Cylinder head flatness - is milling really necessary

[rossiz]

not weighing in on whether this is the right thing to do - out of my league here... but if your home oven won't work, most foundries have heat treating ovens that are large, very accurate and set up for large parts and long, constant bake cycles.

not an expensive proposition if you have your head set up, mounted/shimmed/etc. and they just take it and bake it.

[Dave WM]

interesting read. I am sitting on my spare N42, trying to decide if its worth taking the head off and risking warping, Or just use as is and see how it performs. The compression test pointed to ok not great, lots of oil leaks from seals but no obvious head leaks (oil in crankcase was not milky). Rebuilder mentioned alum heads almost always are warped and need milling, most likely both sides an then use cam  tower shims (I ordered some .015" set). I sure like the idea of getting it as straight as possible with heat and pressure before any milling takes place. That seems the best way to avoid having to mill the top and mess with the shims. I wonder how the pros do this (shops that specialize in rebuilding L28's). I had goals of having a like new engine, but there seems to be a lot of different views on how to get there.

[siteunseen]

Take a carpenter's square, the big L shaped one, and lay the big edge on the bottom. If it's bad you'll see the gap.

Edited January 26, 2019 by siteunseen

[240260280]

Granite Tombstone (surface plate) and a big piece of sand paper.

 

[Zed Head]

Seems like devising some sort of torque plate to attach to the head before skimming the bottom sealing surface would be the way to go.  Then when it's bolted to the block it's all flat and smooth. You might have to mill pockets on the bottom surface for the bolt heads  though so that you can fly cut the bottom in one pass.  Pull the top of head up against a flat surface.

[Rooney]

(Edit: it was mark maras, madkaw, and eurodat that got me thinking it was possible and helped inspire the methods i used. I wanted to refer to their previous comments but had to go back to find their names, thanks each of ya. It's the only reason I made an account here, just to thank you.)

I just did a bit different approach to the similar problem, not with an opel but I have a Ford truck with a head gasket failure,  and found it warped about .033 up in the center.

I didn't have a thick plate of steel to bolt onto, but found a girder and hoped to make it work.

The approach I took was much different, rather than air heating and cooling, I figured that oil heating would more effective to thoroughly heat everything through to temp, taking notes from the kitchen chefs, and also slowly cool it. Borrowing from old blacksmith forgings.

So far it appears that the head is not nearly as crooked, wheras before you could stand back ten feet and eyeball it and see where it warped at.

I used washers about .090 thick, heated the head, and bolted it to the cool c-beam, bastardizing a feeler gauge set to do some math and combine multiple shims to brace between the beam and head, stacked between each L-R row of head bolts:

 

Began with .033 warp, with .090 washers at the corners, and from what someone said here I went half the distance past center? It was a long weekend, but I basically stacked the feeler shims in a combination equal to what distance was needed, increasing in the stack sizes towards either end, with the old head bolts, nuts and lock washers on the beam side

And with an old metal oil drum cut in half, two old gasoline Coleman camp grills, a propane weedtorch, digital thermometeras well as industrial use temp needle gauge that is fitted in processing equipment, I basically deepfried the cylinder head. It had already been fried once! But this time, heated the head upside-down so the c-beam would be out of the oil, in an attempt to keep it from distorting as well, if I could manage to keep it somewhat cooler than the head and thus remain more rigid while subjecting the head to the heat, and also left the mounting bracket on the head so I could dip it in or pull it without reaching in.

 

I also had several fire extinguishers on hand, and a forklift to lift or lower it.

 

Currently, I'm looking at it, it looks like it may be straighter, but I'll admit I'm nervous to unbolt the thing. Even with the criss-cross outermost and working in, what if somehow I made it worse? 

Edited August 6, 2019 by Rooney

[Captain Obvious]

9 hours ago, Rooney said:

I basically deepfried the cylinder head.

You use peanut oil, or motor oil?

Pics or it didn't happen.

[Rooney]

3 hours ago, Captain Obvious said:

You use peanut oil, or motor oil?

Pics or it didn't happen.

I'll try to get pics uploaded after work. Phone won't let me.

Used Delvac 1640, but for how bad it stunk I'd rather have used peanut oil! This GA boy stuck in KS would have felt right at home

Edited August 6, 2019 by Rooney

[Rooney]

On 10/18/2015 at 5:16 AM, EuroDat said:

I have seen a technician at work hobbying on his old Opel inline six head.

He used a piece of 200mm channel steel and drilled 6 holes using an old head gasket as template...

Sacre bleu! 200 mm, that's 8 inch in English. 

I may work at an oil refinery that has a scrap heap of old components, but I'm not sure I can manage to get a hold of something like that. Perhaps a local metal recylclery?

[Rooney]

Got another idea, might not be possible for a head in particular with the intake and exhaust ports on the same side, i do have the spark plug holes on the opposite side, so maybe?

Idea: with some sturdy bolts on both sides of the head, and some arrangement of mounting brackets down the length of the head, and making some sort of bracing apparatus to place over the head that still allows access to torque the head bolts themselves, connect the side brackets with the upper apparatus by a series of tensioners or slide adjusters, similar to bolt tensioners or like tie-rod sleeves, and adjust it until the head is completely flat and passes a straight edge & feeler check... then mount the head and gasket to the block with it stretched even, torque the bolts in sequence while this way avoiding the slippage and damage to the new gasket, when everything is torqued in place, remove the apparatus and proceed with reassembly as normal? Could that work? 

[Mark Maras]

 Installing a warped head with a way to pre-straighten it during installation would seem to be an improvement over torquing down a warped head. Any apparatus I can imagine would have more mass and weight than the head.

[Zed Head]

As I mentioned above it really doesn't take much force to flex the head.  Experiments with longitudinal clamps might show something.  

If it's bowed up on the ends then it might be as simple as tightening the center bolts first.  If it's bowed up in the middle, clamp it from end to end and drive some wedges under the middle of the clamp.

Who knows, it might actually be simple to do. 

https://www.harborfreight.com/1-2-half-inch-pipe-clamp-3813.html