# Machining a cylinder head



## Otho21 (Nov 21, 2013)

In a past life I operated a mill and lathe to repair and fab replacement parts for broken industrial equipment. Later I purchased both for to make dies. Now I am tinkering with cars and the local machine shop is going down hill FAST! I would love to use my mill to resurface cylinder heads but I'm not sure what tooling I need, feed speeds, etc. 
I'm certain machining a head isn't totally uncommon because I see milling marks on them regularly. If anyone could offer any advice I would be grateful!


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## enfieldbullet (Nov 21, 2013)

what cylinder heads are we talking and what operation?

you have to consider that lowering the heads will increase the compression ratio. so badly twisted heads will be better off replaced.

usually a fly cutter is a good option as tooling goes.


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## Otho21 (Nov 28, 2013)

enfieldbullet said:


> what cylinder heads are we talking and what operation?  you have to consider that lowering the heads will increase the compression ratio. so badly twisted heads will be better off replaced.  usually a fly cutter is a good option as tooling goes.



Enfieldbullet, thanks so much for responding. Sorry I have taken so long to respond but I'm new and learning to navigate the forum on a new device. I actually have the specs and the most I "should" face them is 40k, however 50k is not uncommon and I have seen them all the way to 60k which I consider too much. Specifically I am dealing with the jeep I6 4.0 inline and the dodge 5.9 v8. Both are steel heads not aluminum. The work would of course be jigged and a Kool most spray is mounted  on the mill. A stock inline six head should deliver around 130 pounds compression per cyl. A head shaved down 50k seems to deliver around 145-150. And a head shaved to 60k is delivering around 155 - 165. We haven't had any problems yet but I don't like the 60 k head ( my partner did that one ) it seems a bit high on the compression side. I will look into the fly cutter, do you have any suggestions on feed speeds or bit type?
Regards and thank you again, it is much appreciated!


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## kvom (Nov 29, 2013)

You can also use a face mill if your machine has sufficient horsepower.  Much faster than a flycutter.


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## Otho21 (Nov 29, 2013)

Excellent! I was looking at face mills, which seemed an obvious answer at first. I just needed to hear someone with more experience point me in the direction. The mill can certainly take it. It is an older enco using an r8 shank. Very heavy mill. I can actually afford both the face mill and the fly cutter form a tool maker I have found. As soon as I get them in I'll have a go at it and  post results with both. Thanks for the suggestions and if anyone has anything to add please don't hesitate to do so! I welcome all comments and suggestions!


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## gbritnell (Nov 30, 2013)

I haven't responded yet by feel that I should say something about what you are proposing. Yes a standard mill can be used to surface a head, it's been done many times but here's some things to look out for. The mill has to be indicated for the entire length that the head will be mounted to and it should be flat. The face mill needs to be sharp to the point that when your overlapping cuts are made the transition is seamless. As there are no perfect points to set the head up to other than the spotfaces for the head bolt holes you will need to level the head with an indicator then when you clamp it tight re-indicate it to get the same readings otherwise you'll be introducing a warp into the head. Another thing I would suggest is to see if you could get a junk head to practice on. One small error and you'll end up with another junk head. 
gbritnell


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## Otho21 (Nov 30, 2013)

Thanks to everyone who has responded to the thread so far! I welcome any input and appreciate the responses so fat. I realize this might be a bit off topic for the site, but who better to ask than a collection of machinists!  I realized that the face would have to be indicated and Very Close if not dead on. So I'm on the same page there. I ran across a fellow that jigged heads so that's a thought too. In my case I'm only dealing with two types of heads and It might be cost effective to do that. Does any one know how cylinder heads are usually faced, I have heard it is done on what is essentially a big belt sander. However I have not been able to find such a piece of equipment and do mot know what it would be called. 
Again thanks of far and if anyone has anything to add..... Please do so! I welcome all comments. I'm just here to learn, ( and build steam engines )! Thanks everyone )


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## Badhippie (Dec 1, 2013)

