The Hodaka Club Forum

Bah, I've just installed my third countershaft in a 250SL -- the splines have been shearing on the sprocket. The problem appears to be unique to me and my 250, but that's a digression.

Anyway, on first ride the clutch is slipping now. Cable free play and actuation point seem to be in spec -- but it still slips and showed no previous instance of slipping before this latest rebuild.

The actuating lever (on the engine) has free play too. HOWEVER, could this still be a clutch disc spacer issue (too many/too thick) regardless of everything else appearing normal?

I hope it's just a solvable mechanical issue and not one of those spooky things (like the countershafts) only an exorcist can remedy.

Any thoughts or encouragement before I open it up again?

Thanks Guys!

when the bike is sitting on a stand with the rear wheel up does the rear wheel spin easy as in no drag in any gears? i can see your engine having some kind of drag in it and the back wheel / chain using the sprocket to bang the crap out of the splines, ......my mind is a terrible thing sometimes......albert

Sorry about the bad language in the subject line...

There was a perfectly rational explanation for the clutch slipping after all: an extra .5mm clutch disc spacer. No voodoo involved as with the shearing countershafts (Albert, the wheel does turn without any undue resistance).

Configuring the spacer discs to reduce free play to 5/32" on the actuating arm resulted in partly disengaged clutch (don't ask me how or why though). Reducing the stack thickness from 1.4mm to .9mm let the clutch do its job.

DO
Will we get to see you @ HD’22 next month?
Bob

Bob, HD 22 is on my to-do list. I was one of the first to sign on for the Bad Rock Ride.

Darrell

Darrell,

I occasionally drift off to sleep musing about what the heck could be causing your repeated contershaft spline failures. Still with no real brain-storms.

Question: Are your rear hub cushions and your chain tensioner in good working order?

Ed

Bullfrog wrote: ↑Thu May 26, 2022 5:06 am Darrell,

I occasionally drift off to sleep musing about what the heck could be causing your repeated contershaft spline failures. Still with no real brain-storms.

Question: Are your rear hub cushions and your chain tensioner in good working order?

Ed

Thanks Ed, at least the problem seems to be putting you to sleep -- better than losing sleep over it!

And yes, the hub cushions and chain tensioner are good. There's also that nylon upper rubbing block that was showing some wear so I just replaced it with a new one

This time I sourced an "experienced" countershaft from a late production 70A that had over 6,000 miles and (so far) showing no evidence of spline damage or shearing. My bike is is number 180 in the Model 70 production I've considered the possibility of improper hardening of first-run countershafts. That's all I can think of anyway, but haven't taken them for a Rockwell hardness analysis to test that theory.

Darrell

Now the THIRD countershaft has sheared at the sprocket . Why oh WHY?!

But I'm so demoralized that I'm not ready to talk about it yet...

Well dang! That IS depressing!

When you get to the point that you can talk about it . . .

It seems like we are seeing only two data points on these shearing failures - "New" . . . and "toast". Have there been any "mid-life" inspections which show things are starting to go south?

I know, I know . . . this particular mechanical interface should be as reliable as a rock . . . but SOMETHING is going on. Why, oh why, does seem like you need regular sprocket/shaft inspections every 100 or 250 or 500 miles (pick a number)?

OK. Here is a crack-pot idea. Have you been installing special "long life" custom made countershaft sprockets which have been hardened to just shy of diamond . . . and you've been forgetting to tell us about that? (Hmmmm, what does the interior of the sprocket look like after one of these shearing failures?)

I have one idea which might be helpful - but since it too leans toward "crack-pot" . . . I'm not going to verbalize it just yet. Oh-Oh . . . and ANOTHER crack-pot idea just came to me . . . and I'm not going to verbalize it quite yet either.

At this point, I'm more interested in deciphering why it is that Darrel has a cosmic monopoly on shearing the splines on Hodaka 250 countershafts. THAT is an interesting question! It reminds me of the time (long, long ago) when I discovered how to break the rear hub on Thunderdog's on command. A situation which was quite unusual for me, since I normally don't break things much at all. But that problem had a relatively easy to figure out solution - quite UN-like this situation.

Ed

How tight of a fit is the c/s sprocket to the splines on the counter shaft? I have seen where a c/s sprocket from another bike was fitted and it appeared to be right, but the inner dimensions were just a little off. This resulted in not enough engagement between the c/s sprocket and the c/s splines and as they wore against each other the problem got worse until the result looked like yours. If you pull up JT sprockets website it list dimensions for sprockets. You will notice some sprockets have almost identical dimensions, but one will be a mm or two less on spline height.
An example would be compare a JTF 259 to a JTF 416. They look almost identical, but one has an inner diameter of 18 mm's while the other has a 16mm inner diameter (giving it must more contact between the sprocket and c/s splines. Another would be to compare a JTF 1264 to a JTF 416. One has an inner diameter of 17mm's compared to the 16mm's of the other. Otherwise, the dimensions are the same.
Just a thought.

I would think there's some kind of drag somewhere in the drive train , rear wheel or engine that allows the counter shaft or sprocket to hammer away at each other . Just a shade tree mechanic thinking

Dirty_rat might be on to something. It's hard to tell from the pictures for sure, but it seems to show that the diameter of the sheared portion might be slightly larger than the minimum diameter of the depth of the splines on the shaft, potentially indicating that the inner diameter of the splines on the sprocket may be larger than the inner diameter of the splines on the shaft. This would leave the threaded portion of the shaft carrying the bulk of the load. He may have nailed it, I hope.

Awwlllriiiight! While I was coming up with (yet unspoken) crackpot ideas on how to "fix" Darrel's problem, y'all may have hit upon the cause of the problem! When Darrel gets to the point that he can talk about this situation, it would be good to get some accurate dimensions regarding the diameter of the "valley" of the splines on the countershaft and the inside diameter of the "peaks" on the sprockets. It wouldn't take much of a difference to seriously reduce the load the carrying capacity of the splines. (and if the "peaks" on the countershaft and the "valleys" in the sprocket were a pretty good match - the sprocket would probably feel "right" when installed)

Ed