Layshaft BALL Bearing Upgrade - "in situ" - Techniques And Tips Help?

B+Bogus · Dec 31, 2023

Wow! looks like a visit from the Tooth Fairy

Never seen a broken selector fork before. I can guess the failure mechanism could have started with a broken tooth, followed by a lockup with a side order of broken dogs & selector fork.

My 850 Mk2A had bad spalling on the 2nd gear pair, so I replaced them both and fitted a layshaft roller bearing.
Because shimming the kickstart shaft was causing problems with getting the lever to fit (RGM folding lever rubbing against the case) , I later went back in and fitted a TB bearing, which fixed the problem.
The gearbox had done less than 1K miles in the meantime, but the new gear pair were spalled up like the originals. I concluded that this was where both shafts were suffering maximum torsional flex.
I also wondered if those Mk2A gears went through the same heat treatment process as late 850 cams...

concours · Dec 31, 2023

B+Bogus said:
Wow! looks like a visit from the Tooth Fairy
Never seen a broken selector fork before. I can guess the failure mechanism could have started with a broken tooth, followed by a lockup with a side order of broken dogs & selector fork.

My 850 Mk2A had bad spalling on the 2nd gear pair, so I replaced them both and fitted a layshaft roller bearing.
Because shimming the kickstart shaft was causing problems with getting the lever to fit (RGM folding lever rubbing against the case) , I later went back in and fitted a TB bearing, which fixed the problem.
The gearbox had done less than 1K miles in the meantime, but the new gear pair were spalled up like the originals. I concluded that this was where both shafts were suffering maximum torsional flex.
I also wondered if those Mk2A gears went through the same heat treatment process as late 850 cams...

There is sooooo much more at play.

Kip · Dec 31, 2023

Concours, it seems like "play" might be the operative word! What happened anyway?

I still suspect condensation, poor lubrication, stacked gear shafts, and too much sitting around between rides and inspections, as the root cause. (I know for a fact that old 4-speed Harley Big Twin boxes were water traps, more of which "died" because of that, than any other issue - metallurgy, abuse, and "pilot error" included.)

I'm also of the opinion that small radius 14-tooth MS gears are overworked. Is any other gear more likely to develop bad teeth than that one?

Once this project is completed, every oil change will also include gear oil. No more letting well enough alone in the gearbox.
I favor synthetics since they "cling" far better than conventional lube. Once the film between gears shears (or drains off the teeth) in this "60hp in a 30hp gearbox" situation, you're faced with Hertzian fatigue. Hertzian contact stress refers to the localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads. Old EP90 gear oil had lower limits when it came to preventing metal-to-metal. Frequent changes of higher quality gear oil is one thing we can do to help nowadays.

concours · Jan 1, 2024

Kip said:
Concours, it seems like "play" might be the operative word! What happened anyway?

I still suspect condensation, poor lubrication, stacked gear shafts, and too much sitting around between rides and inspections, as the root cause. (I know for a fact that old 4-speed Harley Big Twin boxes were water traps, more of which "died" because of that, than any other issue - metallurgy, abuse, and "pilot error" included.)

I'm also of the opinion that small radius 14-tooth MS gears are overworked. Is any other gear more likely to develop bad teeth than that one?

Once this project is completed, every oil change will also include gear oil. No more letting well enough alone in the gearbox.
I favor synthetics since they "cling" far better than conventional lube. Once the film between gears shears (or drains off the teeth) in this "60hp in a 30hp gearbox" situation, you're faced with Hertzian fatigue. Hertzian contact stress refers to the localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads. Old EP90 gear oil had lower limits when it came to preventing metal-to-metal. Frequent changes of higher quality gear oil is one thing we can do to help nowadays.

You have it in your mind, all you've written, that frequent oil changes will prevent gearbox failure.
A lot has been documented.
The gears pictured above exloded , rolling on WOT in second. I MAY (or may not) have performed an incomplete snick into gear, I was distracted momentarily.

If your bike is to be parade driven, you should have no trouble.

Kip · Feb 3, 2024

Oops! By the time I got all the parts together and finished this task, I got going on the rest of the list for my winter project Commando, and forgot to to update this thread. It turned out I needed a main shaft first gear as much as a roller bearing upgrade for the layshaft. I also found it wise to replace the inner cover nuts with the thin-wall later (MkIII) type (Thanks Greg) and found surface rust on the shift fork shaft, so replaced that as well. All in all, a bit unexpected but nothing totally surprising. My Kickstarter was the 750 type and has (worn)splines all around - loose forever more. Rather than mess around, I went ahead and ordered the NYC (Triumph T160/RGM) type from Kenny. It will be here later today.

Once that is installed, the gearbox is done, but other items on the list remain. IF- all goes well, this thing should be easier to start, run better, and hopefully provide some (relatively) worry-free riding this coming season. Thanks to one and all for opinions, advice, and interest.

B+Bogus · Feb 7, 2024

The kickstart upgrade is a good move.
Old, loose kickstarters can be made to get a grip again by grinding off a few splines either side of the pinch bolt slot.

Layshaft BALL Bearing Upgrade - "in situ" - Techniques And Tips Help?

B+Bogus

concours

Kip

concours

Kip

B+Bogus

Similar threads