GPW head thickness

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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John Ayres
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GPW head thickness

Post by John Ayres » Mon Feb 23, 2015 8:57 am

Anyone know if there is a spec for what the minimum thickness is for a GPW head as we are intending to deck the head but don't know how far we can go or if there are oversize gaskets available. Thanks, John Ayres


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Chuck Lutz
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Re: GPW head thickness

Post by Chuck Lutz » Mon Feb 23, 2015 9:12 am

Measure from the machined surfaces of course:
Head Thickness - 2.140 JF.jpg
Head Thickness - 2.140 JF.jpg (20.78 KiB) Viewed 898 times
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Re: GPW head thickness

Post by dpcd67 » Mon Feb 23, 2015 9:18 am

I never heard of OS gaskets but you aren't going to mill that much off of it and they need some extra compression anyway. I took .030 off the last one did to clean up the warpage; the machine shop did I mean.
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Re: GPW head thickness

Post by gearhead » Mon Feb 23, 2015 11:56 am

No need for "special" head gaskets.
I wish mine had 8:1 compression!

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Re: GPW head thickness

Post by tazmo2004 » Mon Feb 23, 2015 12:10 pm

What is the max limit before you get valve to head clearence problems?
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Re: GPW head thickness

Post by dpcd67 » Mon Feb 23, 2015 5:12 pm

I don't know; never had one milled that much; have your machine shop remove only enough to make it flat and then use the putty method to determine valve clearance.
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Re: GPW head thickness

Post by Chuck Lutz » Mon Feb 23, 2015 6:30 pm

Todd....measure your head and compare to the factory spec. Many heads you find off running motors have 1/2 or less of the 7/32" in thickness from the shoulder down to the milled surface....if you have CLOSE to that 7/32" then your machinist will have plenty to work with.
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GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
Bantam T3-C 1947

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Re: GPW head thickness

Post by tazmo2004 » Mon Feb 23, 2015 7:51 pm

Thanks Chuck.
This was a curiosity question since the compression ratio statement came up. My M38A1 has the hermaphrodite engine but a buddy has a GPW, a little more power never hurt anyone. I would do the mill work on the head in my shop and it wouldn't be fun to look at him when I cut into the water jacket and go "guess that's to much". Kind of funny that the factory spec/drawing is measured with a yard stick too. :)
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Re: GPW head thickness

Post by Michael Browne » Tue Feb 24, 2015 1:05 am

John Ayres wrote:Anyone know if there is a spec for what the minimum thickness is for a GPW head as we are intending to deck the head but don't know how far we can go or if there are oversize gaskets available. Thanks, John Ayres
To John,Todd & others,

The heads of MB & GPW all vary and you wouldn't rely on casting shoulders for a guide for how far to machine it down. That may be ok for a fresh cast head from the factory but could land you in trouble with any head that has been used and possibly machined many times before. Sometimes during the casting process the sand cores move and the wall thickness of the head can be very different to the factory drawings.

Rule of thumb, only remove enough to make it flat. Any further to gain a compression ratio gain is a total waste of time . The head chamber around the valves is where a side valve engine loses compression ( or should I say, is unable to gain compression higher than 6.9) as that area is to great to allow any more than 6.5 to 6.9 compression, simple maths. In any case you won't notice the slight difference in performance with a milled head.

If you want more compression get a willy willy head and do it right, I think Marty had a post with dyno performance specs with one of these aftermarket heads.

Also the easiest way to check for valve to head clearance after machining is to simply sit the head loosely on the block WITHOUT the gasket and rotate the engine 2 full turns checking to see if the valves lift the head off the block face. If it doesn't then all is ok to use.
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Re: GPW head thickness

Post by John Ayres » Tue Feb 24, 2015 10:38 am

Much thanks to all for your input as we try get this engine back in service. John Ayres

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Re: GPW head thickness

Post by Cuz » Sat Oct 30, 2021 7:19 am

Chuck,

Do you have a copy of the entire factory drawing for that head you can share with us?
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Re: GPW head thickness

Post by dpcd67 » Sat Oct 30, 2021 6:42 pm

This thread is 6 years old and I don't think CL is on here any more.
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Re: GPW head thickness

Post by JAB » Sat Oct 30, 2021 6:57 pm

-Jeff

GR8GPN2U!!!

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Re: GPW head thickness

Post by Cuz » Sat Oct 30, 2021 8:04 pm

Thanks Jeff.
Cuz (AKA Wes K)
45 MB, 51 M38, 54 M37, 6? M101A1, 60 CJ5, 76 DJ5D & 47 T3-C


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