Bore distortion vs head gasket type and thickness

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Pablo
Member
Member
Posts: 59
Joined: Sat Aug 23, 2008 2:05 am
Location: Fallbrook, CA
Contact:

Bore distortion vs head gasket type and thickness

Post by Pablo » Wed Mar 22, 2017 3:11 pm

I've learned that the gasket fire ring is responsible for much of the bore distortion when a head or torque plate is installed.
It makes sense with a composition HG. The fire ring requires much more force to compress than the composite area around the bolt holes. It doesn't take much to realize that as a result, the deck of the block around the bolt hole gets pulled upward slightly when torqued. I imagine that this is what is responsible for pulling the bore outward in the area next to the bolt holes.

If I'm imagining this correctly, it would stand to reason that the thinner and stiffer the gasket, the less distortion there would be. A thin steel shim should produce substantially less distortion than a thick composite gasket.

Has anyone noticed this in practice?

PackardV8
Guru
Guru
Posts: 5037
Joined: Sun Jul 30, 2006 2:03 pm

Re: Bore distortion vs head gasket type and thickness

Post by PackardV8 » Wed Mar 22, 2017 3:26 pm

It's a good practice to countersink/chamfer all head bolt holes in a block.

The Studebaker and Packard V8s are available with either the old-school .025" steel shim head gaskets which compress to .020" and the Best composite gaskets, which compress to .035". We don't notice much difference in the deck surface, but then these are old arn. They have negligible bore distortion difference when a torque plate is used and the modern thin-wall stuff definitely does.

The Studebaker and Packard V8s have so much iron between cylinders, I'm always shocked when looking at no iron between cylinders of a big-bore BBC. I'm amazed the gaskets hold while making 600-800 horse.
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering

pdq67
Guru
Guru
Posts: 6316
Joined: Thu Mar 04, 2010 8:05 pm

Re: Bore distortion vs head gasket type and thickness

Post by pdq67 » Wed Mar 22, 2017 6:39 pm

This might be why Chevy used the .020" steel shims from the start in small blocks.

My OEM '67 350SS engine had them in it.

pdq67

User avatar
MadBill
Guru
Guru
Posts: 12624
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: Bore distortion vs head gasket type and thickness

Post by MadBill » Wed Mar 22, 2017 8:30 pm

Some of the distortion is from the female thread 'swelling' a bit as it tries to climb away from the male one... Some used engines show shiny stripes paralleling the bolt locations...
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

pamotorman
Guru
Guru
Posts: 2303
Joined: Thu Mar 06, 2014 11:55 pm

Re: Bore distortion vs head gasket type and thickness

Post by pamotorman » Wed Mar 22, 2017 8:37 pm

some head gasket fire rings have copper wire and some have stainless steel wire inside. the one with stainless puts more pressure on the top of block and the head because the ones with stainless wire put a impression of the wire in the aluminum heads and the copper wire one does not

KnightEngines
Guru
Guru
Posts: 1733
Joined: Fri Jan 09, 2009 8:51 pm
Location: Australia

Re: Bore distortion vs head gasket type and thickness

Post by KnightEngines » Thu Mar 23, 2017 2:19 am

Yes, using MLS head gaskets & studs will show less distortion than using composition gaskets & bolts.

That's why it's best to use the style of gaskets & fasteners that will be used in the engine when using a torque plate.

The distortion produced by a MLS gasket is very similar to a torque plate bolted on with no gasket at all.

That's my observations anyway, FWIW.

groberts101
Guru
Guru
Posts: 1301
Joined: Sat Mar 08, 2008 3:08 pm
Location: Minneapolis

Re: Bore distortion vs head gasket type and thickness

Post by groberts101 » Thu Mar 23, 2017 10:26 am

KnightEngines wrote:Yes, using MLS head gaskets & studs will show less distortion than using composition gaskets & bolts.

That's why it's best to use the style of gaskets & fasteners that will be used in the engine when using a torque plate.

The distortion produced by a MLS gasket is very similar to a torque plate bolted on with no gasket at all.

