Thursday, July 26, 2012

EL Bonnie, Part 2: Never Easy

In my last post on EL Bonnie, I stated that the next step would be to mock the engine up to check/blueprint the breather timing. As is so often the case, easier said than done! My intention was to perform this quick and dirty, without regard to cam bushing clearances, but no such luck. I knew that I was dealing with an inferior aftermarket cam cover, and so at some point the bushings would need to be replaced and line reamed for proper fitment, but I thought I could get by with them for now.  The lineage of the cover was quite evident.  A certain company who will remain nameless to protect the guilty, reproduces these covers and puts them on their reproduction Knucklehead motors.  I have seen one other in the past; it too had damage to the bushings from misalignment.  One has to wonder how big a hammer it took to get one of these covers installed the first time.  It seems that S&S made the right call in casting their name into the covers they make, if for no other reason than to keep them from being mistaken for these gems. 

Did I mention that this motor is being done on a budget?  It has much in common with something I would build for myself in that respect; a lot of "spare parts" coming together,  in some cases those parts finding their way to the build based on availability and price rather than on fitness.

Before assembling the case halves for the mock up, I put the cam into the gearcase with the cam cover to ascertain how much it bound up in the bushings- the answer being plenty! Still thinking I could get this done quickly, I chose to line ream the cover bushing an extra couple thousands (the particular reamer I use for this operation is adjustable) since that would surely alleviate the bind and keep things moving. Wrong again! Apparently even the additional clearance was not enough to compensate for the mis-alignment between the case and cover. Time to re- think this.

After an appropriate bit of soul searching (to make the decision sound infinitely more dramatic than it actually was) it appeared to be the perfect opportunity to follow the old adage; when life gives you lemons, make lemonade!

The cam choices available are a (new) old Sifton 110 or an S&S FHP 420.  Both of them happen to be set up for a Torrington needle bearing in the crankcase rather than a bushing (the shaft for a Torrington will be approximately .0007" larger O.D. than one for a bushing).  That means that either the crankcase cam bushing would need to be reamed oversize (the original cam bushing had enough wear that it already fit) or the case would need to be bored for the larger outer diameter of the Torrington.  The bearing would have the added benefit of slightly less friction, so it seemed that the logical thing to do would be to use a Torrington on both ends of the cam.

Now, machining to install a bearing in the crankcase is pretty straight forward:  indicate in the existing hole and bore it to size.  The cover is an entirely different matter though, especially in this case, given there is good reason to suspect it was manufactured with the hole in the wrong place.  I decided to create a template.  I already had a 3/8" thick aluminum plate with the two dowel pin holes correctly located.  By installing the plate on the crankcase half and mounting it on the mill, I was able to indicate in the cam  bushing hole, and then going through the bushing hole, bore the aluminum plate. 

Indicating case bushing hole

Boring hole in template

Indicating template hole

Once I had a hole in the template, it was simply a matter of fabbing a couple extra dowel pins to align the cover to it.  Fortunately, at some point in the distant past I had built a fixture for holding generator cam covers level while installing and pinning bushings.  This made mounting the cover in the mill quick and easy.  Then, by indicating in the new hole in the template, I had the correct relationship between dowel pins and where the new cam bearing was to be installed.  BTW, the original hole in the cover checked as being only .006" off: I expected worse.

Boring cover for Torrington bearing

Once the new hole was bored and a bearings installed in both cover and case, another test fit with right case, cam and cover gave the results I was looking for: a totally free spinning cam!  Since I was in cam cover mode, I also tackled the pinion bushing.  I chose to go ahead and try installing a new bushing and line ream it, rather than going to extreme measures.  Kind of a "why go looking for trouble" approach, and in this case it paid off.  Another test fit with the cam cover bolted on the right case and the new S&S pinion shaft with bearings in place resulted in a very pleasant surprise.  Absolutely no binding even with only .0007" shaft to bushing clearance!  It appears that the cover manufacturer managed to get half of the bushing holes in the correct place.

Checking pinion shaft for binding

By the way, if any of those of you who are anxiously waiting for this motor are wondering, you may feel better knowing that the writing is lagging behind actual progress.


Knucklenutz said...

Great News Lee :
We have Fairbault Harley-Davidson on board. They have volunteered their ! dyno for break-in and tuning

St. Lee said...

That's great John, though this will be a real racing motor, and so won't need any break-in; at least not in the traditional sense. The dyno tuning will be invaluable though!