TOPIC:

Alright guys I need your help. Here's the issue. Last fall I ended the season with the valve guide oil seal failing after a long time of leaking. I saw this coming so it was not surprise and I tore down the engine and replaced them. It took me most of the winter to put it all back together and lap/reshim the valves back to spec. Ive had the bike running now for a month or so and its been running like a champ. Ive been checking the plugs and they seemed perfect except for a little amount of carbon build up on the RIGHT cylinder. No worries there. Today about 20 miles into a 130 mile trip home from college, I almost lost my shit. The bike started to loose a little bit of power until, within a few miles, I knew for sure that I was running on one cylinder. I pulled over and it died immediately. I was pissed and I had to turn around and try to limp back to school. On the way back it starts leaking oil out of the exhaust just like it did when the valve guides did last time they went. And its really weird because its ON THE SAME CYLINDER THAT FAILED LAST TIME. I'm just wondering, what could cause new valve seals to fail on the same side, after less than 500 miles?? It was my first time replacing them so I could have botched the job but it ran for 300+ miles with no issue at all. It all looked good when I put it back together as well. Sorry for the novel but I'm just wondering if anyone has thoughts before I spend another weekend rebuilding the head.

really weird. Maybe the thing was bad? Was it VITON seal or old style butyl rubber?

If the seal was good, only thing that could make it fail is damaged when installing?

It was VITON rubber seals that where new. It is really weird though. What I did to put them in was put the valve in then put the seal over the end of the valve then push it so the spring seals over the end of the guide. I don't know what could have gone wrong. I guess it didnt seal properly then come off eventually. Could there be a problem with the valve or guide?

The symptoms do not appear to be just a single valve seal gone bad. Major Loss of power, running on one cylinder. I am thinking maybe a valve guide issue causing a valve not sealing properly,...therefore losing compression. Was there a lot of white smoke coming out of the pipe?

There wasn't any smoke that I noticed expect for when I came to a stop and had to keep the throttle pretty far open to keep it running then I got a lot of smoke. The major loss of power wasn't too pronounced until just when it lost the cylinder. It was running 100% on par until it missed a bit, increased, then was on one. Would a valve guide be something to go bad while running and happen all of a sudden? Just looking for something else to be wrong.

Valve guides or valve guide seals ? You use both terms and they're not the same.

I'm going to assume valve guide seals, because if you replace the guides then you need to grind the seats. not lap them.

Did you check the guides when you lapped the valves?

Valve guide seals is what I have replaced. I know the valve guides are the the seals attach too and are what actually "guide" the valves. But explain what you mean by check them? they looked fine and there was no resistance when the valves where put in.

You check them by raising the valve off the seat and attempting to wriggle the valve. The procedure and spec is in the manual.

JimB wrote: The symptoms do not appear to be just a single valve seal gone bad. Major Loss of power, running on one cylinder.

That's what I was thinking. On my 750 twin: before the last rebuild at 75k miles, one of the valve seals had failed so completely that the whole center section was just GONE. No seal at all. But me engine ran fine until I parked it and oil would run down and foul the plug, then it wouldn't start because fouling one of the plugs kills them both because they are wired in series. When it was running, it ran OK and didn't even smoke that I noticed. Hard to believe a bad seal could cause all that much mayhem.

Steell, thats good to know. I must have missed that section in the manual. I will check that during this rebuild. Are the valve guides a somewhat common part to wear out? I know replacing them is expensive because they have to be removed/installed by a machine shop.

bountyhunter, thanks for your reply. That is some really interesting information and it makes me super worried. When the valve seals failed last time, or at least that's what I thought, the right cylinder wasn't firing and oil was leaking from the exhaust seal at the engine and blowing out of the exhaust. I didn't know what else it could be and when I replaced the valve seals, it ran fine. About 400 miles later, the same exact thing happens and I am lead to believe that same thing happened again; a valve guide seal failure. With your information, it seems to disprove that the valve guides are the issue, or at least what is causing this problem. What else could cause the oil leakage, cylinder not firing, in a good compression cylinder with no other known problems? I am at a total loss. Thank you so much for your help!

That much oil has to be coming from somewhere. Steel might be right in suspecting a valve guide. If the valve is moving around it would beat the seal up pretty quick and would also let a lot of oil pass by into the cylinder.

bpchura wrote: ...What else could cause the oil leakage, cylinder not firing, in a good compression cylinder with no other known problems?....

Is it for certain that compression is up to spec in both cylinders?

A failed oil ring is another possible reason for oil entering the cylinder and blowing out the exhaust.

Oil ring failure would probably not be evident from the usual compression test or from a leak-down test.

Good Fortune!