Yanmar 3gm30f rebuild

[Badsanta]

If you had enough cylinder wear, would you go with a rebore and oversized pistons, or go with cylinder sleeves and normal pistons. I'm just thinking out loud. Many thanks

[a64pilot]

If they are wet sleeves, I wouldn't consider boring them, in fact I've never heard of that being done, but go with new Pistons even if yours Mike out OK.
If they are dry sleeves, meaning that they take a machine shop to replace, I wouldn't consider trying to replace them as that often doesn't work that well and I have only seen done to replace a cylinder that had something bad happen in that cylinder like a wrist pin retaining clip come loose and dig a deep groove.
I think my 4JHE has wet selves, but don't think that is common in these little Diesels, I don't know about yours.


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[Seymore]

A Yanmar 3GN30F's cylinders are not sleeved. They are solid cast.

[Badsanta]

Yes that is true.

[Cheechako]

How many hours? Mine had one bad cylinder, it was rebuilt without boring at <2300 hours. New pistons/rods though. Cylinder wasn't that worn. Piston cracked.

[Badsanta]

2,000 hours. I haven't completely taken it completely apart yet. I was hoping for a bad head gasket but that looks ok. I'm worried about getting the injector pump right if this goes that far. I'm hoping for bad rings or piston. We'll see.

[sailorchic34]

In my case I had just one hole bad. The other two holes measured new after 1100 hours. So for that I had the bad hole bored and sleeved with a new sleeve and the other two lightly honed. It was cheaper then boring three holes 10 over and honing. Standard piston and rings is ~$100 a hole. 10 over is $150 ish a hole.

If all the holes have the same wear, I would just have them bored 10 over (.25mm).

As someone mentioned the newer 3gm30f's are not sleeved, but a good machine shop can easily bore and sleeve the block. When you have one bad hole, it sort of makes sense.

I've somewhere north of 220 hours since my rebuild with nary a problem.

[sailorchic34]

Originally Posted by Badsanta

2,000 hours. I haven't completely taken it completely apart yet. I was hoping for a bad head gasket but that looks ok. I'm worried about getting the injector pump right if this goes that far. I'm hoping for bad rings or piston. We'll see.

The injector pump is timed with shims, so make sure you have all the shims, before taking the block to the machine shop. Other then that, it's set the cam timing reinsert the shims and bleed, bleed, bleed till it starts. The only tricky bit is making sure the injector pump rack pin is in the groove of the governor/throttle.

[Badsanta]

Sc you make it sound so easy. Lol thanks

[Cheechako]

Originally Posted by Badsanta

2,000 hours. I haven't completely taken it completely apart yet. I was hoping for a bad head gasket but that looks ok. I'm worried about getting the injector pump right if this goes that far. I'm hoping for bad rings or piston. We'll see.

What are the symptoms? No need to remove the injector pump at all is there? If you are doing a simple overhaul.
A complete rebuild ....degunk etc ... that's different I guess.

[Badsanta]

Low compression, water in oil, thick black smoke at higher RPMs. Not over piched. Not in gear. One cause is missed timing. Gust collectng info and thoughts. Thanks

[sailorchic34]

Originally Posted by Badsanta

Low compression, water in oil, thick black smoke at higher RPMs. Not over piched. Not in gear. One cause is missed timing. Gust collectng info and thoughts. Thanks

First guess is head gasket, from the water in the oil.

[Badsanta]

Thats what I was hoping. The orriginal head gasket looks nothing like the the replacement. Same size and shape but orriginal almost looks like a sheet of tin or aluminum.