John Deere 755

[dbandgb]

A question I cant answer. A John Deere 755 with 3 cyl diesel what should the compression be on a new motor.

 

[rScotty]

Here is a chart from the people who made the JD755 motor. This one is for a normally aspirated non-turbo Yanmar with a 23:1 compression ratio. The JD version is the same....maybe a little lower.

1.The "retainer" they speak of in the procedure can be made up out of an old injector using the injector threads on one end and weld or braze an adapter for the compression gauge on the other end. Its function is to hold a little inside piece called the "indirect injection insert" in position. Normally the injector holds it. You don't have to use their particular adapters, but use something to hold the insert in the head in place. A lot of people skip this step because they hope that on an older engine the carbon will hold the insert in place in the head - and usually it does.
2.Take out all the injectors, not just one.
3. Pull the hand throttle all the way to OFF
4.It helps to get some idea of the cranking RPM - Some use a handheld tach on the crankshaft, but the engine tach is OK if it goes that low.
5. Do all the cylinders, cranking each for the same length of time.

In my experience these numbers are a little optimistic. If you get within 20 psi call it good.
luck,
rScotty

 

[dbandgb]

Thank you very much for the reply. Just what I was looking for.

 

[rScotty]

Thank you very much for the reply. Just what I was looking for.

I remember when I first read that shop bulletin, it my first response was, "That is far too much detail. I already know how to do a compression test."

Then I sat down and thought about it....
Glad you found it useful.
rScotty