thinnest head gasket

S

silver slotege

Member
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2002 Mazda Protege5
Quick question guys...
I am having to do some head work (rebuild and machining) and was wondering what the thinnest head gasket available was? I know the turbo guys like the thick cometic gasket, but what's available to the NA crowd?

Also, thinking of having the head shaved to increase compression. I read that the block can't be machined more than 0.020". I assumed this is because of piston travel. I am wanting to take 0.030 or 0.040 off of the head... Anyone know the right number to shoot for?
 
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silver slotege said:
Nothing guys? Really?
No one has machined their heads? Haha.

Guess I will be a guinea pig...
Click to expand...

I don't have any experience in this area, but if you can't take more than 0.02" off the block b/c of piston clearance, why would you be able to take more than that off of the head?
 
According to the Mazda FS engine manual the head has a grinding limit of 0.006"
The limit on the block is 0.008". No experience with machining Mazda heads or blocks, I'm just quoting the Mazda FS engine manual.

I assume their term grinding means the same as machining.

Clifton
 
Ok, what I read was 0.020, but I can't find it again so I can't verify. If the manual says .008, then that settles that.
As far as machining head vs block, machining the head will bring the valves closer to the piston whereas machining the block will bring the piston closer to the head. Essentially, you could run in to a point where the piston could hit the head at TDC if you take off too much of the block. But the piston does not travel past the length of the cylinder, so you will not hit the head if you shave too much off the head. But you will bend valves if you break the timing belt. And we bend valves in that situation anyway, so its no biggy.
I am trying to figure out if I will need adjustable cam gears if I machine 0.030 off... Some info says yes, others have had success without it (none of which were FSDE). I will have to see on that.
 
silver slotege said:
Ok, what I read was 0.020, but I can't find it again so I can't verify. If the manual says .008, then that settles that.
As far as machining head vs block, machining the head will bring the valves closer to the piston whereas machining the block will bring the piston closer to the head. Essentially, you could run in to a point where the piston could hit the head at TDC if you take off too much of the block. But the piston does not travel past the length of the cylinder, so you will not hit the head if you shave too much off the head. But you will bend valves if you break the timing belt. And we bend valves in that situation anyway, so its no biggy.
I am trying to figure out if I will need adjustable cam gears if I machine 0.030 off... Some info says yes, others have had success without it (none of which were FSDE). I will have to see on that.
Click to expand...

Eh, very debatable.
 
silver slotege said:
Ok, what I read was 0.020, but I can't find it again so I can't verify. If the manual says .008, then that settles that.
As far as machining head vs block, machining the head will bring the valves closer to the piston whereas machining the block will bring the piston closer to the head. Essentially, you could run in to a point where the piston could hit the head at TDC if you take off too much of the block. But the piston does not travel past the length of the cylinder, so you will not hit the head if you shave too much off the head. But you will bend valves if you break the timing belt. And we bend valves in that situation anyway, so its no biggy.
I am trying to figure out if I will need adjustable cam gears if I machine 0.030 off... Some info says yes, others have had success without it (none of which were FSDE). I will have to see on that.
Click to expand...

1. you probably got the .020 from the max over bore mazda recommends
2. You said the same thing twice, if you machine the head or the block, either way it does the same thing, piston getting closer to the valves is the same as the valves getting closer to the pistons
3. We dont bend valves when we break the timing belt, the engine is non interference, ive tested it out multiple times to see and trust me, if you break the timing belt, you wont bend anything

edit: damit ninja'ed by slavrenz on 3
 
The result is the same, higher compression, but the way it is acheived is completely different. Far less risky in machining the head.

And I know about the interference vs non debate. I look at it this way, if it bends a valve 1 out of 100 times, then it is interference. And I put my experience against yours in that I tested it once and the valves bent. You tested it a few times and they didn't bend... So I default to my assessment that it is interference. But I know the debate will never be settled. Haha.
 
But i want to know: will it give any good gains with gasket and machined head? You would need to run higher octane?
 
well normally you need to run higher octane in higher compression...but im not sure exactly how much shaving the head will raise the compression so its hard to say
 
Yes, I will have to run higher octane with the increased compression. I don't have any hard numbers of what hp to expect. Different engines will react in different ways, and with 150k on the odometer, I think my piston rings will be the weak link preventing me from seeing the most out of doing the machining.
I wouldn't recommend anyone taking their head off to do this, but if its coming off anyways, might as well.

But I will post what I do, how much I machine, and what my butt-dyno assessment is.

But still, no one seems to know who has the thinnest head gasket? Haha. Oh well.
 
Alright, so a quick calc and I seem to get exactly 1 degree of timing retard from shaving the head by 0.035. Seems to raise the compression from 9.1:1 to 9.988:1.
But anyone know what 1 degree of timing retard will do? I know give me power in higher rpm range, but I don't spend much time up there, let alone know if the benefits are even seen in an achievable rpm range. Is it worth it to buy adjustable cam gears for 1 degree? Anyone tried to adjust their stock cam gears?
 
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I'm gonna say there will be more to it to get any sort of gains out of higher compression then just adding compression. Gonna need some sort of tune for higher octane and compression to make it worth your time. Adjustable cam gears would be a plus, not much adjustment to be done on stocks.
 
you're going to machine the head to get higher compression, but you say your piston rings are probably bad? why not say to hell with the head and get the 10.4:1 pistons and new rings/bearings put in. Rebuild the engine.
 
alright, so an update will be coming... Still waiting on my ARP head studs to arrive...
But the head was rebuilt, new valves, valve job, new seals, lifters adjusted, and head machined down only .015. To go with that I am porting, VTCS removal, OBX header, and MP3 ECU flash.
Machine shop would only go .015 since I did not have adjustable cam gears. I told him I would take care of it, but he said he would feel more comfortable without taking off more.

Heres is my question... I got the head back from the machine shop with the cam gears in a separate bag, along with a couple of brackets and seals, from the rest of the head. So what is the correct orientation of the gear to pin on each cam? For instance, on the exhaust cam gear, does the pin go in the slot opposite of the E mark on the cam gear?
 
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