Hey all! I've had my XS400 up and running well for the past several weeks now thanks to all the input here in the forum. I've got a new problem now though. Was running it the other day and the left cylinder shut down and oil started blowing out the exhaust at the head. Got all over my purty little engine too!! I figured maybe a blown head gasket or something. To make a long story short, I broke the engine down, pulled off the valve cover and the cylinder head. The cylinder head gasket (metal) looks fine. The valve cover has no gasket! Weird! Here are some things that are noteworthy: the tops of the pistons are dry, just some charring; the cylinder walls are smooth; the valve openings on the left side are very charred; and the spark plug on the left side was fouled and charred pretty bad. Talked to some grease monkeys and they think that the valves are leaking and need to be re-seated. Any thoughts?? I don't know if this (re-seating the valves) is taking me in the right direction or not. Thanks!

it sounds to me like the valve guide is leaking, getting oil into the combustion chamber and fouling everything up (inc not running) get a few more ideas in this thread before you make your mind up!!

it sounds to me like the valve guide is leaking, getting oil into the combustion chamber and fouling everything up (inc not running) get a few more ideas in this thread before you make your mind up!!

i would also check the piston rings. they may have broke but not scratched the liner. re-grind the valves anyway as you have the head off. another thought is check your air box for oil from the crank breather it may be pulling it into the cylinder.

No oil in the air boxes, and I'll check the pistons too. One thing I noticed when I took apart the valves. . . the valve stems do not come out of the valve guides, except for the one exhaust valve that was blowing oil, the valve stem slid completely out of the valve guide. Any thoughts on that? Can you shed some more light on re-grinding the valves? I imagine this is something that I need to take to an actual mechanic to fix as opposed to me fixing myself??

No oil in the air boxes, and I'll check the pistons too. One thing I noticed when I took apart the valves. . . the valve stems do not come out of the valve guides, except for the one exhaust valve that was blowing oil, the valve stem slid completely out of the valve guide. Any thoughts on that? Can you shed some more light on re-grinding the valves? I imagine this is something that I need to take to an actual mechanic to fix as opposed to me fixing myself??

how do you mean that only one valve slid out ? they should all slide out after you take the collets off them.you should be able to feel a slight resistance due to the film of oil on them. be careful not to get the valves mixed up. they must go back to the corresponding barrels that they came from. as for regrinding the valves it is an easy job. go to your local car spares store and ask them for a valve grinding kit. it contains a wooden rod with a sucker on the end and two small tubs of paste,one coarse, one fine. you start with the coarse compund and smear a little on the seat of the valve(the v shape where it sits in the head) and you attatch the sucker to it and turn it between the palms of your hands (as if you were lighting a fire) and the paste grinds the face of the valve and the seat together. keep doing this until the v shape is of a uniform colour adding more paste as required. when this is done wipe the paste clean and use the same procedure with the fine paste. be sure and get all the paste of before re-assembling the engine as this will destroy it. wash it out with gunk or desiel and blow it all out. also check that the valves are not bent by rolling them over a flat surface like a kitchen worktop. hope this helps

if the valve seats are really pitted/pock marked it would be better for an engineer to recut them. other wise just using the smooth paste should be enough.

the exhaust valves are the ones which wear the most as they take away the hot gases.

valve stem clearances;

inlet 0.010 - 0.037mm

exhaust 0.030 - 0.057mm

also it would be prudent to check the cyl head for warpage by using the glass pane/feeler gauge method suggested by shed hermit.

I dont get this thread! If the valve seals are leaking there will be huge amounts of smoke out of the exhaust, there has been no mention of this, also if it were valve seals, how do you get oil on the engine sincce it will all end up in the exhaust? I think were looking a gaskets here!!