That's my observations anyway, FWIW.

Kinda funny.. I just wrote that very same thing in his other thread. Personally speaking, bore distortion aside, I prefer an MLS on just about anything I build these days even if it's below 400 hundred horsepower of cylinder pressure. Much more durable and long lived. With proper smooth RA deck finishes they're reusable too.

Newold1
Expert
Expert
Posts: 826
Joined: Fri Apr 08, 2016 9:50 am

Re: Bore distortion vs head gasket type and thickness

Post by Newold1 » Thu Mar 23, 2017 6:06 pm

That's pretty much why I use stainless MLS head gaskets in most but not all applications. Sometimes flat copper with sealing rings are needed for certain engine types. JMO

rebelrouser
New Member
New Member
Posts: 42
Joined: Tue Sep 15, 2015 2:25 pm

Re: Bore distortion vs head gasket type and thickness

Post by rebelrouser » Fri Mar 24, 2017 12:31 pm

This thread mentions MLS head gaskets, which seem to be all the rage right now. I have seen a lot of older iron engines that they used them on and they did not spend the time and money to get the head and block surfaces to the right RA and seen some problems from this practice. For a performance engine I believe a copper gasket with an O-ring installed in the block, and a receiver groove in the head on blown applications is still the best sealing method I know of. I know Top Fuel cars still run them,, and I am sure if something better was around they would use it. If the block and deck are finished right I have good results as well from MLR gaskets. Or am I just being old fashioned?

Newold1
Expert
Expert
Posts: 826
Joined: Fri Apr 08, 2016 9:50 am

Re: Bore distortion vs head gasket type and thickness

Post by Newold1 » Fri Mar 24, 2017 2:35 pm

I don't think you are being old fashioned, just a little to narrow on your focus.

The problem with the copper gasket and sealing with receiver grooves in the top of the block is that for NON high boost applications where turbos and blowers are not being used this type of head gasket sealing is sort of overkill and expensive when not being used for uses like top fuel, etc.. Once the deck of the block is grooved to resurface the deck where more than 3-5 thousands must be taken the grooves must be re-cut to set proper depth and that is more cost and work and it deck thickness is marginal to begin with it could limit the re-use of the block. If this block was sold or re-used for a non o-ring situation then the deck will have to have a substantial cut made and the final deck height of the block will mean potentially custom compression heights on pistons to achieve good deck heights on pistons.

Most machine shops resurfacing decks on blocks and heads are aware of and achieve much lower RA's with proper speeds and newer cutters than in older times, so getting usable RA's for MLS gaskets is not a big issue in my experience. Good MLS stainless head gaskets with their Viton coatings like those from Cometic are pretty simple and trouble free to use. In some cases I and others have reused them more than once on a quick tear down. If the deck and head surfaces are flat, straight, a decent RA and !CLEAN! the MLS gaskets in my opinion work great when things are properly tightened down with proper torque. I know there are limited uses where copper gaskets are the better way to go but those are far less in numbers that the street, strip, marine and race engine uses that probably make up 95% of the uses in total.

There is nothing wrong with composition head gaskets that are still being used in large numbers today. They are less expensive than MLS and when properly assembled and used do just fine for most builds. I just happen to like the way I feel MLS gaskets help eliminate possible deck and bore distortion and the better seal during deck or head flex that composition fire ring gaskets have a harder time dealing with. When it comes to which type of head gaskets are preferred by most you will get a wide range of preferences from any different group of users. JMO

roc
Pro
Pro
Posts: 433
Joined: Sun Sep 02, 2012 9:41 pm
Location: Columbus, IN

Re: Bore distortion vs head gasket type and thickness

Post by roc » Fri Mar 24, 2017 5:19 pm

Newold1 wrote:I don't think you are being old fashioned, just a little to narrow on your focus.

