John Deere 950 Tractor Yanmar 3T90J rebuild.

   / John Deere 950 Tractor Yanmar 3T90J rebuild. #1  
J

JPriami

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May 7, 2011
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4
Tractor
JD 214 / JD 155C
I recently bought a John Deere 950 with the Yanmar 3T90J diesel in it. Serial number tells me it's from the 1979/80s. It ran when I looked at it to buy it. Got it home and its ridiculously hard to start. Cleaned fuel filter & replaced fuel & did several other things. I won't go into long detail.

Looks like it's low compress issue from wear. So I guess I'm going to order a rebuild kit. I seen the rebuild kit at weavers online for this model engine. Is that a good one to buy? Or should I look somewhere else?
 
   / John Deere 950 Tractor Yanmar 3T90J rebuild. #2  
The JD950 was a Yanmar built to JD specs tractor.
I have no knowledge of Weaver’s so sorry no help there.
I know that for lots of parts for your model, Hoye Tractor in Texas carries lots of parts. Again since that is not a model I own, my knowledge of specific available parts is limited, but worth checking out.

On low compression issues, one often overlooked maintenance item is valve adjustment. Specs should be in the manuals. But around 0.006-0.008” of lash would be close. A non closing valve results in a loss of compression for a given cylinder. Worth checking before a rebuild.
How many hours are on the tractor?
 
Last edited:
   / John Deere 950 Tractor Yanmar 3T90J rebuild.
  • Thread Starter
#3  
I got the technical manual for it. We did try a valve adjustment the other day with no luck.

Hour meter says 806 hours. But I'm uncertain if it works or not.
 
   / John Deere 950 Tractor Yanmar 3T90J rebuild. #4  
K7LN said:
Let's make that .006-.008 inches, and I tend to favor things on the looser side.
Click to expand...

Good catch! Yes my brain said 6 thousands but not what I typed. My bad!
Not sure if it will let me edit that or not. I shall try!
 
   / John Deere 950 Tractor Yanmar 3T90J rebuild. #5  
Just out of curiosity did you do a compression test and what was the PSI you got out of each cylinder?
 
   / John Deere 950 Tractor Yanmar 3T90J rebuild. #6  
I would also recommend a compression test. I used the Weaver kit on a 950. It’s acceptable with the exception of the head gasket. I bought a Deere there. The head should be tested as many, if not most are cracked. I’ve checked two heads and one was cracked. I remember the words of the old school machinist when I called in the other, “well you got a rare one here, no cracks”!!!
 
   / John Deere 950 Tractor Yanmar 3T90J rebuild. #7  
JPriami said:
I recently bought a John Deere 950 with the Yanmar 3T90J diesel in it. Serial number tells me it's from the 1979/80s. It ran when I looked at it to buy it. Got it home and its ridiculously hard to start. Cleaned fuel filter & replaced fuel & did several other things. I won't go into long detail.

Looks like it's low compress issue from wear. So I guess I'm going to order a rebuild kit. I seen the rebuild kit at weavers online for this model engine. Is that a good one to buy? Or should I look somewhere else?
Click to expand...

The 3T90J is John Deere specific with the 90mm pistons. IF you would have gotten a JD850, life would have been so much better. The 90mm setup is more rare than people can imaging. The 80mm is popular among the Yanmar community. The 3T80 is shared between the brands and the 3T90 isn't. There is a 3T90LE engine that may have the same head. It's used on industrial Yanmar engines like generators and small boats.

The Yanmar YM4300 has the 3T90. Like the JD950/1050, it comes in 2 flavors, non-turbo and turbo.

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They list a 950 available. Len's team can get all new as well.

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Your info page didn't say your region, so I can't really list much more.

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