What is the compressed thickness of the head gasket?

G'day all,
i am wanting to have a set of custom pistons made for my latest flathead motor build and need to find an important piece of information to help with the correct specification of piston to chamber clearance required. I am after the expected crush or compressed thickness of a Felpro gasket for an 8BA flathead? If there is someone out there that can help with information it would be greatly appretiated. Thanks

 

Depends on what gasket you are going with as they all differ in compressed thickness depending on material and what not. Felpro catalogs or tech center could give you the thickness of it. Most engine builders use .040" as a rule of thumb.

 

tom, have you asked felpro?.
Al.

 

My Felpro #s7525/7526 gaskets measure .063" (on average) after torquing to 50 ft/lbs.

 

I have measured several as they come off old engines, dont know the brands, most are at .045

 

thanks to all for your comments and direction, i will pursue Felpro!

FenixSpeedShop - i was also thinking of just giving this indicative known number as the thickness to work with but just wanted to explore all of my options and try and learn from hottrodders who have done the hard yards. These custom pistons will not be cheap and i want to get the most bang for my buck and really make them work.

V8 Bob, i should have taken the serial number down of the Felpro head gasket and posted it, but when i measured the un crushed (new) thickness on the steel ring section of the combustion chamber area it measured on average 0.072" so i was assuming that it is typical for ahead gasket to crush 30 thou so around about 40 - 45 thou is what i was probably thinking?

G'day Big Al how you going?

 

Hi Tommy,
Take this information in the spirit that it's given; from real world experiences. Back in the late 50's when I was a kid I helped and worked on my uncles race car. He was the late New England Race Car Hall of Fame , Ollie Silva. At the time he ran Flathead's and later Chevy's. When we pulled the heads off we always measured the head gaskets and they measured. .038". Fast forward to the 1970's and I was racing World Class Hydroplanes running both injected small and big block Chevy's. We would start with a new gasket and they measure .043" and when they are installed and torqued down will crush to .038". We used the old gaskets over and over again each time measuring looking for .038". If they drop below the .038" to say .037" they got discarded. The trick is to clean the used gasket with lacquer thinner and when coat it with copper coat and let it dry. The great part about using the head gasket over again is that you don't have to re torque the heads. When I first learned this I didn't beleave it and would re torque the head but after twenty or more times with the results always being the same I finally believed it.Years later after I had stopped racing I was at the Circle track trade show in Dayton during speed week and at the show the Felpro people were set up. Just for kicks I went over and talked with the engineers, being one myself about gaskets and if what we had been doing for forty years was what they found. Come to find out they told me that that's what they would tell the racers and they were surprised at how many wouldn't ever consider using the head gasket over again. They just shrugged their shoulders but did say thinking like that was good for buisness. At that time the new gaskets were being coated with I beleave a graphite coating on them and they crushed to .043". This is my real world experience and it should give you a base line to work off.
As far as having new pistons made for your flathead your deck height shouldn't be below or even with the deck so you should be good figuring .038 as a gasket thickness. Just a little warning; if you shaving the head to the point that the piston may hit the head you have gone to far. I realize that you know that , but what I'm trying to say is the very little that one gains by shaving the head to these extremes is folly. We raced those flatheads back in the day and if it was for my hot rod today or a street cruiser I would build the thing for reliability; once again I realize you know this.
Well you have a base line to work off but others may chime in; in the end it's going to be your call.
Keep in mind the .038 is for the Chevy so the flathead may be larger.
Johnny Sweet

 

Thanks Johnny Sweet i truly appretiate learning from your experiences your story was very interesting thankyou or sharing. Your flathead experience certainly justifies what i have been thinking and reading from the other posts it's the sweet spot!!, so it's looking like 40 - 45thou. thanks again for you help mate! ohh i like the use of the word Ineptocracy in your saying!!

 

My new 7525/7526 gaskets measure about .070" at the steel rings. They will only compress about .010". Other brands and/or composition may be different.

 

V8 Bob I will be taking the head off one of motors that had a set of Felpro gaskets fitted and will measure these for compression result. Thanks for your direction I will check this out before making my decision.

 

Tommy,
I have a "well used" Felpro 7525/26 set that measures .055" average, and since my new set that measures .063" with only 50 lbs torque, .015" may be more accurate compression with normal 55-60 lbs torque. I stayed with 50 during the build/piston clearance check so they can be reused.

 

Thanks a bundle V8 Bob!

 

Just a note,I am a engine builder and have a few hot flatheads pass through my shop recently.
Compare your dome radius on the pistons to the head,there seems to be a problem on manufactures agreeing upon a number.
From what I have seen the factory is about a 7 inch radius and cast pistons are at a 5.
Had a set of ross forged and they were the close to 7. This cost me a day to make a cutter to reshape the chambers. It turned out to be a win win to have a even squish area,but It could have been avoided.
Just throwing it out there,check everything and trust no one.

 

thanKs to all who have posted on my thread and helped me to understand my path forward on gathering the information i was seeking. I have measured the gasket thickness of a compressed Felpro gasket that was in one of my rebuilder motors and have measured on average 50thou. This is the number that i will go with. I have commissioned a company to proceed with a set of custom pistons being made for a blown flathead using Baron heads with a customised combustion chamber design.

Thanks again to all you hotrodders who have contributed and shared your knowlegde.