2012 john deere 772GP Low compression in 2 cylinders

[Leighva]

Any one else having engine problems with this 2012 machine? I have 9000hrs on this machine and have low compression on 2 holes.
If so was it mechanical or electrical?
What was the cause?
Thx in advance

 

[mg2361]

A machine serial number please.

List your compression readings.
List your stored and active codes.
Did you perform a leak down test of the cylinders?
Has any injector work been done to that engine in its lifetime?
How are the valve adjustments?
Been serviced regularly?
Has oil sampling been a regular part of the maintenance? If not have an oil sample done now to see if there are hidden gremlins in the oil.
Even armed with all this information we still may not be able to determine what caused it until a tear down.

 

[56wrench]

if the low compression is in 2 adjacent cylinders, it may be a blown head gasket between the 2 affected cylinders

 

[Leighva]

John Deere did the service on it and a county shop. I just bought this machine. I called John Deere and they did an air to air test on the inter cooler. Compression was not an issue that they know of at that time. Later it was brought back to Deere because it was missing. Computer said low compression. They pulled all the injectors and did a mechanical pressure test and found #1 @ 300 psi, 2-5 in the normal spec range, and #6 @ 260 psi. The service tech I spoke with said they then found one hose that was in question that might have caused damage to the two low pistons. They said this was the first time they had one of these graders with low compression in two cylinders.
Additionally they also found a bit of end play in one turbo and recommended replacing it when they did the compression check.
My thought is the since I see no smoke at start up or while running it I might be a valve issue. I rain it 4 hrs and it didn’t seem to be missing too bad or smoking that I noticed.
I’ve yet to put a camera in 1 & 6 to see if it is scored. that’s my next step now that I just got it to the shop.
it would also seem that if a hose came apart it would have burned out the exhaust causing no cylinder damage. It would seem possible something could be stuck in a valve seat on the intake or exhaust Valve and not burned out completely holding it open.
Any other thoughts?
All the fluids were changed before I got it so I have no history on the oil.
I’m thinking ill look in the piston and see what shows up their. If nothing I’ll run it for awhile and see what shows up. I’ll also change out the turbo in question.

 

[mg2361]

A serial number would help for accurate information.

I find physical compression tests only reveal severe issues like valves or a hole in a piston, but seldom work on ring issues. I say that because I had an 4 cylinder engine with a hard start issue and had 450 psi across the board on the compression test but all 4 cylinders had broken top rings. So your engine with 300 and 260 has an issue I believe is not ring related (unless they are destroyed).

So my suggestion would be to get yourself a cylinder leak down test kit and perform the cylinder leak down test. That will tell you exactly where your compression is leaking to.

https://www.napaonline.com/en/p/SER...ster&keywordInput=cylinder+leak+down+test+kit

 

[Leighva]

Thx for the suggestion. I’ve not do one of these tests but seems like a good test that will give me some facts to work from. Again Thx.

 

[Fatgraderman]

What is blowby like? Crankcase vent doing it’s impression of a steam engine? Some have had a camshaft issue. Not sure how much that would affect compression though.

 

[Leighva]

What is blowby like? Crankcase vent doing it’s impression of a steam engine? Some have had a camshaft issue. Not sure how much that would affect compression though.

Oh that’s very helpful information to know they have had cam shaft issues. I’ll look for that and blow by.