The Stovebolt Site Forums The Shop Area Engine Shop 261 to rebuild or not to rebuild

I bought a 1950 3100 1/2 ton last March and it came with a 235 that was manufactured in 1962. The engine had a few bent push rods but other than that the pistons and cylinders looked clean. However, I was after a 261 and ended up getting a 1957 261 several months later and have only now been able to break it down. I knew it was .080 over but had only been used minimally then removed and stored. Unfortuantely in those years in storage it developed some pitting in 3 cylinders.

The engine is currently in the machine shop to see if the pitting can be removed by boring out to 0.100! and Egge does sell a pistons upto this size if I do chose to go this route. The machine shop also they stated they could sleeve is necessary but that is a significant step up in cost. My original thoughts were to go with the 261 and risk the 0.100 over but keep the 235 and eventually get it up and running but the idea of putting a bunch of money and time into the 261 and having it perhaps short lived due to the large overbore and/or sleeving is concerning. Thoughts?

Thanks

It would be a LOT smarter and less expensive to sleeve the pitted cylinders and re-use the pistons you have already. A 3/32" wall sleeve won't require much more machining, and it's likely that the metal in the sleeves will be better quality than the original block material. I've run small block V8's with all eight cylinders sleeved back to standard bore, after competitors on the race track were ready to discard a "worn out" 60 over engine. After they started getting beat by their own junk, it got hard to scavenge anything, though!
Jerry

I ran into a similar situation not too long ago and Jerry helped me sort things out.

I had found a 261 block without the head half buried in the desert. Once I blew all the sand out of the cylinders, I could see that they were pitted. The block had been bored .060. The pistons were shot.

I confirmed, as you have, that Egge carries pistons and rings in .080 and .100 sizes for the 261. My machinist bored out the cylinder with the worst pitting to .080 and didn't get past the pits, so he bored it to .100. There were two pits that were still questionable, so I had the engine sleeved.

Different than you, my pistons were shot and needed to be replaced.

When I had the block sleeved, I had it bored out to standard size. That way, someone in the future could get more rebuilds out of the block.

Some of it comes down to economics. The .080 and .100 pistons from Egge run about $250 per set. The rings are a bit expensive, too. A set of standard size Federal Mogul pistons can be purchased for about $125 per set if you look around and the rings are less expensive. Same think with .020, .040 and .060 sizes. It's the .080 and .100 sizes available through Egge that get more expensive.

It would have cost me $80 to get the block bored. It cost me $520 to get all six cylinders sleeved. So I paid about $645 plus the cost of the rings for the sleeved block with the new pistons compared to what would have been $330 for boring and the pistons if the .080 or .100 boring would have worked.

I'm glad that I got the block sleeved. The question you will need to answer, as Jerry points out, is whether to get the newly sleeved engine bored .060 so that you can reuse your pistons or if you want it bored to a smaller size. It's about a $125 question because you will need new rings regardless. Want more displacement with fewer future rebuilds on the block by using the .060 pistons that you have or do you want more chances to rebuild, are OK with the stock displacement and are willing to pay $125 for new pistons?

Hope this helps,

Matt

Good advice, except his engine is bored 80, not 60. The same logic applies, as the cost of a set of pistons can be deducted from the sleeve cost if they can be re-used. Sleeving only 3 holes and recycling the pistons would be the least expensive way to go in this case. One thing I don't have to consider is machining cost, since I have my own boring bar(s) and cylinder hones, so the only cost involved is buying the sleeves. I realize that's not the case for everyone!
Jerry

As much as I would like to say, devil may care go the .100, in my heart I just cant because I would not do it myself. I am a .080 man. That is the most I am really willing to go with either 235 or 261 blocks. A .060 over 261 is not terrible so I am with Jerry, sleeve what you need to sleeve to get them all to .060. The extra cubes over the 235 are worth the aggravation of saving that block and as you know, these 261 blocks have gotten hard to come by.

READING
IS
FUNDAMENTAL!

His block is 80 over, not 60! Fit three 3/32" wall sleeves, bore them 80, re-use the pistons, and put the thing together!
Jerry

Well then I guess I am not all that fundamental, lol.

Thanks for all the great advice guys.

