PI swap question - Head surface? - TCCoA Forums
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post #1 of 8 (permalink) Old 06-12-2004, 09:39 PM Thread Starter
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PI swap question - Head surface?

I getting ready to do a PI swap on my T-bird and this guy at work scarred the crap out of me about getting the heads to seal on the 4.6's. Apparently he used to work as a Ford mechanic, and talked about a bunch of horror stories and needing a mirror finish on the heads and block. I just wanted to get some info from some of the veterans swappers here.

This is the first for me. I have done several engine swaps, tranny swaps, changing manifolds and such, just have never done a set of heads. So this is all new.

The heads I have are used, in very good shape. They appear to have been hot tanked and reassembled. How good does the finish need to be? I could not understand the specs in the manual, do they really mean microns? What prep work should I do to the block/heads to have a high chance of success? Also, I have a set of Ford head gaskets, should I get a different brand?


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post #2 of 8 (permalink) Old 06-13-2004, 10:51 AM
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i had alot of little scrathes but it didnt make a problem with the seal...

Car isn't running now so hmmmm who knows....

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post #3 of 8 (permalink) Old 06-13-2004, 02:44 PM
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Well there is a teflon coating on them that you arent supposed to damage when cleaning the heads. There is a plastic scrapper and special compound used to get the old gasket material off. May have alil discoloration left but as long as you cant feel any large material. My friend has done several head gasket changes due to the oil leaks. You want to try to keep it scratch free as possible. Im sure light scratches wont effect it very much but try to keep them scratch free.

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post #4 of 8 (permalink) Old 06-13-2004, 08:16 PM
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You actually want a slightly scarred surface. It is possible to get it so clean nothing sticks to it.

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post #5 of 8 (permalink) Old 06-13-2004, 08:42 PM
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True, a rougher surface is better. Not TOO rough, or it won't seal. Anyone ever use JB weld before? Before applying it, you should "roughen" up the surface, for a better bond. Used it at work for our "aged, out of date, prototype Soda-Blaster" lol... what a piece of junk.

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post #6 of 8 (permalink) Old 06-14-2004, 12:06 PM
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aoldenbu - I think your co-worker/ex Ford mechanic might be right. A while back I found this article and other similar ones about how smooth the surface must be for the MLS gaskets to seal properly. I believe the SHM 4.6 book also references needing an almost mirror smooth finish - like in a range of 3-8 RA!

head surface finish article

From the reading I've done, a rough surface can seal fine for a while, but after continued heating/cooling cycles, the rough surface will tear the MLS gasket apart due to the different expansion/contractaction rates between the steel block and the aluminum heads. It may not be a problem at the beginning, but it might create problems down the road.

Last edited by tedh98; 06-14-2004 at 12:14 PM.
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post #7 of 8 (permalink) Old 06-16-2004, 06:25 AM Thread Starter
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This has not given me a lot of confidence. I really took a close look at the heads again, and there are some slight grooves where the fire rings seal at. But for the most part the rest of the surface is clean, with slight discoloration in places. No pitting around any of the water passages. I'm going to get a second opinion, and most likely get then surfaced just to be safe.

Thanks guys

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post #8 of 8 (permalink) Old 06-16-2004, 06:51 AM
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I would HIGHLY recommend that you research this more. According to EVERY Ford manual and everyone that I've talked to about the 4.6L engine, the Ra (Roughness average) is not the same as on other engines. It is a lot smoother and can't be obtained by just milling the heads and block. A lot of machine shops can't get the RA to be correct and don’t even have a way to measure it. So if a head or block has been surfaced, it probably does not have the correct RA.

The head and the block have to be much smoother than a normal engine.

Some reading:

However, there is a new gasket that can be used that does not require the surfaces to be as smooth. I have them sitting at home. I think they are Felpro, but I'll have to double check. They are made specifically for the 4.6L engines that do not have the correct RA number to use the OEM gasket. The gasket if more “forgiving”.

I researched this and am pulling my DOHC apart to just replace the head gaskets for this reason. I've read about a dozen articles in machine shop magazines that have gone into depth on this subject and the general consensus is that the Ra has to be correct to use the OEM gaskets. Not only of Ford, but any engine that uses a Multi Layer gasket.

Now with that said, and before someone tells me I'm talking out my arse, there are probably a lot of people that have just bolted the engine together and not had a failure.

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