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Re: 261 Rebuild questions [Re: bigblack'74] #1311662
Thu May 23 2019 04:39 PM
Thu May 23 2019 04:39 PM
D
Dragsix  Offline
Shop Shark
Joined: Dec 2017
Posts: 432
Pennsylvania
261 blocks can be a little funky in the overbore bore department. Between the Siamese set up of the cylinders, the use that these motors were put, and the years of rust deterioration on the outside of the cylinder in the coolant jacket, going .080 may lead to more trouble then that block is worth. Generally, the 54-55 blocks, the so called first series, are the thickest and can take pretty big over bores - sometimes as much as an 1/8. The later 55 through 62 blocks, and the service replacement blocks, are all over the place. I have a 261 block that showed a rust through spot at .030. that block was a service replacement block and when I sonic checked it, yep, every cylinder was thin, too thin to go any further. Other of the later 261 blocks were fine to .060. So I think between just the bore taper from use, and the rust issues emanating from the inside of the block/cylinder, going further then .060 should really entail a sonic check no matter what series block is involved, and even then its no guarantee that a spot wont appear after the boring bar does its work even if the sonic examination suggests the cylinder can take an .080 bore.

So I might consider a sonic check as a first step before you start sinking $$ into this particular block.


Mike
Re: 261 Rebuild questions [Re: Dragsix] #1311798
Fri May 24 2019 03:28 PM
Fri May 24 2019 03:28 PM
B
bigblack'74  Offline OP
Wrench Fetcher
Joined: Nov 2013
Posts: 37
iowa
I personally honed my cylinders in our shop yesterday and they *appear* to be ok once I got them cleaned up.( zero ridge, no scratches or pitting and all mic. basically the same)

I am going to have the machine shop check them next week when it goes for hot tank, freeze plugs and cam bearings.

On a side note I did find that we had the stock 261 cam still in the motor (3836390) so I sent it and the lifters to Delta for a cleanup and light regrind. (I believe it was a stock replacement cam during the 1st rebuild as it has very little wear.)


1953 Chevrolet Handyman Wagon 36k
1938 Buick 38k
1947 Hudson Commodore 18k
Re: 261 Rebuild questions [Re: bigblack'74] #1311998
Sun May 26 2019 03:05 PM
Sun May 26 2019 03:05 PM
B
bigblack'74  Offline OP
Wrench Fetcher
Joined: Nov 2013
Posts: 37
iowa
My micrometer dimensions of the bores are as follows in order from front to back, not firing order:

#1 3.8080
#2 3.8070
#3 3.8065
#4 3.8070
#5 3.8065
#6 3.8065

I checked them each three times at the top of the cylinder with zero ridge after a light hone.

The bottom of the cylinders are less than .006 difference on all bores.

Pistons all measured 3.8035 with no material differences.

I remember thinking .005 max difference was fine for a hone and re-ring and I appear to be within that window.

Are those numbers ok or do we need to knurl the pistons?

We are at .060 on bore now and dont want to bore any further.

Last edited by bigblack'74; Sun May 26 2019 03:08 PM.

1953 Chevrolet Handyman Wagon 36k
1938 Buick 38k
1947 Hudson Commodore 18k
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