PDA

View Full Version : 1.0mm vs 1.2 mm headgasket.



CA19DET
01-16-2003, 03:10 PM
for my goal of 400 HP which gasket should i run?? i have JE pistons with a 8.5:1 CR and the bloc kand head will need to be skimmed/decked to get back a smooth flat sealing surface. my question is really should i get the 1.0mm now or wait the 10 weeks or whatever it will take to get here from japan??

i am leaning towards the 1.0mm GReddy gasket as it is in stock, will it leave my compression around 8.5 or so.. or should ii get the thicker one to drop compression a bit and make up for the skimming of the block and head.

also i see that the gasket has a bore of 85mm will this be adequate for the 84mm pistons that i am using??

- aaron

SRFiveTen
01-16-2003, 05:02 PM
gasket for 86m/m bore sr is advertized to have 87m/m bore.

if you change the cam sprockets ~ crankshaft geometry by shaving the block, head or changing head gasket thickness, you should be compensating the screwed up valve timing by staggering the crank sprocket key, or by tweaking the cam sprockets. or else, you might experience rough idle, hesitant pick up, sputtering etc.

uiuc240
01-16-2003, 05:36 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
if you change the cam sprockets ~ crankshaft geometry by shaving the block, head or changing head gasket thickness, you should be compensating the screwed up valve timing by staggering the crank sprocket key, or by tweaking the cam sprockets. or else, you might experience rough idle, hesitant pick up, sputtering etc.

[/QUOTE]

Could you explain WHY this is? Seems to me, the chain is a preset lenght, and the sprockets are a set ratio. Given this circumstance, as long as the chain will "stretch" the extra .3mm (from .9mm to 1.2mm), you shouldn't have to F with the timing at all. The only reason would be if you had to add a link.

Right?

Eric

asad
01-16-2003, 05:54 PM
The chain doesn't stretch.

The chain is a fixed length, and the extra "slack" in the chain is taken up by the tensioner, which, in doing so, will pull on the cam gears and rotate them relative to the crank.

Asad

uiuc240
01-16-2003, 06:14 PM
I still disagree. It's just like the tensioner on a bike. For instance, I converted my mountain bike to single speed, and it has a tensioner to make sure that the chain stays taut at all times. Thing is...my pedaling is always directly linked to the speed of the tire (except when freewheeling...but cars can't do that).

So, once again...if the gear ratio is fixed, and the chain is a set lenght, the tensioner has no effect on timing. Keep in mind that the teeth are lining up no matter what you do....they mesh in a consistent pattern just like a bike.

Eric

P.S. I *can* see how this would be different if it were a grooved belt (like the water pump) because then friction and slip come in to play. But in this case, as long as it doesn't lose tension and skip a tooth, timing should NEVER CHANGE.

89SX
01-16-2003, 06:47 PM
However, this is something I'm thinking of and could be proven wrong, if the cams move closer to the crank pulley, they rotate slightly to keep the chain at the same length+ tight, that's what causes the slight change in timing.

uiuc240
01-16-2003, 06:54 PM
Well, yes, when you mess with the chain, you have to reset the timing if the cam moves in relation to the crank...

BUT...once again, given XX number of links and YY number of teeth on the gears, the ratio and relationship will remain the same. It's a fact.

If the ratio is say, 13/26 for the crank gear and the cam gear, the ratio is 1:2. This relationship will remain constant as long as there are the same number of links in the chain.

Eric

asad
01-16-2003, 06:57 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
Thing is...my pedaling is always directly linked to the speed of the tire (except when freewheeling...but cars can't do that).


[/QUOTE]

Speed, yes. But can you guarantee that the phasing of the front and rear gears are the same? In a bike, relative sprocket timing doesn't matter.

To use your example, if you kept the same length chain, but moved the sprockets closer together, what would happen...think about it.

Asad

asad
01-16-2003, 06:58 PM
Eric, you're confusing two separate issues -- the relative SPEEDS of the gears will remain the same, but the PHASING will not.

Asad

89SX
01-16-2003, 07:04 PM
Asad is correct, it was never said that the ratio's would change, just that the cam timing would be off.

uiuc240
01-16-2003, 07:13 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
To use your example, if you kept the same length chain, but moved the sprockets closer together, what would happen...think about it.

[/QUOTE]

That's what happens when you have horizontal dropouts...you use them to adjust the tension. As long as the tension is enough to keep the chain from skipping a tooth, the phasing remains the same. I have 32:16 gears on my bike. The chain meshes the SAME way all the time regardless of tension. The only thing you can do is use too MUCH tension and it wears out the gears and causes binding (but that's not what we're talking about here).

