I had the CRRC GP26R 2 stroke gasoline engine on the stand for a month and got the engine broken in and running great. I was ready to put it in the plane and decided to try it on the stand one more time. There was almost no compression and of course it wouldn't start despite a good spark and plenty of gasoline getting into it. The cylinder and piston look like there in new condition no scoring or anything. What can make this happen. All the engine did was sit on a table for a few months.

I would check the reed valve unit. as it is probably stuck or jammed open or closed somehow.
It is located in between the carburetor and the engine. It maybe just needs to be cleaned as something is keeping it from working.

The ethanol in the California gasoline will ruin any carburetor that has been dormant for a few months. Get a rebuild kit for it and replace all the gaskets and diaphragms. Dan.

Did you do the pressure pulse line mod for the fuel pump?

Even if your carb is stuffed or the reeds stuffed you should still get compression when turned over.
The compression occurrs when there is a good seal between the piston and the cyl, moving the piston up compresses the air/fuel mix trapped inside.
You either have a loose plug or a stuck ring.
I'm not familiar with crrc, but you should be able to take the muffler off and move the piston to a point where you can look in and see the ring.
Look for a lot of carbon/black. If you have been running it too rich or something awful like lawn boy, you may have this issue.
As a last resort you will have to take the jug off, no big deal, just 4 hex bolts, check that the ring is moving freely or isn't broken.

I was going to make a joke about putting the plug back in as that is about the only thing that might cause your problem besides stuck rings which are unlikely. I have broken plugs before so make sure nothing knocked against it and caused a crack. Taking the head off is good advice and you can check how tight those bolts were in the process. Hope you don't have anything serious.

Take the plug out and put a 1/4 tsp of oil in the cylinder and turn the crank several times to distribute the oil .Drain out remain oil and reinstall plug . If you now have compression enough to start the engine the ring was probably cooked when bench running the engine.

I took the engine apart and put it back together. Still the same problem no compression. Everything looks good and fits and smoothly turns. Just no compression. There is a spark and the fuel is being delivered into the crankcase - I dumped a bunch out when I took it apart. The CM6 plug looks like new and runs good in another engine I have. It's like someone put a curse on my nice engine!!

Is it possible the cylinder just went slightly egg shaped for some reason.

I'll try to start it again - I think the ring may have lost a small piece off the end there looked to be a angle cut on one side of the ring I don't remember seeing one on the opposite side but I'll take it apart again and check it.

When you slid the jug over the cyl, did it go on like there was no resistance, or did it take a bit of work to get it into the mouth of the jug, then showed fair resistance while inserting it?
It seriously sounds like your ring is stuffed, I'm not sure if Frank Bowman makes a ring for that engine, maybe look into that.

BTW I just don't get why people just have to break gas engines in on the stand. They don't have the cooling properties that glo engines do.
All you need to do is tune it to run reliably and go fly it! That way you are at far, far less risk of overheating and cooking parts.

It was very hard to get the piston with the ring back inside the cylinder. I tried oil and turning it and it din't want to go in. Finally it went in.

I have worked with many engines and will always try to get them off the stand as quick as possible but if there's excessive vibration or tuning problems you have to keep them on and running until they run properly.

This engine had too much vibration. When I took it off the stand the last time it was idling great and very smooth I don't know what happened to it sitting around.

Basil, there has to be a leak somewhere, either the ring is missing part of it, or the jug is cracked or the spark plug is stuffed or not sealing.
Have a good look at the jug for cracks.
Also get some dish washing liquid and make up a soapy mix. brush/slop some of that around the base of the spark plug and turn the engine over, look for bubbles being produced.

The piston has a pin in the ring groove. It's supposed to capture the ring gap and prevent the ring from rotating and potentially snagging on a port. Was the pin and ring gap lined up during your struggle to get the cylinder back down over the piston? If not, safe bet you have a broken ring now, if not before.

On another wavelength, this is the rear carb version? A broken or hung up reed valve can cause big starting issues, as well as affecting compression. If the crankcase can't hold pressure as the piston comes down, the cylinder may not fill completely when the ports open, which can directly affect your compression (making it hard to start). Something you might want to have a look at anyway.

I have had several CRRC engines and I was not impressed with quality or performance. I don't anymore...............for good reason, sick and tired of some problem or another, always.

I also have the CRRC Pro 26cc side carb engine with the standoffs and read cylinder head, it was a pretty good motor but this rear carb version was a dud. I think the carb being on the cylinder head intake was more of a reliable system. When they designed this engine they were trying to make a rear carb version with beam mounting flanges which is a great improvement but they missed something.
It's possible the newest version of this engine has the bugs worked out.
The red head 26cc did run pretty good for 5 years and I still have the engine to put into another plane. I would rank them just under DLE but I also had a DLE that was a dud but since I purchased it from Tower they just replaced it. I can't send this one back to china.

Remove the ring from the piston and push into the cylinder with the piston.Check end gap,shouldd be only .001to.003.If more ring is worn out or broken,Get a Bowman ring for your engine.
BCCHI

Where can I get a Bowman ring

Hi Basil, Frank doesn't have a website as he is in such demand he doesn't need one, (lucky/skilled fella).
Send him an email of what you need, he is in the states.
[email protected]

PS do what ahicks said also, if you have starting problems this is certainly something to look at, but if you have lost compression altogether then get a new ring.

I'll get a hold of him for a ring it couldn't cost too much and I think it might resolve the proble.