The Stovebolt Site Forums The Shop Area Engine Shop 261 Rebuild questions

I have several questions as I begin a 261 Rebuild.

Are there .070 pistons still available?
We are on .060 bore and it's not great looking and am not sure we can get away with a hone job.

What is max safe milling on head and block WITHOUT modification to pistons to clear valves?

I assume we use all our clutch and bell housing from the 235 in the car now? Can I use a larger clutch inside stock 1953 235 car bell housing?

Thanks

I myself have not seen 0.070 pistons but could be wrong. Going to .080 might be the only way.

To the bigblack, dont be driven off so fast, your 261 needs the cylinders sonic tested to see if you can over bore it that far. That is if you can even find .080 pistons, I know .030 and .060 are available for the stock 3.75 bore. Im in the middle of my 261 rebuild now. You might need six sleeves, then open your wallet for that one.

Maybe Pre68 Dave will chime in, or machinist Jerry

Steve

I’ve always been told that .060 is a usable limit. The walls aren’t too thin and reliability is still there. If you do a search I bet you’ll find more to read. I have 0.060 pistons in my 261 and it runs very well.

If the OP is still monitoring this post (I hope so) drop me a PM. I've got a few constructive suggestions.
Jerry

Assuming the question of 261 overbore is still of interest... Egge lists 0.080" and 0.100" oversize # L2033-6 pistons as available. Agree that sonic testing would be a good thing before going that far, as Steve suggested. Egge isn't cheap, but probably cheaper than 6 sleeves, if the block is good for the overbore, I guess.

Thanks, drdoug,

It would be nice to hear from members that have a 261 with 0.080"/0.100" overbore/oversize.

Hi. O.K. I cleaned out the stalls here of the fresh manure, dunno what all that was about.


To clarify a few things though:

The founders/owners/editors of Stovebolt.com have always allowed discussion of the bits and pieces that are shared between the trucks and cars that fall into the pre-1973 category. Things like the engines, transmissions, axles... the drivetrain basically... maybe the heater assembly or the electrical system.

They are aware that some Chevy/GMC truck folks have old GM cars as well and would like to ask their stovebolt buddies about their engines or what not. As long as the post is about the bits and pieces and placed in the appropriate forum and it is disclosed it is about a car or wagon whatever, there is no issue.

Now, if someone started a whole thread about their non truck project, that would probably get the ax.

The original poster did nothing wrong asking for information about their 261 engine which clearly falls within the purview of the 'bolt and more specifically here within the engine shop.

Please help them out with any information you may be able to share.

Carry on and happy wrenching.

-Woogeroo / The Engine Shop moderator

Bigblack, check this out if you haven't already, there is a segment on cylinder bore taper too, a good read.

https://www.stovebolt.com/techtips/engines/261%20rebuild/index.html


Steve

Woogeroo, if there was a like button I'd apply it to your post.

Carry on
Dave

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.

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.)

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.

i just built a 58-62 261 engine, my block is bored for 0.100 pistions, my machineist had to go after market for the rings. my main guestionin off topic to WOLFCUB- i want to know if you still have and sell the carter/weber sync adapters for the dual carb set up, i am a new member and have been reading abouy you kit , thank you mike gannon

Knurling Pistons is just a band aid solution, do it right.

Ed