View Full Version : Sealer on SBC head gaskets

04-29-2009, 05:54 AM
I put together a SBC during the winter.Nothing special,just a 305 with 9.25 compression and a mild cam.The engine block was bored and parallel decked,the heads milled .010.I mocked up the engine before assembly to check that everything fit as it should,no problems.The block and head surfaces were clean and oil free before assembly,the head bolts and dowels don't bottom out.The heads were gently lowered onto the block, torqued down in 4 steps,a little more each time.
It runs great has about 1000 miles on it.However the engine has a very slight coolant seepage between the head and block along the lower row of head bolts both sides.It's for sure not leaking past the headbolts,just slightly wet all the time along the bottom.
I pulled the heads,no problems to be seen.The block and heads checks out true as it should after being machined.The headgaskets crushed evenly all the way around.
Now.... this shop that builds a lot of performance Chevies told me to install the Felpro Permatorque gaskets dry,Felpro says to install them dry.I'm thinking I better use a head gasket sealer this time,What do you say?

Thorkle Rod
04-29-2009, 05:58 AM
Never had a problem with Permatorque head gaskets they are great. Sometimes it's hard to follow the directions as is, if your like me, "my brain is not always my friend"

04-29-2009, 06:08 AM
No sealer, and did you retorque the heads after a couple of heat cycles?

Thorkle Rod
04-29-2009, 06:11 AM
Forgot to ask if you have had the heads and block Magna Fluxed or die penetrated to check for cracks?

04-29-2009, 06:22 AM
The block and heads were Magnafluxed and the heads were also pressure checked.
Retorque? That's the feature of Permatorque gaskets,a one torque job.With sealer required on SBC headbolts it might not be wise to retorque and risk upsetting the sealer and maybe getting a false torque reading from the sealer.
But I did check the bolt torque before pulling the heads just to see.Backed off the bolts a 1/4 turn,retorqued to 70 pounds and the bolt head was in the same position as before.

04-29-2009, 06:57 AM
Are you sure the leak was coming from between the heads? could it be from the front or rear intake? I'm sure you checked there first if you ended up pulling a head back off, but you never know. I always use a gasket sealer called "The Right Stuff" {most auto parts stores sell it} on those ares of the intake.

04-29-2009, 07:02 AM
Be sure to use thread sealant on the bolts that go into the water jackets. Also, the "Right Stuff" is the right stuff to use... :cool:

04-29-2009, 07:22 AM
No intake cooolant leaks,for sure the slight seep is at the head gasket.I use Permatex 300 Aviation sealer on the headbolts,never had a problem before.In fact I never had a headgasket seepage,this is the first time.

04-29-2009, 08:14 AM

A retorque after running is recommended.

Sealer must be used on all the head bolts.

04-29-2009, 09:00 AM
I don't know,Felpro says no retorque is necessary on the Permaseal gaskets.That's the feature of them.The heads were torqued down,then checked twice after a few hours.As I mentioned,before pulling the heads I did check torque and it was ok,the gaskets didn't take a "set".
The machine shop says they will check the heads again,for free.And loan me a machinist straight edge to check the block although both block and heads were resurfaced.The shop also said if a Perseal seal gasket seeps after a proper torque down,something is fishy and a re torque probably won't fix it.They do a lot of mostly performance engine and once in a great while one leaks a bit for no good reason.
This is a very slight seepage only along the bottom edge of the head,some guy might not even notice it.

04-29-2009, 10:23 AM
I use Permatex 300 Aviation sealer on the headbolts,never had a problem before.

If you used this on the bolts, I would retorque the bolts with no worries. It stays pliable, and retorquing won't affect the thread seal.

Shifty Shifterton
04-29-2009, 10:46 AM
I agree, something is fishy. SBC with a felpro gasket should not require re-inventing the wheel by requiring special sealers.

It would be unusual since it's both heads, but I've seen a bunch of chevy heads with a hairline crack coming off the sender port that only opens up when you install the sender or plug. End result is what you describe though.

good luck

04-29-2009, 11:10 AM
Thanks,no worry about the #300 Permatex sealer then.Well,I had to drop the exhaust manifolds to get at the bottom row of bolts,and next thing ya know the intake and heads are off.Get the heads checked again and check out the block,headbolts and dowels for bottoming out even though I did check it before.I guess sometimes shit happens despite thinking I'm doing it like an expert which I ain't.

04-29-2009, 11:14 AM
use a ton of thread selant on the head bolts. gasket sealer on head gaskets is a big no-no.

Engine Pro 5X
04-29-2009, 11:54 AM
Your head bolts are leaking. Use liquid teflon on the threads when you re-assemble and make sure the bolts are in good shape !! I see people using used bolts with bad threads and this leads to coolant leaking >>>>.

04-29-2009, 12:08 PM
So what about silver spray paint??

04-29-2009, 12:15 PM
Ive had something similiar happen. Installed head gaskets that the engine builder gave me when he assembled the short block(not felpro), used permatex on the bolts, new head bolts, and both sides leaked. Lasted through break in and leaked on the way to the exhaust shop.........

Bought the liquid teflon and felpro gaskets, ended up having to enlarge the water passage holes in the felpro gaskets, bolted it up and its been fine for 3000 miles.......never found out what exactly failed........but i'll always use felpro and liquid teflon from now on..........good luck

04-29-2009, 12:23 PM
Did you use new head bolts on any of the re-assembles? If you know the heads are straight, then it must be the block