1st/2nd gen head?

[ben99]

Can a 2nd gen head bolt onto a 1st gen block? I have a 1990 cummins and I've read on here that the heads are prone to cracking... would a second gen head work or do i need to find a later 1st gen head with the 7mm injectors... Sooner or later i'm thinking :nos:

 

[cummins king]

Prone to Cracking...... What

No it wont work you have a pre 1991.5 so its a 9mm head, so you will need new injectors, and maybe lines (not 100% sure on the line part)

 

[G-dubs]

i thought the 2nd gen 12 valve head would bolt on...hmm

 

[rockjeep73]

yes the head will work but you will have to change the injectors to intercooled or aftermarket, 7mm like stated.

 

[ben99]

i could have sworn i read a post here that said the 9mm injector heads would crack... mabye i'm wrong? I sure hope so!

 

[Richie O]

i could have sworn i read a post here that said the 9mm injector heads would crack... mabye i'm wrong? I sure hope so!

You are correct. 9mm heads crack from injector bore to one of the valves.

 

[ben99]

So I need a 7mm head right?

 

[G-dubs]

So I need a 7mm head right?

if you build extreme heat i would prolly get a head from a 91.5-98 but like rockjeep73 said you will need injectors with 7mm tips you have 9mm but remember 2nd gen 12 valve heads will work but the 2nd gen 12 valve injectors will not work with a ve pump

 

[slowleak]

so it would be fairly easy to change to a 2nd gen head on my 93, correcct?

 

[BC847]

so it would be fairly easy to change to a 2nd gen head on my 93, correct?

As others have said, the only real difference in the earlier 1st gen heads and the later 1st gens are the injector bores. The earlier 9mm heads had an issue with cracks developing between the injector bore and an adjacent valve seat.

A 2nd gen head will bolt right on but be aware, where the throttle linkage bracket attach's to the 1st gen head, the 2nd gen head doesn't have the bolt boss's drilled and tapped.

It's no big deal to correct, just drill the holes and tap them with the bracket in the same relative position. You'll most likely drill into the intake manifold log so just be sure to use some thread sealant on the bolts.

 

[peobryant]

You are correct. 9mm heads crack from injector bore to one of the valves.

I I remember correctly, that is the reason when they put the '91.5 intercooled model out they went to 7mm tips.