Nex Posted January 18, 2011 Share Posted January 18, 2011 I'm currently working on rebuilding my p79 head, which has damage to multiple quench pads, thanks to some foreign objects in the cylinders. My original plan was to do the 0.080" shave, but as I've dismantled the head I've become more and more worried that the previous owner may already have shaved it some. So now I've got to figure out A) has the head been shaved, and if so, how much. My big hint that it's been shaved are cam tower shims, which I haven't seen in pictures of stock heads. They measure 0.0172" thick, which doesn't seem to line up with any that I've seen for sale, or any standard sheet metal thickness (in between 26 and 27 gauge.) The bottom surface of the head has clear machining grooves in it, but I haven't seen an unmodified head to know if they're original or not. Other than some marks transfered from the head gasket, the bottom of the head is totally blank - there are markings stamped into the top end of the block, so maybe heads came with markings too? If so, that'd confirm that it has been shaved, at least some. Does anyone have a disassembled p79 head available to measure so I have something to compare to? Mine is 4.229" from head gasket surface to the valve cover gasket surface. If anyone has better ideas on how to determine the amount that I need to shave in order to get a total of 0.080" shaved over all, I'd be glad to hear it. Thanks, Nex. Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 18, 2011 Share Posted January 18, 2011 The stock head height is around 107.9mm (4.248"). So it looks like they shaved it 0.020", which is pretty common since that is what cam tower shims typically available as. Maybe you were off a little when you measured the shims? 4.248 - 0.080 = 4.168 (what you should shave it to). I'm sure you already know that there is a lot more to this mod than just shaving the head. Pete Quote Link to comment Share on other sites More sharing options...
Nex Posted January 18, 2011 Author Share Posted January 18, 2011 Thanks for the quick reply! I'm pretty sure about the shim measurement, but I can't repeat it, since I promptly dropped and destroyed my 1" micrometer after my first measurement. The previous rebuild doesn't seem to have been done with any particular care, so these shims may just have been 'close enough.' And yeah, I know there is more to the mod than the shave, going with the cam tower spacers and N47 valves. Quote Link to comment Share on other sites More sharing options...
Derek Posted January 18, 2011 Share Posted January 18, 2011 And now for my shamless plug about cam tower shims. I sell the .080 shims if your interested. PM me for the details. Oh and I feel your pain about the micrometer. I dropped my 0-1" Mitutoyo on the floor about a year ago. I still keep it in the drawer next to the new one to remind me not to be so careless! Derek Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 18, 2011 Share Posted January 18, 2011 Thanks for the quick reply! I'm pretty sure about the shim measurement, but I can't repeat it, since I promptly dropped and destroyed my 1" micrometer after my first measurement. The previous rebuild doesn't seem to have been done with any particular care, so these shims may just have been 'close enough.' And yeah, I know there is more to the mod than the shave, going with the cam tower spacers and N47 valves. Don't forget about head gasket thickness and compression ratio. Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 18, 2011 Share Posted January 18, 2011 Is a P79 so rare an animal (or has it been port worked and you want to salvage it) that getting a used one and starting fresh is prohibitive. For the cost of the decking, likely you can buy a used one without the issues. For a P79, that is the direction I would likey pursue if I was in your place. You can always come back to this head years down the road if you need to do so. If the parts are avaialble, get them now while they're cheap. They won't be any cheaper 10 years from now! Quote Link to comment Share on other sites More sharing options...
bradyzq Posted January 18, 2011 Share Posted January 18, 2011 The stock head height is around 107.9mm (4.248"). So it looks like they shaved it 0.020", which is pretty common since that is what cam tower shims typically available as. Maybe you were off a little when you measured the shims? 4.248 - 0.080 = 4.168 (what you should shave it to). I'm sure you already know that there is a lot more to this mod than just shaving the head. Pete I have been told that good machine shops can also true the top surface of the head by shaving it a touch. This would impact your overall height measurements. You would end up with the right thickness of cam tower shims but might be off on the combustion chamber side. I don't know if this is ever actually done, but it warrants consideration..... Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted January 18, 2011 Share Posted January 18, 2011 I sold a p79 head for about $70 during summer. It had been milled once. Just saying that a lot of people don't want those heads and there are pretty available in junkyards if you want to start with a fresh head. Quote Link to comment Share on other sites More sharing options...
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