Need Advice on Machining the Intake Surface of the Head (gasket crush)

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1970 TA

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Got my open chamber heads (3418915B's) back from the machine shop. They removed 0.012 from the deck side to reduce the chamber size to adjust compression. They did not take any material off the intake side of the head. I've performed a trial fit of the intake manifold / heads on the motor with the head gaskets in place. I fabricated some washers the approximate thickness of the Felpro intake gasket (0.055 / 0.060) to place between the head and intake, and used clay between the head / intake to measure theoretical gasket compression. The head bolts were just snugged up.
These photos show the actual thickness of the clay. The measurements show that the desired compression is reversed, i.e., the compression is greater at the top of the port, less on the bottom of the port. The compression also varies front vs rear. I'm using the guidelines in this article, http://www.hughesengines.com/Upload/TechArticles/INTAKE_MANIFOLD_SEALINGJULY2015.pdf, i.e., for example, add the clearances at the top of the port for the front positions, do the same for the bottom of the port, you want 0.006 / 0.008 more clearance at the top of the port for proper sealing.
Using my measurements,
Front position (top of port): 0.050 + 0.050 = 0.100
Front position (bottom of port): 0.053 + 0.065 = 0.118
So there is 0.018 more compression at the top of the port.
The rear positions:
Rear (top of port): 0.051 + 0.056 = 0.107
Rear (bottom of port): 0.055 + 0.060 = 0.115
0.008 more compression at the top of the port.
The machine shop has the heads and they will come up with a proposed solution.
Just thought I'd run this by the machinist / shop owners on FABO to get their input.
Thanks in advance for any inputs.

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A .060 thick gasket will probably work but .008-.010 should have been taken from the intake face.

Looking at your numbers a good gasket will seal that up. The gasket is there to take up some variance in machining and fit.
 
BTW, again looking at your numbers it's not unusual to see twist and roll in a machined surface like that after it has been run. You can indicate the face of the head in the mill and correct it but damn, it just isn't worth it to me. Make a clean cut running the average from end to end and side to side and take .010 off of it and go.
 
yellow rose said:
Wait...why did you put the washers in there? I'm not getting that. Take the washers out and see what you have.
Click to expand...

"I fabricated some washers the approximate thickness of the Felpro intake gasket (0.055 / 0.060) to place between the head and intake"
 
yellow rose said:
Wait...why did you put the washers in there? I'm not getting that. Take the washers out and see what you have.
Click to expand...
I used the washers to simulate the thickness of the intake gasket and limit the crush of the clay. I plan on using the Felpro gasket that leaves the heat crossover open. The gasket measures 0.055 / 0.060. On the drivers side head, that gasket thickness looks marginal on bottom the ports. Did you read the Hugh's reference article? They use steel washers with their wax material.
 
The correct amount to take off the intake surface is 95% of whatever was taken off the head gasket surface. 95% of .012" is .0114".
 
That wouldn't be enough for me to worry about, get a good gasket and bolt it on, I always use a little gray RTV for coolant around the water passages anyway. Cometic will make gaskets any thickness you need.
 
69_340_GTS said:
The correct amount to take off the intake surface is 95% of whatever was taken off the head gasket surface. 95% of .012" is .0114".
Click to expand...

Every time I have had the intake side cut, they take off to much, they tell me they use a use the same formula they always do and it is correct but if you take .030 off the head you can't take 28.5 off the intake, it's to much.
 
rednesss said:
"I fabricated some washers the approximate thickness of the Felpro intake gasket (0.055 / 0.060) to place between the head and intake"
Click to expand...


Right, so the shims are changing his readings. Who says the shims are flat? Who says they are exactly parallel to each other?
 
U r measuring an uncrushed new gasket? I cut my heads .017", and like a good squeeze on the intake gaskets, did not cut the intake faces.
 
brian6pac said:
Every time I have had the intake side cut, they take off to much, they tell me they use a use the same formula they always do and it is correct but if you take .030 off the head you can't take 28.5 off the intake, it's to much.
Click to expand...
95% is right out of all the Mopar engine building books, even the one that Mopar wrote. I seriously doubt if the number is incorrect. Also, it is recommended that only the two surfaces on the heads be machined. If you machine the intake manifold it won't be interchangeable to other engines.
 
I have always used the Mopar numbers. Never, ever had a problem. Not sure why people need to question the people who had the design specs at their disposal?? And I always mill both sides of the head. And I mill the heads of any engine I rebuild. If you want to cheap out, you can probably get by. You only have to do it once. Once the heads have that many heat cycles they don’t change much.
 
1970 TA said:
I used the washers to simulate the thickness of the intake gasket and limit the crush of the clay. I plan on using the Felpro gasket that leaves the heat crossover open. The gasket measures 0.055 / 0.060. On the drivers side head, that gasket thickness looks marginal on bottom the ports. Did you read the Hugh's reference article? They use steel washers with their wax material.
Click to expand...


I read very little from Hughes. I guess I could read it, but then I'd probably be pissed off for a while. I like Dave, and he makes some parts that I use but he and I disagree on most everything from tune up, to port work, to intake manifold and his selection of cam shafts.
 
