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Photo by Andy Miller, UK,
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Jokulsarlon, Iceland



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  #1  
Old 21 Jan 2008
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Airhead valves
Hello all,
I'm going to change push rod tubes seals on my R100GS and at the same time want to inspect cylinder heads. The bike has 115000kms on the clock (it might be more, I own it since 70000), engine takes little oil, I'd say less than 0.1l per 1000kms and it isn't noisier than other airheads I've heard. The thing I'd like to know is if I should have valves and guides replaced and seats recut on the bike with such a mileage even if they are in their wear limits. I'm preparing the bike for a long trip and want to have everything 100%.

Please advise
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Old 21 Jan 2008
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0.1 l oil per 1000 km is pretty good for an engine of that mileage.

If you prepare the bike for a long run tour I would have overhauled the cylinder heads. I did it at 150kkm and it was needed.

It might be smart to check the pistons and rings to. My rings and piston (R80GS) were good at 150 kkm but at 180 kkm they where far outside the tolerance – but the engine was running nice.

Timing chain and clutch should normally last a lot longer the 115kkm but it might be smart to change them if they are original.
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Old 21 Jan 2008
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Cool
While the engine is open, check the main bearings in the crankshaft as well. When I had to exchange the seals for the push-rods I checked my bank account and had the pistons & con-rods balanced on my R80GS. Jeez, what a difference! The engine runs so nice & smooth now.

Hans
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Old 21 Jan 2008
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I would not take apart a good running engine to do this, but seeing that you have the valves out, i would fit new exhaust valves keeping everthing else that was in specification. If you change the guides, you will have to recut the seats. I would avoid removing metal for as long as possible.
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Old 22 Jan 2008
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Thank you guys for your input.
I agree with oldbmw. I don't like to remove any metal unless it is necessary. I'll take a look at seats and I'll inspect guides using method described in repair manual. If they both look OK I'll probably replace only valves as a precaution against split exhaust valve head. I've heard or read warnings this may happen on the engines with high mileage. Is there any reason why I shouldn't fit new valves into old guides if they are in good shape?
BTW does anyone know new valve stem diameter? I know they are stated to be 8MM but I'm guessing they are slightly smaller. 7.98?
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Old 25 Sep 2008
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How did it go ?
What did you chose to do ?

Ever heard of metal fatigue ?... get new valves!
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