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im pretty sure ive seen it on here before but i cant find it now, will an aluminum head actually expand when it gets hot and cause a loss in compression? or is that a bunch of garbage?

Cody
 

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Considering you typically allow about .006" for lash because of head expansion with alum. heads (BB Chev), and valves and pushrods may grow a couple thou...say the head expanded .008"...would that be reasonable?
You can take .005 off the deck for 1cc of chamber volume, so if the entire head is growing even .010", how much could the chamber be growing? Maybe couple-three thou in each direction?
Just thinking this through out loud...doesn't seem to be terribly significant for most cases.
 

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and I bet aluminum blocks don't grow either...

a good running comp or PS motor today if you used your theory...you would have one hell of a rod bearing bill at the end of the year!

Never said aluminum blocks don't grow....they do smart ass

so do the heads.......we all know that

he ask if it would lose compression....you think so????

depending on piston material, lets say the chamber opens .006

now lets say we have a 2618 piston with a little dome

Will it grow .006 ............. so I SAY, no change in compression

or if there is a loss, it's MINIMAL.............bring your brilliant mind

SO WE CAN ALL LEARN.............:rolleyes::rolleyes::rolleyes:
 

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think about it this way....

what happens if you surface a head .006" Probably a cc or so depending on the head.... would you agree?

now... think about the entire surface of the combustion chamber...not just the diameter getting .006" removed... or even in some cases .008-.010". depending on the chamber design would you agree 1.5-2cc's is possible?
 

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HIS simple question is will you lose compression when hot

Yes, you may, BUT IT IS MINIMAL.....

DIDn't ask if compression goes up from cutting the head....

Think about piston dome growth the same way as they head.

would it not grow also??....i think SO
 

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HIS simple question is will you lose compression when hot

Yes, you may, BUT IT IS MINIMAL.....

DIDn't ask if compression goes up from cutting the head....

Think about piston dome growth the same way as they head.

would it not grow also??....i think SO
i agree..

you guys wanna talk about growing and valve lash...you wouldnt beleive how much mine grows..alum 10.2 block and big duke heads...
 

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HIS simple question is will you lose compression when hot

Yes, you may, BUT IT IS MINIMAL.....

DIDn't ask if compression goes up from cutting the head....

Think about piston dome growth the same way as they head.

would it not grow also??....i think SO
of course the piston grows...but the majority of the mass is horizontal not vertical. If the deck is ..250" you would expect a .002 growth max vertically.

I guess minimal is relative... on a small high compression motor... say a 325 2 cc's would equal 6 tenths of a point of compression.
 

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Talking about lash growth....is it necessary to re-adjust a hydraulic cam after break in? Do they grow like a solid lifter does?
 

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Compression raise or lower?
If the aluminum is EXPANDING, material is getting bigger...
would the chamber area actually get smaller??
The head is getting warmer and growing...
Lets look at it as a domed surface, centerline of the cylinder lines up with the centerline of the chamber's dome.
Diameter of cylinder is the same as the diameter of the dome and their "walls line up.
The as the aluminum grows, would it not grow towards the centerline? or in that direction also? Why would the diameter get bigger? That would be a less material condition. Head would not just grow away from the chamber...
 

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I think you may have a point...

If the rocker bar on the top of the head, grows providing more clearance for lash... then it is reasonable to consider that on the other side of the head, the same condition is occuring.... the expansion always moves outward.... I think people are forgetting that outward, is all 4 sides of the head.... not just on top.

That being said, the deck is also growing..... eliminating the premise that the chamber is moving toward the piston.

In the end, I say there is no change in compression.
 

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If the growth is proportional, it should stay the same. I would think that if you had an aluminum rod/iron block you might even get a compression increase.
 

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reher morris had an article on preheating a dragrace engine before a run.His determination was that this was counter productive because all of the engines they tested made more H.P. dead cold and if built and tuned properly has no affect on the longetivity.I wonder if outside of the obvious cooler denser air charge if there could be other factors like this discussion that may occur and also lower hot engine power.Not taking sides just wondering if it may be true
 

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I think the comp goes up,,,,, not because of the head but because of the ring end gap and oil cylinder seal should get better
 

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reher morris had an article on preheating a dragrace engine before a run.His determination was that this was counter productive because all of the engines they tested made more H.P. dead cold and if built and tuned properly has no affect on the longetivity.I wonder if outside of the obvious cooler denser air charge if there could be other factors like this discussion that may occur and also lower hot engine power.Not taking sides just wondering if it may be true
Oil hot, block cold
 

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I think you may have a point...

If the rocker bar on the top of the head, grows providing more clearance for lash... then it is reasonable to consider that on the other side of the head, the same condition is occuring.... the expansion always moves outward.... I think people are forgetting that outward, is all 4 sides of the head.... not just on top.

That being said, the deck is also growing..... eliminating the premise that the chamber is moving toward the piston.

In the end, I say there is no change in compression.
If that theory was correct.... why would you heat an aluminum head up to insert a seat? Wouldn't the seat press increase if everything was "growing"? :D
 
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