Its Back to the Drawing Boards for me maybe

[David Jackson]

I took a look at the nylon chain tensioners from my HD engine after somewhere between 4,000 miles and 5,000 miles at the very most. They have lots of pits in them where the chains rub. The edges are not disintegrating but the contact patches are pitted. The question becomes, "where are all the little pieces of nylon which used to be part of the shoes?" So many times when a motor comes apart it is expensive just because when parts are measured or just when seen, you will say"Oh I can't put that part back!" even though the motor was working OK before it came apart!

Anyway; four to five thousand miles is really kind of crazy for nylon shoe life. And so ... back to thinking about gear drive cams. I have only carefully listened to one gear drive cam TC engine and it is silent at idle; but whines at even moderate throttle. I called Bobby Wood and asked him about his belt drive system, because it is supposed to be quiet; and when it might be available, he said 60 to 90 days and cost around $800. He is still deciding on whether to go wet or dry he said. He also said that gear drive cams should be silent if the cam drive gears are sized correctly. HD used to color code those. On his site is a method of checking gear lash. He said if it is less than .001" the drive will be quiet. He also mentioned runout at the pinion shaft; the website does not say but I seem to remember something about .003" or less. Apparently if both those specs are met a gear drive cam set will be quiet, he says.

Mike; what do you think? Can the gear drive cams be made quiet? If not, I suppose I can run nylon shoes for one more summer until the belt drive system gets perfected.

(PS the jugs are not in at the local dealer yet so the cases have not been machined yet. Do you need some $$ to hold the breather parts?)

Regards;

David Jackson

[Mike]

No need to hold parts, we stock them normally. Bob Wood is correct in that if the tolerances can be met, the gears will be quite. The problem is, 1; How do you correct pinion runnout of more than .003?, new crankshaft?, 2; S&S only offers one over/under gear size, if these do not correct lash then you are out of options, so the potential for noise is still there. A whine indicates too tight of a gear fit, and most (not all) engine builders would prefer a loose fit vs. tight due to gear wear and heat buildup. Note that the noise is not a problem as far as engine performance and longevity is concerned. The belt drive should be very quite. Does the $800.00 include cams?
Regards, Mike

[David Jackson]

Hi Mike;

Thanks for the heads up about parts being in stock.

1. I don't know how you correct pinion runout; remember I am just an ignorant layman here. I leave that sort of technical
work up to the experts. If you have no answer then I guess the problem is unsolveable except with a new crank assembly
and it could be out as well! What that means in the real world is that it may be impossible to correct the noise issue of it is
partly caused by a crankshaft/rod assembly being out of true.

2. I will have to check but somehow I got the impression (and it could be the wrong impression) that Bobby W. has different
size gears available exchange, if they are exchanged before the motor has run. I could be wrong about that, it may be that
B.W. has only the S&S gears, and I don't know how many sizes are available.

2a. If whine is cause by gears being too tight, what is too tight? If the outer diameter is shaved does that solve the problem or is
the problem caused by teeth meshing too far into one another; as in the base circles being too close to one another?

2b. I do understand that the noise will not affect performance. I have tinnitus and that sort of steady whine is something which
would upset my ears and cause buzzing.

2c. I don't think the $800 includes any cams.

2d. Of course any time a developer of a new product says "60 to 90 days" you could be looking at a much longer time than
that for actual product availability; which is one reason for going back to the drawing boards about gear driven cams for
me and my motor.

A NEW QUESTION !! Have you and your techs any experience with polishing cam drive chains? If you have does it help? Also; have you found cam chain tensioner nylon shoe debris in any critical engine cavities, impeding oil flow to critical areas and things such as that?

Regards;

David Jackson

[Mike]

A tight gear fit is a function of the "base circle" mesh, that's a good simple analogy. Gear tooth profiles are extremely complex and even with todays grinding technology, tolerances are difficult to hold. The over/under size gears are really just gears that are out of spec. I do not know if other gears are available, specifically sized. I'll do some checking.
You are correct about the crankshaft runnout. Even a new assy may be out of true. TC cranks are difficult to correct in some cases, although a spread condition usually can be improved. We check crank trueness whenever they are out of the cases and correct what we can. The guys at Baisley are working on fixturing to correct alignment but I do not know when it will be done.
There is a concern that tensioner material could find it's way into cavities and creat blockages or cause scoring. We have not seen blockage but have seen scoring in the oil pump return gears believed to be caused (in part) by tensioner material. This has been one of the main arguments in favour of the gear drives. H-D's thought is that the motor is capable of processing this material without undo harm.
Polishing the chains is now done in the Jims's 120's. It's curious because H-D's position has been that you cannot adequately remove the polishing compound, thus risking motor damage and they have strongly recommended against it (although tensioner material is OK!?). Apparently, Jims (or the chain supplier) has solved this problem. It might be neat to order the chains from Jims
Regards, Mike

[David Jackson]

Hi Mike;

There's an IDEA! Ordering chains from Jim's.

Yes it is interesting that the engine can gobble up nylon and that a tiny bit of polishing compound is a problem.

Regards;

David J.