Small Block & Big Block Chevy Specific - head gasket compressed thickness 8.1L 496 ?
03-05-2012, 12:58 PM
will be pulling cylinder heads on the 8.1L in my 2006 sierra because of exhaust leak and broken exhaust manifold studs.
Anyone know what the compressed thickness of the oem head gasket is?
any recommendations for what brand head gasket to go with?
03-06-2012, 05:44 AM
I haven't found anywhere that tells me the factory compressed thickness. I bet it between .028-.032. When you get one off you can measure with a 0-1" mic
These fep pro gaskets are .049" compressed
Cometic has some at .021 compressed for GM 8.1L marine applications which I'd think they'd still work
03-07-2012, 12:50 PM
what's the deal with replacement head gaskets being extra thick like that?
last thing i want to do is drop compression.
i'm starting to wonder if i should get the oem gasket from the dealer and shell out the dollars.
03-07-2012, 03:23 PM
Hi FMF, Yeah you dont want to lower your CR. Mic your gasket. Here's the link i saw the Cometic .027 gaskets. Cometic is a superior gasket. If you can't get the same thickness, you'll have to go to the dealer. But when I worked at the dealerships, the replacement head gaskets weren't as thin as the originals. Car manufacturers get away with using thinner gaskets because of their torque procedure compared to everyone else, even your top professional engine builders and dealerships can't dupicate it unless they have the multi-million dollar machine which is doubtful. At the auto makers engine factory the machine torques all the head bolts all at once, not in a sequence like we all have to.
03-08-2012, 02:00 PM
thanks for the link.
I called dealer and they said they can get the head gaskets in a day and were only $10 more than what felpro and victor reinz were on rock auto but he couldn't tell me what the thickness was.
do you know what piston deck clearance or height?
I'm wondering if maybe an 0.041 gasket is ok, i don't know what the combustion chambers on the head look like but if the piston comes up out of the hole +0.005" which i thought was common on gen 3/4 engines then an 0.041 head seems good ?
03-08-2012, 05:52 PM
Looking around the web for block specs for deck heights, says the block is at 10.2" , the stroke is 4.37, the rod lenght is 6.69" and the piston CH is 1.368-1.372 and doing the math indicates the piston is .043 above the deck, which doesn't make any sence. The fel pro gasket is .051". I could see maybe .005-.010". I don't think the deck height is correct because that far out of the bore is way to much for a flat top piston. It would hit the head. When you get the head off measure it with a 0-1" depth mic. Seems like I saw somwhere the deck height was over 10.3, but I can't find that link. The cylinder heads are cast iron closed chamber design. don't have the cc for the but the 7.4L vortecs are 100cc closed chamber. you can call me if you want 77-777-5388
03-15-2012, 09:19 PM
i bought the helm manual for the truck, here's some info out of that
bore: 4.25" (107.95 mm)
stroke: 4.37" (111.0 mm)
compression ratio 9.1:1
firing order 1-8-7-2-6-5-4-3
cylinder head deck height from centerline of crankshaft 10.231" - 10.241"
there is no mention of rod length or compression height.
i plan on measuring everything when i get it apart. the plan as of now is to order head gaskets after i measure what's on there and wait a week for shipping if i have to.
I got an email back from victor reinz (mahle/clevite) and they said their head gasket #54348 and 54349 had a COT of 0.049" and was also compatible with dexcool. Not sure what COT stands for.
04-02-2012, 10:44 AM
if i remember correctly the pistons did stick out on my 8.1's
why are you pulling the heads, you are aware the head bolts will have to replaced as well. personally i have used gm replacements for head gaskets
04-05-2012, 02:23 PM
i have a broken exhaust stud on passengers side, planning on doing both sides and having more studs break. I pretty much have everything lined up on rockauto including head bolts, the unknown has been head gasket thickness.
04-06-2012, 09:53 AM
90 degree drill and drill it and tap it...
04-07-2012, 10:41 PM
Just go to the dealer and order the stock gaskets.Don't even think about Cometics unless you are doing a complete rebuild and know exactly what the deck and head surface smoothness are.Even Felpros are more forgiving on prep of the deck.