Cooked exhaust valve

[jlaban]

'99RT 68,000mi. at high speed left cylinder failed. Diagnosis is one of the exhaust valves is cooked. I'm asking for probable causes. Could ethanol have contributed? I used Stabil for winter storage, but not since riding this spring.

John

[nhbmw]

'99RT 68,000mi. at high speed left cylinder failed. Diagnosis is one of the exhaust valves is cooked. I'm asking for probable causes. Could ethanol have contributed? I used Stabil for winter storage, but not since riding this spring.

John

I doubt the absence of Stabil or the presence of ethanol had any effect. Most common cause of burnt exhaust valves (in my experience) is tight valve lash or lean mixture.

My local independent BMW shop had a hexhead in last week with 190psi compression left and 10psi right. Rider said the bike lost power and ran rough while in the road. He didn't stop or investigate, just kept going. The rubber air hose had slipped off the right throttle body, which let the right cylinder breathe more freely than the left. 2 burnt exhaust valves.

I'm sorry for your problem, John, but I don't think fuel additives were responsible.

Art

[GSAddict]

Had a similar thing happen to mine at 120 km hr, hard throttle passing.
Sounded like very loud pinging all of a sudden
The head specialist said 4 things contributed to it. (these guys are the guru's up here)

Lean mixture (fuel map)
Ethanol in the fuel ( I had just bought some no name gas in washington state)
Carbon chunk breaking off and holding the valve open momentarily
Excessive lean as the ambient was 43F (worst case for lean)

Had heads redone, no problems since, use seafoam every 10,000 now.

[billpierce]

Were the valve adjustments kept up? If the clearances get tight and a valve doesn't close completely will burn in short order.

[GSAddict]

Were the valve adjustments kept up? If the clearances get tight and a valve doesn't close completely will burn in short order.

Yes, I am meticulous about regular valve adjustments, and checked them before disassembling the engine.

[jlaban]

Yes, I am meticulous about regular valve adjustments, and checked them before disassembling the engine.

Me too. Had mine done 500mi ago.

Thanks for the responses.

John

[jdiaz]

Did any of these bikes have a remote fuel filter conversion -OR- use an aftermarket fuel filter? That might be a source of lean-ness as well.

[GSAddict]

Stock OE on mine in tank

[jlaban]

Did any of these bikes have a remote fuel filter conversion -OR- use an aftermarket fuel filter? That might be a source of lean-ness as well.

Same as above. Mine is stock.

John