Othro
It has been my experience that if you are just wanting to clean up the surface of the head or remove any warp ness
is to use a surface grinder. The only time I would use a mill is when you are trying change the CC. of the engine in other words
raise the compression by lowing the CC's of the engine but then you must be careful of any Smilies face's that might happen in the piston
from a little valve to piston contact

              Hope this helps 
               Tom


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## enfieldbullet (Dec 1, 2013)

you don't really lower the CC's of the engine, you just lower the CC's of the combustion chamber.

the engine displacement is given by the stroke of the piston, and that is not changed unless you change bore or crankshaft throw.

valve to piston contact is a serious possibility. very bad if happens.

you can do it in the mill but you have to put a very fine feed so as to get a smooth surface. it'll have a gasket anyway so it's not too critical as far as surface finish goes.

you can also glue some sandpaper to a flat glass and 'lap' the heads like that for a better finish.


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## Badhippie (Dec 1, 2013)

Enfield 
You got me i should proof read my stuff a little better yes you are correct you are only changing the CC's of the combustion chamber
Also something i did forget to mention was no matter what method is used make to sure to take the time and remove the edge from the finished
Surface of head


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## Otho21 (Dec 2, 2013)

This is good stuff guys! You just helped me solve another issue I had been thinking about. You can't get much of a straighter edge than glass. It at could be used to indicate low spots on a un cleaned head if backed to eliminate flex. And you are correct Bullet. Cc only changes with the bore and stroke. However that is easy to confuse unless you really think about it. I'm going to flip over to enco and look at surface grinders, I've wanted to do this way too long and as I mentioned the local machine shop it on the way out. I had to turn a friend down over the weekend who wanted me to surface a head as a favor. Thanks for the tips everyone! Please..... Keep them coming! 
Happy tinkering everyone! )


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## deverett (Dec 4, 2013)

Just a thought...
If the local machine shop is 'on the way out', would you be able to get hold of some of their gear, probably a lot cheaper than buying new.  If they did good work, then there will be life left in those machines.

Dave
The Emerald Isle


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## Krutch (Dec 6, 2013)

When you remove head surface material, you move the valves closer to the piston. Check for clearance after milling and before running the engine. 

 I do Harley heads from time to time and check for clearance after I do.
 I only clean up the head surface for warpage and pulled inserts. Taking as little as I can get away with. I also engrave the amount taken off into the head next to the gasket surface so the next guy knows how much has been removed.


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## russ57 (Dec 6, 2013)

"in the old days",  I recall adding a thick copper gasket to make up for excessive skimming - usually required after repair of a crack... Possibly not really good practice,  but cheap! 
-Russell


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## Otho21 (Dec 10, 2013)

Krutch, I have noticed an occasional engraving in the rear passenger side of some heads, I think that is the exception and not the norm. This is an old school courtesy  that is not observed as often as it once was but valuable to any mechanic. I wish it was standard so we don't work blind. 
Russ, most current head gaskets are gasket material on both sides ( top and bottom) with a lead core. When the gasket is set with the specified torque and heated under normal conditions. The lead core conforms to the imperfections of the head and block. My research has indicated that there are actually roughness specs that should be met for he head gasket to properly seal. Use of a secondary gasket would inhibit the seal of the current gasket systems. However, this practice was very common before the current type gasket was used. In fact, performance drag racing motors used copper o-rings to seal cylinders. Apparently the compression seal was superior to what we have now but the trade off was massive oil and water leakage.
Cutting the valve shoulders back seems to be part and parcel to the resurfacing job. If you think about it, it would help keep the valves in spec in relation to the piston and help prevent mechanical damage to the valves and pistons during operation. 
Thanks guys, great food for thought! Hopefully I'll have a tooling arriving soon and I can get my hands dirty! ;-)


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## enfieldbullet (Dec 12, 2013)

you can lower comp ratio back down shaving the combustion chamber all around, removing a little material at a time and checking the volume of the combustion chamber. this can also be done to get the compression on all cylinders similar. however it won't get the valves back up.

you can also use pistons which are shorter ahead of the conrod pin, making a higher deck height, if that won't get the piston too thin it should bring things back to original relation. (piston to valve clearance and compression ratio)

in vw engines that copper head gasket works because of the way the cylinders sit inside the head.