Eric

89SX
01-16-2003, 07:20 PM
So what exactly are you talking about? It wouldn't matter if the chain gained 25 new links, the ratio is still unchanged. The tensioner takes up the slack, what happens is that the cam's are slightly rotated because they are now closer to the crank changing their timing. It was never said that the cams would rotate at different ratio to the crank(at least that's what I think you are saying)

Kookz
01-16-2003, 07:26 PM
No, that's not it. If the sprockets were moved closer together, the tensioner would pull in some extra slack. Let's see what I can type up...

<pre><font class="small[/img]code:</font><hr>
c
l \
t
l /
c

</pre><hr>
So if the vertical part of my diagram doesn't change, then you are golden. However, here's an extreme example.
<pre><font class="small[/img]code:</font><hr>
c __
l __--t
c

</pre><hr>
Ok that one was a PITA to type...but anyway, if the lower sprocket were to stay still while the tensioner was moved to the right, then the upper sprocket would rotate clockwise, throwing off the phase. Does that make sense?

uiuc240
01-16-2003, 09:56 PM
iight...cool. i think i am visualizing it now. it just wasn't making sense to me before, since the links/gears are meshing at a given rate. but yeah, you all are right. got it.

Check what AKAdriver did:
http://mywebpages.comcast.net/akadriver1/images/timing.gif
http://forums.freshalloy.com/ubbthreads/images/icons/laugh.gif

Eric

97 S14
01-16-2003, 10:41 PM
10 weeks? www.projectsilvia.com (http://www.projectsilvia.com) has greddy headgaskets in stock... in multiple thicknesses, saw them myself about a week ago.

SRFiveTen
01-17-2003, 05:35 AM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
has greddy headgaskets in stock... in multiple thicknesses, saw them myself about a week ago.

[/QUOTE]
for ca18det?

jspecusa
01-17-2003, 09:55 AM
depend on your turbo size and how wild your cams are, you'll want to go with 1.2mm or 1.5mm gasket.
in japan they even use 1.8mm gasket.
cheers,

sam http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif

CA19DET
01-17-2003, 11:06 AM
i am running a T3/T04E tubo and probably CROWER OE reground cams or CA16DE cams, and will upgrade to a modified head later in the year with wild JUN/TOMEI cams, sprimngs etc... running about 10psi street and 20psi race boost w/ race fuel etc.

as far as the belt tension form skimming the head and block, i am building a CA that has a timing belt, is this a recipie for slippage?? the belt tensioner should pick up the slack, no?

i was thinking of using a 1.5 or 1.8mm metal headgasket. but i rememeber reading conflicting opinions about gasket thickness and if to use metal headgaskets at all... i was going with the 1.2 or 1mm as they were close to stock, but offered the durability and streanght of a metal gasket once sealed and torqued down properly.

opinions??

JSPEC ya'll got any in stock? cna ya'll get them? PM me if so.

- Aaron

asad
01-17-2003, 11:36 AM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
as far as the belt tension form skimming the head and block, i am building a CA that has a timing belt, is this a recipie for slippage?? the belt tensioner should pick up the slack, no

[/QUOTE]

Probably -- the service manual has limits on how much material can be removed from the block deck and head surface, so as long as you're within that limit the tensioner should still be able to function effectively.

However, you'll STILL have the problem of the altered cam timing -- it's a trait shared by all overhead cam engines. Unless you have tensioners on both sides of the belt or chain, and can ensure you can take up the slack equally on both sides, then the cam timing will change slightly if you change the distance between the crank and cams.

Asad

Asad

CA19DET
01-17-2003, 11:53 AM
well my engine only has one tension pully. cam cam gears help? ir is this just something that i am going to have to live with and make adjustments for in the future?

thanks

-aaron

asad
01-17-2003, 12:13 PM
Yeah, cam gears are the way to correct for it.

Asad

97 S14
01-17-2003, 01:35 PM
whoops... didnt see it was for a CA.

Hugh
01-17-2003, 02:26 PM
Just curious, but how much do you think it would actually make a difference like on my engine - normal head and block with a 1.5mm head gasket? Do you think the .5mm thickness which I am sure some of which is lost in compressing it will make a noticable difference?

asad
01-17-2003, 02:30 PM
You can estimate it with the diameter of the cam gear -- it's what, 2" or so in diameter? which is about 50mm, which gives a circumference of about 160mm .

(0.5/160) * 360 degrees = about 1 degree of camshaft rotation.

Remember, of course, this is an estimate only, but it should be around that order of magnitude.

Asad

uiuc240
01-17-2003, 02:35 PM
I had bad math. Asad learned me. Oops.

Eric

SRFiveTen
01-17-2003, 05:35 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
the service manual has limits on how much material can be removed from the block deck and head surface, so as long as you're within that limit the tensioner should still be able to function effectively.

[/QUOTE]
with shaved head/deck + thinner headgasket, one needs to check the squish area clearance (squish, did i get that right? the non-chambered part of cylinderhead directly above the piston); as carbon build up on piston surface/cylinder head may cause severe reduction in piston top to cylinder head clearance, leading to rod or rod bearing failure.... not good.