Resurfaced heads..... machined or belt sanded?

[Ben_Pow!!]

Okay, not a machinist here, something seems a bit screwy. I had my heads resurfaced a long time ago by Napa. I got them back and the surface was nice and shiny, perfectly smoothe. I had another set of heads done recently by a performance shop Pro-Motor which a lot of people seem to like the place. When I dropped them off, he asked if they had been previously belt sanded. I didn't really think about it until I got the heads back and you could see the tooling lines. He used what appeared to be a CNC mill w/ a large-diameter round disk with the tooling mounted near the outside of it. Were the heads belt sanded smoothe before? I would assume this is not a good idea. One of my concerns is the machining lines can be felt w/ my thumbnail, is this going to be a problem? I did a little google image search and found both situations, anyone have any inseight on this?

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the reason the heads are off is a graphite head gasket failure, bought multilayered steel this time.
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[colt45 gto]

once the heads are milled they should be smooth you shouldn't feel anything.

sounds like a poor job to me. dunno what they mean about belt sanding? never heard of this on heads before.

[UTRacerX9]

Some shops don't have the proper tooling to mill a cylinder head. But if they have a decent sized belt sander, you can usually fit a V6 cylinder head on there. It isn't the most professional way of doing things, but unless your heads were severely warped, they should be fine.

[j2k4]

once the heads are milled they should be smooth you shouldn't feel anything.

sounds like a poor job to me. dunno what they mean about belt sanding? never heard of this on heads before.

If you were told they were "belt-sanded" I'd be going over them every which way with a straight-edge to check them.

As far as milling, generally they should be pretty damn smooth, with just the faintest tool marks.

Depending on the application/head-gasket type, some shops will run a higher feed rate on the mill to give the head a bit more tooth to "grab" on the head surface - less of that going on, these days, but.

[CoreyB]

I would never belt sand heads.

[colt45 gto]

i would claim for a new head if a machine shop belt sanded my heads, only a milling machine can get a perfect surface.

[AaronVR4]

I used to rebuild heads in high school. Would belt sand before competitions.

[Ben_Pow!!]

Yeah, I'm sure the surface itself is not warped after the job, but it's the machining "grooves" I'm concerned about. I imagine if they are too deep, this will allow gas to escape and right into the oil/coolant passage they pass through, but I don't know. Like I said, it's not very deep, but you can certainly feel it w/ your fingernail and visually see them. This shop is always busy w/ work, so I have a pretty good % of beeing OK. I'm going to give him a call and see what he says about it.

[colt45 gto]

post a pic up ben

[green-lantern]

Mine had these groves you speak of and they were done by a reputable shop also. I didn't like it at first but was assured it was OK. I haven’t had any trouble yet.

[Boostaddict]

You always need to ask before having heads machined to see what equipment they are going to use, and what surface finish quality they will provide. Both sanding and milling are common (there is milling, and there is head finishing). Both can have either good or poor results depending on the resulting surface finish. Generally speaking if the surface isn't pretty damn shiny you are screwed if you plan to run big boost. For a DD or non-turbo you'd probably be okay with just about any surface finish as long as they are flat (that is key) and as long as they haven't been milled too far beyond spec.

[colt45 gto]

they are or will be micro grooves so it more than likely wont make any difference.

this is why i have a dedicated machine shop that does all my resurfacing, every head comes back with a mirror finish, crack tested and VSS done and valves reground in. they also supply my gaskets so its a one stop shop.

[Flamer]

It depends on the sander they used and how skilled they are with it. Using a belt sander makes it possible to have valleys and mountains on the heads surface due to inconsistent pressure across the surface of the head.

[Amphiron]

It depends on the sander they used and how skilled they are with it. Using a belt sander makes it possible to have valleys and mountains on the heads surface due to inconsistent pressure across the surface of the head.

Maybe they were talking about a surface grinder?

[mcshooter]

i have seen exhaust header flanges belt sanded and you could not get a .001 feeler under a staight edge. i would think that would be good enough for a engine head

[pos-vr4]

on a shit box DD i would (if i had to) install a beltsanded head, but on a 6G72, always have them surfaced with the proper equipment.

if they cannot mill it with a 50 RA or finer finish, just keep walking. these cars a just too pricey to do short cut work like that on.

the belt or Table sander that they use can make an irregular surface on the head, if someone were to push a little more on one side or the other the whole head can go cock-eyed.

in a milling machine the head is fixed and leveled before cutting begins.

http://www.youtube.com/watch?v=BlLkuczYJxU&feature=related

[mdcrose]

50 microinches is still quite rough. It's not really hard to get in the 20 microinch range with a milling machining and if you want near mirror finish you are going to have to get to and RA of 10 or less.

