Low compression / weak cylinder

4wheelfurry · Dec 3, 2019

I have a 40hp 3cyl (2010 Massey with Iseki 81C 1.5L turbo) So over the course of about a year it slowly slowly developed a skip start and eventually became weak / slow burn / black fuel under load on one cyl. No noise and no other indication of an issue. Never ran hot and it only has 600hr on it. So I pulled a compression check cyl #3 is at 180psi. #1,2 at 400psi. So I popped up the rockers and shot shop air and it's blowing by into the crankcase. So I dropped some oil in the cyl and retested, sure enough compression shot back up to 400psi. I'm not a diesel guy i've wrenched on gas engines my whole life so my question is what could cause ring failure issue in one cylinder withought any warning? Some additional FYI I use it very little it sits most of the time, injectors pulled and inspected/cleaned and swapped around problem stayed in #3. Also all valves were in adjustment. I changed the oil this summer it looked fine no flakes and nothing has ever given me problems on the machine.

Agvg · Dec 4, 2019

Might be so easy that it needs to work hard, real hard over some time.

redman135 · Dec 4, 2019

Has this tractor been "run in"?
I would follow Avgv's advise and give the tractor some real work.

RickB · Dec 4, 2019

Poor coolant circulation around #3 overheated it and damaged the rings or scored the cylinder wall.
Putting it to work might not hurt it, if my long distance diagnosis is wrong it might help.

4wheelfurry · Dec 4, 2019

It has never ran hot and I keep check on coolant, everything is good on the coolant circulation end of it IMO.
It has seen it's share of hard work over the years however in the last year or two I haven't used it much.. I did have the fuel shut off solenoid go out on me so I pulled it and cut off the plunger and ran it like that a few times until my replacement came in. Can't see that as an issue. Fuel wise I have always changed my filter and always run off-road fuel, never a problem with that either...
I wonder if by oiling up the cylinder then running it if it will continue to hold proper compression? Guess that's my next try before removing the head and oil pan...

Shaneard · Dec 4, 2019

Can you run a bore scope down the injector hole and see if the cylinder wall is scarred? That may tell you if you have a broke ring, if you do running it won't help matters.

Also look in the radiator and see if there is any oil, I've heard of head gaskets failing and getting oil in the water but water in oil is more common.

mike48130 · Dec 4, 2019

Borescope it if you can. Amazon has some cheap USB scopes the would probably fit in the injector hole. Then run it hard for awhile and I would pour some solvent in that cylinder and let it sit just before the next oil change if you are having issues. I've seen rings just get gummed up and stick, so if you can get it cleaned some, it will probably work itself out.

4wheelfurry · Dec 4, 2019

mike48130 said:
Borescope it if you can. Amazon has some cheap USB scopes the would probably fit in the injector hole. Then run it hard for awhile and I would pour some solvent in that cylinder and let it sit just before the next oil change if you are having issues. I've seen rings just get gummed up and stick, so if you can get it cleaned some, it will probably work itself out.

This is what makes the forums so invaluable, I don't stay up with new tools and such as I don't do much wrenching anymore, I mechaniced for a living back when GM and Ford were beginning to introduce FI, it was mainly carbs and points/rotors ect lol.. I had no idea they now make scopes that can attach to your phone! So a scope is on order and I will go from there. Thanks all for the input!!

4wheelfurry · Dec 4, 2019

So after trying the oil trick today compression didn't hold and it even sounded a little worst after a few min of running so I went on and pulled the head. One medium and 2 or 3 light vertical scratchs in the cylinder pretty sure broken ring or piston or both... Now to figure out how to drop the front drive shaft to access the pan!