My 77 F150 has a freshly-rebuilt engine that runs good except for the idiot who assembled it with the head gasket on backwards on pass side. I got all the parts to R&R the heads, and now I'm getting greedy. As long as the heads are off I could take them over to the block shop and have them milled. This is my first 400 and I am assuming they can be safely milled 0.060" . Is this right? Next question is how much does the intake side have to be milled?
Thanks in advance,
R.

 

That's a lot to take off those heads. I wouldn't want to mill them more than 0.025" myself.

Don't forget, if you have a stock-type non-adjustable valve train, you might have to replace the pushrods to accommodate the height change.

The intake side of the heads doesn't have to be milled, but all of the intake manifold mating surfaces (both head surfaces, as well as the block mating surfaces) may have to be milled to compensate for the lower head height.

Any competent machine shop that mills the heads for you will know how much to mill the intake manifold to fit.

 

Let me explain some more - I do not want to swap pistons but more compression (I'm also in Denver) probably wouldn't hurt. So what is the safe limit to mill the heads? Most other heads I have run into such as small and big Mopar, most chevy, etc, can be milled 0.060". with an open chamber head this may increase the compression ratio one number or so, that I can calculate.
But what is the safe limit?

Second, it makes no sense at all to mill the head and then mill a manifold face, now you have a non-standard manifold. If you mill the head and then mill the intake face of the head at least you have confined your machining to the heads. Is there a commonly-known multiplier to go from the amount milled off the heads to the amount milled off the face?

I do not trust a machine shop to "know" the answer. When I was a teenager my brother and I built a 400 Pontiac with forged pistons and the works, the machine shop operator was "an old hand" at high perf engines. He put the engine together with 0.001" piston to bore clearance and that damn engine ran hot for years until the pistons finally wore down. There was no way he would admit he was wrong, either, but he said he set the piston clearances so the engine would last a long time. In other words he didn't know crap. I would much rather find out the answer and get agreement from the machinist before the work is done.

R.

 

I know that 335-series (351C/351M/400) heads can be milled 0.060", but I do not know what the limit is.

Yes, indeed, now you have a non-standard manifold to fit your non-standard heads.

When you mill the heads, the ports and manifold mounting bolt holes move closer to the centerline of the crankshaft, along the line of the cylinder bore axis, and the manifold's ports and mounting bolt holes will not align with the heads.

The only way to correct this is to mill the manifold's port faces so that the manifold moves down to align with the heads. Depending on how far the manifold moves down, you may need to mill the manifold's end flanges to maintain block/manifold clearance.

If you mill the heads more than 0.020" (or so, rule of thumb I've seen), you must mill the manifold to line up with the re-positioned head features.

If you mill the intake face of the heads, you'll increase the space (width) between the heads, but that doesn't correct the manifold's misalignment with ports and mounting bolt holes. In fact, it just creates another problem you'll have to correct with thicker gaskets or spacer plates.

Sorry to hear about your old Pontiac, but if there's a critical clearance on an engine, I check it myself. If I don't have the tools or know-how to check something myself, then I have to trust the machine shop to do it right. If I can't trust the machine shop, I find a different shop I can trust.

 

Milling the heads involves removing material from the surface of the head which meets the engine block effectively shortening the heads. How much it increases the C.R. depends on how much that actually reduces the size of the combustion chamber. I don't have any information on exactly how much reduction you would get so I can't calculate the increased C.R.

However I do know that if you 'shorten' the heads that much your intake manifold ports will no longer match up correctly and even if they did it probably wouldn't seal correctly. Milling the surface of the heads which meets the intake won't do anything except exaggerate the mismatch and make it almost impossible to seal. You have to mill the intake block seating surface so it will lower the intake down and make the ports match up then mill the surfaces facing the heads so it will seal correctly.

I suppose you could mill the head surfaces to match the intake on this particular operation but you can't get away from the necessity to make the intake sit down further.

 

Guess I'm going to have to take it apart to see why this would be any different than say a 440 mopar in terms of intake fitting after milling the heads. But I am new to this engine line and maybe there is something new in there.

My point about the machine shop was there's no way to tell if what they "know" is correct if you don't know what is correct going into the shop. Waiting until you find that the shop has screwed up your part and then finding a "new shop you can trust" is not an option for me, I would much rather spend the time to get the facts straight before moving the metal.

That was exactly the lesson on the Pontiac engine. By the time we found out that we needed to get a new machine shop we could trust, the damage had already been done. If we had gone into the shop the first day with the forged pistons and said "we want them installed with 0.003' to 0.004" clearance" then it would have been done right. Once bitten twice shy.
R.

 

I'm not familiar with big MOPARS but I don't know why this same principle wouldn't apply to any V8 engine.

 

I don't see why it would make any difference which surface gets milled. If you mill the heads .060 (heads to block), the heads are going .060 closer to the crankshaft and closer together (exact amount closer together I don't have). This causes a stock intake manifold to "ride" higher because it is now too wide to fit between the heads properly.

If you mill half of the amount that the heads came together, off each intake to head mating surface, the intake is narrower and will now fit in the new space.

If you mill half of the amount that the heads came together, off each intake surface of the head, you have made the space wider, and a stock intake will fit.

As long as all the milling is done at the original angle of the gasket surface, all ports and bolts should line up fine.

 

And how do you deal with the manifold to block surface? Most intakes will take up to around .025" of head milling and you'll still be able to get a good seal although you'll have to toss the end gaskets out and use silicone. I don't think you'll be able to do that if you take off .060". The intake will be sitting too high on the block.

 

That was never an issue with the 289-302 engines that I used to drag race. I had 351W heads on them with .060 cut and the intake surface cut the appropriate amount and I still used the rubber end seals on the intake.

 

Is it possible the W heads were taller than the 289/302 heads to begin with?

 

I don't believe so. If you bolt on a set of stock 351W heads on a 289-302 block, a stock 289-302 manifold fits. The combustion chamber is larger which requires you to mill to restore compression.
Is a 400 manifold so close to the block (end seals) that they don't use cork or rubber seals? I would think that the seals would have to be more than .060 thick.

 

OK I posed the original question to a machinist friend of mine who's also a Ford guy. His take is basically that assuming the correct angles are maintained i.e. the head surfaces are taken down .060" evenly, the theoretical drop in the area where the intake block mating surface meets the block would be .0424". His experience with intakes is that with most manifolds you have somehwhere between .040"and .062" of air space which is normally taken up by the end gaskets. If you have enough space then you could get away with no milling to the intake. Since the head is effectively moving straight down the angles should stay correct but the ports may be off which would necessitate facing the manifold.

 

what CR are you looking for? flat top pistons will yield about 9.5:1
with the stock 2v heads . you're obviously looking for performance ,
so i'm sure to say you are going with the non-emmission 2v heads! ( NO AIR PASSAGES IN THE EXHAUST) correct? IF you really want to PLAY... you need to get a set of 4v closed chamber heads AND the manifold spacer kit which allows you to use a 351C intake on a 400M...
TRUST ME ...its a sleeping giant!!!
I forgot you can also get a set of domes that will raise the C/R
but personally i'd go with the large heads...its cheaper!

 

440 Mopar has a separate valley pan to seal under the intake. No intake to block clearance issues.