combustion chamber volume

[old grumpy]

I am trying to find information about the combustion chamber volume. Probably there are somewhere here, but where?
The old "tube" head and the newer Arrow range head.
Anyone who knows?

 

[Tom H]

I measured my 1725 Alpine head when it was a virgin head, no skimming, no valve job, no vizard. I measured 39.2cc. I was pretty careful in doing the measurement using a plastic plate, colored alcohol, and a 60 CC medical syringe that I calibrated carefully using a gram scale - 1 gm =1cc.

If you use that figure, standard bore and stroke, 0.026" gasket thickness, and 7.2 cc as piston dish volume (factory spec is 6.9 to 7.5), and 0.018" as deck clearance, you will calcuate a Compression Ratio of 9.21, which closely matches factory spec of 9.2, so I have a high confidence that 39. 2 is pretty accurate for a factory original head. In other words, if you calculated the volume from all the other figures incl specified CR, you would arrive at about 39.2, the same volume I measured.

The CR spec and all other factors are indentical for the early "tube type" head as well as the later heads so I cannot imagine the volume being differrent. My measurements were on a non "tube type" head

I further calculate that you reduce that volume by about 1 cc for every 11.4 thou you skim from the head surface.

Furthermore the volume increases as the valves recess or are ground. That increase is approx 0.029cc per thousandth of an inch on the intake valve and 0.019 cc per thousandth of an inch on the exhaust valve.

Tom

 

[old grumpy]

Thanks for the professional and accurate calculation!

Yes, the old and new head look similar in that area. It's the inlet channel that appears different.

 

[old grumpy]

Have just been out in the workshop and with my primitive tools (a syringe)
I measured the head. It has been skimmed and reworked and all four was (about) 39 c.c.

 

[Tom H]

Sounds reasonable. Did you use a fairly large syringe- 50 or 60 cc? My first attempt was with a 10 cc syringe and got a lot of error due to multiple measurements per chamber. Did you use a plate- a clear plastic plate with a hole for the syringe and sealed to the surface head with vaseline? Without that you are forced to make an estimate of when the chamber is full. Big chance for error there.

Tom

 

[old grumpy]

No, I did it with some "error". The large syringe was difficult to empty into the little hole in the plastic plate. I had to use a 20cc without plastic plate. Used diesel fluid. Didn't seem to have much capillary effect. Anyway, after several times I got some "overall" result. With some "error" probably
Better then nothing anyway.

 

[Tom H]

Ahah, yes, some error, but you can probably get more consistency than actual accuracy. You mention "capillary" effect. I assume you mean surface tension effect.

I am curious about using diesel fluid. I assume it has a similar surface tension like water, but maybe not as much. When I used water and no plate it was difficult to gauge by eye when the chamber was full. The surface tension allowed me to fill it above the surface such that when sighting across the surface, the water would bulge up and I would measure MORE volume than actual, based on the liquid ejected from the syringe. But if I stopped filling before the bulge appeared, then there would be a small volume gap along the edge and I would measure LESS volume than actual. Maybe using diesel this issue is reduced. Using water, I think it was about 2 cc error either way. I guess taking the average would be pretty close. But using a plate solved all issues for me.

Tom

 

[old grumpy]

The explanation is very simple: I had diesel in front of me, so I thought, I give it a try. It was very flat. Didn't creep up the walls or bulge when it was at the top. Everything is relative. My aim was mostly to see if the chambers where even.

 

[Tom H]

Great. As I said, your measurements could be quite consistent and that's what you were looking for. Thanks.

Tom

 

[Ken Ellis]

Alex Trebek: Ken?
Ken: What is "meniscus"?
Alex: Correct. And with that, we'll take our first break...

Ken

 

[Jim E]

I use a 50 cc and a thick piece of Plexiglas with a hole drilled in, little grease of any sort for the seal, rubbing alcohol and sometime need to jiggle the head to get the air bubbles out. Fill the syringe to 50cc fill the chamber and see how much fluid you have left. Figure am within a cc or so on accuracy what with difference in filling a spilling chamber to chamber. I am sure you could buy a set up to do this that would give you more accurate readings if you wanted to be dead spot on.

Oh and I suck the alcohol back up and put it back in the bottle for the next round. Lose some but a bottle will go a loooong way think I have been using the same one since I did my first head work.

 

[old grumpy]

A pipette maybe for a slow fill........and yes, save that alcohol!!!

 

[Tom H]

Jim, You're the source I learned this method from a few years ago. I took it one step further by calibrating my syringe at 40 cc by checking it on a high accuracy weight scale used in my employer's receiving inspection dept. 1 cc of water weighs 1 gm. I found my syringe was off about a half cc at 40cc.

Ken, A friend of mine tore his "miniscus" a couple years ago, but let's keep knees and knee injuries out of this discussion

Tom