1989 Ezgo 3pg 105 compression

[kingja68156]

My compression is low. 105psi. Here is what I’ve done so far.

I rebuilt the top end about 4 years ago.

HEI conversion just completed and had plenty of spark

Rebuilt starter

It’s getting fuel to the cylinder the spark plug is wet.

Gas is new, pre mixed to 128:1

Cleaned and inspected the reed valves

Took the head off and the rings are intact, the pin holding the piston to the connecting rod was hard to pull out.

[kingja68156]

Here is a pic of the pin

[cart around]

105 is very acceptable.

[kingja68156]

Originally Posted by cart around

105 is very acceptable.

I’ve read that it needs to be 120+. Anything 100 and below is not good. 105 is low. What do you think about the condition of the piston and cylinder?

[cart around]

120 is new. 100 is acceptable. 90 is worrisome. Most quit running at 60.

Can you feel the scoring in the cylinder, or is it all visual?
It looks like there was a lot of blowby past the rings. That is burned oil. I don't see the alignment pin in the ring groove. I have to wonder if the rings were installed correctly.

I'll guess that it was taken apart because it quit running, and you weren't sure where to go with it. You saw a wet plug, and assumed that you lost spark, so you performed the HEI modification. You were really bummed when that didn't fix it either.

A wet plug doesn't mean it's getting gas from the right place. It could have very easily been a ripped lower diaphragm in the fuel pump. That will foul the plug, and make it look like you are getting fuel.

[CP241]

CA is right on the money as usual.

That's an awful lot of scoring, blowby, and wear on the piston skirt. I dont know that was ever installed correctly to begin with, if the alignment pins for the rings broke. Or what. But that looks pretty bad. No reason you should lose that much compression in that short of a time.

How much play is on the big end of the connecting rod? Worn bearing on the rod can cause the piston to slap around and wear itself out like that too. Might need a crankshaft if so.

[kingja68156]

I measured the piston diameter and it is slightly off. 71.71mm to 71.91mm. so it’s not exactly round.

The rings when I put them in are directional. I put them in using the notch instead the ring groove. Is there a special way to install them?

[cart around]

They are called Keystone rings. The bevel side goes up. Each ring groove has a tiny steel vertical pin. The ends of the rings should be at those pins. Ring end gap should be around .008-.012". It really looks like those rings never seated properly.

I don't understand what you mean by using the notch instead of the ring groove.


This link is the 3pg manual. Each chapter is broken down into a separate pdf, but it's all there. https://app.box.com/s/3habgxrtgz
You will be most interested in pages H-20, 21, 22, and 23. They are all about measuring the piston, and cylinder along with installing the rings.

[kingja68156]

Thanks for your reply. Also I did notice that the sea clips holding the pin in the piston were bent. Not sure what could have caused that. I’m going to have to order new rings and pistonThanks for your reply. Also I did notice that the sea clips holding the pin in the piston were bent. Not sure what could have caused that. I’m going to have to order new rings and piston and gaskets.


I have one other question. I took a picture of the read valves. I’m not sure if I’m able to find replacements. But can you take a look and tell me if you think I have an issue

[cart around]

I know that in theory the reeds need to be airtight. Since I can't say what will happen when they are actually installed, I have to defer to somebody that has more practical reed experience.