"Angle Milling" heads

tubman

tubman

Well-known member
I have just gone through a couple of "Aluminum Foil ball" cycles on the Edmunds heads I want to run on my new 258" engine. The passenger side seems to be real close (it seems that I need to do a little clearancing on one chamber to get to .050" squish, and then all I have to do is fill the pits in the heads). I purchased some "JB Weld High Temperature putty" and started filling some of the pits. Although it is kinda hard to work with (kneading it with my old arthritic hands is tough) I think it's gonna work just fine.

My problem is with the drivers side head. I checked it two times (the first with about 2 foil balls on the valves and one ball on the top center of the piston, and a second time with 8 balls on each piston top) and both times it indicated that the front of the head has about .025" more clearance than the back. It looks like if I can have this head milled so it takes .030" off of the front chamber tapering to .005" at the back piston, it will bring everything back to where I can get my "squish" and compression right. Since it is a weekend, and I can't call the machinist, I decided to ask here. Is it possible to do this kind of (front to back) angle milling on this head? Should a regular automotive machine shop be able to do this, or is it a specialized operation that needs to be done by a high-end shop? I don't have any valve clearance problems (Isky Max-1 cam), so my only concern is the combustion chamber clearances.
 
Shouldn´t be a problem to set up the head for milling in an angle front to back or sideways.
If it´s a dedicated engine machineshop they probably have adjustable setup for just this aplication...or just shim it when setting it up on a milling machine.
 
deuce_roadster said:
That going to cause trouble with studs if holes aren't 90 degrees from the surface?
Click to expand...

I never thought about that, but with the "slop" in the bolt holes that are common with these heads, I should be all right. When I get them back, I'll drill a couple of holes to 1/2" so I can use the 7/16" aluminum tubing spacers I have been using for keep the heads from moving. I guess I'll have to see. I don't know now if the taper across the head is a result of flawed production or a previous poor resurfacing. I do know my other set of Edmunds heads didn't have this problem. Plus, I am using bolts, which should make things a little easier.
 
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Are you certain that the issue is in the head?

I've seen a number of blocks where the crankshaft bore is not completely parallel to the top of the block deck.
Yes, the bores were perpendicular to the crank centerline so that was not a problem.
Measure your deck height of the pistons at TDC.
 
I do know of new heads that the combustion chambers were not machined equally and a couple at one end needed to be machined deeper about .025. I have a friend with a machine shop that made a cutter for those particular heads. Before you do any machining of the head surface check the depth of the combustion chambers.
 
I know this doesn't help you but I've done business with machine shops that surface heads on a big belt sander. That's probably what happened to yours.
 
Also,keep in mind that not only the bolt holes become "un-square" with the head gasket surface, the spot face for the bolt heads become "non-parallel" as well resulting in torque problems and leakage.
 
Wow, I'm glad we aren't paying you by the hour:D:D.
No, really I understand how little bit here and little bit there adds up to a lot in the seat of the pants. Good Luck.
What was that trick Smokey Yunick pulled with a Hudson? Something like not being allowed to mill the head he found a paint that would stand up to combustion temps. Then He set about building up the chamber to get what he wanted.
 
Looks like I may have to do a little math after I get done measuring. I really suspect the heads, because they are an unknown quantity, while the short block was done by a guy with all of the proper tools who knows his stuff. I want to find the angle that will result from this amount of removal of material and how much it will effect the bolt holes and washer surfaces I used to know this stuff in the 10th grade. Let me see, is that the "Tangent" function? Maybe the "Sine" or "Cosine"? What was "Secant" for? Back to the books (or most likely Wikepedia).
 
You are on the right track. first determine whether the problem is the block or the head. As mentioned, measure the piston height above the surface at the front cylinder and the last one. Do this for both banks while you are at it. Chances are you will find the block deck is OK. Then look closely at the underside of the at the size/shape of the combustion chamber major diameter where it meets the flat surface. If you can see the difference from front to back then you know that the head was surfaced incorrectly. At .025 difference, you should see a difference by visual inspection, (look closely or use calipers to measure the "diameter"). This will confirm that the problem is in the head (most likely) and you are good to go on surfacing the head at an angle to get it back to parallel. The stud holes will be back to correct perpendicular.
An ole timer showed me that with a little practice you can determine how much a head has been milled by just looking at the underside and be within a couple of thousandths. If it is milled crooked, the difference is really evident. Good luck. My money is on the fact that the head is angled.
My opinion
 
Maybe it is the block ! I know when they were checking the heads at the track after a race we had the BLOCK ground to get what we wanted ! !!!!!!!!!!!!
 
