Honda GX 240 low compression

[bladeZjack]

Hello engine mechanics!
Greetings. Bought a non working Honda GX240 for $50. Was told been sitting out in sun and rain for years. I installed a new carburetor, new spark plug and new gas tank. I have confirmed there is spark on the spark plug. I just did a compression test and it’s only reading around 25psi. I have made sure the compression testing equipment was screwed in tightly. I’m planning to disassemble the engine to see what the piston is looking like. But before I do the whole disassembly, any thoughts or insights on what else to do to get this motor running? Thank you!

 

[Whitetrashrocker]

I would assume it's toast. You might get it running though. Complete tear down and I mean everything. The rings might be stuck and need replacing. The cylinder will need at least a hone job.
Could have a wore out cam, or burnt valve. That little compression is concerning.
Could just be a stuck valve.
Tough little engines. But expect the worst.

 

[bladeZjack]

Thank you. Just in case there’s something I could pour into the cylinder (snake oil maybe hehe) to help before I do the disassembly. I’m hoping it’s just the piston rings. I don’t really know much yet about small engines. This will be a very good learning experience.

 

[Whitetrashrocker]

You can try dumping a little motor oil down the spark plug hole and try your compression test again. It won't fix anything but if it gets better than you have a ring problem. If it doesn't then you have a valve issue.
I prefer a leak down test over just a compression test any day. The results tell you where your leak is and not just you have a leak.

 

[bladeZjack]

You can try dumping a little motor oil down the spark plug hole and try your compression test again. It won't fix anything but if it gets better than you have a ring problem. If it doesn't then you have a valve issue.
I prefer a leak down test over just a compression test any day. The results tell you where your leak is and not just you have a leak.

Okay I’ll try that. I’ll YouTube leak down test also. I’m not familiar with it. Thanks!

 

[panchothedog]

Marvel Mystery Oil is good stuff. A little thinner than motor oil. Might get into the rings a little better. Also pull the valve cover and pour it all over the springs while rotating the engine. FWIW. The couple of times I have tried to measure compression ( on a freshly built high performance 212 ) I was quite surprised how low it registered. This is due to the compression release built into the cam to keep the engine from kicking back when pull starting. It might be shot, but don't assume that it is from your compression test. Pour in the mystery stuff, rotate many times, pour in more and let it sit for a few hours, flush, add fresh motor oil. Make sure to clean out the gas tank. If it's really funky, after draining, put in a couple of dozen nuts and a quart of clean gas. Shake REAL HARD. You will know by what comes out how many times you need to do this. When they have been sitting a long time, I like to spray a little starting fluid in the intake to help it out a little. But I am pretty old and get tired fast.

 

[Denny]

Pancho has the best advice. Also some Sea-Foam in the gas tank and down the cylinder will help free up rings.

 

[Master Hack]

Also some Sea-Foam in the gas tank

This shyt?

 

[Denny]

Not quite there big guy.

 

[Darren]

try doing a compression test with the tappet gap set at 2mm before dismissing the engine and using it as a paperweight. You may be carrying out the compression test against the compression relief.

 

[panchothedog]

Just try to get it to run. If it won't, you don't have anything to lose. If it runs O K then the compression was alright. The compression release giving a false low reading is exactly what I explained in post #6.

 

[bladeZjack]

Okay thanks so much! Haven’t gotten around to it. Still learning all this new technical terms. Kind of hard to accomplish a task when one doesn’t truly understand what’s going on. hehe