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Head Machining Info Required by hippiekiller on 18 Jan, 2012 08:47
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I recall that there used to be some good info on here regarding machining of the aaz heads,, but I cant find it
What would be the maximum amount of milling required before one would have to worry about valve clearances, cam aligment, etc...I am looking at having a local head shop do some work for me and I need to tell him exactly whats involved (flycutting prechambers, etc)
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#1 by R.O.R-2.0 on 18 Jan, 2012 08:52
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only have it machined enough to clean up the imperfections..
milling anymore than necessary is ill-advised..
i would ask the machinist to make the precups stand .003-.005 proud of the surface if this is going to be used on a performance build.. -
#2 by hippiekiller on 18 Jan, 2012 09:03
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Some information I have found on this forum suggests that the pc's can be done in the head with a grinding machine but not with a milling machine.....
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#3 by R.O.R-2.0 on 18 Jan, 2012 09:25
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Some information I have found on this forum suggests that the pc's can be done in the head with a grinding machine but not with a milling machine.....
some sources say you can grind the INCONEL precups.. some say to flycut the bores..
me personally, i wouldnt make those precups any thinner than they already are.. and the fact that inconel work hardens, that gives it more of a chance to crack once there back in your engine, and being heat cycled..
im on the "flycut the bores" bandwagon, personally.. it makes more sense to me to have them stand a little bit proud of the head deck, so they clamp down on the head gasket better, and they are retained in there original position better, also..
we have come up with this theory, that if the precups are FLUSH with the head, being that inconel does not expand as much as aluminum, the aluminum expands more, and leaves the precups basically LOOSE in their bores.. no telling how much more the aluminum expands than inco, but if they are FLUSH @ whatever ambient temp they were ground at, then think of it, they will be RECESSED at operating temperature, and will be bouncing around, and eventually will break apart, and TRASH your engine..
this is what happened from FLUSH precups..
(yes Lucas, i stole your picture..) -
#4 by hippiekiller on 18 Jan, 2012 12:39
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Ouch.
This is just a stock daily driver. 15 psi max. boost. But I can see the point.
How much warpage in the head before one should be concerned with checking cam alignment and getting the line boring done?
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#5 by theman53 on 18 Jan, 2012 13:06
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My engine guy that didn't do my head said if he has to make the precups shorter so they only stick out .003-.005 this is what he does. He touches the face of them to make them look pretty, surfaces the head with them out, puts the PC back in and measures, if they stick out more than .005" he knocks them out and takes it off the "other" side so the face that gets subject to the pistons compression and all the heat isn't any thinner than needed.
I don't know what to do about my next one yet. I have thought of making it a one time use head by taking the precups to a recess of 1mm and having my welding guy weld the aluminum head over top of the precup except for the hole in it. Then having the machine shop mill it off and surface the head. Might be a bit extreme but the last precup cost me about 1600.00 in engine and 6200.00 in a new car as that one is not functioning even today and I needed the 40+mpg for my job. My thinking is if it will work I would rather spend 200-600 for another head than to trash my block ever again. -
#6 by hippiekiller on 18 Jan, 2012 14:09
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I dont have a bentley, Ive heard that the allowable deformation on the head surface is 4 thou. So depending on the piece, could up to .01 be taken off a head? I would think by that time the cam journals should definitely be rebored?
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#7 by BillyWillicker on 18 Jan, 2012 15:04
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OK. The PROPER way to repair these heads is to STRAIGHTEN the head with regards to the cam bores. After it is straight and the cam spins with the right clearances, the head is then checked across the deck surface. Most likely these heads warp in the "lift in center" warp and can be straightened and cut to be reusable.
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#8 by Alcaid on 19 Jan, 2012 12:23
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I have thought of making it a one time use head by taking the precups to a recess of 1mm and having my welding guy weld the aluminum head over top of the precup except for the hole in it. Then having the machine shop mill it off and surface the head.
By doing that, the precups woud not match up as good to the piston bowls (piston@TDC) as they do originally. How much that affects performance and combustion, who knows
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#9 by theman53 on 19 Jan, 2012 16:51
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I thought of that, but really don't care as long as it starts, runs, doesn't smoke too bad at idle, and most importantly doesn't drop a precup into the engine. I was figuring on taking it off the glow plug side of the pre chamber and welding over the entire precup surface, milling out the precup hole so if anything there maybe less precup volume than before...hopefully making the quench and volume OK. I will never know unless I try it.
Back to topic. Yes you are supposed to heat the head to "plastic" state and have it pressed flat again. Then clean up the surface if need be. Just as Billy above stated.