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[stinkwheel]

Mine was a competition valve

Also, the shavings are aluminum and have more danger of plugging up an oil passage than actually scratching something to death.

.

Yes. But that's the danger. A blocked oil passage is catastrophic. I found aluminium in the crankcase, all the gauze filters, the main oil filter, the scavenge pump pickup oilway, the transfer oilways in the timing chest and a little packed into the rocker blocks for good measure... I also never found the end of the sparkplug electrode.

Had the crank been salvageable, I'd have been pumping loads of oil through because there was almost certainly some in there too.

[Adrian]

Indeed, but they don't tell you whether they made from one piece of steel or not.

A.

[Daiwiskers]

Have to say it I agree with everyone else

Strip and rebuild time do it now over the winter then you know it will be right for the spring

If you just rebuild the top end the chances are you will have to pull it apart in a few miles

Sorry can't be anymore positive Dai

[stinkwheel]

Indeed, but they don't tell you whether they made from one piece of steel or not.

A.

They are friction welded. That's where mine broke.

[Wheaters]

As Eric Morecambe used to say about Ernie Wise……

But you can, if you look carefully.

[John G]

I had a mechanical disaster on my Honda XL 250 ohc single, some years ago. There was a light metallic pinking noise from the top end, which I decided to ignore for the time being, it being Summertime, etc. On a run one day there was a metallic clank, and the engine died. The camshaft sprocket had worked loose, split into pieces, wrecked the camchain, bent valves, the works. I partially dismantled the engine, got out all the nasty metal fragments, and was contemplating reassembly, when I decided it was better to go the whole hog and check everything. On inspecting the oil pump (a trochoid type), I found a cracked rotor, caused by a metal fragment jamming in it. This was not obvious at all, and had I simply reassembled the engine there was a second disaster waiting in the wings .....

[stinkwheel]

I bought an enfield with a freshly rebuilt engine. The more I looked at the bike, the less happy I was with the previous owners work. I eventually decided to strip the motor and found two bits of broken piston ring in the bottom of the crankcases. Not, I might add, from the ones that were fitted.

[Wheaters]

Years ago I heard a story about a BSA Gold Star where the engine blew up at full throttle. At first it was thought that a valve had shed its head because of the mangled innards and a holed piston, but then it was found to have something unknown in the cylinder, which briefly caused a lot of head scratching until it was found to be a battered coin. The owner had pulled it out of his pocket with his handkerchief and couldn’t find it. It had obviously dropped into the GP carb bellmouth and lodged there till the throttle was fully open.

[Adrian]

A 50p piece, someone published a picture or two following that incident, including one of the mangled coin recovered from the engine.

A.

[Wheaters]

My favourite publication back then was Motorcycle Mechanics, so it was probably in there.