L-36 stock rebuild - .032" Head Gasket ??

[Keith B.]

My L-36 is being rebuilt for the first time. I really need your best advice on this one. My mechanic called me today and told me the passenger side of my BB block is ten thou higher than drivers side. He is trying to establish the right quench and CR. He really would like to shave off that 10 thou but he recognizes that is NOT going to happen with my factory broach and stamp pad #'s. So he was trying to find a .032 thick head gasket for the pass side w/out any success. He tried SCE gaskets but they will not work with my application. He is now considering lengthing 4 connecting rods to achieve his goals??. The drivers side is not a problem at .039"-.042" with a thicker gasket.
Duke tell me," this is a common "issue" on OE machined blocks - different side to side deck height/clearance by more than a few thou and using different head gasket thicknesses is the easiest way to solve it." Joe L is not aware of any thinner gaskets at .032" but doesn't rule out somebody might now of some out there
I hope I got this right explaining this too you w/out sounding stupid. Basically the pass side it ten thou higher than the drivers side.
Do you know of a steel head gasket at .032" specs that would work on the passenger side for my application, ie type and company name.

Any advice here is sincerely appreciated.

[Duke W.]

Re: L-36 stock rebuild - .032" Head Gasket ??

The drivers side is not a problem at .039"-.042" with a thicker gasket.
.

I don't understand what you're talking about here. Is this number the gasket thickness? Deck clearance? Quench clearance?

I suspect your "engine builder" is obsessing over "quench clearance", which they have a habit of doing.

FORGET ABOUT QUENCH CLEARANCE!

Select head gaskets to achieve no more than 10:1 on each side.

Do you have accurate data for the other numbers you need to do the CR calculation on all eight cylinders - deck clearance - cylinder head volume - net piston volume?

Have you used the cgnet calculator to compute the compression ratio of all eight cylinders with readily available head gaskets? What are the results?

If the quench clearance is no more than about .080" you have nothing to worry about as long as the highest CR is no more than 10:1, and you still have the option to knock the highest cylinders down with a little chamber grinding to bring the highest to no more than 0.1 more than the lowest.

Duke

[Keith B.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Duke: I was not given any of deck or quench clearances. He is referring to the head gasket thickness. As noted the the drivers side is ten thou higher than the pass, which is norm as you stated. So he is trying to correct this with a thinner gasket on the pass side, and is looking for a .032" head gasket for the pass side only but unable to locate.

If this does not sound right, I will reconfirm tomorrow...thanks...

[Duke W.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Unless you can communicate accurate and full context data, neither I nor anyone else can help. So the first step is for you to, personally, take control of your project and direct the "engine builder" to provide the following data:

The deck clearance of each cylinder?

The head chamber volume of each cylinder.

The net piston volume including and whether it is a dish or a dome.

Post the data.

The above information will allow you to calculate the compression ratio and quench clearance of each cylinder with various available head gasket thicknesses. Follow the previous guidelines for maximum allowable CR and variation, then direct the "engine builder" to use the gaskets you choose.

Duke

PS Your attempt to delete the redundant thread was unsuccessful. It's still there. Try to delete it again so responses don't get scattered or post a reply saying "do not reply to this duplicate post."

[Stuart F.]

Re: L-36 stock rebuild - .032" Head Gasket ??

As this is so far kind of an unclear subject, let me question one item as well; Why are you worried about machining the driver's side block surface with regards to your stamp pad? Does not the big block have the stamp pad on the passenger side like the small block???

Stu Fox

[Joe R.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Keith,

It sounds like it's a bit premature to pick the head gaskets. But when you are ready, I think you'll find the following thread useful:

https://www.forums.ncrs.org/showthre...inted&uid=3398

In the thread there is a link to Summit Racing that shows various head gaskets for a 427.

Joe

[Duke W.]

Re: L-36 stock rebuild - .032" Head Gasket ??

As this is so far kind of an unclear subject, let me question one item as well; Why are you worried about machining the driver's side block surface with regards to your stamp pad? Does not the big block have the stamp pad on the passenger side like the small block???

Stu Fox

He said the right (passenger) side is high, which is the side with the stamp pad.

If the left side was high it could be machined down with no consequences as it is undetectable in Flight judging.

So in order to equalize CR on both banks the right bank needs a .010" thinner gasket. This would also mean the left side has about .010" more quench clearance, but this will be of no consequence as long as the compression ratio is not excessive.

On a restoration engine you cannot achieve both ideal CR and ideal quench without decking the block or going to other extremes like resizing the rods for different than OE length.

The primary concern should be achieving a reasonable CR. Quench clearance is a secondary consideration, but there are a lot of "engine builders" who think it's the holy grail.

"Ideal" quench clearance is .035-.040", but most OE engines came out of the plant in the range of .050-.060" due to typical higher than nominal deck heights and gasket thickness including the incidents of double gasketing as was the case of mid-'62 to '63 SHP/FI engines.

Duke

[Michael H.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Duke: I was not given any of deck or quench clearances. He is referring to the head gasket thickness. As noted the the drivers side is ten thou higher than the pass, which is norm as you stated. So he is trying to correct this with a thinner gasket on the pass side, and is looking for a .032" head gasket for the pass side only but unable to locate.

If this does not sound right, I will reconfirm tomorrow...thanks...

Keith,

In my opinion, trying to correct a .010" difference in deck between one side and the other is a waste of time and money for a restoration engine.