Ok, I'm done with a couple of days of measuring and checking and I think I know what the problem is. I first measured the heads; the combustion chamber diameter and depth, as well as volume are quite similar, and what differences there are, are between random cylinders (do not increase from back to front). Next, I measured the height of the edges of the pistons below the block at TDC, and it decreased between adjacent cylinders by about the same amount that the clearance shown by the aluminum foil balls decreased. (The front cylinder had the piston down by .070 with clearances in the .080 range, while the back cylinder is down .040 with clearances in the .050 range.

Obviously, the deck is not exactly parallel to the crank shaft. As near as I can measure, there is about a .030 difference between the front cylinder and rear cylinder. After thinking it over, I believe the solution to this problem is still to angle mill the head from front to back to bring the chamber clearances back to a uniform number. Luckily, I have enough clearances at minimum that I still have good "squish" on the back cylinder and the angle milling should bring the other cylinders back in the ball park. I am sure I will have to massage the heads to get everything exactly right, but I've been through that before and am sure I can handle it. I don't think there will be any problem with non-perpendicular bolt holes or washer surfaces because the angles will cancel each other out. The block and lower head surface won't be exactly parallel to the crankshaft, but the top head surface will. In the end, I think I will have another good set of Edmunds heads that will perform well. It's a good thing 8BA heads don't interchange side to side.:)

I can't blame this on the machinist, because I gave him strict instructions NOT to deck the block unless it was absolutely necessary, and to call me even then. This problem either came from the factory, or was a result of an earlier imprecise rebuild. I'd rather try to correct this by working on a set of $300 used heads than a fresh $1500 short block. What do you experts think?
 
I would bring the short block to the machinist and have him back up your measurements of block height, then have the block decked to the lowest point measured. IE if cylinder 1 has a deck height of -.020" and cylinder 4 has a deck height of -.050" - have the block decked to -.018 ...
presumably the other side is similar.
Either way, you want to make your block deck parallel to the crank centerline.
This is how to do it right.
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To clamp a head to an angled block deck means that your head studs are not perpendicular to the block deck, the nuts will not provide a good seat on the heads.
Don't worry about quench / squish until you have a good foundation to work with.
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My opinions only...
 
I think you got it.
Too bad I lost all my money on betting on the head.
Measuring, measuring, visual inspection and measuring again and you have the problem sorted out and a solution. Good Job
My opinion
 
Big-Foot said:
I would bring the short block to the machinist and have him back up your measurements of block height, then have the block decked to the lowest point measured. IE if cylinder 1 has a deck height of -.020" and cylinder 4 has a deck height of -.050" - have the block decked to -.018 ...
presumably the other side is similar.
Either way, you want to make your block deck parallel to the crank centerline.
This is how to do it right.
---
To clamp a head to an angled block deck means that your head studs are not perpendicular to the block deck, the nuts will not provide a good seat on the heads.
Don't worry about quench / squish until you have a good foundation to work with.
---
My opinions only...
Click to expand...
I do not agree with this statement for the reasons I stated. If I had infinite money and infinite time I might consider getting the block right, but that would require complete disassembly of a completed and painted short block; valve train, crank and pistons, everything. I am talking about .039" over a span of 20". I don't think this is enough to be consequential. I would be willing to bet that thousands of flatheads left the factory or rebuilding shops with this much of an error if not more, and ran fine for many thousands of miles. Then we get into the question of deck thickness. There is a good chance that this block has been decked before (albeit rather poorly). Given the notorious thinness of flathead blocks, I would rather take a chance on he .039" than making an already thin deck thinner. If I'm right I'm right. If I'm wrong, what could go wrong? With the extent of the cut I'm talking about here, I doubt anything serious; a leaking head gasket maybe? If anything goes wrong, it would be time to re-think this.
 
So will it be apart thursday and i free up some space in the surfacer ;)
Or what bore is the new block you bringing home going to have...ouch im being bad right now...
Seriously...if we´re talking blueprinting it´s both deckheight side to side and compared to the other bank that has to be done.
 
If you're going to proceed with angle milling the heads, at least have the machine shop spot-face the head nut seats.
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Sorry if I ticked you off - I build engines and I find it difficult to take short cuts and expect a quality job that will last.
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Good luck!
 
You haven't "ticked me off"; far from it; I came here looking for advice. But... Think about it. The deck is not parallel with the crank. It is at a certain angle to it. If the bottom of the head is milled to the same angle, but in the opposite direction, everything mates together with the top surface of the head coming back into parallel with the crankshaft.

Here's a rough sketch of what I'm talking about. Nothing is even close to scale, but I think you should be able to get an idea of what I'm proposing. If I'm wrong, please show me where.
 

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