Hey all, I've been readin post on here for awhile but I need some personalized help now!

I've got an '84 xl600 that I've been rebuilding, and it smokes like crazy when its running. Cold, warm, hot, still smokes.

My guess is that oil is burning, and i had a mechanic do a leak-down test, he said the valve seals needed to be replaced. So I replaced the seals, and lapped the valves, put it all back together and STILL SMOKE!

I have taken it back apart again, and when you look at the bottom of the head, that auto-decomp valve seems really wet? Is that a good (bad) sign that its leaking?

Also thought that the rings might be bad but the cylinder walls seem clean?

I will post some pics up after work, any and all help is appreciated!

Thanks!!

Sounds like rings to me. I would check the cylinder to see if it needs a re-bore. and does it have the stock piston? If so I would guess it is time for a bore, new piston and rings. my opinion.

I would tend to agree with outlaw. The mileage may be decent, but you dont know how it was ridden. Cylinder may be smooth, but it can still be worn. Is there a lip or ridge at the top of the cylinder? Can you move the piston inside the cylinder at all? Obviously cant diagnose it without seeing it, but in this case, sounds like a top end with bore, piston and rings.

Just curious, and not insulting anyone, but what color is the smoke? Just want to confirm.

Piston is most likely stock, and idk how many miles on it but i would guess around 25k.

At the top of the cylinder there is what looks like a bronze lip? I'll put some pictures on here but all i've got is my cell phone =/

The orange hue on the cylinder picture is just the lighting

And the smoke was a white/blue color, really thick

When you say that small valve in the head is really wet what do you mean??
Wet with fuel or oil??. It's possible the valve guides may be damaged
or at least one of them may be. Can we assume the mechanic replaced just
the small rubber seals on top of the valve stems. There's other seals on
the valves as well at the base of the valve deep inside the head.
I've never replaced any as I think the guides need to come out to do it
and getting them out is a specialists job..it's also rare for them to need
replacing but you never know. I suppose it could be likely that the small
decompression valve may have something wrong with it's guide or seals.
Course it needs a rebore and new Piston and rings to eliminate them as the
issue also..Although in saying that yours appears in good shape though
looks can be deceiving.

The small valve looked wet, where as the intake/exhaust valves were dry.
I would guess oil but it did smell a bit like gasoline as well...

All that the mechanic did was a compression test, and told me air was being lost on the exhaust valve. Thus I replaced the rubber seals at the top (which were pretty brittle and old) and lapped all four of the valves.

I think a bore and new cylinder will be the path I take for now, anybody know what I should expect to pay?

Thanks for the help, you guys rock!

<p>Do not rule out a problem with that Valve..Get it checked somehow.

Cover bases or you'll possibly kill only one bird when you want both with
the one stone.Rough guess no change $300 odd
Piston, Rings, Rebore, Gaskets,,,that valve sorted or inspected,,dunno.

Oil getting into the combustion chamber = smoke.
A few choices are and can be one or more:

Scored cylinder ( Visual inspect)
Piston / ring gaps/ cylinder diameters out of spec ( measure)
Valve guide seals ( replace)
Valve stem seals ( inspect / replace)
Valve guides ( measure and check for wear)
Leaking valve seals ( bench check)
Leaking head gasket / oil passage near exhaust.

You can do a leak down test before pulling it apart but if it smoking I would just pull it apart and start looking at everything. You can do a hillbilly valve seal inspection by sitting the head on the bench and putting a shot of ATF fluid into the intake runners so it runs down to the valve seal area. Let sit overnight and look for leaks on the opposite side. If its apart just pull the valves and check for wear.

My 650L got a case of the fighter bomber hit / going down smokin and I pulled the top end. In my case it was a combo of issues. The valve stem seals were hard as rocks and oversized (no sealing). Viton replacement for $12 fixed that. All of my ring gaps were oversized so it made it easy for a JE piston replacement. Runs sweet and no smoke.

I have an 83 XL600R mine did the same thing. After I installed new rings and reworked the head it ran good for about fifty miles then started smoking again (burning oil). After tearing it down I discovered that the small end of the connecting rod was wore causing allot of piston slop. This caused the oil ring separator to make contact with the cylinder wall. This in turn caused the oil rings to not work properly. For what it is worth my oil would turn dark gray in a matter of minutes before I replaced the wrist pin and connecting rod. Also check your timing chain for stiffness!!!

Mark

I just finished tearing my 1993 yamaha xt350 apart because it was smoking real bad just like yours. What I found was that the rings have a .212 ring gap when they should be between .010 -,016 . The valve guide seals are rock hard which means they are no good as well . The cylinder is smooth but there are no traces of any cross hatch marks so I'm guessing I will have to bore it to the next oversize and install a new piston and rings along with a good valve job on the head . If I were you I would measure your ring gaps and the cylinder itself to see what you are working with and go from there . Good luck ! Richard .