Engine valve timing

Last weekend I finally found what problems I have been having.

Initially I did set up the valve timing according to the manual. and yes the engine ran quite nicely. But when it came to test runs and flying, it barely came of the ground. So we started looking into the problem.

I did find that I had my tappet clearance set wrong, I blame the manual for not being clear and myself for never worked on engines before. I got a bit more power, just enough for getting of the ground. But I need a lot more.

So Warren and I and later Wayne, started looking into the valve timing. And after I did a whole lot of measurements, mainly valve position against crank shaft position, with detailed position of the #1 and #2 cylinder valves, and just opening times for all other valves, I found:

  • The exhaust valves open very early, and as a consequence close early, and the same for mixture open and close times.
  • The time #1 exhaust valve is open is a lot longer then all the other ones, and the should be the same, so something is wrong with that one.

So I started changing the cam timing to get valve open and close times that make more sense. Its then when “the coin dropped“. The initial valve timing setting was wrong because the #1 exhaust valve has a timing problem. We expect a bigger cam roller for that one.

When increasing the tappet clearance on the #2 and #5 exhaust, after all had been set to reasonable timings, the exhaust valve closed at the time described in the manual, at TDC (top dead center).

Great, so the manual has been correct all the time. Its just the wrong #1 exhaust valve timing that changed everything.

So currently taking more of on the back of the engine to investigate this silly exhaust valve!!!!!

Leave a comment