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Old 06-23-2011, 05:16 PM   post #1 of 21
Alchymist
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Default JD 750 (Yanmar) engine question

Anyone rebuilt one of these piggies? Engine is out, oil pan is off, and I can't seem to get the spacer off. There is a 17? mm bolt head (picture 1 red arrow), that may be holding the spacer down- but the recess is too small to get a socket in to remove it. Any one know if this has to come out? Nothing in the manual indicates this.

Picture 2 shows the crank journal on the left, and the bearing cap on the right. Looks like I might get away with the cap, but the journal definitely will need turning.

Picture 3 shows the insert - obviously it was turning inside the cap.

Now I have to get the cam out to see if it's boogered - if so I guess it's scrap time - no bearings there - cam runs in the aluminum block.
Any suggestions appreciated.
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Old 06-24-2011, 09:02 AM   post #2 of 21
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Default Re: JD 750 (Yanmar) engine question

No one out there ever work on one of these?
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Old 06-24-2011, 09:20 AM   post #3 of 21
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Default Re: JD 750 (Yanmar) engine question

hang tight--someone will come along--a Service manual for that engine would be in valuable to you at this point..

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Old 06-24-2011, 09:57 AM   post #4 of 21
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Default Re: JD 750 (Yanmar) engine question

I have the service manual - no reference to the bolt in question. In fact, the manual is kind of whacky - it jerks around from subject to subject and lacks a lot of info on disassembly. On the other hand, it is full of info.

Here's the page referring to the spacer:
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Old 06-24-2011, 10:18 AM   post #5 of 21
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Default Re: JD 750 (Yanmar) engine question

Is that the JD service manual, or the Yanmar engine service manual? I noticed on my 160 (ya, a lot smaller, but perhaps the principle is the same), they don't cover a heck of a lot about the Kawasaki engine in it... Because you can get the full Kawasaki engine manual from Kawasaki... Saves JD a LOT of paper/electrons (if you have the electronic version)...

Edit: Of course, a quick search for the Yanmar 3T80 engine manual (which is what TractorData says is in your 750), turns up that it looks like Yanmar does the same thing as Deere, they charge for their service manuals

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Old 06-24-2011, 11:52 AM   post #6 of 21
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Default Re: JD 750 (Yanmar) engine question

The manual I have is "3TN & 4TN Series Yanmar Diesel Engines" by John Deere Horicon Works, CTM3 (03JAN90.
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Old 06-27-2011, 09:02 PM   post #7 of 21
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Default Re: JD 750 (Yanmar) engine question

I did my 650 and was not bad but I only have 2 cylinders the book I have does not mention that bolt either
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Old 06-27-2011, 09:04 PM   post #8 of 21
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Default Re: JD 750 (Yanmar) engine question

Forgot to mention my book covers 650 750 850 not a very good book
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Old 07-23-2011, 07:24 PM   post #9 of 21
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Default Re: JD 750 (Yanmar) engine question

D@mn All! Guessed wrong on the bolt size, ground down a 16mm socket, too small! Should have guessed it was probably 17mm.

Anyway, ground down a 17mm, got on the bolt, and can't budge it. 3/8 socket with an adapter and a 1/2 breaker bar - will not budge. Anyone have any ideas? Certainly hope I don't wind up drilling it out...would be a nightmare for sure. (It's the bolt in the circle in 1st picture of OP).
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Old 07-23-2011, 07:48 PM   post #10 of 21
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Default Re: JD 750 (Yanmar) engine question

Could it be reverse thread? What about using an air impact on it?
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Old 07-23-2011, 09:15 PM   post #11 of 21
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Default Re: JD 750 (Yanmar) engine question

Quote:
Originally Posted by DJ in WV View Post
Could it be reverse thread? What about using an air impact on it?
Thought of LH thread - won't budge either direction. Don't have impact anyway, nor air to drive it. Head is quite shallow, so any socket that will fit in there would probably just split with an impact anyway. I am beginning to think it's put there to discourage non-dealer repairs! (Shhhh...it's a conspiracy!).
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Old 07-23-2011, 09:28 PM   post #12 of 21
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Default Re: JD 750 (Yanmar) engine question

Looks like another one of those "thin walled" sockets is going to be required. I'd say hit around it with some PB blaster and let it sit for a day or two but there shouldn't be any rust in there! I think you're going to have to just torque that one out of there.
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Old 07-23-2011, 09:36 PM   post #13 of 21
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Default Re: JD 750 (Yanmar) engine question

Wouldn't surprise me to find a steel bolt in the aluminum block - corroded in.
Guess I'll fill the hole with 50-50 acetone and ATF and let it sit a while.
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Old 07-24-2011, 11:27 AM   post #14 of 21
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Default Re: JD 750 (Yanmar) engine question

This is my opinion, so take it for what you think it's worth. I suspect that bolt does not retain the girdle, but the head protrudes through it. It could contain the oil pressure relief valve. Most likely, the girdle is stuck to the block (which should be cast iron) by the use of sealer. Look for several tabs on each surface where you can pry them apart with a screwdriver. Even if the bolt was holding the girdle, you should be able to see some movement on the opposite side.

As far as the cam bearings are concerned, they would be the last to go, as they do not have the same speed and load as the rod bearings do. At this point, let's hope you didn't spin any mains, you might be looking for another engine at that point.
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Old 07-24-2011, 11:40 AM   post #15 of 21
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Default Re: JD 750 (Yanmar) engine question

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Originally Posted by rscurtis View Post
This is my opinion, so take it for what you think it's worth. I suspect that bolt does not retain the girdle, but the head protrudes through it. It could contain the oil pressure relief valve. Most likely, the girdle is stuck to the block (which should be cast iron) by the use of sealer. Look for several tabs on each surface where you can pry them apart with a screwdriver. Even if the bolt was holding the girdle, you should be able to see some movement on the opposite side.

As far as the cam bearings are concerned, they would be the last to go, as they do not have the same speed and load as the rod bearings do. At this point, let's hope you didn't spin any mains, you might be looking for another engine at that point.
The block is aluminum, as is the spacer. The spacer is "loose", as I can insert a thin wedge in between, and spread it about a 1/16 inch at the far end. It appears that the bolt is what is retaining it. Regardless, it shouldn't be that hard to move, especially if it contains a relief valve. Wonder if it were loctited in place?
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