Heads - anybody measured?

[FarmerJon]

8 hours ago, 48jumpdoors said:

so I just pulled the head off of my 1948 Plymouth because I had zero compression on number six. I found that I had a stuck valve which I have since freed up and is now functioning correctly. While freeing up the valve I noticed that the pistons came all the way flush at the top of the cylinders, so your comment of a 230 coming all the way up flush caught my eye. So can I assume that I have a 230 in my Plymouth? The motor has 0.040 oversized pistons in it so possibly when it was rebuilt a 230 crank was installed or maybe they found a Dodge motor to swap out? I took the head to have it inspected and to have 0.030 shaved off of it, do you think this is a good idea? after reading the above comments maybe I should just have the gasket surface cleaned up at a maximum?

Throw a tape measure into a cylinder, and know for sure. 

My spare engine is a 217, but the .030 pistons come all the way to the top, only .005 or so down.

I can't know if the block has been decked, or if the aftermarket pistons moved the pin location to tighten quench, or if it was designed that way from day one.

 

[48jumpdoors]

6 hours ago, FarmerJon said:

Throw a tape measure into a cylinder, and know for sure. 

My spare engine is a 217, but the .030 pistons come all the way to the top, only .005 or so down.

I can't know if the block has been decked, or if the aftermarket pistons moved the pin location to tighten quench, or if it was designed that way from day one.

 

I would be measuring from the top of a piston that is all the way down to the top of the cylinder? I guess it would be hard to figure if you dont know what the pin location is. 

[Merle Coggins]

Measure the stroke length to determine if it's a 218 or a 230. With the head off it's pretty easy. If the piston is flush with the block deck at the top just run it down to the bottom and measure from the block deck down to the top of the piston. 4-3/8" = 218. 4-5/8" = 230 

[Bryan]

On 3/9/2022 at 8:36 PM, Sniper said:

Minimum recommended piston to head clearance is .040", that can vary a bit tighter is you are adventurous.  Being that the head gasket is usually at least that thick, if not twice as much, you should be ok there, but verify.

I was looking for more piston info and got to looking in the manual. My manual says .028. Is it different for the 25" engines?

[Sniper]

.028" piston to head clearance is what your manual says?  That's tighter than the head gasket thickness, compressed.  That is some serious quench going on there.

[Bryan]

7 hours ago, Sniper said:

.028" piston to head clearance is what your manual says?  That's tighter than the head gasket thickness, compressed.  That is some serious quench going on there.

 

[Sniper]

Good thing these are low revving engines, that tight a clearance would let the pistons kiss the head at higher rpm's.  Crazy.  I wonder what the actual clearance ended up being.  I know Chrysler wasn't real good about hitting blueprint specs in the muscle car era.

[Bryan]

1 hour ago, Sniper said:

Good thing these are low revving engines, that tight a clearance would let the pistons kiss the head at higher rpm's.  Crazy.  I wonder what the actual clearance ended up being.  I know Chrysler wasn't real good about hitting blueprint specs in the muscle car era.

I'll look into others' posts to see what they are doing. Seen it mentioned. A lot to learn. Still have my block and heads out for cleaning/crack checking.  Been sick this week. Covid test negative. I need to solve the piston compression height problem. I haven't found a manual or any written info on what the stock compression height is.  EGGE is listing 2.000, others 1.980 or 1.978. Imagine the mistake of getting EGGE (and their info being correct) AND decking the block too.  Trying to learn.

[Sniper]

Did you measure your piston deck height before you pulled it apart?  Be interesting to see how close Chrysler got to the published specifications.

[Bryan]

3 hours ago, Sniper said:

Did you measure your piston deck height before you pulled it apart?  Be interesting to see how close Chrysler got to the published specifications.

Naw, wasn't thinking of it then. It was almost to the top but not perfectly flush. 2nd pic one looks kind of flush.

[Sniper]

I think the spec in your manual must be a typo.  Since there is no way it was met with the piston down the hole and the stock type head gasket about .050" in thickness.  The piston would have to pop out the deck and that would be an impediment to flow.  But I am guessing, so who knows.

