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Old 11-19-2017, 05:59 AM
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davidej
 
Join Date: Nov 2002
Location: West Mersea, UNITED KINGDOM
Posts: 138
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Default Help with valve guide

I have a 38cc air cooled four stroke model aircraft engine.

http://www.justengines.co.uk/acatalo...l_Engines.html

The engine stopped in flight and made expensive noises when I tried to restart it. I removed the head and found it had dropped a valve and its guide. Instead of conventional collets, the valves are retained by an 'E' (or is it 'C') clip. I can't quite understand why, but the guide is an easy sliding fit in its location - I thought it should be an interference fit and thus hard to press back in but this is not the case. I wonder if the guide was not properly fitted from new and it dropped, forcing the valve down and shattering the clip. but that is all conjecture.

My local engineer was going to make a new guide which would be an interference fit, but then decided it was too difficult. The guide is about 6mm dia with a 3mm hole for the valve stem and about 15 mm long.

I can buy a complete new head but this is barely economic on a second hand engine, so I wondered if there is way to fix it. Anything is worth trying as it can't make things worse.

Is there any grade of Loctite or epoxy which would work at these sorts of temperatures? Alternatively, could the guide be knurled in a way to raise high points which would hold it in its location? How would I go about this? The guide does not really have axial force acting on it so it should not be too hard to secure it.

Any suggestions would be welcome.
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