Broken Tranny Gear

[BBrown626]

Gray, or others,

Last weekend I was blitzing through the rhythm section at Milestone Ranch on my '04 450. It felt like I hit the brake on the face of a big whoop/double and was nearly thrown over the bars. To the disappointment of onlookers I managed to keep control and avoid a crash, but my bike wouldn't move after restarting it. It ran, but the countershaft wouldn't turn. I disconnected the chain and pushed it to the trailer.

Yesterday I took it apart and found the 4th gear was in 3 pieces. An adjacent pinion was missing 2 teeth. Another gear has damage from passing a chunk through it and a cracked tooth. Some cogs have burs on one gear/pinion. Both shifting forks have scoring from the radius of the gears. The shafts look great, as do the remaining pinions/gears. I'll be replacing 5 gears/pinions and the forks, associated gaskets, snap rings, etc... I inspected the case halves and found insignificant damage.

I found no clear cause for this casualty. One cog (on the side) looked warn rather than broken, but who can say when it happened. I frequently shift w/o the clutch. Is shifting w/o the clutch enough to break a tooth loose? Maybe I hit the shifter and dropped it a gear while hard on the gas through the whoops. Would that do it? ?

While I have it open I am changing the timing chain. Any advice on other engine components that should be checked or replaced while I have this thing in pieces?

Thanks,

Brent

[grayracer513]

3rd and 4th gear failures in the 4 speed are somewhat rare, but not unheard of. Repeated landings under power, or just the abuse of running under heavy throttle over rough ground can get the better of them once in a while.

Carefully check both shafts for straightness by turning them in a pair of bearings while a dial gauge rests on their mid point.

While the cases are apart, check the rod clearances, and install a full fresh set of crankcase bearings.

[BBrown626]

Gray,

are you suggesting replacing the crank bearings or all the bearings mounted in the cases?

Thanks,

Brent

[grayracer513]

Gray,

are you suggesting replacing the crank bearings or all the bearings mounted in the cases?

Thanks,

Brent

All of the crankcase bearings. You have to split the cases to change any of them, they aren't particularly expensive (although there are several of them), and you can't necessarily tell by looking at them how much longer they will run without failing. Just seems wise. The trans bearings are a must after a gear failure like this. The only exception would be the bearing on the shift cam, since it moves so little.

[BBrown626]

I priced them out and it seams reasonable. I had my doubts about the reliability of the tranny bearings, as they must have taken a hard hit.

Can you press them all in with an automotive type puller/press or do I need something special?

Thank you,

Brent

Brent

[grayracer513]

The only one that is a pain is the left hand main shaft bearing, which, conveniently, is the bearing most likely to fail out of the whole set. You need a blind bearing puller for that (generic slide hammer types work).

It will also help if you heat the case. Use an oven or an outdoor grill with a thermometer so the temperature can be controlled, and heat the case for 10-15 minutes at 275 degrees F. Obviously, you will need gloves to handle the case. If you get really lucky, you will be able to slap the case down sharply on a board, flat on its open side, and have the bearing drop out, but even if that doesn't work, the bearing will be much more cooperative than with the case at room temp.