Awesome!!! Thanks so much for the details! So. . . I don't actually have to replace the valve stems or the valve guides!! Is this process considered "re-seating" the valves? What I meant about the valves not sliding out was. . . three of the four valves are still in the valve guides that are still in the cylinder head. One slid out easily, but the other three won't come out. Now, I haven't tried very hard to get them out as I didn't want to bang them up and what not. Should I just put a nail punch on the ends and pop them out or. . .??? Thanks again.

Awesome!!! Thanks so much for the details! So. . . I don't actually have to replace the valve stems or the valve guides!! Is this process considered "re-seating" the valves? What I meant about the valves not sliding out was. . . three of the four valves are still in the valve guides that are still in the cylinder head. One slid out easily, but the other three won't come out. Now, I haven't tried very hard to get them out as I didn't want to bang them up and what not. Should I just put a nail punch on the ends and pop them out or. . .??? Thanks again.

dont go near them with a punch!!! you said that one just slid out, did it slide out itself or did u remove the retaining colletts?

I thought it was blowing out of the exhaust near the head which could be an exhast gasket, but it doesn't explain the oil.

but I'd still check the head for warpage!!

Here is a view of your valves, the springs are held by collets but i expect you know this as you will have removed them, check you valve stems are clean and not worn and fit new valve stem seals upon re assembly after you have done the grinding in

I dont get this thread! If the valve seals are leaking there will be huge amounts of smoke out of the exhaust, there has been no mention of this, also if it were valve seals, how do you get oil on the engine sincce it will all end up in the exhaust? I think were looking a gaskets here!!

There was some smoke out of the exhaust at the head, however, the pipes were loose at the head too. I didn't want to run the engine too much for fear of screwing something more up. Plus the plug had fouled out and that cylinder wasn't working. I think maybe a good fix from here would be to re-seat the valves, change out the gaskets and put on a new exhaust system (as the old one is pretty bad). What do you guys think?

I thought it was blowing out of the exhaust near the head which could be an exhast gasket, but it doesn't explain the oil.

but I'd still check the head for warpage!!

he said that one valve slid out easily, has he maybe dropped a valve and cracked the head????

I removed the retaining cotter, the springs, the . . . aw hell, I took apart the valves like the service manual said. Basically removed everything, then the one valve stem I was able to pull right out. The other three I can pull all the way down, but they wont come all the way out of the valve guide. It's almost like they get stuck right at the end.

I removed the retaining cotter, the springs, the . . . aw hell, I took apart the valves like the service manual said. Basically removed everything, then the one valve stem I was able to pull right out. The other three I can pull all the way down, but they wont come all the way out of the valve guide. It's almost like they get stuck right at the end.

Ok theres some burring at the end, have a look and a feel around the area of the collet groove, run a fine file round the top of the valve if you find burring

I removed the retaining cotter, the springs, the . . . aw hell, I took apart the valves like the service manual said. Basically removed everything, then the one valve stem I was able to pull right out. The other three I can pull all the way down, but they wont come all the way out of the valve guide. It's almost like they get stuck right at the end.

they should all slide out be careful not to bend them

Okay, cool. I'll give it a run. Thanks!

I had a similar problem. Smoke all out of the exhaust port on the head. It turned out to be bad valve seals. Just replace those. My valve springs where a bitch to get off, but it isn't a bad job.

The valve cover is only sealed with liquid gasket. It was the later year XS (post 83?) that had a valve cover gasket.

I had a similar problem. Smoke all out of the exhaust port on the head. It turned out to be bad valve seals. Just replace those. My valve springs where a bitch to get off, but it isn't a bad job.

The valve cover is only sealed with liquid gasket. It was the later year XS (post 83?) that had a valve cover gasket.

And it can be a real pain to get that valve cover to seal properly. It can work the first time if your lucky, but it took me 4 tries before it sealed properly.

your not supposed to put anything on the valve cover as the camshaft runs directly in the head and cover. introducing anything else will open the bearing gap and you may, at worse, lose oil pressure, or the camshaft will "jump around introducing wear!!!