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1994 XR650L smokes on cold startup after rebuild.

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Hi guys, After a complete rebuild, piston, rings, cam, 2-intake valves, valve guide seals. After about 6 hrs on engine it has started smoking on cold startup. Quite a bit of white smoke, for about 2-3 minutes then quits. Used 10.5-1 piston so had to bump the main jet two sizes, pilot two. Plug is light tan, runs perfect. I'm assuming the problem is with the valve seals. But would appreciate feedback on anything I may be missing. Machine shop did the valves.

Thanks guys!

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Guessing it's a forged piston.
They are more dense, and machined smaller than cast to achieve the right diameter at operating temperature.
The 2-3 minutes may be expansion time.
If you did your valve guide seals and it had a valve job, where else would it come from?

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There are 2 sets of seals at each valve...

 

the valve GUIDE seals......they are under the pressed in guide.......rarely an issue..

the valve STEM seals.....they are just under the valve springs,and usually the culprit...

 

if it smokes like a bugger when you start it and then goes away ,,completely goes away and does not smoke at all when reved up...then it`s likely just the stem seals...

The worst offender is the exhaust seal on the left front...when you park the bike on the sidestand the bike leans left and a big pool of oil stays at that left front seal and drools in slowly past the bad seal and down the guide and lays on the exhaust valve head or drips into the cylinder too.. while the oil is blistering hot,, it is really thin like water ,and smokes like a retard when started next time...

 

if you ever pulled the valve cover on these engines after it was running and left on the sidestand,,you`d see a freeking pile of oil come rushing out that left side very front corner after loosening the valve cover bolts..

 

hot thin oil,,weak or cheap seals  = mosquito fogger at start-up..

 

B

 

Edited by brianhare
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Brian, Your describing exactly what I think is going on. I had pulled the valve cover caps to inspect oil puddling. I used a syringe to draw oil from each valve spring pocket. And got a large amount of oil out of the front left exhaust valve pocket. None from the others. I wonder if I tried, either standing the bike on its rear wheel, or leaning it on its right side for about 2 minutes prior to starting cold. If less smoking occurred, it should confirm the valve seal leakage on the front left. Another question is, are there better stem seals I can get? Thanks for the feedback! 

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you would need to lean the bike immediately on the right side after shutdown,,right after riding...that way the oil would drain down the cam chain tunnel quickly,,,leave it at that angle about 5 minutes or so,,then set it up on the sidestand..if it doesn`t smoke or very little,after sitting till cold,then you know for sure its either the upper valve stem seals,,or lower guide seals..

 

You can`t let it sit and then lean it over,,,after it sits on the stand the hot oil is already trying to get past the seals,,,if you wait till restart it`s already too late and the oil is down the guides waiting to burn..

 

If you could elevate the front wheel till the valve cover is perfectly horizontal,,,and the lean it over on the right side would be even better..

 

B

Edited by brianhare

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I was able to pull up my work stand ramp and get the angle of the head slightly above the horizontal line. Held it there for a couple minutes, then rolled it down and layed it down on its right side, handle bar in a chair for a couple minutes. Then returned it to the kickstand. I'll check for smoke in the morning. After looking at a picture of my head. I determined the oil drain passage goes rearward, under the cam, then right into the cam chain opening. We'll see in the morning.

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now if it hardly smokes it`s either the valve stem seals just under the springs,,,or the seals under the pressed in guides..

 

hopefully just the stem seals,,I've only seen three engines that the guide seals were roached from over heating..and the guides had to be pressed out,new seals installed and new guides installed and reamed to size..

 

If you get seals,,,go OE  or there are actually VITON seals on ebay which have proved to really work well,,Viton is a very high heat material and does not harden like a rock when subjected to repeated heat and hot oil..

 

B

Edited by brianhare
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Well, I started the bike this morning... and (No smoke) nada, none! Which brings me to believe the valve stem seal is the culprit. As a bad o-ring under the guide should still produce smoke. I will look for the viton seals. Brian :thumbsup: Thanks for confirming the process.

On 5/23/2017 at 5:12 PM, brianhare said:

If you could elevate the front wheel till the valve cover is perfectly horizontal,,,and the lean it over on the right side would be even better..

I really appreciate your feedback!!!!!

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