Union Models

Wondering if you guys may be able to help. I treated my trusty YS63FZ-S to a new set of bearings and new piston ring, as it was down on power.

Ive noticed the inlet and exhaust valve seats leak, a gentle hiss is heard. I know about relapping the valve seats. Should both the inlet and exhaust valve be a totally leak free, or is slight bubbles blowing from the seat normal.?

With a new piston ring, would I need to run the engine in again, as if it were new.?

Thanks Mike.

kenh3497

In an ideal world the valves should seal 100%. If this were my engine I would make sure there is no carbon on the valves. In my experience the exhaust valve is usually the culprit as a "little" carbon seems to collect on the sealing surface. A light Scotch Brite on the valve and then a light lapping should help.

In my opinion a new ring should be treated as such and use a normal break in procedure. Some will not agree with me but I tend to run my engines (YS) only enough to set the high speed mix and get a somewhat reliable idle then fly them just slightly rich to finish the break in process. Your needle settings shouldn't have changed much, if any, so i would set it a bit rich and fly it. A couple tanks of loops, climbs and dives should get you most of the way there. As always listening to the engine during the flight and landing if anything sounds not quite right is prudent.

Ken

Union Models

Thanks Ken for your reply. I will clean up the valves and give them a lap and run in as you say.

Thanks, Mike.

Four Stroker

I have found that carbon on the exhaust valve stem as well as the seating surface can be a problem. I scrape off all I can with a #11 and then clean up with a wet Brillo pad. The 3 mm valves on the 63 are close to 1/8" and can be chucked in a Dremel tool. I stick the valve spinning in hot water and clean with the Brillo. I also wrap a bit of Brillo pad around the end of a chop stick with a small rubber band and clean the valve seats. Lapping can be done with tooth paste - gritty whitening kind. The newer engines have better valves and chromed seats. I have stopped lapping since it did nothing. If the exhaust valve seating surface is not shinny after cleaning up replace it. I have burnt and warped valves. Sport flying should never do this however.

Union Models

Thanks for your reply, I took the valves off today and the exhaust did have quite a bit of carbon as expected. I cleaned off the carbon with wire wool and cleaned well. Later I'll give the valves a lap and see if the seal is any better.

Mike