I've got a friend's JD955 that was overheated and failed last summer. After the tractor overheated he tried to make it back to his barn but it was too late. Oil/coolant was leaked (one way or another) and the tractor was left sitting for about the past 6 months. Pulling the head, looks like the head gasket is blown. At first glance looked like was not gonna be a big issue. Cylinders look good but after closer inspection there are some what look like nicks or bumps on 2 of the three pistons. not sure what to make of them and wondering if I'll need to tear the engine completely down. Going to pool some oil in the cylinders to check for obvious leakage but based on these pics any opinions/advice on these pistons? the anomalies are at about 3-4 oclock on each.
Thanks, Nim
dodge man
Super Star Member
Kind of looks like the top ring failed to me.
dodge man
Super Star Member
I see the edge of the piston look like they unraveled a little. I’m not sure what else would cause that.
Yeah I decided to tear the whole motor down. I'll be pulling the pistons tomorrow to determine if there is any more damage. Couldn't get past the fact that one of the pistons was intact but the other two were not pristine.
Nim
Nim
So. No broken rings but the pistons were definitely scraping against the cylinders. The only place there was contact was above the rings. Some aluminum from the pistons was scraped onto the cylinders at the top. I'm gonna try a light hone at the top to remove the material since the rest of the cylinder walls are intact. I'll be replacing the pistons and rings and hoping for the best.
Nim.
Nim.
Update. Honed the cylinders, installed the new pistons and rings, and waiting for other parts. Determined the root causes of the failure. Broken motor mounts caused the engine to drop the oil filter adapter onto the frame and broke the base allowing coolant and oil to mix. Cleaned the block and passages as well as I could and looking forward to fire this beast back up.
Nim
Nim
WinterDeere
Super Member
- Joined
- Sep 6, 2011
- Messages
- 5,442
- Location
- Philadelphia
- Tractor
- John Deere 3033R, 855 MFWD, 757 ZTrak; IH Cub Cadet 123
You probably already know this, but just in case not, it's normal to have a ridge at the top of the bore. This is caused by the rings never traveling quite to the top of the bore during the cylinder stroke. The ridge can be quite pronounced (i.e. .010" or .020" diameter difference) in high-hours motors. There are tools called ridge cutters, which you can use to remove this prior to honing.
I've never really thought of this before, but I'd guess a badly worn rod bearing could cause ring damage, if the top ring were ever allowed to slam into this ridge. When you see something weird like that turned-up lip on the cusp of the piston in your first photo, then like dodge_man, my mind went toward top ring damage of some sort. Never seen anything like that, having taken apart several motors, although I'm no pro.
I've never really thought of this before, but I'd guess a badly worn rod bearing could cause ring damage, if the top ring were ever allowed to slam into this ridge. When you see something weird like that turned-up lip on the cusp of the piston in your first photo, then like dodge_man, my mind went toward top ring damage of some sort. Never seen anything like that, having taken apart several motors, although I'm no pro.
Follow up:
So, after closing up the machine and fixing or breaking up all the defective parts, she fired right up and is running great. Of course all the other issues came to light afterwards (PTO, FW/Rev pedal alignment, some electrical issues) but got her all fixed and back to work. Thanks to all for the feedback and suggestions!
Nim
So, after closing up the machine and fixing or breaking up all the defective parts, she fired right up and is running great. Of course all the other issues came to light afterwards (PTO, FW/Rev pedal alignment, some electrical issues) but got her all fixed and back to work. Thanks to all for the feedback and suggestions!
Nim
