G1 new rings = low compression

[caddylac camper]

Originally Posted by bigredhemi

Compression tested with throttle wide open, rod straight, rings aligned with pins.

The ring gaps are supposed to be staggered, are you saying you have them aligned so they are in the same place?

[GMB74]

2-stroke pistons have alignment pins in the ring grooves to keep the rings from turning and getting caught in a cylinder port. You cannot misalign them and get the piston into the cylinder. Not without breaking the rings anyhow.

Stuck reed valves will not affect cylinder compression unless they are somehow stuck closed and keeping intake air from being drawn into the engine.

I second the notion that the exhaust or possibly intake is plugged giving you this low reading. An engine is an air pump. You must get air in and air out for it to work properly. Remove the muffler and carburetor and retest your compression.

Is your guage working properly? You might want to check it on a known good engine to be sure.

[bigredhemi]

Before the rebuild when then engine quit running......while attempting to start the muffler would get very warm while cranking..I will change muffler as I have a few spares and then will post an update.

[bigredhemi]

Took muffler and card off an retested compression. Still only reading around 30psi. What would happen if the sent me the wrong size rings? The piston is snug in the cylinder, with no slop. I guess I will have to tear down a totally rebuild......any other ideas?

[caddylac camper]

If there is no restriction on the intake side and you know your compression gauge is good then i would say you have to start dismantling the engine to look farther. A plugged muffler will certainly affect how the engine runs but not affect a compression test as you are basically measuring one stroke of the piston. Could the rings be upside down, or the piston oriented the wrong way? Check cylinder head gasket, any debris caught between the cylinder and gasket or under the head could cause a leak. This usually sounds like a squeak as the pressure escapes.

[bigstik40]

I agree with Caddylac, time to start measuring parts. Make sure jug, piston, rings are all matched and not a mixture of std./oversize parts. Make sure the old jug and new jug are the same length. Not sure how the jug interfaces with the crankcase, but make sure the new jug meshes correctly into the crankcase. Seems funny (strange) that you are getting the exact same compression after new parts. - good luck and be sure to let us know the end of the story. - RAY

[bigredhemi]

Well, spent some time yesterday disassembling everything and then broke out the calipers and started measuring eerything. Come to find out that apparently I was sent some wrong parts. The jug appears to be .5mm oversize, the piston and rings are .25mm oversize. So I started searching around my pile of golf cart parts and managed to find a .25mm oversize jug. Put everything back together and it is finally alive again.

From now on when I order a new jug I will wait until after measuring it to order the piston and rings.

Thanks for all the help and information.

[caddylac camper]

Glad you have it going now bigred

[Nikwho]

Bringing bback from dead, but still realative. Anyone here have their original jug bored out? I was thinking tbsp that to avoid this, I would buy an oversized piston and take the cylinder and piston to the machine shop and specify what the piston clearance specs are and have them bore it and hone to proper dimensions. I kinda trusted this process more than some cheap Chinese cylinder off of eBay. Also, I was thinking that it may be worth squirting a bit of oil in the cylinder to see if a coating of oil on the cylinder walls would help compression. That will tell you if it's a ring/piston to cylinder wall issue or if it's an issue with the cylinder head or plugged intake/exhaust.

Also, I was going to post elsewhere, but how much do you guys typically see these things needing to go oversize? My cart has about 90 PSI. It runs, but is hard staring. I've done the muffler bbq. I found mine needing a new fuel pump. Wanted to order the piston, rings, gaskets and crank seals at the same time to freshen it up. Thanks,
Nik

[Spicyunicorn]

thats what i did when i rebuilt mine this winter i just ordered a new over sized piston and took it a a local machine shop that way you know you have a true round cylinder but before you order new piston take it apart and make sure of what piston is currently in it it should be stamped 'STD' means standard, 010 or 25 means the first oversize, 020 or 50 means second oversize. 040 or 1.00 on the stop of piston