How much can be safely shaved from PRV heads?

[Morpheus]

Hello all,

I have my D's heads (and the rest of my engine bits) at a shop right now for measuring & cleaning.

I was just informed that one of them is warped .009 and the other is .008.

My question to you brothers is this:

How much can these heads be machined safely? The engine reconditioning manual does not give this info, it just says


"max warp is .05 over 100mm"
NOTE! Do not level a warped cylinder head, replace it.

What say you, bretheren?

[Delorean Industries]

Hello all,

I have my D's heads (and the rest of my engine bits) at a shop right now for measuring & cleaning.

I was just informed that one of them is warped .009 and the other is .008.

My question to you brothers is this:

How much can these heads be machined safely? The engine reconditioning manual does not give this info, it just says



What say you, bretheren?

You can mill up to .040 off the heads safely. We perform clean up cuts all the time ranging from .005 to .015

[David T]

I would try to remove the minimum amount possible. If you have to remove more than around .040 you are affecting all of the geometry and would have to start compensating for the misalignment. You do not have to remove the same amount from both heads. If a head is that warped that you need to remove more than .040 you should be replacing it because it probably won't stay flat anymore.
David Teitelbaum

[Morpheus]

So, given my circumstances, taking off .010 would be sufficient?

[David T]

It may be but the machine shop will do their cuts and then recheck for flatness. When you remove metal you remove some stress and create new stress. The heads may warp again and it may require another finer (smaller) cut to finish. Some shops cannot (or will not) remove less than .010 per cut. Depends on their equipment and the operator's skills.
David Teitelbaum

[dmc6960]

Or you could go the route a few of us have done, and take a whole 1mm off of the heads. Then get Ed's camshafts at DMCEu which are cut with the 1mm timing retard offset in them already for a plug and play high powered operation.

[Ron]

You can mill up to .040 off the heads safely. We perform clean up cuts all the time ranging from .005 to .015Is the .040 due to head integrity, chain/geometry, or, thicker head gaskets/shims are unavailable? Or? Please elaborate.

[Delorean Industries]

Is the .040 due to head integrity, chain/geometry, or, thicker head gaskets/shims are unavailable? Or? Please elaborate.

The camshaft timing is off just a little bit by that point as the tensioner system is over extended on the chains.

[Ron]

OK, I thought that was probably the case.
So people are actually buying heads instead of getting head gaskets made!?! -- Damn!!!

[David T]

Milling a lot off the heads will affect valve timing, on one side advancing it and on one side retarding it. You will also have to enlarge the bolt holes in the intake manifold so you can get the bolts in and you will wind up with some port mismatch unless you start porting the heads and/or the manifold. You also increase compression and at some point it will cause you to have to use a higher octane fuel. One way make up for removing a lot of materiel is to use a spacer or you might be able to double up on head gaskets. The factory thought so much of this that their recommendation is that you are not allowed to mill the heads at all! Probably because of the EPA certification.
David Teitelbaum

[dmc6960]

You will also have to enlarge the bolt holes in the intake manifold so you can get the bolts in and you will wind up with some port mismatch unless you start porting the heads and/or the manifold.

No you will not have to enlarge the bolt holes. I took off 1mm, and while that is likely the limit for the OEM "fudge space", it still worked fine. Port alignment was no worse than the OEM alignment. Same with the Timing cover plate which actually has intentionally elongated holes for the bolts into the head. Regarding the valve cover/timing cover mating area, there you will have a discrepancy which is best to be made up for with "Great Stuff" sealant, and a cut-off gasket piece if you went as far as a whole 1mm.

If Josh says you can go up to .4mm then I trust that, he's tested it. If you just want to go all-out, get Ed's camshafts and call it a good 1mm.

[Ron]

If a head is that warped that you need to remove more than .040 you should be replacing it because it probably won't stay flat anymore.
David Teitelbaum
...

