Offset Cylinder Boring

Posted By: TrWaters

Offset Cylinder Boring - 02/06/11 09:14 PM

I searched for an hour on here and found many references to offset boring of cylinders (side to side....not front to rear) to compensate for block core shift, but nowhere did I find what might be considered an acceptable (or maximum) amount of offset. Are there considerations other than the combustion chambers? Thanks.

Posted By: B G Racing

Re: Offset Cylinder Boring - 02/06/11 09:44 PM

Boring parallel to the centerline of the crankshaft

Posted By: CRE2004

Re: Offset Cylinder Boring - 02/06/11 09:51 PM

I don't understand your statement/question. What are you looking to do? The "acceptable" level of offset would depend upon the available material thickness. Then keep in mind you'll have to make sure you have piston pin boss to rod clearance. I've moved them up to .060".

Posted By: Crizila

Re: Offset Cylinder Boring - 02/06/11 10:55 PM

Quote:

I searched for an hour on here and found many references to offset boring of cylinders (side to side....not front to rear) to compensate for block core shift, but nowhere did I find what might be considered an acceptable (or maximum) amount of offset. Are there considerations other than the combustion chambers? Thanks.

I'm running a 71 360 block with one hole offset bored with no problem. Wasn't done for core shift though. Had some detonation problems with a 408 motor that was already .030 over. Broke a top ring land and did minor bore damage. Had the hole bored for a .040 over slug to fix the damage ( .009 on the damaged side and .001 on the good side. Worked great. I guess I'm one of the few guys that is running a 410 ( or there abouts ) stroker motor.

. If I remember, the damage was towards the front of the block, but I would guess you could easily get away with that much offset ( and probably more) anywhere 360 degrees in the hole.

Posted By: polyspheric

Re: Offset Cylinder Boring - 02/06/11 11:07 PM

The change affects the clock position of that piston vs. its crank throw.

Assuming the pin eye as the focal point, an RB has a radius of 1/2 stroke + rod = 8.635", = 54.255" circumference circle, = .151" per degree.
That makes any re-location almost invisible, like .030" is 1/5th of a degree.

Someone check my math, please?

Posted By: DavidDean

Re: Offset Cylinder Boring - 02/06/11 11:28 PM

Good Post Im having to offset the bores of my X block. Im having to shift to the front about .050 to correct wall thickness.There's also some good reading at speedtalk.com.

Posted By: TrWaters

Re: Offset Cylinder Boring - 02/06/11 11:46 PM

Quote:

I don't understand your statement/question. What are you looking to do? The "acceptable" level of offset would depend upon the available material thickness. Then keep in mind you'll have to make sure you have piston pin boss to rod clearance. I've moved them up to .060".

By acceptable I meant before other issues would come into play. But as Jeff posted, it is a non issue.

Thank you.

Posted By: MR_P_BODY

Re: Offset Cylinder Boring - 02/06/11 11:46 PM

Quote:

Good Post Im having to offset the bores of my X block. Im having to shift to the front about .050 to correct wall thickness.There's also some good reading at speedtalk.com.

I dont understand... why not just sleeve it

I knew if you wanted a big bore they did it but to
correct for core shift or a broken cylinder I would
have thought just sleeving it would do

Posted By: Oyvind Mopar

Re: Offset Cylinder Boring - 02/06/11 11:55 PM

Should not be an issue. The factory did move the c/l of the pistonpin .060 to the side, and some have turned this the other way around, and other pistons do have them in center. So the geometrical difference would be similar to offset boring to the sides. I have salvaged many cylinders by offset boring. My

Posted By: TrWaters

Re: Offset Cylinder Boring - 02/07/11 12:35 AM

This particuliar block has good numbers on the outside walls.... drivers minor thrust and passenger major thrust, with fair numbers down the inner walls. Thanks for the replies.

Posted By: DavidDean

Re: Offset Cylinder Boring - 02/07/11 05:39 AM

Quote:

Quote:

Good Post Im having to offset the bores of my X block. Im having to shift to the front about .050 to correct wall thickness.There's also some good reading at speedtalk.com.

I dont understand... why not just sleeve it
I knew if you wanted a big bore they did it but to
correct for core shift or a broken cylinder I would
have thought just sleeving it would do

In my case I would have to sleeve 4 cylinders and this X block hasnt been bored at all

Posted By: mr_340

Re: Offset Cylinder Boring - 02/07/11 06:50 AM

Quote:

Boring parallel to the centerline of the crankshaft

I'm curious to what Bob has found by boring offset to the crank centerline? Does this allow a better push on the piston for more torque? I heard the PS guys were doing it several years back. Any results that can be divulged?

Posted By: B G Racing

Re: Offset Cylinder Boring - 02/07/11 10:41 AM

Quote:

Quote:

Boring parallel to the centerline of the crankshaft

I'm curious to what Bob has found by boring offset to the crank centerline? Does this allow a better push on the piston for more torque? I heard the PS guys were doing it several years back. Any results that can be divulged?

It eliminates any odd angle loading(friction)caused by the bore location and allows all pistons and rods to traval in the same plane or designed angle. .Any time you can decrease friction you can gain RPM,HP,TQ.