Piston Ring Blow-By
 

Hi; I have a K&B .61 [6550] that I think needs a new piston ring.
When you turn the prop over you can hear air coming out of the exhaust on the compression stroke. I assume that would be blow-by around the piston ring, right, or is that normal? If it is the ring, is it normal practice just to replace the ring or do you replace
the ring & sleeve. Veco
PS- The glow plug was in the engine with a new gasket.

Piston Ring Blow-By
 

Hopefully someone with K&B knowledge can answer your question. What I want to say is that it may be normal depending on a few things. I don't remember if this engine has a Dykes ring, or conventional ring. If it's a Dykes, it seals best while actually running. How does it start and run_bob

Piston Ring Blow-By
 

If this plane has not flown in a while and the cylinder is dry, this can happen because you don't have a good seal. Try either adding a little fuel to the engine to see if it seals or just start it and check the RPM and stop the engine and check the compresion again.

Piston Ring Blow-By
 

The cylinder is wet with fuel and it is a conventional ring. Veco

Piston Ring Blow-By
 

When you run it, what engine RPM do you get?
I have seen several glow engines that have little compression when turned by hand but run great and are strong.

rpm
 

The engine at full throttle gets up to its normal rpm, although it does'nt have alot of power...........Veco

Piston Ring Blow-By
 

Ring groove in on exhaust side of cylinder , no problem the ring will rotate on the piston or you can relocate the grove but will probably will be back some time or the other.

Piston Ring Blow-By
 

The only option seems to be to remove the piston and measure the ring and cylinder clearance.

Ring leak
 

All rings rotate on the piston if they are not pinned . try to catch
the end gap where u can see it.it should be .010/.020 max if more the ring needs replaced ( wear increases the end gap first)
(2) leakage of this sort is a cc per second type of thing & leak per piston stroke @ 10 or 12k is a minoramount per stroke.

ring replacement
 

IIf I do need a new ring what is the proper procedure of replaceing one ? Jim

Piston Ring Blow-By
 

of you do it slowly, then yes, you will hear that. it is metal to metal, not rubber to rubber. however, rings do ned to be replaced from time to time. i would get a new sleeve too and break it in again if i were you, but you can just get a new ring and sand the inside fo the sleeve with 1000 grit sandpaper. i know it seems just wrong, but sometimes the ring will scratch the sleeve and they will wear together that way. you need to eliminate that posibility. you don't have to be able to see it. you can take the backplate off, detatch the con rod, and jsut slip the piston out. the ring will expand, and maybe even crack. what you do is when you get a new one, look closely around the ring cradle for a little something that sticks out. that is there so that the split in the ring hugs that keeping the ring from rotating. it is important because if the split in the ring comes around to the exhaust port, you are screwed. it will expand and destroy your engine. to put it back on, you probably won't need a ring comnpressor. if you look on the bottom of the sleeve, you are likely to see a bevel on the edge. that will compress the ring. just put the piston back in the engine without the sleeve, and then shove the sleeve in. rotate it, and the ring will compress allowing it to slide back in. you will need to break your engine in again.

piston ring
 

Hi; Thanks for the information. I have never replaced a ring before but looks like I am going to try. Thanks........Jim

Piston Ring Blow-By
 

I'm not sure you got the answer you were looking for. I'll look in my 2 stroke bible tomorrow and give you a page number for ring replacement . A couple of years ago I bought a book by Dave Gierke called, " 2 Stroke Glow Engines for R/C Aircraft." It is a comprehensive guide to Understanding, Running, and maintaining our little engines. It covers from design history to field operation of the modern glow engine. I thind Dave writes for one of the model magazines. If not, do a search and pick it up. It's well worth it. Good luck_bob