[backwoodsplayer86]

New to the forum thanks for let me joint long story short I bought a 2004 yamaha rhino 660 bone stock last year now out nowhere started smoking really bad I can see oil at the tail pipe im going to b replacing the top end just wondering why started smoking is still runs good I will check valve seal while I have apart any suggestions

 

[HighDezRhino]

Welcome! Sounds like the rings are worn, which can be confirmed with a compression test.

 

[backwoodsplayer86]

Welcome! Sounds like the rings are worn, which can be confirmed with a compression test.

I did compression test 130 psi but when I did leak down test it was about 40%

 

[sandbuster]

Agree with High Dez - Rings probably shot and when you do top end DO replace the valve stem seals.

 

[racerdave]

My 07 would burn oil from the full mark on the dipstick to below the fill line on a 30 mile ride. And it still ran great. Piston, rings and cylinder were all worn. So sounds like you prob do need a top end overhaul.

While replacing the valve stem seals, also check that the valves are not loose in the valve guides, and check if the valve faces and seats need to be cleaned up. I manually lapped the valves a bit on mine to clean them up. Don't know if it made a difference but I figured I've got it apart, why not do it?

 

[sandbuster]

I don't know if it's still being done today, but shortly after I started in the auto repair business (late 60s) my shop owner invested in a valve guide knurling kit and we were all taught how to knurl the guides back to a proper stem fit. I'll have to Google that just out of curiosity...

 

[racerdave]

Yep, I remember knurling valve guides also.

 

[sandbuster]

Checked with Mr & Mrs Google and they advise practice of knurling has pretty much gone away - mostly due to repairs not lasting long. Was a quick fix in it's day but the practice seems to have been short lived.. Most advise using bronze inserts or totally new guides.