Engine rebuild

I have split my engine to replace the crank seals, all the bearings are good so just going to pop it back together. I have not taken the gearbox out, it's still held in the left hand case. It's still in neutral and I was just going to push the cases back together and leave it like that, but I have read that it should be in 4th gear. As I haven't touched it surely it will be okay to put it back as it was? Is that right?

If you have a primary kick engine like 1981 430CR/WR or 1982 250 or later, it is not necessary to have transmission in fourth gear. If working on the non primary kick engines six speeds it is best to put transmission in 4th just before splitting the centercases.

Jonny...what year model engine? would help the forum if they knew but like Jimspac said above is correct

Thanks for you replies, I really appreciate you taking the time to answer. My bike's a 1982 XC250, so I guess it should be a fairly straight forward rebuild. I decided to do a full bearing and seal replacement while I had it apart, I want to race the bike so I want it as good as it can be.

I've split and reassembled the cases on a few non primary kick six speeds and never gave it a second thought what gear they were in while doing so and had no problems. Having never heard this before I have to ask, why is it best for a non primary kick 6 speed engine to be in 4th gear when splitting the cases?

before you reassemble, check the match between the casing transfer ports and the barrel. if your going to race it, best tidy everything up while its apart.

he said wednesday his bike is an 82 250. nothing like your link...altho thats helpful for older stuff

Thanks again for all you replies, I have finally managed to make time to put it all back together and I've really just got to put the top end back on. One thing, there doesn't seem to be any kind of head gasket. I've looked at the parts manual and it's not showing anything. Should I use some kind of sealant or is it just metal to metal?

Just metal to metal. best since apart go down to auto parts store pick up some valve grinding
paste. Put some on the area and just lap/twist back and forth to two areas together. Does not take long to do. And do a nice clean up.

Take a look how smooth and clean the area s are after.

After lapping the head to the cylinder, and cleaning the lapping compound, apply a drop of oil to the mating surfaces.

also check the shorter bolts dont bottom in the cyl before tightening down the head. check the thrad length vs bolts. ive seen this before cause numerous issues.

Got everything back together today and it started second kick. All new bearings and seals so it runs smooth with much less vibration. I'm going to run the first gallon through at 25:1 mix, then maybe 40:1 but that's a whole new topic! Thanks for all your help, I don't think I'd have had the confidence to do this without knowing I could get information here when I got stuck. Next on the list is a Lectron carb, better get saving!

good move with fuel mix, should bed her in nice. run it up gently through the revs, just touching the band and up shift. by the time yr thru the best part of the second tankfull you should be pushing it into 2/3rds throttle in the band and letting it get a bit of load on. good luck

your plan sounds right on