84 250R engine rebuild

[rugbyflanker]

Hi guys, I had a shift fork jam in my 84 250r and lock up the engine and transmission. I had to pull it out and completly disassemble it to figure out what was going on. I hadn't split the case on an engine before and thought I was in over my head. Im learning alot by doing this and going though it with a lot of attention to detail. While i was cleaning up the two halfs of the crank case i noticed some wear in the middle near the seam below the crankshaft. I looked at my parts engine and that case does not have any wear there. Should i be conerned about that? Any tips or pointers on the rebuild would be appreciated.

Thanks

[yaegerb]

no its fine. how bad are your crank bearings?.....They look pretty shot. That wear could be from a bearing that's out of tolerance and a crank tin slightly grazing the case halves. I would replace those while you have it split. It could also be an out of true crank. Either way, get the crank rebuilt/trued and get those crank bearings replaced.

[rugbyflanker]

Thanks. I have new crank bearings, counter weight bearings and chain output bearing to put in. I also got the wrist pin bearing, but was unsure of how to do the connecting rod. It doesn't seem to have much play but don't want to skip a simple step as long as i am this far into it. Would any engine shop be able to look at the crank or would that be a speciality performance shop?

[yaegerb]

To get the crank rebuilt, send it to either Carlos @ BDT motorsports or Jeff @ Farm and Sand Toys Racing (F.A.S.T). Or you could try crankworks as well.

[350for350]

If you're already in it that deep, it would be stupid to not replace the lower rod bearing in my opinion.

[rugbyflanker]

What are your thoughts on the Hot Rods vs Vesrah Rod kits?

[yaegerb]

Hot rods rather than vesrah.

[rugbyflanker]

So I know the answer, but is this piston reusable? What would cause the wear like that? Reading some other post are there supposed to be holes in the exhaust side of the piston or not on the 81-84 air cooled R's?238749238752

[yaegerb]

What does the cylinder look like?

[barnett468]

So I know the answer, but is this piston reusable?

Absolutely if that is the only damage, however, that area should be cleaned with carb cleaner and a plastic or brass toothbrush then wet sand any it lightly with 400 grit then 600 grit . Sand up and down in line with the mark . You do not need to remove all the scratches in the metal . Post a close up photo after sanding before you put it back it.




What would cause the wear like that?

Hard to say since the studs don't go all the way through the cylinder but I would check the piston to cylinder clearance.

What type of oil are you using and what ratio are you using?



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[rugbyflanker]

Well that is good news. I have been running AmsOil Interceptor at 32:1. I will post a pic of the cylinder tonight.

[rugbyflanker]

What's the best way to check the piston to cylinder clearance? Pics of the cylinder are below. Some wear spots but nothing that catches my fingernail. Will the old damage on the head effect anything?238803238804238805238806238807

[rugbyflanker]

If you're already in it that deep, it would be stupid to not replace the lower rod bearing in my opinion.

I didn't look to close before tonight but it did have a hot rods crank in the motor but no idea how long ago it was built. I have owned the trike for 9 years. Probably smart to rebuild it anyway right?238808

[yaegerb]

So personally, I don't like the marks I see in the cylinder and it looks like the rings may have been catching on the bottom of the sleeve nearest the intake port. I would definitely send that out to have a dial bore gauge run on it. At the very least you would need a hone and I would definitely get the bottom of the sleeve chamfered better. You can send it to Jeff at fast along with the cylinder out of round specs so he can determine if you need a bore or hone.

To test the rod, pull up and down on the rod while holding the tins on the table with your other hand. There should be zero up and down play. Then you need to check the big end rod gap with a feeler gauge. The specs for this are in the manual.

You can also get the head cleaned up on a lathe but that will mess with squish so you will probably end up having to mill the cylinder surface to get squish back in alignment.