[kencombs]

59 minutes ago, Sniper said:

I think the spec in your manual must be a typo.  Since there is no way it was met with the piston down the hole and the stock type head gasket about .050" in thickness.  The piston would have to pop out the deck and that would be an impediment to flow.  But I am guessing, so who knows.

I suspect that spec is for piston to block top rather than piston to head.

[Bryan]

On 3/19/2022 at 11:00 AM, Sniper said:

Did you measure your piston deck height before you pulled it apart?  Be interesting to see how close Chrysler got to the published specifications.

Not yet,,but here's something on the same topic. Will get to it.  Never realized there was such a thing as "rebuild pistons" ..Chevy 350 rebuild questions | Hot Rod Forum (hotrodders.com)

[Sniper]

I question the wisdom putting 305 heads, HO or otherwise, on a 350.  lol.  I guess there was a time you could get non-rebuild pistons and not lose that bit of compression, but now days with "maximize profit" its cheaper to just make the rebuilder pistons and let the end user worry about anything more than that.

[Bryan]

37 minutes ago, Sniper said:

I question the wisdom putting 305 heads, HO or otherwise, on a 350.  lol.  I guess there was a time you could get non-rebuild pistons and not lose that bit of compression, but now days with "maximize profit" its cheaper to just make the rebuilder pistons and let the end user worry about anything more than that.

If EGGE pistons are true 2.00 compression height I might spend the extra $100 for them. I'll call them my "custom back to normal" pop up pistons.   And dang, just another $400-500 I could get custom Ross pistons.  I need to stop.. ?.  Will settle for the EGGE ones.

[Bryan]

On 3/19/2022 at 6:19 AM, Sniper said:

Good thing these are low revving engines, that tight a clearance would let the pistons kiss the head at higher rpm's.  Crazy.  I wonder what the actual clearance ended up being.  I know Chrysler wasn't real good about hitting blueprint specs in the muscle car era.

Was looking at it again, waiting for the temps to warm up outside.  On higher performance engines with thermal expansion and RPM stretch could lessen gap by as much as .02.  Minimum Quench / piston to head clearance ? | Hot Rod Forum (hotrodders.com)   Given people on this forum were stating compressed gasket thicknesses of ABOUT .040 don't think I'd ever want my pistons more than flush.  Not building a hot rod but don't want to lose any HP.

[James_Douglas]

I do not get it if the piston is flat with the deck or even a little over it but below height of the top of the valve...

 

The valves which stick up above the deck, plus their over .3xx lift, will hit the head long before the pistons...

 

What am I missing?

 

James

 

 

[kencombs]

Th

48 minutes ago, James_Douglas said:

I do not get it if the piston is flat with the deck or even a little over it but below height of the top of the valve...

 

The valves which stick up above the deck, plus their over .3xx lift, will hit the head long before the pistons...

 

What am I missing?

 

James

 

 

The area over the valves is much taller and more open than the opposite side where the head is completely flat.  Only the head gasket provides piston to head clearance in that area.

[Bryan]

3 hours ago, James_Douglas said:

I do not get it if the piston is flat with the deck or even a little over it but below height of the top of the valve...

 

The valves which stick up above the deck, plus their over .3xx lift, will hit the head long before the pistons...

 

What am I missing?

 

James

 

 

The valves and spark plug are way on the other side and totally away from the piston.  Easy to forget on these engines. Done it a few times.  The piston can only meet the flat part of the head.  

[James_Douglas]

Ok, I had to look at one of the heads to remember that. If the deck is cut and the piston is flat with the deck and the head is cut...

 

The final compression ratio may be too high. One could mark and have the head flat area milled twenty thousands to make up for the deck and head cut and provide plenty of clearance. That is assuming that one can take material off that area and not weaken the head.

 

In the end, custom pistons with exactly calculated compression ratio's is the way to go or find a better block or head that has not been cut.

 

James

[Bryan]

Today I measured my original head gasket that I took off my 48 motor, a Victor V-1066-C  gasket, copper on both sides, hard to tell what's in the middle. Anyway it measured .0620 to .0635".