88 R100GS , was running fine idle was a little tricky to get even ! Spent my New Year tearing it apart and found this valve was the worst of it , bores and pistons look great . I haven't had this bike very long , when I got it it ran like crap so did the usual valve adjustment and tried tuning the carbs with limited success so I pulled the carbs and did the rebuild and clean on them , it ran much better but still that idle was off . I'm amazed it ran at all and very pleased I pulled it down when I did , that valve is so cracked it must fall apart very soon .
Right on the money Mate 70,000 . Did you have to do the seats too ? I haven't pulled the valves yet so am wondering how bad the seats will be .
I didn't bother to do the seats. I ordered stainless valves, used a little lapping compound and just hand lapped them to the existing seats. The contact faces weren't textbook perfect but, it still had a decent, continuous ring of contact. They worked fine for another 3K miles before the bike was wrecked. Idle and power were immediately normal after replacing those valves.
Holy cow, Mark :huh Glad you found that before something on the catastrophic side happened to that motor.....while on a road trip in frozen Kansas somewhere with a buddy who hates to push dead bikes
So I am guessing that you got the exhaust off. Good find, well at least you found it before it caused any real damage. Marc
I would replace the exhaust seats as well. With a valve burned that bad, the seat may have gotten hot enough to relax the press fit and drop out.
How much 'better' are the stainless valves? I'm looking at rebuilding a set of heads I have on the shelf. Just curious ...
It is possible for a valve like that to 'pull' the seat out. Happened to me once.....got to a rally site, killed the motor for 30 seconds, started the bike again and out it came. I figured that the motor stopped with the valve closed, and that the exhaust seat cooled enough to grab the 'step' on the valve.
Marc I tried with your tools but it was a no go , ended up slicing the collars with my dremel and then using a cold chisel to split them , they were frozen solid !
With 70K your intake can't look much better. Do both valves, guides and at least exhaust seats. ROBTG is one of the best cylinder head rebuilds out there.
Wow! I thought only '81 to '84 valves did that! No, not really since I am always pointing out that ALL the models do this sometimes. Having done well over 100 airhead valve jobs myself, I totally agree with robtg and want to add another danger from what I have seen. If that cooked seat doesn't drop out, a new hard valve is likely to hammer the seat in and you end up with the same problem only different. In my experience, the intake valves can last a long time. The intake seats can last forever. This is a perfect example of why I always recommend doing a leak down if an idle issue persists. It's very often a leaking valve in my experience. Usually the intake but . . . . Just last year I leaked down my '92 and both exhaust were leaking at 101,000 miles. The valves' and seats' looked perfect but my exhaust guides were done. I didn't even measure the stems because I new I was going to 45* exhausts anyway. You really should do the same thing shearboy2004. Sticking with 30* valves doesn't work most of the time. It's hard to explain but trust me.
I think too many of you guys are too eager to just start pulling valve guides and seats. The bike I had the problem with was also a 1988. I don't know about other years and problems but, I can tell you from my own experience inspecting those valves and seats that those 1988 valves were absolute crap. They managed to do all that damage with almost no evidence on the valve seat. Yes, the seat had worn a little but--as I posted--lapping compound was all it took to reveal a decent-width sealing ring all the way around; not too wide, not too narrow. Bottom line: if you're of the mind to rebuild the heads, go for it. Now is as good a time as any. If you're a little short on cash and don't want to drop a grand right now, you can always carefully inspect the seats and put some new valves in there. If it gets you another 10-20K miles, you might be at a place where you want to go through the whole engine anyway.
Mate thanks for the input , I was waiting for you to turn up , In the pm's we exchanged you told me this was probably the problem and were right !
I might write more but when it comes to valve jobs and airhead tranny repair, robtg has a LOT more experience than I do! Lots of other stuff as well but I try!
There is certainly a bit of a cash flow problem at the moment and a complete rebuild is somewhere down the line but I'm also thinking of a rather large dirt ride this year so the brain is fighting with itself right now ! The correct thing to do is as Supershaft suggests but couldn't afford it right now.
If you can'tr afford it you can't afford it but keep your fingers crossed! Dropped seats can tear up EVERYTHING!!!!
If the guides are anything like this '89 model had, it would be plain stupid to leave them in. Mouse over the image to see the slop: http://largiader.com/articles/valves/