The problem with the copper gasket and sealing with receiver grooves in the top of the block is that for NON high boost applications where turbos and blowers are not being used this type of head gasket sealing is sort of overkill and expensive when not being used for uses like top fuel, etc.. Once the deck of the block is grooved to resurface the deck where more than 3-5 thousands must be taken the grooves must be re-cut to set proper depth and that is more cost and work and it deck thickness is marginal to begin with it could limit the re-use of the block. If this block was sold or re-used for a non o-ring situation then the deck will have to have a substantial cut made and the final deck height of the block will mean potentially custom compression heights on pistons to achieve good deck heights on pistons.

Most machine shops resurfacing decks on blocks and heads are aware of and achieve much lower RA's with proper speeds and newer cutters than in older times, so getting usable RA's for MLS gaskets is not a big issue in my experience. Good MLS stainless head gaskets with their Viton coatings like those from Cometic are pretty simple and trouble free to use. In some cases I and others have reused them more than once on a quick tear down. If the deck and head surfaces are flat, straight, a decent RA and !CLEAN! the MLS gaskets in my opinion work great when things are properly tightened down with proper torque. I know there are limited uses where copper gaskets are the better way to go but those are far less in numbers that the street, strip, marine and race engine uses that probably make up 95% of the uses in total.

There is nothing wrong with composition head gaskets that are still being used in large numbers today. They are less expensive than MLS and when properly assembled and used do just fine for most builds. I just happen to like the way I feel MLS gaskets help eliminate possible deck and bore distortion and the better seal during deck or head flex that composition fire ring gaskets have a harder time dealing with. When it comes to which type of head gaskets are preferred by most you will get a wide range of preferences from any different group of users. JMO
^^ agreed!

createaaron
Member
Member
Posts: 69
Joined: Tue Oct 18, 2016 6:48 pm

Re: Bore distortion vs head gasket type and thickness

Post by createaaron » Fri Mar 24, 2017 7:08 pm

It very much depends on fasteners type, block material and of course gasket type. If you took, for example, an LS engine where they have factory MLS headgaskets and change it to a .020 thinner gasket, you may see potentially more distortion because of the bolt having more thread grab. Just a theory.. Studs vs bolts makes a huge difference. Production blocks seem more prone to bore distortion that aftermarket blocks.

turbo2256b
Pro
Pro
Posts: 296
Joined: Sat Jan 28, 2012 5:48 pm

Re: Bore distortion vs head gasket type and thickness

Post by turbo2256b » Sat Mar 25, 2017 4:28 pm

bore DISTORTION COMES FROM THE BOLTS PULLING on the blocks head deck. Ford USED LONGER bolts grabbing at the bottom of the bore crank case wall dost work either might be a bit better though. Separating the cylinder wall from the deck and using the shorter bolts now the deck isnt attached to the cylinder deck or crankcase wall so the bolts dont pull on the cylinder wall when torqued. Many euro engines and northstar caddy do it that way. Tried to convince Ford
by comparing it to an egg held side ways in your hand and crush it. Then try it holding it end to end and it wont crush. Might not have been the best comparison. 4 OR 5 YEARS after I RETIRED a friend still working at Ford called me and stated some engineer proved it was true.

Geoff2
Expert
Expert
Posts: 581
Joined: Mon Nov 09, 2015 4:36 pm

Re: Bore distortion vs head gasket type and thickness

Post by Geoff2 » Mon Mar 27, 2017 5:59 am

Agree with turbo that bore distortion comes from bolt holes, too close to the bore &/or tied to the bore. SBCs in particular have bolt holes close to the bore, & seem to suffer from distortion more than blocks where the bolt holes are farther from the bore, B/B Chrysler being a good example.

Newold1
Expert
Expert
Posts: 826
Joined: Fri Apr 08, 2016 9:50 am

Re: Bore distortion vs head gasket type and thickness

Post by Newold1 » Mon Mar 27, 2017 9:31 am

This is were aftermarket blocks using thicker decks have less bore distortion in the bores when torqued to full values. This is also the reason boring blocks with torque plates properly torqued will tend to put the bores in a more un-distorted state when the engine is finally assembled. I also see engines once in a while that have torque numbers on head bolts higher than recommended values. Over torquing does not make for a better seal and it can damage threads and make bore distortions worse. More is not better.

Post Reply