Shifting problem identified

[brian kirby]

I dont know about you guys but I think this is pretty likely to be the source of my popping out of gear problem on the MC5 400:



I've seen a lot of damaged shift forks, but I've never seen one of those pins that rides in the grooves of the drum damaged like that. There is also damage on the shift fork opposite that, and the dogs on the gear that is engaged in that direction (3rd) is also damaged.

Brian

'72 Berkshire

[slvrbrdfxr]

Brian,
I'd say you found the culprit. Don't think I've seen one wear like that either so wonder what caused it to wear like that ?? Could it possibly be worn from riding with a toe resting on the shift lever ??
Dave McCullough

[brian kirby]

That could be Dave. The bike had the short shift lever when I got it, and you could hardly ride without hitting the shifter. I have since cut off the tip and welded on an extension with a folding tip. I'm looking forward to riding this beast without having to constantly worry about it popping out of gear and killing me.

Brian

'72 Berkshire

[G Ellis]

Brian I have seen this on a few motors I have rebuilt. Make sure you look at the gear clusters. Make sure all of the bearing cages are there. Make sure that the shifter drum has no grooves in it.If you have any questions call me. Later Gary

[joe novak]

You have obviously found a worn transmission part.  I would not stop there, but continue to inspect the remaining transmission parts.   Look for uneven wear in those gears which you seem to be slipping out of.

[tomale]

That is amazing, I quess I would be wondering what was the cause... I had a Maico that kept having transmissions Problems, it turned out to be a matter of shimming...and a bent shifting fork.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)

[brian kirby]

It really is strange, that pin is not ground its "hammered" like the wide end of a wood splitting wedge or a punch that has been hit a lot, the metal is actually peeled over. Its almost like it was not heat treated or lost its heat treating.

The shift drum looks perfect, but a couple of the gears are damaged. I'm just going to replace all of it.

Brian

'72 Berkshire

[tomale]

That is strange, sounds like a good Plan.... My newest rule when it comes to old dirt bikes. if there is a question of the integrety of a Part, it needs to be relaced...

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)

[brian kirby]

I got some eBay parts and they look just like the ones I took out. The gear dogs look better, but the shift fork is worse. Seems like it is some kind of problem with the heat treating of those KTM shift forks.

Brian

'72 Berkshire

[454MRW]

Brian,
I have a complete 78 400 KTM transmission and all 3 forks show no wear as well as the drum shows no wear. I was just getting ready to pack the tank to ship to you. Do you want me to send you the forks and shift drum, or any other trans parts with the tank? Mike [email protected]

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[Merlin]

Brian, that was done way before you had that bike, takes a bit of work to do it.
The main reason a fork pin would get beat like that is from shifting under a load, not backing off or using the clutch to unload the gears for a shift when the engine is peaked.

Quote: Thomas Jefferson, We are all born ignorant, some work to remain that way.
 Quote:Peter Villacaro, "it is impossible to teach those that wish not to be taught".

[joe novak]

The engineers design the parts with specific hardness of metal so that they work best (not too brittle as to shatter, but not too soft as to wear easily).  Be thankful that the shift fork pin was a softer hardness than the drum, or you would be replacing the entire drum and more.   Lots of good suggestions in the other posts.  Shift smoothly and correctly, use the clutch without hammering it (ref. Merlin), and a folding shifter tip are all great ideas (ref. Brian Kirby).  Rebuild it and enjoy you vintage motorcycle!

[brian kirby]

Thanks to Mike Winter I replaced all the shift forks and the shift drum with some used parts that look NOS. I never use the clutch for shifting, except for Sachs engines, but I always let off the gas to properly unload the transmission. These transmission dogs are back cut to allow shifting without using the clutch provided you dont try to force the shifts under load, and as Merlin pointed out you can do just as much damage by using the clutch but never letting off the throttle.

Brian

'72 Berkshire