[Ben_Pow!!]

Looks like I'm going to take them to another shop the next town over. I talked to him over the phone. They have a specific machine, can't remember what he called it to do heads. He said the bits they have has a bunch of cutting edges and he claims they can get near perfect finish. He said the machining marks are very hard to see. Already have the front head mounted..... good thing I've got an extra set of head gaskets I can steal one from. This is going on my 15G car on E85 so I probably don't want to short cut it on this car. I'll take some pics from this job, then after the new re-surface for comparo.

Now my concern is how much material is taken off at this point. The 1st time I had the heads done, they said they had to go almost to the recommended limit in the service manual. This last time he said he only took off a little. There is still some meat between the surface and the valves, but I'm wondering how much valve to piston clearance there is going to be...

[BaadVR4]

Piston to valve clearance is probably not an issue. Of greater concern is how much the milling "opens up" the cooling passage holes. As the heads are milled, the size of these openings gets slightly bigger. It is possible to have them open up to the point where they are larger than the gasket sealing surface, causing coolant leaks. Maybe not common, but common enough to warrant checking before installing the heads. Just my 1.5 cents worth.

[mcshooter]

i guess you could get a shop with a surface grinder. around here you would be lucky to get any good finish

[green-lantern]

You always need to ask before having heads machined to see what equipment they are going to use, and what surface finish quality they will provide. Both sanding and milling are common (there is milling, and there is head finishing). Both can have either good or poor results depending on the resulting surface finish. Generally speaking if the surface isn't pretty damn shiny you are screwed if you plan to run big boost. For a DD or non-turbo you'd probably be okay with just about any surface finish as long as they are flat (that is key) and as long as they haven't been milled too far beyond spec.

Well Wayne, that doesn't make me feel to warm and fuzzy. lol I plan to run over 20 and run e85.

[Flamer]

Now my concern is how much material is taken off at this point. The 1st time I had the heads done, they said they had to go almost to the recommended limit in the service manual. This last time he said he only took off a little. There is still some meat between the surface and the valves, but I'm wondering how much valve to piston clearance there is going to be...

It's been a while since I've had my car torn apart but aren't there markings on the head that indicate when the heads have past the allowable clearance?

[Ben_Pow!!]

Well Wayne, that doesn't make me feel to warm and fuzzy. lol I plan to run over 20 and run e85.

You had a shitty job done on yours?

If it may help anyone, I didn't blow my graphite gaskets till I ran about 19-20psi for about a month, I can't believe how tore up the gaskets are, graphite stinks.


It's been a while since I've had my car torn apart but aren't there markings on the head that indicate when the heads have past the allowable clearance?

I don't recall ever seeing anything in the service manual, but I will look at these heads and see if anything stands out to indicate that.

[Ben_Pow!!]

I think the service manual only calls for a .008" tolerance, that sure isn't much, so I don't see how any kind of marking could be used on the cast itself.

[mdcrose]

Yeah, there is a service limit indicator in a corner of each head, it's a little circular boss with in another circular bore. When you get to the disk in the center, the heads have been resurfaced to the limit.

[Boostaddict]

Yeah, there is a service limit indicator in a corner of each head, it's a little circular boss with in another circular bore. When you get to the disk in the center, the heads have been resurfaced to the limit.

Except that if you ever meet the bottom of those cast-in indicators your heads might be far out of spec from what I've measured. The head needs to be set flat on a surface plate and the overall head height needs to be measured. The spec is 84mm nominal with a -.2mm limit. It only takes a couple passes/clean-ups before heads are out of spec. Granted, they can still be succesfully used past this limit (many are) but head lift and valve contact risk increase. Ray's head lift fix can help counter this but as I mentioned, the primary importance for boosted 6g7x engines are head flatness and surface finish quality (coarse milled radial tooling marks are more desirable than coarse directional sanded IMO but you want as smooth as possible to a certain extent).

[Ben_Pow!!]

Alright, just looked over them again and they aren't as bad as I had in mind the 1st time. You can barely feel them w/ the thumbnail, the marks are noticeable, but the finish is very smoothe and somewhat reflective for the most part. I'm going to go ahead and put the other on and go w/ it. Wish me luck.