stuart macrory Posted November 26, 2008 Share Posted November 26, 2008 hi all,i have an sc 52 fs engine which has has approx 20 flights from new,but recently i would get the occasional dead stick and when i go to start the engine it has lost all compression.the strange thing is if i unscrew the crank case head i have compression again and when i screw it back on the plane will fly for another handfull of flights.i checked the inside of the head for any marks but it is spotless.anyone any ideas? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 26, 2008 Share Posted November 26, 2008 If you mean the cylinder head...then this sounds like the valve clearances may be wrong. By slackening the head bolts you are effectively raising the valves away from the piston, and rescrewing it back on again may be allowing the necessary gap to develop. I know the rocker gear is part of the head....but it just sounds obvious to me that valve clearance is your issue.Are you checking the tappet clearances when the engine is cold , and what gap are you setting? Quote Link to comment Share on other sites More sharing options...
stuart macrory Posted November 26, 2008 Author Share Posted November 26, 2008 sorry timbo yes its the cylinder head,to be honest i have not checked any clearances as i dont know how to,is it easy enough to do? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 26, 2008 Share Posted November 26, 2008 yep. ensure engine is cold, and remove the rocker cover ( single allen screw )use a feeler guage ( available from car accessry shops and the like ) and move the prop around until the piston just raises the pushrods and you can see the valves being pushed down....keep turning slowly and the rod will then start to drop down, as the valve seals tight, there will be alittle play between the rocker arm and the pushrod, and this will also result in there being lay ( a gap ) between the other end of the rocker arm and the top of the valve stem. This is the gap you need to check with your feeler guage...it should just slip in smoothly without pushing the valve down at all, but not be a sloppy loose fit. You adjust it by slacking off the screw and locknut. Do a google for more info if you cant figure my instrcutions out . The gap should be 0.1MM / .004” / 4 THOU. ( whichever flavour you work in ) Quote Link to comment Share on other sites More sharing options...
stuart macrory Posted November 27, 2008 Author Share Posted November 27, 2008 thanks timbo ill give it a try at the weekend Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.