I have a Yamaha 2001 600 grizzly that is burning oil. It will burn oil when I first start it up cold and or after I have ran it some and it has sat for about an hour or so. It will only smoke for about a minute and then it will clear up. Its smells like when I'm ridding it its burning oil but, I can't see any traces of blue smoke behind me and I can smell it burning oil when I stop and idle. Nothing is leaking anywhere.

I just did a complete top end job. I had the cylinder bored 1mm over, a complete valve job including new guides, valves and seals. I rebuilt this engine all new parts, piston, rings and gaskets. I used Yamaha's service manual to check all the specs and torque settings when I put this engine back together. The piston rings are indexed properly and the markings on the rings are facing up like it calls for. I did have the machine shop deck the head and cylinder. I'm running 10w-40 oil in it and the oil level is correct in the sight glass when it's not running. When the engine is running, I can't see any oil level in the sight glass, but when I shut the engine off the oil level is back to normal, 2/3 sight glass full.

The bike runs very well but, its just smoking on cold and warm start ups. I did a leak down test and a compression test after I ran one tank full of gas through it. The compression was at 166 pounds and the leak down test was good. I did have to add about 2oz of oil the crank case after I ran one tank of gas.

I'm lost on this one. Please help because the costumer is waiting.

 

i think your compression test might be a little low, but other than that im baffled. i would consult with your local mechanic.

 

After looking at the yamaha spec for compression pressure. Book says at sea level the standard is 121psi and the minium is 114psi and the max of 128psi. My compression test is showing 166psi at sea level. I did go with a 1mm over sized pistion when I went back together. Could be why my compression is higher or my comperssion release on the cam is not working like it should. Never the less its still smoking on start up but clears up in a minute or so.

 

You say you decked the head and cylinder, so I would expect your compression to be a little higher than spec's.

A couple of things come to mind......
Typically, you would expect the symptoms to be related to the valve side.......

1) On the new valve guides, could it be possible that the guides were over-reamed, causing the stem clearance to be a little too big until heat expands the guide and valve stem? This could possibly be "cured" by a little knurling of the guides.......

2) Did you check your ring gap after the bore - could it be that piston skirt to cylinder wall is a little too much? Even though our machinist has been boring ATV/Motorcycle cylinders for years, we always check his work - just in case.........

3) Did you replace the O ring at the bottom of the cylinder - this O ring is there to prevent oil from coming up between the sleeve and cylinder casing........

 

Ujoint,

Thanks for the help! I did not check the new valve guides after the machinist installed them and the valves. I did look to see if they put on the new seals. The head was cleaned, check for cracks and it was all put togetther when I got it back from them.

I did size the rings to Yamaha's spec's before I installed them on the new pistion. The pistion to cylinder wall was in spec I did check that before I put it back together.


Also, in the new gasket kit. I did replace the lower oring on the bottomf of the cylinder. There a grove for it to fit in and when I put the cylinder back on I watched things closely as things went into place.

Today, I took off the ext. header and looked at the vavle stems before it started it up. It sat over night and there was no oil found on the valve stems when inspecting them.

I'm sure its something so small and I'm just over looking it. Thanks for the help!

 

What you are describing is classic valve guide/seal problems. It's a text book desciption.
What did it leak down to % wise? ANY air out either the exhaust or intake at all. ANY?
What was the piston to bore clearance?

I have a VERY good machinest. Do I check his work? YEP!!! People do have bad days.

I bet a $20 bill that the valve to guide clearances are out of wack. Not my life, but $20 bucks, sure!!!