One way make up for removing a lot of materiel is to use a spacer or you might be able to double up on head gaskets.
David Teitelbaum

=>:umm:<=

[Nicholas R]

One way make up for removing a lot of materiel is to use a spacer or you might be able to double up on head gaskets. The factory thought so much of this that their recommendation is that you are not allowed to mill the heads at all! Probably because of the EPA certification.
David Teitelbaum

I understand that this was something people did in the past, but personally I think this is a horrible idea. Double gasketing ANYTHING is a recipe for failure, let alone head gaskets! Can we just take this off the list of car repair home remedies? We can throw it in the trash along with using compression fittings on brake lines, running stretched tires, and using pretty much any kind of "snake oil".

[Morpheus]

Or you could go the route a few of us have done, and take a whole 1mm off of the heads. Then get Ed's camshafts at DMCEu which are cut with the 1mm timing retard offset in them already for a plug and play high powered operation.

Will I still be able to use the stock pistons if I do this? I intended to get Josh's performance cams; are they much different than Ed's?

[David T]

Will I still be able to use the stock pistons if I do this? I intended to get Josh's performance cams; are they much different than Ed's?

You only have to go for forged pistons if you have forced induction and want to go above 5 lbs boost. I am not endorsing spacers or double-gasketing, I only mention it as possible methods to solve a problem. I agree it is not a good answer but as we have all seen, people do many things that aren't exactly Kosher. Some of them actually work, some only work for a while! If you have to remove .040 or more to get your heads flat, you need to decide if it is better to replace the head or try to flatten it. Unless you are trying to up the compression too. By the time you do all that machine work and buy the cams you could probably replace the heads for the same price. Hotter cams won't do you much good unless you also replace the exhaust system. Now what are you spending and how much performance are you really getting?
David Teitelbaum

[Morpheus]

My intention is to also replace the exhaust system. I wasn't referring to forged pistons, I was asking if there is any risk of the valves hitting the top of the stock piston. IIRC, dmc6960 also installed custom pistons along with his head shave and cams...

Stock heads a hard to come by (or extremely expensive, I have been told). And, while I had originally intended to replace the pistons and liners for this motor, the $250 a pop price tag forced me to rethink my options and re-use my stock setup.

[dmc6960]

My intention is to also replace the exhaust system. I wasn't referring to forged pistons, I was asking if there is any risk of the valves hitting the top of the stock piston. IIRC, dmc6960 also installed custom pistons along with his head shave and cams..

Yes, I did do Ed's custom pistons as well. However I do not believe that is a requirement for the valves and the head decking and his camshafts (otherwise how could he sell them as a standalone item?). The new pistons do have valve pockets in them, but I believe it was due to a combination of those particular pistons with the dome in them, and another more radical camshaft grind Ed has worked with which when revved extremely high caused the valves to float and contact the pistons. He could confirm for sure, but I'm fairly confident you dont need to worry about anything.

There is another thread somewhere here where I had made the same suggestion to somebody and Ed did chime in and agree. Need to do some searching to find that and remember exactly what was said.

[dmc6960]

There is another thread somewhere here where I had made the same suggestion to somebody and Ed did chime in and agree. Need to do some searching to find that and remember exactly what was said.

Well, Ed hasn't posted too often here. I looked at every post he's made and there is nothing of what I remember. Perhaps I was remembering a thread before the crash.

[David T]

If you have any doubt about valve clearance against the pistons, mock everything together and put some clay on a piston and see what happens. You may need to make a pocket (or pockets) in the piston to maintain enough clearance. The custom cams may also have a higher lift than stock. That, combined with shaved heads, could cause an interference problem. Better to check it than find out later! Whenever you deviate from stock it is always "Good Practice" to check, double-check, and recheck everything. If the cams do have higher lift you might also have to replace the valve springs. Whoever is supplying the cams should be able to give you guidance on what you need to do.
David Teitelbaum

[DeLorean937]

Keep this post going! I'm getting ideas for my engine rebuild thats coming up soon! Brandon, you can come help with yours is done ;) I'll put you guys up in the hotel