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By GreyHouse
#99041
I bought this bike with 4000 miles and I have put on another thousand. A couple days ago it broke the head off the exhaust valve at about 3900 RPM in 5th gear. I suspect the valve stuck open in the guide and the piston smacked the valve head and broke it off. It made quite a mess, making a big hole in the top of the piston. I will be upgrading to the 535 bore kit and a new cylinder head and upgrade valves. There were no shavings in the engine oil main sump but the suction screen had a lot of shavings on the outside of the filter.
Here is my question. Can I clean everything out well enough without removing the engine and splitting the crankcase? If I flush it with lots of kerosene, will that clean it out? Also, what would cause this to happen?
Any advise is appreciated.
Dan
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By LanesExplorer
#99043
I would agree with the Duke, Dan. That's really too major a failure not to do an engine strip, especially as you don't yet positively know what caused the failure. For peace of mind, I wouldn't hesitate to do a complete strip and thorough clean. On the way you'll probably find the root cause of the failure.
Peter
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By stinkwheel
#99045
Split it. If it holed the piston, there's a good chance alloy swarf will be everywhere you don't want it.

Out of interest, was it a standard valve or an upgraded one? Just you are telling a familiar story...
Image

I was glad I stripped mine because it turned out the drive shaft was also loose in the crank flywheel, just being held in by the key. Althought I don't think that's what caused the failure, it looked like there had been a fatigue fracture through the friction weld holding the valve head on judging by the blueing on the broken edge. Not sure how/why.
By Beezabryan
#99046
Can I clean everything out well enough without removing the engine and splitting the crankcase? If I flush it with lots of kerosene, will that clean it out?

No
User avatar
By LanesExplorer
#99048
And think of the incredible feeling of satisfaction you'll get from knowing that you've got a completely clean engine! It really is the only way to be 100%sure.
By Duke of Wybourne.
#99050
I've done two motors that have suffered the same fate. My own opinion is that the cause was straightforward valve failure, in both cases exhaust valve, just about at where the taper ends from valve head to stem, one on a 500, the other on a 535 GT, both standard trim. One thing I noticed was that both bikes would have appeared to have been running hot due to the heavier than normal discolouring on the downpipe and silencer. I replaced the valves on my own bike with quality replacements.
By GreyHouse
#99052
Thanks for the responses, but none of you said what I wanted to hear. However, the reasons for spitting the case to do a complete teardown seem to be for piece of mind and in case I might find something else wrong. Removing the engine and disassembly seems like a duanting task to me, where so far removing the piston was relatively easy.
I will not discount all your advise, but I will try flushing first to see how much I can get out. Also, the shavings are aluminum and have more danger of plugging up an oil passage than actually scratching something to death.
And yes, this was a stock exhaust valve, and it broke at the base of the head.
I should say that for the last 500 miles I have had a muffler from Hitchcock and a cone air filter from BAAK. I have read that this will run lean and two days before this happened I installed a Powertronic Fuel controller. I took it pretty easy on the bike until I got the Powertronic installed.
Dan
User avatar
By Adrian
#99053
AFAIK the standard UCE valves are made with a separate head and stem welded together, common practice. If you go over onto the US forum and have a search, I think someone was offering one-piece valves (i.e. MADE from one piece of metal) which are less likely to drop a head into the engine. Haven't checked to see if our hosts have anything like those.

A.

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