Core Shift Data
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Joined: May 2001
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From: Puyallup, WA
Core Shift Data
Measured for core shift on my would-be 6.5 liter motor, and it looks like I'm a little short. In going through some of the rennlist postings I've saved regarding minimum required wall thickness, I had one source post that .250" is the minimum thickness stated by the manufacturer, but that they had gone down to .220" without a problem. Mind you, the blocks weren't designed to be taken down this far, so you do so at your own peril.
Using the .220" minimum wall thickness, which is the extreme, and adding 2mm (.0787") to it (which is half of the 4mm overbore), leaves you with a minimum .2987" wall thickness to start. Using the .250" manufacturer's minimum leaves you with a .3287" minimum wall thickness to start.
Attached below are the wall thickness measurements I took. The top measurement is about an inch from the top, the bottom measurement is about halfway down the bore. The measurements on the left are the wall thickness, and the measurements in parenthesis are what would be left after removing 2mm from the bore job. Hole 1 and 3 are right on the minimum, hole 6 is .005" to thin, hole 7 is .001" too thin, and hole 8 takes the cake being .013" to thin. I'll be reassessing my options here, but at this point it looks like this particular block is only going to be good for 6 liters.
I'm open to any questions or comments regarding my math or methods.
Using the .220" minimum wall thickness, which is the extreme, and adding 2mm (.0787") to it (which is half of the 4mm overbore), leaves you with a minimum .2987" wall thickness to start. Using the .250" manufacturer's minimum leaves you with a .3287" minimum wall thickness to start.
Attached below are the wall thickness measurements I took. The top measurement is about an inch from the top, the bottom measurement is about halfway down the bore. The measurements on the left are the wall thickness, and the measurements in parenthesis are what would be left after removing 2mm from the bore job. Hole 1 and 3 are right on the minimum, hole 6 is .005" to thin, hole 7 is .001" too thin, and hole 8 takes the cake being .013" to thin. I'll be reassessing my options here, but at this point it looks like this particular block is only going to be good for 6 liters.
I'm open to any questions or comments regarding my math or methods.
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Joined: May 2001
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From: Puyallup, WA
That's a great question Glen, I'll do up some measurements. I was assuming a 100mm bore (pistons are tolerance group 1), but you're right, I should measure and see how big they actually are. Maybe I'll get some of the distance back.
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Old post brought back to life 
So what is the min. wall thickness? Actually to ask a more accurate question, what is the min. people have done on a N/A running stroker motor ?
I have an 85/86 block that I started to measure and the thickness varies all over the place.
I question how I can get an accurate measurement with a set of good calipers. The outside of the bore is a pretty rough casting.
Any recommendations on a good place have the block bored?
What is the bore tolerance using the 968 pistons, same as the 968 spec.?
So what is the min. wall thickness? Actually to ask a more accurate question, what is the min. people have done on a N/A running stroker motor ?
I have an 85/86 block that I started to measure and the thickness varies all over the place.
I question how I can get an accurate measurement with a set of good calipers. The outside of the bore is a pretty rough casting.
Any recommendations on a good place have the block bored?
What is the bore tolerance using the 968 pistons, same as the 968 spec.?
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From: Anaheim California
John V. I really do not know how many blocks have actually been bored to 104 , 104.5 . BUT I do not think that very many have been . Engine Dynamics in Garden Grove , California has done some for Mark / Joe Fan .