Measure the thickness of a used gasket, that is real world. Notice how head gaskets are listed as compressed thickness. You can have the head intake faces angle milled, but your actual top to bottom average difference is only .005". If things are not perfect, and they never are, u want more gasket crush. Cut the surface and u get less gasket crush
 
Just wanted to add that the intake is an aluminum 6 Pack manifold.
brian6pac said:
That wouldn't be enough for me to worry about, get a good gasket and bolt it on, I always use a little gray RTV for coolant around the water passages anyway. Cometic will make gaskets any thickness you need.
Click to expand...
I was more concerned about sucking oil from the valley into the intakes if I don't seal well on the ports.
I called Cometic about thicker gaskets. They have a 0.060 like Felpro, the next size up is 0.094 thick. Nothing in between. You have to pick a thickness from their stock of materials.

yellow rose said:
Right, so the shims are changing his readings. Who says the shims are flat? Who says they are exactly parallel to each other?
Click to expand...
I made the shims from an old Felpro 0.054 head gasket.

Marcohotrod said:
U r measuring an uncrushed new gasket? I cut my heads .017", and like a good squeeze on the intake gaskets, did not cut the intake faces.
Click to expand...
I measured a new Felpro MS 90109 gasket. Measures 0.054 / 0.059 across the raised sealing beads. I don't know the prior history on these heads, but the machine shop said the deck side had been resurfaced before. They didn't say anything about the intake side being resurfaced.

Marcohotrod said:
Measure the thickness of a used gasket, that is real world. Notice how head gaskets are listed as compressed thickness. You can have the head intake faces angle milled, but your actual top to bottom average difference is only .005". If things are not perfect, and they never are, u want more gasket crush. Cut the surface and u get less gasket crush
Click to expand...
The used Felpro gasket measures 0.039 / 0.047
 
1970 TA said:
Just wanted to add that the intake is an aluminum 6 Pack manifold.

I was more concerned about sucking oil from the valley into the intakes if I don't seal well on the ports.
I called Cometic about thicker gaskets. They have a 0.060 like Felpro, the next size up is 0.094 thick. Nothing in between. You have to pick a thickness from their stock of materials.


I made the shims from an old Felpro 0.054 head gasket.


I measured a new Felpro MS 90109 gasket. Measures 0.054 / 0.059 across the raised sealing beads. I don't know the prior history on these heads, but the machine shop said the deck side had been resurfaced before. They didn't say anything about the intake side being resurfaced.


The used Felpro gasket measures 0.039 / 0.047
Click to expand...

I wouldn`t worry about only taking only .012 off the heads. I`d gasket match it perfectly using hughs gaskets, elongate the bolt holes in the intake just a hair (IF) needed
, and don`t look back. I`ve had that milled and didn`t have a problem.
 
Mopar Performance #4120094 are a pair of Felpro 1008 if you go that route. I bought them for my 340 build. Apparently the only way to buy them as a pair and the only hi performance sb hg by Felpro. Got it from Dodge store cheap. I haven' installed yet. Can get you uncrushed thickness if it helps?
 
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why use spacers and clay, makes no sense, oh hughes said to? If u want to see what the actual gap is use just clay. your average top gap is .052", average bottom is .058" - with spacers artificially holding the intake away from the heads
 
famous bob said:
I wouldn`t worry about only taking only .012 off the heads. I`d gasket match it perfectly using hughs gaskets, elongate the bolt holes in the intake just a hair (IF) needed
, and don`t look back. I`ve had that milled and didn`t have a problem.
Click to expand...

Agreed. That isnt enough to cause any issues
 
70 TA,
Can the machine shop mill a bit more off of the tops of the intake sides of the heads than off of the bottoms? Wouldn't that give a more even crush to the intake gasket and a better fit?
Also, shouldn't you take test measurements of the gaps at the front and rear rails too? You don't want to have a coolant leak out of the rear corners of the intake manifold.
It will be interesting to see what your machine shop suggests for milling the intake sides of the heads.
Richard
 
Marcohotrod said:
why use spacers and clay, makes no sense, oh hughes said to? If u want to see what the actual gap is use just clay. your average top gap is .052", average bottom is .058" - with spacers artificially holding the intake away from the heads
Click to expand...
The only things you can really measure with clay is the RELATIVE gaps top-to-bottom with the intake undistorted by the intake bolts. The washers just make the numbers more consistent side to side and easier to interpret and to visualize in the actual installation IMHO.

However the relative gaps top-to-bottom will be the same with the washers or without. You could use washers half the thickness or just clay (no washers at all) and get the same RELATIVE top-to-bottom gap measurements.

Marcohotrod said:
U r measuring an uncrushed new gasket? I cut my heads .017", and like a good squeeze on the intake gaskets, did not cut the intake faces.
Click to expand...
As long as the intake bolts are not hitting against the upper edges of the holes in the intake as torque increases (and thus limiting the intake's movement downward), then the crush for a given bolt torque does not change with the heads cut or not. But IMHO it is wiser to do as above and start the intake 'riding high' a bit as you try to start the bolts.
 
It would have been best if these measurements had been taken before the milling as well.
You don't know if the machine-shop created this skewed plane, or if it was there in the casting from factory.
It's also difficult to tell if the heads have been milled before.

Having worked with a Van Norman head-surfacer a couple of times for instance, I know it can be a hassle sometimes to properly clamp down heads that only have angled surfaces on the sides.
It's easy to mill at a veryslight angle if you're not careful mounting the head.
 
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