How do I measure cylinder to see how much has been milled off???

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duster360

duster360

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Can someone tell me how to measure a cylinder head to see how much has been milled of the surface? I also need to know the specs for a stock head. This is a small block J head.
 
That is a great write up and I will be saving it to my favorites on my computer. But cc'ing won't help in my situation. I have aftermarket valves that look nothing like factory. The reason I need to know is my intake manifold is not sealing good and from what I can tell it is not seating far enough down between the heads to get a good seal. I suspect the heades have been milled, which would bring them closer together and not let the intake seat correctly. I have had this engine since 1975 and my dad was the first to go into it and there was no milling done to my knowledge. The stock intake sealed good until it was parked in the early 80's. I had them reworked when I went into the engine. No one at the machine shop I use mentioned doing any serious milling, so I just assumed they just surfaced them.
 
What you're going to need to do is find someone with the same casting as yours that has not been milled. Measure with dial calipers from the valve cover rail to the head deck and see what they have, then compare to yours. That's about the most accurate way.......and because of machining tolerances, it ain't real accurate, but it should give you some idea.
 
Thanks RRR. I will do that I have several sets of heads I will measure them and should be able to come up with a usuable measurement now that I know how to do it.
 
duster360 said:
This is a small block J head.
Click to expand...

What's the casting number on the runner. I'll check mine and measure them.

Do you have a set of calipers?


What you're going to need to do is find someone with the same casting as yours that has not been milled. Measure with dial calipers from the valve cover rail to the head deck
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Spark plug side I'm assuming?
 
I would try both sides. Maybe on each corner.
 
There are tooling "flats" near the spark plugs in the combustion chamber. The dimension from the block surface of the head to the flats should be .713 to .727 for unmilled heads. Measure all four and use the shortest two. Then you should be able to get close enough to figure how much has been milled.
 
RustyRatRod said:
What you're going to need to do is find someone with the same casting as yours that has not been milled. Measure with dial calipers from the valve cover rail to the head deck and see what they have, then compare to yours. That's about the most accurate way.......and because of machining tolerances, it ain't real accurate, but it should give you some idea.
Click to expand...


I would also think a depth gauge from the rocker shaft saddles to the head / deck surface should be fairly close, as these originally did not have adjustable rockers. I'm pretty sure I have at least 4 heads that to my knowledge have never been milled, including my old J heads which I just got back
 
Thanks for taking the time to take pics and measurements Bad Sport. Much appreciated.
 
Measure from the deck to the quench pad on the intake side of the chamber with a depth mic or a depth attachment for a calipers. Should be roughly .095" from the ones I have checked.
The area at the lower portion of the chamber in this picture.
attachment.php


The rocker rails are cast so poorly its not a good reference point.
 
66fs said:
There are tooling "flats" near the spark plugs in the combustion chamber. The dimension from the block surface of the head to the flats should be .713 to .727 for unmilled heads. Measure all four and use the shortest two. Then you should be able to get close enough to figure how much has been milled.
Click to expand...

THIS! Because A lot of the time they are angle milled.
 
CPMotorworks said:
Measure from the deck to the quench pad on the intake side of the chamber with a depth mic or a depth attachment for a calipers. Should be roughly .095" from the ones I have checked.
The area at the lower portion of the chamber in this picture.
attachment.php


The rocker rails are cast so poorly its not a good reference point.
Click to expand...

I think that this is the best way to measure. It is what "the engine sees" as best that we can measure in a garage.

You can also use the cover plate that I have in my compression write up to help measure. Don't bolt it down, and rest it on the head face and measure through the fill hole. Use the cover plate as a floating reference from the head/block face of the head.


You have to measure what you have, and not depend on "what they usually are". There are casting tolerances and production tolerances. There is no way for us to know "where they were running" for these dimensions from day to day. They vary. It's part of manufacturing/machining.

The foundry could have variation on their datums and locating pads from time to time. Then there are machine tolerances that also depend on where the machines were running the day that they machined your heads.

They also batch run heads to be milled in the engine plant for recycled heads. If the block sealing surface of the head gets scratched/gouged on an engine that has been built, found to have a problem, then stripped down and the parts recycled, they will batch run the heads through the machine line and mill some off the face to clean up any marks or scratches on the face.

They batch run these as they have to set the machines to mill deeper than the regular production heads, and then reset the machine back to run the first time through production heads. They tend to set the head face milling operation not to cut too much off of the face (run them "fat") so there is enough material left in case they have to be resurfaced if they get any damage in handling at the engine plants.

Basically, it's difficult to tell if they have been milled or not. To measure that accurately would require a special built gauge to measure from the machine datum to the head face or put them on a CMM (Coordinate Measuring Machine), both of which is way too expensive for us hobbyist to have in our garages. The best way for us to get an indication is measure the block face of the deck to the combustion chamber depth of the head, or cc the heads. But even then, it's not for sure.
 
Open chamber heads ain't gotta quench area.
 
I'm fairly sure any "as cast" surface isn't worth using as a reference point. They can vary a ton and even the surface features of cast metal can throw off a measurement enough to make a mess. I have not tested this - I tend to fit the intake "by eye" once the longblock is together - but I'm told the two machined surfaces to measure are shown in Bad's 1st picture... The surface spot faced for the last head bolt. Measure that thickness from the head gasket surface to the machined flat and it should be 1" if it's not machined. Again - with the varying casting quality, and the crazy factory machining I'm not sure that's 100% either - but I'd much prefer measuring two machined surfaces than try and make sense of any as cast surfaces.
 

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These are the Tooling Pads used to machine the head surfaces. This is the best way to try and determine if the heads have been milled and how much they have been milled.





 
moper said:
Measure that thickness from the head gasket surface to the machined flat and it should be 1" if it's not machined. Again - with the varying casting quality, and the crazy factory machining I'm not sure that's 100% either - but I'd much prefer measuring two machined surfaces than try and make sense of any as cast surfaces.
Click to expand...

66fs said:
These are the Tooling Pads used to machine the head surfaces. This is the best way to try and determine if the heads have been milled and how much they have been milled.
Click to expand...

Good info, I'm stealing that tooling mark pic, thanks!
 
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