356 compression ratio

[badsix]

Craig, thanks for the tip on the exh. valve. i would rather get close to my said compression ratio then check valve clearance. this way i will know how much i will need to go on the valve pockets. if i check valve clearance with the cyl. on the case no shims and i get valve to piston contact. but say i need to use a .040 shim to get my compression to were i want it. that will be .040 i don't need to cut or maybe they won't need to be cut at all. i just think this would be the way to do this. maybe i'm wrong i have been before
Jay D.

[badsix]

356JAGER, THANKS, for the link some very interresting reading.
Jay D.

[badsix]

TONY G Thanks for the post very nice i'll get my duck in a row and maybe we can talk again
Jay D

[Craig Richter]

Jay, I find the easiest way to check is to glue (yellow snot) at least 6 short pieces of solder around the piston top, then rotate ONCE thru TDC, take apart and measure the squished solder. This should tell you exactly WHERE things are tight Multiple pieces keep the piston square in the cylinder. ONE turn so nothing can move around, and you get reliable readings when you measure. After you're close on DH, then put solder in the exhaust pocket and rotate thru where the exhaust valve comes closest to the piston. Using light (hardware store) valve springs here makes checking much easier. Good luck.

[Jack Staggs]

We are now machining Craig's new engine's piston crowns to a correction of appox 2.5/3*. As small as it seems, it's that important.
BTW, Harry's "Secret's..." book has the his equation for compression ration calculation. Hidden pertinent info will have to be dug for in the myriads of extrapolation.

[JTR70]

Jack, your building Craig Richter's motor at the moment? Justin

[Jack Staggs]

More like a joint effort (usually without the joint)


Here's Craig with his engine on the stand at the left.


For those that don't know Craig, he was winner of his class at the very first Pomona "Winternationals" in a Speedster, among other awards, and is the author of the well respected book "HOW TO MAKE AN OLD PORSCHE FLY"

[JTR70]

Nice photos Jack, thanks! When will you guys be firing this new motor up?

[RT]

Interesting discussion on CR - sorry to be so late to the party!

The original poster, Jay D, has made some assumptions that are unfortunately dangerous. Like Craig and some of the others who have commented, I've been building these engines for decades and by now I've seen so many things that were screwed up that I've learned you are asking for trouble if you don't check everything as best you can.

I had this one engine where the basic piston-in-cylinder height check was just screwball. Nothing made any sense. So, in order to prove to myself I wasn't going batshit insane, I decided to use those machine shop tools of mine and make some measurement tools that would prove whatever was right or wrong.

This one key tool has become my standard tool now for checking what all we're talking about here. Here's an image of it:




This set of tools allows the cylinder to be torqued into position and then you can measure the height the piston crown really comes out of the top of the cylinder. ...I call this the CAC. If you are using a piston of known crown displacement (the volume displaced by all the material above the deck - I now have a database of a dozen or so), you can then know oh so much more about your engine than you did before.

For example, by knowing ALL the values, and by moving the parts around a bit, you can learn of very subtle differences in the dimensions of all your parts. I used this tool to prove the the centerline of the crankshaft bearing bores in this one particular crankcase was bored on a diagonal in the horizontal plane - it started in a correct place and went hard right! Bzzzt! Wrong! But there it was!

The solution for that engine was to deck the cylinder bases to make them match the new "centerline". Optionally, one could instead crop the tops of the pistons to similar effect, but then you have a weight problem - they must be weight matched!

You can use this technique to find all these errors:

• An improperly ground crankshaft
• Unequal length connecting rods
• Unequal cylinder heights
• Unequal pin heights - the piston pin center to piston crown
• Errors in the bore for the crankshaft (shifted left or right, or angled on the horizontal
• Errors in the cylinder spigot bores (primarily their distance from crankshaft center.

...Unfortunately, these kinds of problems are not nearly as rare as we would like!...

Well, enough for now,

Good luck Jay D!

[RT]

Nice photos Jack, thanks! When will you guys be firing this new motor up?

...Justin, can _you_ see the image I tried to post in my comment here? I can't! It's bugging the heck out of me! I've tried BOTH the "Attachments & Photos" add file button and to link it to an image on a web site - I don't see either one!

Help!

[JTR70]

Thanks for your input concerning this topic Richard and welcome back; long Time. The problems you are experiencing concerning the photo attachments is most likely the web browser your using. Are you using Firefox? For some reason this browser is not very compatible with file attachments for this site. This has been a problem for a few other guys as well. I recommend IE8 or Google Chrome, this change should do the trick if not let me know. Also don't forget to hit the "insert" button on the attachment so it will display large. Justin

[Tony G]

NICE!

[Tony G]

RT,
Looks similar to a tool I made up years ago for the same purpose. One has to check, double check, and triple check everything...then one can sleep better assured.
Tony