Wednesday, November 16, 2016

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.


Primo said...

I'm getting ready to attempt the repair and was wondering if you had any tips on brazing the lines to the cups. Thanks, Matt

Primo said...
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St. Lee said...

The toughest part is getting the tube positioned properly. If possible, its best to mock it up with a head and rocker box. That will also serve to hold the tube in place while you braze. (I keep some used guides around that I can temporarily install with little or no press fit) The biggest problem is that on the front exhaust there are fins in the way. Other than that, just don't use any more heat than needed, and of course have everything well cleaned in advance. Good Luck!