Technical Gasket changes pushrod length?

So assuming no decking of block or head (factory height) if I'm putting on a thicker head gasket that would change the valve train geometry and at some point require longer pushrods?

I'm rebuilding a BB Chryler and have done some things to bring down the compression ratio to be able to use pump gas. However it looks like I won't be able to avoid using an .051 thick head gasket to help lower it. At what point do I have to go to different pushrods to keep the valvetrain geometry honest? This is a hydraulic stock valvetrain except for a mild cam change.

If I do have to go to an adjustable pushrod is it simply a matter of lengthening them by the change in height?

 

A thick head gasket my cause more problems than just push rods.
The quince is very important for any engine even on pump gas.

 

I would think by not changing the length of the pushrod the rocker would no longer be centered on the valve.

 

Is this a hydraulic lifter engine? How much thicker are your new gaskets than the old ones? Will the lifter be able to make up the difference?

 

Depending on the original year of the motor you may be going from a steel shim gasket to a .051 gasket, so you would be increasing your quench somewhere in the neighborhood of .040. Just a guess here,

You want to keep you quench tight on your engine to make it handle fuel more efficiently, they way to lower compression is to dish the pistons not increase the distance from the top of the piston to the face of the head.

Now unless you have adjustable rockers or adjustable pushrods you have significantly changed your preload on your lifters, I like to run 'em loose but not too loose.

Valve gear geometry is only part of the problem, you have other things to think about.

 

Its a big block mopar.....unless he's running close chambered heads, there is no quench

 

Guess I didn't think of that

 

I'm not a Mopar guy, but I seem to remember Mopar running a High Quench to Start with on there Big Blocks?

 

You are confusing squish with quench, quench is the distance measured from the top of the piston to the face of the head and has nothing to do with combustion chamber size. It is the same measurement on any engine. If he is running a MOPAR B motor and has the lazy heads he shouldn't need to lower his compression to run on pump gas unless he is running high compression pistons.

That leads back to my statement that the way to lower compression is with your pistons not by using thicker head gaskets.

 

Here's the deal. A BB MoPar is a rocker shaft engine. If you had a 350 Chevy and you jacked up the heads, you could screw down or up the rocker balls to maintain valve to rocker clearance. But you would be changing the rocker arms fulcrum location and effecting your rocker arm geometry adversely. But on a rocker shaft engine you can't just screw down or up the ball. If it's to loose, it's to loose. So, if your lifters can't make up the difference in thickness, you need a shorter pushrod. I would avoid adjustable pushrods in favor of a pushrod of the correct length. They are available. Adjustable rockers would seem to be the best answer, if you need to make up the difference.

 

The original head gasket would have been about .040 compressed give or take. Is there a reason an over the counter gasket will not work in your application? Also, most hydraulic lifters have between .020 and .060 plunger depression. I wouldn't think an extra .011 is gonna make anything terrible happen.

But, there are people smarter than me hanging around here, listen to everything, make the best decision.

-Abone.

 

tell me how you get quench or squish from this head.....

 

Not that this is what this thread is about but I would have the piston come out of the top of the block.

 

Keith black pistons

 

I knew someone would mention these....

 

I googled "quince" and came up with some yellow coloured fruit.

??????

 

Yeah I should have went back and edit my post but then you guys would know what kind of old burn out wood hippy gear head I am.

 

Quench is Piston Clearance, Steel rods .035 to .045, Aluminum Rods .060 to .070, I've had Mopar friends through the years Talk about as much as .150 on BB Mopars, But as stated earlier I am not a Mopar Guy. Or my understanding anyway about Quench.

 

This is quince:

The word you are looking for is quench.

 

Squish is a slang term used to explain combustion chamber pressure. Quench is an actual term used by men who actually have some idea what they are talking about which you obviously don't. It is applied engine theory, you measure the distance from the top of the piston ( that would be the place around the edge not the dome or dish) to the gasket mating face of the head.

I cannot get quench from the head there are other variables that need to be applied, gasket thickness, deck height, all you get from the head it self is the mating surface. Quench is a distance and is not effected by combustion chamber size or shape. I am sorry that you don't understand, I don't know any other way to explain it to you.

 

Thanks for the replies.

The engine is a '61 413. It left the factory w/ a 10.1 -1 CR, flattop pistons and a closed head of around 73 cc. The piston sat about .070 in the hole. The gasket was probably about .020". Would be nice to play with pistons but there are the original style high compression height or the ones for bread truck applications (Keith Black) that are designed for about an 8:1 CR. (Customs are not in the cards). As said, hydraulic valve train.

I have some higher volume closed heads but they still leave me short of my compression goal hence the need for a thicker gasket. I see the range of thickness of gaskets for BB Chryslers but never see a discussion of effect on valve train height. Chrysler Performance used to offer a .060 shim/gasket advertised to bring down CR but again no mention of valve train. AT some level of lifting the head its got to start to make a difference. I'm just trying to figure out where that is and how to calculate for it.

 

Not gonna get in a pissing contest with you - I know what quench is......look at the head pictured, there is no "mating surface" inside the combustion chamber.....I don't know any other way to explain it to you.....As far as the OP is concerned, I really don't think it matters how far he's down in the hole (within reason) once its over .045....

 

With the piston down .070 there's no quench anyway a .050 gasket you will lose about 1/2 point.

 

The only way to know is to install the head with the gasket and check your lifter preload.

 

Look at the flat surface below (in you pic) the CC...looks to take up about a 1/8th of the hole, isn't that where quench is calculated?

Or is that "up" in the head?

 

on open chamber B/RB Mopars it is "up" in the head...

 

Lots of BS being posted. Dont worry about quench in your application and the thicker head gasket wont really affect it that much slap it together and while u are at it just check valve train geometry i doubt you will have to change anything.

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Been too many years, but if I remember right Mopar used a .060 preload on the lifters. All things being equal (??) the .051 gasket should leave a bit of preload. Like I said been too many years.

Len

 

I have built a bunch of these. Put it together and check the lifter preload. If there isn't enough either get some adjustable rockers or longer pushrods. This is assuming you have no wear on the rocker shafts or arms. I have checked several of these. Even with new shafts and stock arms, preload varied .010-.020.... with a hydraulic it super critical... The lifter makes up the difference. With solids... That is why they are adjustable. You would be surprised at the variance in ratio from one factory arm to the next.



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Meant to say with a hydraulic it is not super critical.....

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