heads off gem same as classic?

[PeterAllen]

Are the heads off a classic efi 3.9 the same as on the gems
Just wondering if they are interchangeable

[p38arover]

Which year model RRC?

[PeterAllen]

Originally 1987 but was reworked by john davis into a 4.6 motor but i am not convinced it wasore like a 4.2. Its an early efi engine.

[PhilipA]

Are the heads off a classic efi 3.9 the same as on the gems
Just wondering if they are interchangeable

They are functionally the same EXCEPT that the 1987 head will most probably have a higher deck height as it was designed for tin gaskets vs the later head which had 40thou taken off to suit composite gaskets.

Be careful to measure the deck heights before taking 40thou off as someone may have done it in the past.
Regards Philip A

[PeterAllen]

So if i strip it any the classic engine has a composite gasket then it should be ok

[PhilipA]

So if i strip it any the classic engine has a composite gasket then it should be ok

Er depends.
Some people don't bother to shave the heads and have a compression ratio of low 7s :1.
Regards Philip A
BTW I just remembered that I have very late 4.6 heads on mine and the hole sizes and threads on the ends of the heads are different on the late heads . They are in the same position for mounting the aircon compressor and alternator( on a 3.9) but are a different size. I cannot remember if they are bigger or smaller , but I think smaller. But this only means that you have to buy a few bolts.
I do not know whether 4.0 and 4.6 GEMS heads are like 3.9 or the late Thor 4.6.

[PeterAllen]

Thanks Phil. Sounds like they should BUT.
I will see if the heads are any good when i take them off the p38 and if no good i will check the ones off the classic for spare if needed. What else should be kept off the classic that can be used on the p38

[p38arover]

Later 3.9 heads have the same casting no. as the 4.6 GEMS heads.

[PhilipA]

I will see if the heads are any good when i take them off the p38 and if no good i will check the ones off the classic for spare if needed

I have never seen a v8 head crack or fail in a way that it was unusable.

If you want to use the 38A heads have them serviced and they will check the guides( again should be OK) , grind the valves and should set installed height, new seals, skim ,and a clean. Last time I had it done about 6 years ago it cost $400.
The only nonos are internal corrosion, or worn guides and even then they can fit inserts. I have never seen a soft one either but I guess it could happen.
Regards Philip A

[bee utey]

I have never seen a v8 head crack or fail in a way that it was unusable.



I have! Cracked around the lower row centre head bolt, weldable though. (early D1)

Early 3.9 heads and later ones have different mounting bolts up front, it pays to check any head mounting bolt holes before fitting.:)

[PLR]

G`day , if your early heads are ERC 0216 you can`t use them without making brackets because they won`t straight swap with a serpentine set up , the # can be found under the rocker cover , top of and mid head .

The heads need to be HRC 2479 or later , earlier HRC 2210 have the same problem of a lack of material and will like the ERC 0216 bolt on if they too are machined to get the right thickness but brackets still need making .

As they come the ERC 0216 don`t have the right guides for the stem seals the p38 uses and the inlet may be wasted stem but the exhaust won`t be .