There are a LOT more items that influence the actual compression ratio/pressure for any side/cylinder. Addressing just the deck height on one side is not going to make all cyl's the same C/R.

Spend the money on "deck plate cyl honing" with a REAL automatic feed precision hone, and balance the rotating assembly instead. Those are items that will be important down the road.

[Duke W.]

Re: L-36 stock rebuild - .032" Head Gasket ??

It depends on the CR. A difference of .010" between decks means that one side is about 0.2-0.3 higher than the other, which could result in detonation on the high CR side if you designed for maximum CR on unleaded fuel.

On a L-36, if you rebuild the engine with about 9:1 compression, the difference in deck heights is not consequential, but it is easy to fix with suitable head gasket selection. If the target is 10:1, and the low deck side is 10.2, I would definitely correct the situation with a thicker head gasket on the high CR side to bring it down to 10:1.

That's why I recommend limits and further recommend keeping variation at no more than 0.1. That way you can achieve maximum torque/power and fuel efficiency without detonation.

Balancing and deck plate honing is axiomatic if you want a precision engine that will perform at its peak potential without any vibration.

Duke

[Michael H.]

Re: L-36 stock rebuild - .032" Head Gasket ??

It depends on the CR. A difference of .010" between decks means that one side is about 0.2-0.3 higher than the other, which could result in detonation on the high CR side if you designed for maximum CR on unleaded fuel.

That's true but if all of the rest of the factors that affect the actual cyl pressure in operation are ignored, just setting deck height is a waste of time and money.

How about cyl head chamber volume? If one head has shallow chambers and the other happens to have deep chambers, there goes your "correct deck height" theory.
And piston dome specs are not all the same in real life. There's usually some veriation from piston to piston.

And then there's the efficiency of the intake manifold runners. They're not equal so cyl filling at anything over 1500 RPM is also not equal.

Low cost replacement cams can/do cause problems too if a few of the lobes are ground on slightly different centers. Not at all uncommon to find several degrees variation from cyl to cyl.

It's all or nothing. It's actually possible that bringing up the deck on the low side could actually cause more problems than it cures.

I think most engine builders make a big deal out of nothing when it comes to rebuilds for a street driven vehicle that probably ran just fine when delivered new from the factory.

I still think most owners spend money on nonsense and ignore things like I mentioned in my previous post.
They buy/do machine operations that do nothing positive, yet, they will hone cylinders with a dry $15 cyl hone from Wal-Mart.

Racing engines are a completely different story.

[Jamie F.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Your issue is very easy to "fix" if you need to. On the low side use a standard laminate type gasket, most have a compression thickness of around .032 - .036". Then on the high side use a steel shim gasket like the 1131 from Mr. Gasket which has a compression thickness of .020"
That should do it.

[Duke W.]

Re: L-36 stock rebuild - .032" Head Gasket ??

How about cyl head chamber volume? If one head has shallow chambers and the other happens to have deep chambers, there goes your "correct deck height" theory.
And piston dome specs are not all the same in real life. There's usually some veriation from piston to piston.

My recommendations for precision engine restoration include equalizing compression ratio to a maximum of variation of 0.1 across all cylinders. This can be done by first equalizing deck clearance or using different thickness gaskets to compensate. Then all head chambers should be measured and the highest cylinders' CR should be brought down to no more than 0.1 above the lowest, and this assumes that a target maximum has been established based on engine configuration and available fuel octane quality.

The above steps require some extra effort, but I think the end result is worth it if you want to push the CR to a reasonable limit to achieve maximum detonation-free performance on available pump premium.

Piston volume variation is a noise level effect as long as the pistons were machined to print.

There are variations in cylinder to cylinder VE and cyclic variation in the combustion PV diagram, and there's nothing that one can do about these issues, but managing the as built CR as above will lessen the chance of detonation on the finished engine.

The min/max CR spread on a production engine can be up to about 0.5, which could definitely cause some detonation problems and is likely why some report no detonation on OE (never rebuilt) engine configurations while others have detonation problems with the same configuration.

Corvette restorers often go great lengths to make their car look better than "typical" production. Consider how much time is spent finessing body panel fit and paint appearance.

Why not do the same thing with the engine, which is the heart of a Corvette?

Duke

[Michael H.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Corvette restorers often go great lengths to make their car look better than "typical" production. Consider how much time is spent finessing body panel fit and paint appearance.

Why not do the same thing with the engine, which is the heart of a Corvette?

Duke

I agree with this part. Unfortunately, most Corvette owners/restorers don't want, or can't afford to rebuild an engine the way some of us would like to rebuild them.

[Keith B.]

Re: L-36 stock rebuild - .032" Head Gasket ??

Duke: As always I appreciate your forthrights manners.....and sincerety to assist all of us here

I know you want all the data but I did not have it at the time and like I stated twice, I'm really just trying to find other gaskets to compensate for the .010 difference, as the pass deck is higher than the drivers. AND Yes, I know what side the stamp pad is on my original engine and others...

Thanks to John Hinckley for steering me towards Cometic Gaskets who were able to custom produce MLS or multi layer steel head gaskets at .030 and .040 that will work perfectly based on the specs for my application.

Duke: I tried to delete my org message 5 times to no avail.......

[Duke W.]

Re: L-36 stock rebuild - .032" Head Gasket ??

I hope your final as-built CR is in a range that will allow detonation free operation. Try as I may I was not able to extract the information. Good Luck!

IIRC the OE steel shim gasket compressed thickness is .028", but...

Duke