No compression

sonic883

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So I broke a piston ring awhile, so I ordered new ones. I put it all together and it ran well, after a few weeks, I got a high compression head and a new cylinder,I took the old cylinder off, and installed the new parts, and ever since then there’s barely any compression, I’ve tightened down the head bolts, and tightened the spark plug,( properly). Just no compression
I am almost certain it’s an air leak. I currently have the base gasket off. It’s a 2 stroke 80cc (66cc)

Pls help
 

Greg58

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When you installed new rings in the old cylinder they seated to that cylinder, when you put on a new cylinder with used rings it’s hard to get the rings to seal. You should always install new rings with a new cylinder, it’s best to add a new piston too. I’ve never tried running without a base gasket but can see a chance for air leaks. As for cylinders did you compare the two to make sure they are the same? All are not.
 

sonic883

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When you installed new rings in the old cylinder they seated to that cylinder, when you put on a new cylinder with used rings it’s hard to get the rings to seal. You should always install new rings with a new cylinder, it’s best to add a new piston too. I’ve never tried running without a base gasket but can see a chance for air leaks. As for cylinders did you compare the two to make sure they are the same? All are not.
When you installed new rings in the old cylinder they seated to that cylinder, when you put on a new cylinder with used rings it’s hard to get the rings to seal. You should always install new rings with a new cylinder, it’s best to add a new piston too. I’ve never tried running without a base gasket but can see a chance for air leaks. As for cylinders did you compare the two to make sure they are the same? All are not.
It fits nicely, could it be that the top of the cylinder and the head are not sealing ?
 

YetiWoodz

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It fits nicely, could it be that the top of the cylinder and the head are not sealing ?
Could be. When I first got my compression head I had the same low compression issue. It came with acorn nuts (nuts with the top covered) and it didn't thread all the way down to the head because of that. I added some washers and that fixed it. Or you can replace the acorn with a regular nut.
 

Cisco

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@sonic883 Your avatar is so sad, I can't help but feel for you buddy. Are you saying that you have low compression, or no compression at all?
 

Cisco

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@YetiWoodz has a good point. I use tall acorn nuts with 10 threads (12mm depth). Standard acorn nuts have 8 threads (10mm depth). Measure the stud length above the head to determine your washer stack. Why aren't you using a base gasket? Crank case air leaks will make your engine run lean. There is so much temperature expansion and contraction on the cylinder, you're bound to have an air leak at the base.
 

sonic883

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Could be. When I first got my compression head I had the same low compression issue. It came with acorn nuts (nuts with the top covered) and it didn't thread all the way down to the head because of that. I added some washers and that fixed it. Or you can replace the acorn with a regular nut.
I am going to try a different head gasket
 

Cisco

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Yes, the engine should have enough compression to lock up the rear wheel when you push it. My rear wheel skids in the gravel for a bit when I let out the clutch to start the engine. Is your clutch slipping?
 
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