Inliners International Forums General Discussion Engines 261 Chevy Max Overbore?

I picked up a 261 block that was already bored .060" over. The problem is the genius who did it, didn't fit the bore to pistons. The only pistons available (that I know of) are slightly smaller then .060" leaving me with .002 clearance. So now I have to go to the next size up which is .080" over. Is this a safe overbore? The block is a 59. I talked to Patricks in AZ and they said the .080 over is pushing it and on top of that the .080 pistons are very difficult to get. Two sets now on back order for about 6 months. How much piston to wall clearance is acceptable? I would think the .002 is too much.

I would keep looking for the .060 pistons before going .080 over, if thats even an option...

.002 on the skirts of a alloy cast piston is not all that bad. I guess you could put a lite knurl on the skirts if it is a worry to you. SCRAP

The Chevy dealer used to list pistons by std. or overbore with a high limit. Not sure about aftermarket on this. The high limit pistons were normally .001" - .003" bigger than a std. piston to allow for wear. If this was the case, they would work perfect for you.

The 261" truck engine can be overbored .125 W/O any problem. I have done it several times.

I have heard boasting of more but that's 'food for the rose garden'..

You can check any Motors Manual for the 'piston to wall' clearence #'s. You simply hone to get what you want etc.

Good luck.

John M., II. #3370....

Book says .0015" feeler gauge. You may be able to get "good enough" by knurling the pistons...

Option #2 is find a set of .080 over pistons. Maybe Kanter or Egge?? or $$$$ on a custom forged set from Jahns, Arias, Ross, etc..

Option #3 puch the holes out bigger and sleeve them back down to a smaller size piston.

Option #4 get another block.

Sonic testing on the cylinders should tell the story, no? My 54 235 is .080 overbore with no problems, also have read about going .125. I'd give Tom Langdon a call on this question, he may have other pistons and some good advise.

I agree with John, 1/8th over bore no sweat. 3/16's is ok on a staight block. Have you tried Egge Machine in the LA area? They list pistons to .080. If a little is good more is better and too much is just right Rick

Good luck finding +.080 cast pistons. After months of looking I was able to come up with four +.080 and two +.120 pistons.
I had the two +.120 machined down to +.080. And even the four +.080's that I did find needed to be machined to fit.
If I had it to do over I think I would put sleeves in all 6 cyl.'s and go with std. bore size, or +.030 over, these are some what easer to find than the +.080 cast pistons.
Egge list the +.080 pistons but didn't have them.
The machine shop that I had do the work had no problem finding my +.080 rings.

Hi all,

I haven’t seen the article about the Cadillac 292 from a 261, wouldn’t this block fit the bill?

I am not sure what is involved, but if you use Cad pistons you might be able to find the size you need.

Just a thought.

Luis

I think Luis has the best idea. Get some cid and get rid of some of those hard to find parts. The 3/16's overbore is fact. I didn't do it on a 261 but on a 235.