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Discussion Starter · #1 ·
I had a ring break off on the PTO side of my 670 and was flying around inside for awhile I would guess. The inside of the head is just battered. Does anyone know if a machine shop could machine down the combustion chambers and then plane the head to bring the compresion back down to normal??? I have already bought a used head so we can ride this weekend, I was wondering if I could use this for a spare in the future if the need arises. My 670 is now a 677!
 

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i`ve got a twin head thats been all filled in with weld then ground down close to original. the most critical area is the outside area of the chamber or sqiush area. mine is abit different, it works ok, i think i got lucky. if your good with body work you should be able to feel the shape of the chamber as you grind of the weld.
 

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My brother did what you're thinking of many moons ago to a 521 head (broken ring attacking head). Mind you he had a CNC machining center to use. I don't know how well it can been done on a standard vertical mill. They didn't do any welding.

How they did it:

1) Clamp the head (gasket surface down) & machine four spots on top of head for the head to rest on while scanning & machining.

2) Clamp head upside down to scan/trace/copy the good combustion chamber.

3) Machine the damaged chamber to clean up damage

4) Then machine the "copied" side the same depth as the damaged side.

5) Take a cut off the gasket face the amount removed from the chambers.

6) He made some copper washers to put under the spark plugs to raise them the amount machined from chamber.

After they were done, you wouldn't have known any different.

I don't recall exactly how they clamped the head, but it may have been thru the spark plug hole to a plate. A good machinist should know what to do. They may have had several strap clamps holding it down during the chamber machining. These would have to be removed to face the head.

If you know of a machinist that can do this kind of work, you'll probably save money. However if you have to pay a shop, the time for set up & machining will probably be the same as a used head.

He had the sled for a few years afterwards & never had any problems running the head.
 

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Discussion Starter · #4 ·
Yeah, that is what I was wondering. My brother in-law runs a Moog CNC Machine at the shop he works at and my uncle is a machinist too. I was just wondering if any one has had succses with this before I get them to jump on it. I haven't asked either of them yet about it.
 

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Post a photo of your damaged head and I'll check if one I have is in better shape (mild detonation and a couple of divots). I have had good success with a jig I machined that is basically some bar stock with a 14mm thread on one end. I thread and tighten it into the spark plug hole of the cylinders then chuck it into a lathe at 100 rpm and cut a new squeeze band matchin both sides. Then mill the same amount off the head's gasket surface.
 

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