CC'ing some late cylinder heads,.not sure what I'm seeing

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Steve Harrison
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CC'ing some late cylinder heads,.not sure what I'm seeing

#1 Post by Steve Harrison » Sat Mar 21, 2015 3:57 pm

I am working on getting my "fun" engine together so I can mothball the original in my car.
Working on a pair of really nice 1966 heads. The part number is 616.104.301.03 and there is another number cast in "KOK.2" as well as the "66" in the date circle. No cracks.

Looks like the heads were worked on by Lukes and Shoreman at one time as there is a stamp L&S and also the number 117. (Have no idea what the 117 means,...any ideas?)
The heads have obviously been resurfaced. (I have checked the depth of the cylinder barrell mating surface and it's good.)
The chamber volume has been restamped at "60.0"....this is not the factory stamp.

My problem is that when I cc the heads,...I come up with 67 CC's for the two chambers on one head, and 66.5 and 65.2 on the chambers on the other head. There are absolutely no "grind marks" or any other non-factory surface finish inside the chambers....see the last picture.

I have never worked with 912 heads before and am wondering if I am missing something in the measuring department?
Could Lukes and Shoreman have gotten their measurement off by 7 CC's? Or am I measuring differently from how they would have?

My method is as shown,...using a flat plastic disc that fits down into the chamber. The first picture shows the chamber in the process of filling. I use a (very) thin bead of lithium grease around the edge of the plastic to make it seal to the cylinder bore landing. I made absolutely sure the plastic disc is resting squarely on the cylinder wall landing.
The black you see there around the edges is the magic marker I used to trace a cut line onto the plastic. I then snuck up on the circle shape by carefully grinding, filling, and sanding the plastic disc to shape. The cracks you see around the perimiter of the plastic are indeed, cracks. The plastic was very brittle,...all the better to stay flat. (The cracks are tight, and do not leak.) I have an air hole in the plastic in addition to the fill hole. Using a 100 Burette I get the above mentioned numbers. What am I looking at here?
GEDC3898.JPG
GEDC3909.JPG
GEDC3910.JPG
GEDC3911.JPG

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Matthew Devereux
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#2 Post by Matthew Devereux » Sat Mar 21, 2015 4:16 pm

Looks like the same process I used. I can see the volume getting smaller but not larger. Are you somehow including the volume in the burette in between the valve and the tip?
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Steve Harrison
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#3 Post by Steve Harrison » Sat Mar 21, 2015 4:24 pm

That's a great suggestion Matthew, but my burrette measures zero at the top line, and counts "up" to 100 as the fluid level drops, so the tip and valve are irrelevant. When the fluid line hits 67,...that's how much fluid has escaped the burrette.
I went over my process twice,..and can't make sense of the outcome.

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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#4 Post by Steve Harrison » Sat Mar 21, 2015 4:30 pm

I am now wondering if L and S just took a slight whisp of a touch off the heads, not enough to require the cylinder wall landing ledge to be deepened,...and simply restamped what the factory had stamped on the heads as the chamber volume without rechecking.
I know anything's possible, but wouldn't expect factory chamber measurements to be off by that much?

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Wes Bender
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#5 Post by Wes Bender » Sat Mar 21, 2015 4:36 pm

Not knowing where the heads have been or what might have been done to them, Steve, I'd go with what you measure. As long as you are consistent, you should be able to use your numbers and ignore what is stamped in them.

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Ron LaDow
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#6 Post by Ron LaDow » Sat Mar 21, 2015 5:43 pm

As far as I'm concerned, Wes is correct here. Who knows who has stamped what on the things? Regarding how far off, I had a set of NOS 912 heads in the factory boxes. They were stamped to the tenth of a cc and not one was within 3ccs of the actual number.
BTW, have you had them surfaced for the cylinder sealing surface? Any ridge in there will give you bad numbers.
Oh, and so long as you over-fill the burrette and 'leak' it down to the beginning mark, the amount in the valve and nozzle is irrelevant.
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Matthew Devereux
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#7 Post by Matthew Devereux » Sat Mar 21, 2015 6:38 pm

