction Knucklehead tappet blocks for him. I really don't recall the specific occasion, whether it was a broken flange, or maybe it was Valentine's day and he wanted a special treat for the old gal. I ordered a set from Flathead Power.

At that point in time, Flathead Power was in no way connected with S&S - it was still "in transition" between its founder, Anders, operation in Sweden, and the acquisition by S&S. That transition period, and the unscrupulous characters involved have been gently exposed elsewhere, so I won't comment further.

Tom installed the FHP lifter blocks with a new set of lifters, and went on his way - which way consisted of putting lots of miles on his '42.

Fast forward through several years of hard riding, and Tom found himself in the need of a complete rebuild following a catastrophic parting of the ways of many of the engine parts which formerly made up his '42. The word grenade could be aptly applied.

As part of the resurrection, Tom opted to use another Flathead Power product which he had acquired, that being a set of FHP Knuck heads (also pre S&S vintage). Here again I was called into the act to provide oversize intake valves along with porting work. Knowing that the master plan called for a high lift cam (by Knuckle standards) I was very careful to get the stem protrusion on all four valves in just the right place to provide for a combination of the correct valve spring installed height and retainer to seal clearance while keeping the guide as long as possible to promote longevity. That is why what happened next left us scratching our heads.

Because of the special order 3-5/8" bore pistons which were chosen to match the 4-9/32" stroke flywheels and provide his targeted compression ratio, Tom mocked up the new engine parts with clay in the valve reliefs to be sure clearances were sufficient. Immediately a discrepancy became apparent. The rear intake valve to piston clearance was approximately .100" more than the front intake. Puzzling to be sure, but a problem...? If this had been a well used set of heads with untold numbers of past valve jobs, it would not have been too surprising, but that was not the case here. Suspecting a possible, albeit unlikely problem with the new Leineweber cam, Tom substituted his older, milder Leineweber cam. Same difference in clearance front to rear. Yet another check with a stock Knuckle cam gave the same results. Mr. Leineweber's name was thereby cleared of any crime in this case.

At this point I was starting to worry that I had gotten the stem protrusion off by .100" on one valve - not such a stretch given the human capacity for mistakes and the fact that my stem protrusion measuring device features a dial that measures .100" per revolution. I had Tom bring the heads back in so I could double check my work. To my relief and consternation, the problem was not in the stem protrusion.

My next thought was that perhaps there was a difference in the height of the machined surface that the valve guide bottoms out against from one head to the other. Some careful measurements which involved placing the head gasket surfaces on a table and dropping a steel rod through the guides proved this also was not the culprit.

I was nearly out of ideas, but there was one logical check still to make. I set up the lower end for my '46 with a degree wheel to perform what is commonly known as "degreeing a cam." Finally! By checking the opening and closing events with both a stock set of lifter blocks as well as with Tom's FHP blocks, it was obvious where the problem lay. The rear intake was opening 27 degrees later on the FHP block compared to both the stock block and to published specs for the cam (measured at .020" lift). And of course, checking the tappet lift at TDC, showed the difference between the valve to piston clearances which Tom had found with clay. The timing for both the exhausts and the front intake all matched those taken from stock lifter blocks. Now the only puzzling thing left to this story is that there was no large noticeable loss of performance when Tom installed these lifter blocks! I certainly would not have expected that.

The drawing below should help you visualize what the problem is, despite the sore lack of artistry. It is not to scale whatsoever, but shows the relationship between the tappet bore and the cam lobe centerline in a way that (I think) makes it understandable.

However, a little closer look at the figures gives a clue. Looking at the .053" lift timing, the difference between the FHP and the stock lifter block shrinks to 20 degrees on the opening side and 16 on the closing. That puts the timing on this rear intake, when used with this performance cam, pretty close to that of a stock Knuckle cam. In essence, for several years, Tom's '42 was running with a "hot" cam on the front cylinder, a hot cam for the rear exhaust, and a stock cam for the rear intake. My guess is that had he been running a stock cam, the performance loss would have been much more noticeable.

An important note. When this problem became evident, I contacted the gentleman at S&S who heads up the Flathead Power division and was pleased to find out that they had found the same issue and corrected it before they went into production, so you can rest assured that if you purchased FHP lifter blocks after S&S took over, they are machined correctly. I procured a new S&S block for Tom and he can attest that the valve to piston clearances now match front to rear.

One other note. I have no reason to think that ALL the pre S&S FHP rear lifter blocks suffer from this defect. It could very well have been just one run of the blocks made during that "transition" period. But that brings us back to the title of this post, doesn't it?