&#%@+ 250SL!

[Darrell]

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!

[givergas]

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

[Darrell]

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.

[bobwhitman]

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

[Darrell]

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

Darrell

[Bullfrog]

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

[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

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

[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...

[Bullfrog]

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

[dirty_rat]

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.

[givergas]

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

[ossa95d]

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.

[Bullfrog]

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

[Darrell]

Alright, I think I'm ready to talk about this now -- and apologies for the bad language in the subject line.

Here's an incident record of my 250SL counter shaft history:
1. At 6244 miles the STOCK and ORIGINAL counter shaft sheared. I sourced a NOS counter shaft and put the engine back together with the original 14T sprocket.

2. At 6800 miles I decided to move up to a 15T sprocket to make the 250 a bit more highway capable. Never could find the 15T Hodaka sprocket, although they seem to have been available one time. Hodaka-Parts has a listing but no inventory. But back in 1981 Cycle World had a Hodaka parts interchange that mentioned, in part, that the Honda XL250 CS sprocket is compatible. When Mike Perret was prepping his 250SL to ride across the country from Pennsylvania to Hodaka Days in 2017 he installed an XL250 sprocket.

3. Further along and rolling up to 9100 miles the NOS countershaft sheared. To replace this one I chose a counter shaft that had done 6600 miles before its bike became an eBay donor, speculating that an "experienced" part might prove more reliable in case the first run of shafts were not properly tempered (my bike is number 180 off the production line).

4. Now, at 10,000 miles this one sheared again... And to note: both sprockets have no discernable or measurable wear or damage.

Now I've acted upon Ed's and Dirty Rat's aforementioned speculations about the sprocket dimensions and have brought out the calipers to measure the I.D.s of the stock and original CS sprocket and the schematic sheet for the 15T I switched to:

Stock CS sprocket:
Distance between the valleys = 25mm
Distance between the peaks = 21mm

Brand X 15T:
Distance between the valleys = 25mm
Distance between the peaks = 22mm

The width of the valleys on both sprockets is = 6 mm

So, the smoking gun is identified by the distance of an extra 1mm between the peaks?

To the eye when physically matching the sprockets the mm is barely discernible.

But when I split the cases to replace the counter shaft and go back to a Hodaka sprocket I still won't be resting easy because of the circumstances (stock and original parts) of the first.

Anyway/ennyway it's good to get this matter off of my chest. In the near future I'll have something to say about the stupid breaker points issues (2X so far) with my 94 Wombat, it's another one-off, never-before issue again I'm sure.

Darrell
Over here in Nanaimo BC

[dirty_rat]

Only thing I might add is to insure that the countershaft sprocket nut is tightened properly and checked regularly for tightness.

[Bullfrog]

So I did some "back of the napkin" calculations . . . and those non-OEM sprockets result in a 25% reduction in the contact area between the contact faces of the countershaft splines and the contact faces of the countershaft sprocket splines. That is obviously not good for long term reliability (as proven by your real world testing). You are going to have to find a sprocket which matches the countershaft splines. The dividing line between "works well in the real world for a long time" and your "works well for a short time" situation, is somewhere between 100% spline contact and 75% spline contact.

Um, does your Wombat ignition issue relate to a broken blue point wire? If so, you are not the only person in the world to experience it. (Whew! I think, maybe.)

Ed

[Bullfrog]

Hmmmm, just for kicks (and to assure that assumptions don't jump up and bite you someplace again), how about measuring the minor diameter and major diameter of the splines on the actual countershaft? It would be a bummer to source a new sprocket with a 21mm inner diameter and find that the countershaft could take one with a 20mm inner diameter. NOTE: I'm suggesting this because you are (to my knowledge) the only person in the world to use up a countershaft with a "stock" sprocket . . . what if it wasn't stock either?

Ed

[ossa95d]

Excellent suggestion

[Darrell]

Thanks especially Ed for your "Whomping wads of wondrous wisdom...". Shades of the original Resonator!

Measuring the minor and major diameters of the shaft spline equals 20.5 mm and 24.5mm respectively.

The possibility of the bike coming equipped with a non-Hodaka 14T sprocket might be slim as the bike only had 830 miles when I took possession and was complete -- except for missing the valve core from the front tire. The PO tossed it out early in its life when the kick start shaft stripped. It got kind of waterlogged over the decades before I brought it home.

The original 14T sprocket has no markings to be seen whatsoever.

Now, I'll replace the counter shaft as I've always done before (expecting favorable results every time). I'll err less on the side of insanity by using a known Hodaka sprocket. And as a hedge maybe I should try to corner the market on the world's supply of remaining Hodaka 250 countershafts