XR100 Top End Help!!

[moto45]

Hello all, I am currently working on a 96 xr100. I just did a rebuild: 1mm overbore hone, new piston kit, new valves etc. The bike was smoking and lacking power so that is why I decided on the rebuild. I went with the overbore for just a little more kick and had the local Honda dealer do the bore with piston in hand.

The problem is that I’ve run it through about 5 heat cycles closely following the break in procedure and it’s still smoking. Not as bad as before but more than it should. I think after 5 heat cycles it wouldn’t be from leftover oil during reassembly. I’m wondering if anyone has any thoughts on this. I don’t think it’s cylinder or ring related. I feel that I assembled them properly. I actually feel that the whole assembly was done properly so I’m stumped? Should I make a jetting change? Thanks ahead of time.

 

[reelrazor]

You started and ran it in on non-synthetic oil, didn't you?

If not, drain it, switch to petro-based oil and start it, let it warm up all the way and then don't baby it.

Checked to make sure the crank breather reed wasn't warped and nothing was holding it open?

Replaced the valve seals?

 

[moto45]

thanks for the reply. yes, non-synthetic oil was used. I replaced the valves and the only valve stem seal. The valve seats appeared good. Can those acutally be replaced on a 96? Anyway, I plan on taking the engine back out and investigating tonight.

Tips on what to look for?

Also, is there a compression tester on the market that fits the small xr spark hole?

thanks, I'll post what I find.

 

[Ol'89r]

I replaced the valves and the only valve stem seal. The valve seats appeared good. Can those acutally be replaced on a 96? .

Tips on what to look for?

Also, is there a compression tester on the market that fits the small xr spark hole?

QUOTE]

Moto45.

If the valves felt tight in the guides and you replaced both guide seals with new ones, the problem may be with the rings.

Did they hone the cylinder after they bored it? Should have a noticible cross hatch pattern. Is it possible you could have installed one of the rings upside down. Marks on the rings go up. If a ring were to be installed upside down it would turn the ring into a oil pump instead of a oil scraper.

Make sure one of your rings did not crack during installation. Also, check your piston clearance when you have it apart.

Valve seats can be replaced, but this has to be done by a machinist. Usually if a valve is not seating properly you will have a loss of compression but, it will not make the engine smoke.

Harbor Freight sells a compression tester that comes with several adapter hoses. The gauge is not of good quality but, I guess you get what you pay for.

Just my $ .02

 

[moto45]

Ol'89r, thanks for the reply. Yes, they did hone the cylinder. I know not to put rings in upside down and the gaps were opposed, but I'll double check tonight.

I did not measure the cylinder afterwards due to the fact that I had the dealer do it with piston in hand. However, I did measure the ring gap and everything was good there.

I will check the piston clearance tonight since I'll have it apart. I've done many top ends on 2 strokes but this is my first on a 4 stroke. I'm trying to cover all the bases. Bike started right up and smoking was minimal. After one heat cycle it started getting worse. Hopefully, I'll know more tonight.

btw, looks like you're a flat tracker? I'll be checking out the Duquoin Magic Mile this weekend!

thanks for the help.

 

[Ol'89r]

btw, looks like you're a flat tracker? I'll be checking out the Duquoin Magic Mile this weekend!

QUOTE]

:cool: Have fun. :yeehaw: :yeehaw:

 

[DougRoost]

If you only heat cycled it and didn't run it under load, I can't see how the rings could have seated yet. If it was me, I'd get out and ride the bike some under different throttle positions, initially on a flat area, then adding some small hills.