The Stovebolt Site Forums The Shop Area Engine Shop 261 pistons in a 235 engine

I have a 1956 235 engine which I plan upon rebuilding and installing in my truck. The head was just rebuilt in SS valves, and it turned out fine. I dropped the block off today at the machine shop, and received the bad news. The cylinders are circa .140 over.

I thought that this left me with a mighty good boat anchor, but the machinist hit the books, and after a while declared that the pistons from a 261 will work.

Have any of you Stovebolters had any experience with a modification like this? If I go ahead with this plan, should I also change to the beefier 261 connecting rods? Is it worth the time and money, or should I just look for another 235 block?

Are the cylinders .140" over or .040" over? If its .040" over, you could bore it .060". .060" pistons are available for 235s. I run a .060" '60 235 in a '54 Bel-Air. If the engine is actually .140" over, then the block is toast. You'll hit the water jacket trying to go any further. Some old 235s could be bored to .080" to .125". Never heard of one at .140" over. Thats insane, as 235 cores are still available.

chip

Are you sure your engine is not a 261?

Hi Chip and Dave,

No mistake, the dirty numbers, with carbon, run to about .140. If it were a modern engine, I would trash it. As it is a 48 year old engine with about 1/4" of metal left in the cylinder walls, the machinist was making sense.

He is the machinist for most of the local hot racers at Englishtown Raceway, and he has a long, and hard earned, reputation for turning small block Chevy's into nitro burning, 400 CID, fire breathing race winners. I know that I just want a street and highway driver, that will last a few more decades. In most respects, that is not the same as a win at all costs, cutting edge technology, one engine per race, deep pocket racer. That is what prompted me to post my question.

I forgot to mention that the serial number on the block is 3837004. According to inliners.com, that is a 1955-1957 235 CID Chevy six.

261 pistons have larger wrist pins than a 235, .060 bigger in diameter.So if you could put in 261 pistons you have to bore out the small rod end, or use 261 rods,the big ends are the same diameter.Looking at a 235 rod, there ain't much on the small end, never mind removing material.
Instant ID on a naked 261 block is the 6 small steam holes in the block deck between the inner cylinders.
Used to be the maximum safe overbore on a 235 is .125,and that depends on an absolutely perfect block with no core shift.
Best to toss the block, they are out there to find, just check the Swap Meet here on Stovebolt.

Thanks gentlemen, and good Stovebolt peoples. I tend to agree with you. I don't want to be the first kid on the block with a super bored 235, that will not last a month.

261's have siamesed cylinders to get enough metal in there. I would find another block, there are plenty around.

Just out of sticks and giggles, has this block been sonic-checked for thickness? And its .140" over? Whats the history of this engine?

chip

Yeah, what brand of pistons were in there?Never seen 140 over ones, maybe from a different engine? Maybe the guy before bored it our for sleeves?

The block was a $50.00 ebay steal deal. It was a very long block engine; fan to bell housing, and everything in between. So I am not complaining. I got my $50.00 in spare parts alone.

The guy I bought it from took it out of a '46 Chevy coupe which was used for racing. The engine was built in late December of '55.

Yesterday, it was determined that it was the mike which was off. Way off. The block can be bored out to a 235 @ .80 over.

Crank journal #6 is gouged, and it will have to be ground down a bit. The cam is toast, so I ordered a new cam thrust plate, and pushrods from Patrick's.

Sonic testing, and boring if it passes the sonic test, will take place next week.

If you had to the block could be sleeved.

I sleeve "worn out" 350 race engines back to standard diameter all the time. It's a bit pricey if you have to pay a machine shop to do all 8 sleeves, but I've got a boring bar, and the sleeves aren't that expensive. I've got 4 or 5 4-bolt main 350's that have been given to me by racing buddies, with either a little chip missing from the bottom of a cylinder where a rod let go, or they've been bored too big to rehab. It's fun, beating somebody with his own junk parts!
Jerry

Hey Hotrod,

I discussed the concept of adding sleeves with the machinist. He kinda wrinkled his nose at the very idea. What gives? Do the sleeves not stand up for street use? Are they good for just short fast afternoons at the track? Or, is the problem that they are just too darn expensive to justify on anything but a 1909 Hudson Model 20?

Prolly cuz the cost of having a shop install 6 sleeves is more than finding a good block and rebuilding it. I ran into the same thing with a Pontiac 428 block. The cylinders were std bore, but so rust pitted it'd need 8 sleeves, 16 lifter sleeves, plus heli-coils and line boring. It was cheaper to find a better core to build.

chip

Actually, the sleeves are made of better material than the original iron in the block. Some machinists claim it weakens or distorts a block to sleeve all the cylinders, but some of my all-sleeve blocks win races regularly, and show no measurable difference on a dyno run to a non-sleeved block. I usually bolt up a "stress plate" on the block in place of a head before boring/honing, which minimizes any distortion, and skip around, boring/sleeving two cylinders on one side, then switching to the other cylinder bank. In a production shop, it would be prohibitive on the labor cost, but I do a block a little at a time between more pressing jobs. Over a couple of weeks' spare time, I've got a standard-diameter block built up, that can be used whenever I need one. Considering that some of the engines I build are in the $15,000.00 bracket, a little time spent sleeving one is negligible in the overall cost factor.
Jerry

My son in law ran a 26 foot cigarette boat with a full house Maynard Troyer 572 big block.He got a bad load of fuel, dentonated two pistons away and cracked the bores.He had the two cylinders sleeved, the machinist said to take it easy on the motor. But the engine lasted another season of typical boat abuse befor he sold it.