Advice needed-yamaha 400 clearance

[2stroke]

I assembled a gearbox today for a 1977 Yamaha DT400. The crank spun just fine after putting it into the first half. Later when I put the second half together, there was a small gap all the way around the cases. I snugged the bolts up little by little and the gap closed but it was more stubborn around the crank area.

Now, the crank will not spin. On the clutch side there is no clearance betwenn the crank and the case. (Im sure thats whats stopping the crank) On the gear side, I an get a sheet of paper between the crank and the case so that ones ok.

So has anybody had this problem before? Ive done about a dozen or so motors in th past, and never seen this before.The crank is not from this motor, but from the same year and model bike. The mains were not changed so I dont think there is a problem with them being seated or not...

Its almost like the crank is too wide for the cases but I cant imagine why that would be....

Any ideas would be appreciated.
Thanks,
Neil

ps....I took the bolts loose and the "gap" around the crank area showed up again on it's own, and of course the crank spins nicely now, but jeez theres a 1/8 inch space there...Im gona split the cases again and take the crank out and I guess Ill start by measuring it against the bad crank I took out of there....AGGGHHH! :ugg:

 

[jmics19067]

I have had a similar problem except that I used one of those "draw thru" crank tools to pull the crank into the left side. When I assembled the engine it was snug on the left side. Simplest solution for me at the time was having to take the good "unknown " crank apart and using it to rebuild the original bad crank. I am guessing the old Yamaha's weren't as interchangeable as I thought. bike is a 1978 yz 400 btw

 

[2stroke]

Thanks for the reply....
I did what I always do for assembly, I froze the crank for 12 hours, and put the case in the oven for 10 min @ 350.
Dropped right in. Then of course, the half w/crank back in the freezer and the other half in the oven.
Works well, and there is NO hammering required heh heh....

Anyway, I think Ive solved the mystery.

The crank has a very slight wobble. I can barely discern it at the ends, but if you watch the crank halves against the cases, you can see them wobble a bit. So its spread a bit at some point, enough to interfere with the case at least at one point in the rotation.

Probably happened in shipping. I had that one mailed in. It doesnt take much to knock them out but theres nothing I can do myself about putting it right. I have access to a press, but Ive got no way to align a crank! Agghhhh...

I hate that theres something I cant do myself. I made a case puller, and even a bearing puller from scratch. Hee hee....really Im just too cheap to part with money for labor

I wonder how much someone would charge for simply aligning the crank? The rod feels very nice anyway....

 

[jmics19067]

I beleive rebuild a crank is somewhere in the 60-100$ range for labor, aligning it should be cheaper.If you have a dial indicator and a brass hammer already all you need would be a truing stand or V-blocks. straighten it out yourself and have a machine shop just double check your work

 

[2stroke]

Yeah, Ive read in my old Clymer manuals about the old brass hammer bit. Ive never tried it. Hmmm.