I spoke with the machine shop and he was essentially trying to keep costs down and thought a new set of pistons for 290 was cheaper than sleeving and decking. He also expressed some concern about sleeving two of the side by side pistons. I forget the reason he said I think it was warping?
I appreciate him trying to keep cost down for me but if I could sleeve with no deleterious effects and possibly get another bore out of it in the future I would prefer to spend the extra money now.

Thanks

a .100" oversize for a street engine is a big mistake, in my opinion. I've seen race built 235's bored .125 over, but those engines aren't expected to last long. 261's have "siamesed" cylinder pairs, meaning that two cylinders share the same casting- - - -no gap between cylinders 1 and 2, 3 and 4, and 5 and 6. Block warp isn't going to be much of an issue if any of those pairs happen to get sleeved because one cylinder braces the other one. The stovebolt block is extremely rigid anyway, not at all like the thinwall cast blocks made in the past 30-40 years. Which cylinders are pitted badly enough to require sleeving?

Another thing to consider- - - -if your machinist is only going to increase the bore size by another .020", that means the pits he's trying to remove can't be deeper than .010"- - - -that's all another 20 overbore is going to cut on the radius. I think that's a very bad gamble.

Here's a suggestion- - - - -ask your machinist how many sleeves he's installed in the past year or so- - - - -the answer might give you an idea whether or not he's familiar with the process, and possibly an insight into why he's reluctant to try it. Doing it right is a disappearing skill set.
Jerry

In the case of a stovebolt, are you sleeving and then boring the sleeve to finished dimension? Or buying a specific sized sleeve that fits pistons?

I’ve always assumed the former, but I also know they sell matched sleeve and piston kits for lots of old tractors.

I am also assuming that the three pitted cylinders will be sleeved then rebored to fit the .080 over pistons that i currently have. I'll ask the shop how they are going to do it and let you know.

Thanks

All repair sleeves are sold "semi-finished" as in several thousandths smaller than the minimum diameter. Then it's bored to whatever size is required to fit the piston. For instance, a sleeve for a 261 will be about 15 or 20 thousandths smaller than the standard bore- - - -3 3/4". After installation it gets finish-bored and honed for proper piston fit, standard or oversize. The cylinder actually gets bored twice- - - -once to provide about a .002" interference fit so the sleeve has to be driven in with a BFH and a piece of steel plate on top of it, then the boring bar is set up again and the sleeve is cut to about .002" or a bit more short of the desired finish diameter. Then, the sleeve is honed to the final diameter, removing the machining marks of the boring tool and establishing the proper cross-hatch pattern in the cylinder for ring seating. That's why half-donkey machinists don't like sleeves- - - -they're too much work to install properly!
Jerry

Maybellene/Jerry,
Hadn't considered sleeving all of the cylinders and bring it back to stock or a little over. The longevity of the engine would vastly improved and it would have more opportunities to be rebuilt if needed in the future, as you stated. Of course that is the most expensive route and would require a new set of pistons. I'm trying to keep this project on a minimal budget overall but there are things I don't mind splurging on if I don't have the skill set to do it or it is just the smart thing to do.
Eric

Eric, either option works.

Using the numbers that I provided in an earlier post, it cost me about $90 apiece to get each cylinder sleeved. If you sleeve three cylinders, that's $270. And let's say your machinist will hone the other three for $25. That puts you at $295 if you have confirmed that you can reuse the pistons and that the other three cylinders are OK.

If you get all six sleeved, once again using my numbers, it will cost you $520 for the sleeve job and $125 for pistons for a total of $645. The difference is $350.

IMHO, the better way to go in the long term is to get all six cylinders sleeved and bored to standard. That basically gives you a new block that can be bored out four more times....020, .040, 060 and .080. That's the better long term approach.

But the long term approach has a price tag of $350. Is it worth it? That's an individual decision that only you can make.

I am running a '64 replacement block 261 bored .080 in my '57 3600. As others have stated, I would also be apprehensive about going with a .100 overbore. You will find posts on this forum advising against a .080 overbore, never mind .100. I'd probably sleeve after the .080 wore out instead of going .100. And, yes, I was aware of the advice against taking a 261 out to .080 when I made the decision to do it, but I did it anyway.

