jd 950 yanmar 3t90 crank shaft replacement

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ffallert
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jd 950 yanmar 3t90 crank shaft replacement

Postby ffallert » Wed Feb 10, 2021 9:07 pm

So I spun a bearing on my 950.
Ordered new crank shaft, main bearings, rod connector bearings, new pistons and rings, seals you get the idea.
As I am putting all the new parts back in the block the crank keeps getting harder and harder to turn. Before I put the pistons in, I could turn the crank by hand. Now that all three pistons are in I have to use a breaker bar to turn it and it takes some effort. I would guess probably in the neighborhood of about 45-50 ft lbs. This is without the head on it, so I am not developing any compression yet. This seems too tight to me. Any thoughts?

winston
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby winston » Thu Feb 11, 2021 10:34 am

Sounds tight to me also. Might try some plastigauge on your rod bearings. https://www.napaonline.com/en/p/SEPSPG1 ... xEALw_wcB&

Aaron
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby Aaron » Thu Feb 11, 2021 11:56 am

I have never measured exactly how much force it took to turn over a freshly rebuilt engine but, I agree, that 45-50ft/lbs seems like a lot (might be normal... but seems like a lot). I'm pretty sure I can't turn one over by hand though. Those big pistons will have some drag - especially when new.

tjrigario
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby tjrigario » Sat Feb 13, 2021 10:50 am

If it rolled freely on the mains, that would seem like your block is fine and not twisted. I'm involved in a similar project right now with a JD1050. My buddy that owns a machine shop said the crank should spin freely a few rotations by hand after setting into the block. Sounds like yours did that prior to putting the rods and pistons in. Do you possibly have a slightly bent rod?

tjrigario
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby tjrigario » Sun Feb 21, 2021 6:14 am

I just put a new crank, bearings, and pistons in my JD 1050 over the weekend. That engine turns over with less than 20ft lbs of torque. I don't have the flywheel on yet, but I'd bet I could turn it by hand once that's mounted. Your engine is definitely a bit tight.

ffallert
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby ffallert » Sun Feb 21, 2021 7:40 am

Update:
I tore it back down and found the main bearings were a not aligned as well as they could be.
Re-Torqued everything and could spin the crank by hand with the flywheel on. Once I put the head on and was developing compression I could not spin it by hand with the flywheel.
After complete assembly it fires perfectly. Not cranking slowly. :D

ffallert
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby ffallert » Sun Feb 21, 2021 7:41 am

P.S. Thanks for all the help and direction.
I am a newbie, this was my first rebuild of this magnitude.

winston
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Re: jd 950 yanmar 3t90 crank shaft replacement

Postby winston » Sun Feb 21, 2021 7:44 am

Another success story, love it.


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