258 Head machining question.

[BlackOmega]

Was about to assemble the engine yesterday when I found some gouges in the freshly decked head from the machine shop. So it's going back and getting machined...again.

I'm not sure how much they pulled off of it when they originally decked it, but I'm going to assume they just "cleaned it up", which typically means <.003".

So now here's my question, how much can you mill the head before other mods need to be done and stay with pump gas?
Don't care if it needs 93 octane, but as long as it doesn't NEED any higher octane than that.

 

[jsohn]

It is hard to tell how deep that scratch is in the picture but you car take off .010 or so and still have no problem with pump gas. Thicker head gaskets are another way to compensate and they are cheap.

 

[BlackOmega]

It is hard to tell how deep that scratch is in the picture but you car take off .010 or so and still have no problem with pump gas. Thicker head gaskets are another way to compensate and they are cheap.

Not really worried about the compression. Actually I want to raise it some. I was just curious as to how much could be removed without having to get shorter pushrods and piston to valve clearance.

 

[BlackOmega]

Just wanted to add, I spoke with my neighbor, who used to be a engine machinist, and he said that I should be able to remove around .020" without much issues.
However, he did state that he didn't have much experience with the AMC 258 i6 / 4.2l , and the .020" figure is just a general rule of thumb.

 

[harleydragon]

according to Clifford Performance you can take off .060 but I personally would probably just go 20 or 30..

 

[BlackOmega]

according to Clifford Performance you can take off .060 but I personally would probably just go 20 or 30..

I haven't checked them out yet: got a link? I'm having some issues figuring out what head is on this '84. Basically the cc's of the head. I'm probably going to de-stumping the exhaust ports.

Also, with it being .030 over (262 CID), how much can I shave off the head to not exceed like 10.5 - 11:1. I was thinking of a total of ~.020". But if I can take more off and get it higher, then that's what I'd like to do.

For what it's worth, the pistons that were installed were dished.

 

[Rejeep]

dont boost the compression too much on a AMC 258 i6 / 4.2l ..
when i rebuild mine I took 5 thou off the head and deck...
im running 100 octane to stop form pinging..

these motors came from the factory with knock sensors... there is a reason why

 

[BlackOmega]

dont boost the compression too much on a AMC 258 i6 / 4.2l ..
when i rebuild mine I took 5 thou off the head and deck...
im running 100 octane to stop form pinging..

these motors came from the factory with knock sensors... there is a reason why

Which pistons did you have in yours?

What's your base timing? I've been reading that you can take off up to .060".. so I'm wondering why you'd need 100 octane really.

 

[harleydragon]

I haven't checked them out yet: got a link? I'm having some issues figuring out what head is on this '84. Basically the cc's of the head. I'm probably going to de-stumping the exhaust ports.

Also, with it being .030 over (262 CID), how much can I shave off the head to not exceed like 10.5 - 11:1. I was thinking of a total of ~.020". But if I can take more off and get it higher, then that's what I'd like to do.

For what it's worth, the pistons that were installed were dished.

dished pistons is what is in their rebuild kit too..they have kits with factory head or with 4.0 head,carb or fi..try this link ..http://www.cliffordperformance.net/html_pages/news_pages/jeep_facts/jeepfacts.html

 

[Tin Medic]

I took 10 off and no problems.

 

[harleydragon]

I do remember reading that if you shaved .060 you would need to use shorter pushrods but I don't know exactly how much you could go without changing them..I would think you would probably be safe at .030