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Leaking exhaust valve

Old 01-14-2006, 01:13 AM
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CigarSlicer
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Default Leaking exhaust valve

I got a Magnum .30 4 stroke off here and it won't run. The exhaust valve is leaking like mad. It just won't make enough compression to fire off. Even with an electric starter. The leaking is clearly heard at the muffler. Anybody got any luck with grinding or reseating the valves or any ideas on how to?

Thanks
Old 01-14-2006, 02:12 AM
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William Robison
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Default RE: Leaking exhaust valve

Slice:

I'll assume you've checked the clearance. You have, haven't you?

99% of leaking valves in model four stroke engines are caused by foreign matter trapped on the valve face or seat. Most of thesse bits that don't blow out by spinning the engine with an electric starter can be blown out with compressed air through the plug hole while holding the vsalve open with your fingers. Be sure to take the prop off before doing this.

Finally, for the one percent, take the head off, inspect the valve and seat. Make sure there's not some gum on the stem and guide keeping it from closing fully. Then clean the valve face and seat with a pencil eraser. Stick the valve back in the head. Hold the head with the exhaust port vertical, pour some medium weight oil in the port and watch the valve face. This will show if it's still leaking. If it does still leak you can try lapping it. I strongly recommend replacement of the valve instead of lapping, but it's your engine.

Bill.
Old 01-15-2006, 02:46 AM
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CigarSlicer
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Default RE: Leaking exhaust valve

I did.. clearence was OK. No dirt. I tore it down, chucked the valve in a micro lathe to check for run out. None. Checked the face and seat with a 10x loupe. Nothing to be found in the way of damage so......I lapped the valve with some compound and finished up with Bon Ami. Put it all back together and what the hell do you know! It RUNS !

Thanks!

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