The Stovebolt Site Forums The Shop Area Engine Shop New guy with old questions and gratitude

Hi all, I think I have read all of the posts on this forum and have found that the level of stovebolt expertise (not to mention the kindest hospitability) to be overwhelming. I especially appreciate the way the wisest responders answer the questions that have been asked a thousand times, without much ado or repremanding. To me, somehow, it is reassuring to hear the same answer over and over again. I am really that inexperienced with these engines........If that doesn't grease the skids for the following questions, I don't know what will: I have 2 1959 to 1962 261's, only one of which is restorable. Both crankshafts have varying size main bearing journals (if journals is the right term). The journal measurements of these shafts are so similar, it seems impossible that they could have worn that way. I have looked for new main bearings with this same variation in size, with no luck. I need to have one of these shafts turned down to accept new bearings. I don't know enough to ask a sensible question, do I? Anyway, the last three numbers on my block are 717, I can get the whole number if necessary. The number on the head of one engine ends with 848, the other is 850. Here is my embarrasing question: Do automotive machine shops know how to properly turn these old shafts to accept new main bearings, if they exist? where to get them? Any other question that I should have asked but didn't? Thanks

All 54-62 crankshafts will interchange in '54-62 blocks. 235s have "tapered mains". This means that the main journals of the crank get larger in diameter from front to back. They were designed that way. The #1 front main is the smallest and the #4 rear main is the largest. Take all parts to a good machine shop, they'll know what to do. And if they don't, they aren't a good shop. These motors are still very common (for an old motor) and a good shop will have seen one in the past couple of years.

The '848' head is the one to use, its got slightly smaller combustion chambers, yielding better compression. Make sure all parts are magnafluxed for cracks. All bearings, gaskets and other parts are readily available for 235s/261s, thru NAPA or online stores.

good luck

chip

not being an engine guy I can't say anything, except Chip: does any of that change if he asked about 261's not 235's?

Bill

Since the 261 is the truck motor brother of the 235, I assume the same holds for them as far as crank design. Unsure if its the same crank as 235 or if the 261 had a longer stroke. The heads will interchange, except for the steam hole issue. The differences are that the 261 used a full-flow filter, and had a later lifespan, like 55 or 56 to 63. I think the 261s all had 12 volt electrics and 2nd series oil/water pumps. But never having worked on a 261, this is mostly parroting others here. But I would assume that all 261 cranks/rods should interchange in a 261.

Back to original poster RonB, keep asking questions here, as there are about 20 different modifications you can do to a 235 (or 261) before you assemble it to make it run better and last longer.

good luck

chip

The 261 and 235 cranks are identical, the GM replacement part number is the same for both.The only real difference is the connecting rods and pistons and of course the block.An 848 head on a 261 will give about 8.75 -1 actual compression ratio, need to drill the steam holes the same as the #850 261 head.

I read on Inliners it seems all Canadian 261's came with factory predrilled 848 heads.

Ron - There are still some shops that can work on the 261. Best thing to do is look in the phone book and call around. If we know where you are there might be another bolter in your area that knows of a good shop nearby.

Tony's right on the crank and heads. The 848 is the preferred head. If you have checked yet, go to http://www.inliners.org and check the casting number on your block. Should be just above or behind the starter. I don't know if that's the 717 number you're referring to, but it doesn't hurt to be sure you have a 261 block.

Another suggestion is to get a factory repair manual that includes the 261, if you haven't already. Lots of good info in them.

Good luck.

I don't want to highjack this post, but... Why did they use bigger bearings front to back? Was there a clearance issue with something? I know some camshafts use different bearing sizes but I never heard of crank that way. Joe

I think they do it to reduce the rotating mass and friction of the crankshaft. Smaller bearings create less loss. The rear bearings have to carry more torque than the front ones because they have more cylinders twisting them. The front one only has to carry cylinders 1 and 2 and the accessories and harmonic vibrations. The second one has to carry cylindsers 1, 2, 3, and 4, and the third and fourth bearing carry all six.

Some 261's had full flow oil systems but most didn't. When I rebuilt mine I found that because it's a truck engine I had to settle for cast pistons and chrome rings, which I would rather had forged pistons and moly rings, but it works okay. I was told that the 235 head would raise the compression by a half point but no one mentioned the 848 casting. These are high nickel content blocks and wear like iron.

[IMG]C:\Documents and Settings\Dale\My Documents\My Pictures\My Pictures\61 Chev.PU[/IMG] Here's a picture of my balanced & blueprinted 261. Clifford 4 barrel manifold with 500 cfm Carter carb. Hedman cast iron headers, Wayne polished aluminum side cover and rocker cover, HEI ignition, Schneider custom cam kit,and full flow oil system.

So much for the picture. I'll have to figure out how it's done.

To THEWRENCH,
It can't be done from your computer. The picture must be uploaded to the internet.