The question is how do you get a cc so big without grinding, machining or sunken valves? I'm certainly no expert on identifying differences in the various 356 heads but the area around the plug looks deshrouded.
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#8 Post by Ron LaDow » Sat Mar 21, 2015 10:00 pm

67ccs is at the large end of the chambers I've measured, but it's also not unknown.
I once fancied I could eye-ball chambers and select for size; turns out that was total fantasy; you remove .010" from the entire surface and you're close to 7ccs right there.
So if Steve is careful with his measuring, that's the best data he has. A stamp of some number or the other from sometime in the history of the things really isn't evidence of much at all.
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#9 Post by Ron LaDow » Sat Mar 21, 2015 10:29 pm

BTW, it sure looks like the chambers did get some re-shaping
GEDC3911.JPG
GEDC3911.JPG (107.35 KiB) Viewed 2555 times
Not sure about the area at the upper side of the illustration (actually the bottom), but the two other areas certainly got cut.
Again, how much? Dunno, but some.
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#10 Post by Martin Benade » Sat Mar 21, 2015 10:46 pm

Also any grinding done to the valves or seats sinks the valve and enlarges the chamber and depending on who does it, it could be quite different on each valve, although it shouldn't be.

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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#11 Post by Steve Harrison » Sat Mar 21, 2015 11:24 pm

Yes, I did have the seats touched up, and also a three angle cut done. They took off the absolute minimum to clean things up, but that does indeed sink the valve a bit more. Also had the valves touched too. But seven CC's? Seems a lot to me to account for.

The chambers haven't been cut or ground on. I'll defer to your trained eye Ron as to whether the chamber looks unshrouded around the spark plug, but I can't see where it has been ground down aftermarket. The cast surface is as factory and untouched across every bit of the chamber. You can tell if there have been alterations to that 'factory grainyness", for lack of a better word, of the original casting. Is it possible the factory was tweaking the chamber shape due to the feedback from the folks who were doing the hot modifications of the day? Dunno, but I'd swear the chambers of these heads have had no die grinders put to them, at least that's the way it appears to me. So,...now that I know (probably) what I am dealing with here in the chamber size department, I have to first: get the other two chambers up to 67, ...and then check and see just what kind of compression ratio to expect with the AA p/c 's I am going to use. I'll have to contact them and see what they figure it'll be, then check it against what I come up with from my own checking, measuring and calculations.

It just seemed like 67 cc chambers seemed a little big to me,...especially since I'm used to dealing with the earlier heads. Much smaller chambers usually. Weird.

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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#12 Post by Steve Harrison » Sat Mar 21, 2015 11:32 pm

And BTW Ron,...great suggestion about the sealing surface ridge. There is a small (tiny really), ever so slight one, but it is there nonetheless. I'll have that knocked down and check again. It's so slight I doubt it'll account for much, but more accurate is better in any event. Thanks for the suggestion, I hadn't thought much about that yet.

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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#13 Post by Ron LaDow » Sun Mar 22, 2015 12:42 am

Steve Harrison wrote:And BTW Ron,...great suggestion about the sealing surface ridge. There is a small (tiny really), ever so slight one, but it is there nonetheless.
Not to beat on you, but simply to pass on what I found:
That "tiny" ridge, if it measures .010", amounts to >5ccs.
I finally took an Exacto knife to an rubber eraser and cut a chunk that measured close to .4" x .4" x .4" and kept that thing in front of me on the bench to remind me what 1cc meant. I looked for a .01" X 3-3/8" disc to remind me what 5ccs looked like, but I never found one. Look at a .01" feeler gauge to see what that means.
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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#14 Post by Steve Harrison » Sun Mar 22, 2015 1:10 am

Yup, I agree that can account for something. It's nowhere near ten thou, but I'll knock it down and give it another whirl,...let you know what I find.

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Re: CC'ing some late cylinder heads,.not sure what I'm seein

#15 Post by Vic Skirmants » Sun Mar 22, 2015 7:37 am

Ron; check your math. .010" times the area equals closer to 1.4cc, not 7cc.

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