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## Walltoddj (Jan 2, 2014)

I work in GM Powertrain engine plant we used a large insert mill on Aluminum because the did not want a glass smooth surface to many gaskets blown out. We also did iron heads with the same large insert cutters and depending on the head were Blanchard ground to size. What every you use has to cut the whole width in one shot done try to cut one side then move over and cut the other. We ran flood coolant where we could and the iron dry the cutters will grow form the heat so watch closely. Hope this will help! 

Todd


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## Swarfing (Jan 2, 2014)

We used to have a guy local to us doing heads from his shed, mainly motorcycle but car heads too. His tool of choice was a diamond cupped wheel for small corrections (with flood coolant). you can also get these large enough to cover the width you need. he did this for years before suffering lung disease so watch that dust


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## jwcnc1911 (Jan 2, 2014)

If you want to clean up the combustion face, I highly recommend a surface grinder.


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## mc_n_g (Jan 2, 2014)

What I have seen is people using large 7-10" fly cutters with ground HSS cutters to get  the whole surface sut at one pass.  The key was to have some very slight cutting marks so the surface is not perfectly smooth.  I have heard (cannot prove and don't have any info on it) that perfectly smooth surfaces for heads fail due to lack of grip.
The fly cutter body was normally made from a large piece of 1.5-3" thick aluminum plate for mass so the interrupted cuts would not waver.
The other problem I have heard is having a table and knee large enough to handle the weight, height and the length of the cut.  The length of the cut also plays into using a fly cutter.


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## Walltoddj (Jan 3, 2014)

The key was to have some very slight cutting marks so the surface is not perfectly smooth.  I have heard (cannot prove and don't have any info on it) that perfectly smooth surfaces for heads fail due to lack of grip.


You are right the key is not a smooth surface at General Motor this is what we did on our heads and yes was to give it grip.

Todd


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## BaronJ (Jan 3, 2014)

Hi Guys,

Following this thread with interest !  But I have a question.  If the head is warped, then what do you use as the reference face when setting up ?


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## Walltoddj (Jan 3, 2014)

BaronJ said:


> Hi Guys,
> 
> Following this thread with interest !  But I have a question.  If the head is warped, then what do you use as the reference face when setting up ?



When we made the cyl heads we used 4 points on the mate face of the head, then had post come in from the back to clamp to for machining the face. This was done last due to all the machining, pressing in the guides, and pressing in the seats with causes the head to twist and bend. If I remember we pressed at about 1500 psi on a 2" ram if was not supported correctly we could break aluminum heads.
Todd


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## Hopper (Jan 3, 2014)

Many a head resurfaced on a milling machine here in the remote colonies where grinders are scarce.
When machining old/warped heads, be sure to shim any gaps between the other surface of the head and the mill table before pulling down the clamping bolts. Otherwise the clamping bolts will pull the head out of shape and when you release them after machining your nice flat surface, it will spring back into a warp again.


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## Krutch (Jan 5, 2014)

Krutch said:


> .
> 
> I do Harley heads. I only clean up the head surface for warpage and pulled inserts. Taking as little as I can get away with. I also engrave the amount taken off into the head next to the gasket surface so the next guy knows how much has been removed.


 

 Seeing as how I didn't add it at the time I posted my thread and reading others comments about gasket surface condition, I should say that after I "make new" said surface I bead blast same to rough it for gasket crush. I have yet to do any CI heads as the only one I'm likely to work on would be Knuckle heads. About as rare as hens' teeth anymore.


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## BaronJ (Jan 5, 2014)

Hi Krutch,

Love your tag line !  (*)


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