Ok, I just got this thing through mecoa and, while I've only owned five or so glow engines, I've never felt one with so little compression.

I mean, I feel almost nothing when the piston reaches TDC and through the stroke. The plug and all the cylinder head bolts are tight. Is there any chance this is normal??? I have another ringed engine- an OS 60 LA- that has much more compression.

Damnit, I don't want to have to send this thing back.

ok, well, first of all, the la series engines are all abc, second, ringed engines usually have very little compression feel when brand new and some never seem to have alot.The design of the ring is to expand on compression but to actually collapse a little on exhaust stroke for more power.I think if you hit that thing with a starter motor you will find it will fire right off and run great .

It's a ringed engine and when brand new it does feel like it has no compression. Mine did too when it was new, you have nothing to worry about... it's a great little engine. It like's the APC 13x6 or at least mine did.

It's a beauty too isn't it?

No longer support RCU

Thanks guys! Obviously I was mistaken about the LA being ringed. I'm sure my GMS is Ok then.

I'm not dead sure but doesn't the GMS use a Dykes ring? Easy to tell though...just look through the exhaust port and if the ring is right at the very top of the piston then it's a Dykes ring. These can have almost no compression when turned over by hand because they rely on combustion pressure to force it out onto the liner. But don't run it in like an ABC!!

Yes it is a Dykes ring...

the thing to watch out for on a Dykes ring is a lean run. It can ruin it in one flight under the right circumstances

Greetings:
My GMS is nearly broken in after 5 flights. It has been turning a 13x5 prop at 12300 rpm and until you mentioned the engine have very little compression, I had't noticed.
When I immediately checked, I found that it doesn't seem to have much compression, but having just flown it wide open yesterday and taching her, I can confidently say, it is not a problem. For the $80 spent, it is a fine engine in my eight-pound Chipmunk. Flies the verticals, and doesn't require a lot of tinkering.

downunder said it best, with a dykes ring the compression comes from the pressure pushing the ring against the wall. You can't create enough of that pressure by turning it with your hand.