Which Head Gasket

[KicknAsphlt]

I know, the thread title is a bit misleading as to a total n00b question...but, I did search (maybe using wrong parameters...I can never seem to get that thing right...lol) and couldn't find anything. I measured my head and block deck heights and it seems that I need a 2.6mm gasket to keep stock compression ratio... From what I've seen, only HKS makes anything close to this, either 2mm or 3mm, so my question is this...which do I go with? Or does/can anyone make a 2.5mm gasket? How much does .4/.6mm really affect compression ratio? This is pretty much the last major piece I need to put the motor together, and I'd like to try and get this ordered within the next week if possible. I am going to remeasure to double-check that my thicknesses are correct, but I'm pretty sure they are... Anyway, any help on this is as always appreciated...car is close to being running again, I'm kind of excited...HA!

Thanks,

 

[Suprizim TT]

What engine is it for? 7M, 1JZ or 2JZ?

 

[KicknAsphlt]

7m-gte

 

[WhtMa71]

I'm fairly certain Cometic will make any thickness gasket you need.

 

[KicknAsphlt]

Bumpity...any more insight/knowledge-dropping?

 

[IJ.]

3mm would be the safe option.

 

[tekdeus]

How much does 1mm change the compression? My car came with a 2mm MHG and my compression test came back between 130-140psi.

 

[KicknAsphlt]

Ok, update...with the new measurements and me realizing my math was a bit off, looks like I need about a 3.6mm gasket....will 3mm still be safe? That's still a .6mm difference from stock, but I think the gaskets are 86mm bores, so will that compensate for that enough?

 

[WhtMa71]

Wow that is huge. What are your measurements and how did you measure? If you don't mind me asking.

 

[KicknAsphlt]

Measured with 12" digital calipers -- block was 198.3mm, saddle to deck, and the head was pretty much 114mm even....114.0X to be exact. I'm going to measure my old head when I get my bearings out of storage tomorrow, just to compare...I know stock height for the head is supposed to be 116mm, but I don't see how even on a used head a full 2mm was shaved off the deck height....makes no sense.

 

[Black88Turbo]

Depends where you got the head from? Was it reworked, or a "new" head? They get rebuild all over the place. I have heard of almost 2mm's of material being removed from a head to make it "true" again. If it is a 2.6mm gap, the 3mm is the safe way to go. Especially if you are going to run over 20psi, just throw Iridium IX plugs in it to help provide a little extra spark. If you shop around you can find those plugs for around 8 bucks each (BCPR6EIX, NGK part #). And make sure to step-torque your ARP head studs, if you don't have ARP studs get them especially with that kind of gap to made up for. I would start standard torque (58ft-lbs -TSRM) and then do 4-8lbs until you reach 70-72ft lbs torque, this will help keep that massive MHG evenly torqued and intact through the assembly process. I wouldn't go above 75ft lbs, regardless of how much boost you are going to apply. And for your engine's sake run a brake-in additive like Redline or Royal Rurple even if you are running synthetic oil.
That's just my take on it... Hope it helps of gives you a few ideas. Good luck with your build. Mine doesn't start until I get back from Guam..

 

[jdub]

1) Iridiums do not provide "extra spark".

2) The ARP torque spec for studs is 80 ft/lbs using moly...use the TSRM torque pattern. I really wish people would stop posting "opinion" torque spec's.

3) Break-in additive? The RL additive contains ZDDP...useful for flat tappet cam motors. RP makes a break-in oil that contains the same thing. Neither will do a whole lot for a 7M break-in and is a waste of $$$. Good ole straight 30W HD oil will do the job just fine.

If this head has that much material removed, it needs to be looked over very closely. It needs to be checked for hardness and the cam saddles need to be checked for straightness. If the material was removed to straighten the deck, I'm betting the cam saddles look like a banana.

 

[KicknAsphlt]

My head guy said very little was removed when they decked the head, certainly not 2mm...I'll have to get a hold of the previous owner of the head and ask him about it.

As far as break-in, don't think I'll need to worry about that, I didn't replace the rings or hone the cylinders...just put fresh bearings in the rods and crank. This motor's only going to be temporary, I'll be using my block to do a proper build down the road. Any way I can check those cam saddles myself -- like with a straight edge by chance?

 

[KicknAsphlt]

Bumpity...see question in last post above...

 

[87tomanymods]

my machinist told me that .013in is the normal limit on the deck hight but you can go .020 just no gaurante on no interferance.

 

[grimreaper]

stopper hg here. What i have read shows guys destroy pistons trying to destroy the stopper. Ij might have ruined one (he has ruined lost of parts ). Thats the end of the line for hg's. Its costly considering i bet the gasket alone rivals your machine work/parts spent to this point for a simple rebuild.

 

[jdub]

Kick - You can check the saddles for flatness with a machinist straight edge.

 

[KicknAsphlt]

Cool -- can I pick one up, or is this something where I should just run the head down to a machinist really quick?