Let's say you get the three cylinders sleeved now to save money. Nothing wrong with that. Jerry or others with more expertise than me can advise as to whether or not the entire block can be resleeved the next time around with all new sleeves (meaning can the three resleeved cylinders get sleeved again?...and fresh sleeves in the cylinders not done). It might be a moot point for you depending on how long you plan to keep the truck, but it might give you peace of mind if you go the inexpensive route knowing that you or the next guy still has options to use the precious 261 block again. Or maybe the next guy can throw caution to the wind and have it bored .100...

Matt

Re-sleeving a cylinder is a risky business- - - -getting the old one out without doing damage to the block is a tricky process. If you choose to sleeve all the cylinders, skip around. For instance, start by sleeving cylinders 1,3, and 5, then go back for 2,4,and 6. There's less chance of stressing the block and creating a warp that way. Back when I was teaching machining and had all the equipment I needed and students to do the grunt work I did a lot of sleeving. When someone at the race track was ready to discard a 350 Chevy block he thought was "worn out", I'd gladly take it and sleeve it back to standard bore. All the expensive prep work had already been done- - - -line boring, decking, etc. Some blocks had even been smoothed up inside and painted with oil-proof Glyptal transformer paint for better drainage back into the crankcase. I was glad to save those blocks from the scrap heap. Eventually some of my competitors figured out they were getting outrun by their own junk, however!

Since labor cost has to be factored into most folks' budget, stuff I would do routinely has to be reevaluated in terms of cost VS benefit. Not everybody has a boring bar stashed away in the corner of the shop!
Jerry

Heard back from the shop the other day and they found the other 3 cylinders that looked good were actually a larger diameter at the top. The mechanic stated he thought it would be good for awhile but would eventually cause problems, also one of the main were scored and would require boring. All in all he thought if I was to stick with this engine it would be best to sleeve all 6 and of course bore the main.....1100 dollars, ugh. So now I have three choices, 1) sleeve it and bore to original an buy new pistons, 2) use my original 235 which actually looks decent besides the bent push rod or two that looks like a mountain curve. It would obviously need work but cylinders and pistons look good or 3) buy another 261 that is available but of course it isnt running. I really would like a 261 but dont want to toss more money at another risky engine.

Or you could get a GMC and fit into your engine compartment.

Ed

Don, I'm confused about 'bore the main'. Are you saying that one of the main bearing journals on the crankshaft is scored requiring the crank to be turned? Or do the mains need to be line bored?

If the crank needs to be turned, that's not uncommon and nothing to be afraid of. Line boring is much more involved, not just in the process itself but the resulting relationship of the cam and crank timing gears.

The 235 you have uses the same crank as the 261, so you could check that one out to see if it is in better shape. You might find that it can be used as-is or simply needs to have the journals polished with 600 grit emery cloth, a process that you can do yourself to save some money.

Sounds like rebuilding your 261 or buying another one will cost more than reworking your 235. Only you can determine if it's worth it.

Matt

It sounds like you need to consider finding another machine shop. Details like you're describing should have been discovered early on, not well into the job like it appears is happening. How much taper is there in the supposedly marginal cylinders? If it's .005" or less, a re-ring job won't be a problem. Honing a little taper out and putting a slight knurl on the piston skirts to re-establish the proper clearance is a procedure that was done routinely for decades. It looks like they're searching for reasons not to continue, which just might affect the quality of the finished product. The only reason I can think of for line boring would be if a main bearing had spun, or failed in some way that scores the block. A scored crankshaft can be turned to the next standard undersize, or replaced. The dimensions of a 261 crank are the same as a 235, and the cranks are interchangeable, but the 261 has a forged, not cast crank. That's not an issue unless you intend to use the 261 as it was designed- - - - -long periods of full throttle operation at or near its top speed, pulling heavy loads in low-geared big trucks. Very few of us hobbyists will ever use our engines that way.

Where are the rust pits located, the ones that began the discussion about sleeving? If they're not in the top 2" of the cylinder, shallow pits don't necessarily make a re-ring job impossible. At worst, pits lower in the cylinder might result in a little oil consumption, but they won't promote blow-by or cause a power loss. If you're building an engine that will be in a daily driver, of will be called on to pull heavy loads routinely, do a top-quality rebuild. If you're building a weekend cruiser or a trailer queen that gets hauled back and forth to car shows, just make sure the engine will run reliably- - - - -you'll be changing oil on a time schedule long before it runs enough to use a quart caused by cylinder pits.
Jerry