Mysterious 1980 Honda ATC110 oil leak

[zinger084]

Hello All,

This is my first post and I imagine not my last. I grew up riding a 1980 Honda ATC110 and just recently dusted her off and did a full tear down to get her running good again.

However, a few things:

1. My compression is around 55-psig and I know it should be close to 120-psig. Oddly enough, it has no issues carrying me plus kid (approx 275lb) up a 20-30 degree gravel lane. Is my compression reading off or is this feasible?

2. The trickier of the two questions. My left foot peg stamped steel support fills up with overflow oil or something of the like. I see oil/exhaust puffing out the bottom open hole here. It’s the hole facing downward in this photo directly left of the tranny hi/lo selector. Any thoughts?

https://photos.app.goo.gl/dUNVn6ChTh8pT48cA

Thanks in advance!

[shortline10]

That lower hole is the crank case breather , low compression could be the cause of excessive crank case pressure in the bottom end and causing the oil leak out that breather hole .
Time for a topend rebuild .
Also your missing a case cover bolt right next to the breather , make sure to put one back just to be sure that’s not a leak as well .

[ps2fixer]

55 psi seems quite low for a running engine, if it runs it must have no power hardly at all compared to a healthy engine unless the gauge isn't getting an accurate reading. If it gives hardly any resistance when you turn it over via recoil it's a solid sign the top end needs rebuilt. I also agree with the statements above. Good luck with the project.


Also I ran the engine number through my decoder page and it confirms it's the matching engine to your 1980 ATC110.

[DAM shop]

It also looks like I see gasket maker around the hi lo case, I would replace that with a paper gasket and check some of your other cases to see if gasket maker was used.

[zinger084]

Alright, so even though this has enough power to bring 270lbs of me and my daughter up a 30 degree gavel lane, I am getting oil blow by.

I looked into buying new piston rings, but I don’t quite get which to get. Some are oversized, I get that for bored out cylinders. However, I know this hasn’t been bored.

Should I remove and see if the walls are scored, or just purchase replacement rings of the normal size? Link to purchase (I can’t find a trusted place).

[350for350]

You should definitely take the cylinder off to check it's condition before ordering rings. You'll at least want to have it honed to get the new rings to seat. This way, you can be certain which size of rings to buy.

[ps2fixer]

The best way is to grab the service manual (free online) and perform the measurements and check the condition (some special tools needed). Shade tree style would just hone and throw in the matching sized rings with a new base and head gasket.

For power, 1hp can move a train, it's all about gearing. Worn out is worn out though, it will probably keep running, but the spark plug and such doesn't do well with engine oil getting on it from the blow by, and the engine bearings perfer clean oil, and blow by can make the oil get dark a lot faster. If the rings are bad, the cylinder could be worn quite a bit too, won't know till it's apart.

Looks like Honda doesn't stock the rings any more so you're kinda stuck with using aftermarket. I don't know brands well enough to really suggest something.

[kb0nly]

Shindy pistons and rings are all i use anymore. Chances are the cylinder is going to need to be bored out to the next size to clean it up. If you have any motorcycle/atv shops around you that can bore and hone a cylinder then have them measure it up against the stock piston and check clearance and see if it can get a hone and re-ring, but if its got enough blow by to puke oil out of the breather i highly doubt that.

I generally just send my cylinders to G&H Discount ATV, they will measure it up bore and hone to match a new piston and rings and ship it all back for a reasonable price. Last 200 cylinder i had done was $155 plus shipping, the only local shop i have left won't even bore one that cheap anymore, small shops are not a thing here anymore, the mom and pop places are gone and only the big shops that need to turn every last dollar are my other choices. Even my local motorcycle shops send them off to be done now rather then locally.

If you are going to go through all the trouble of doing a top end rebuild on it take your time do it right and it will last another 20+ years and your kids can ride it.