Inliners International Forums General Discussion Engines Sleeeving a 261

I have a 261 that is .080 over and three of the cylinders need to be sleeved due to deep pitting. I am debating on whether or not to sleeve all 6 or throw in the towel on this block since it also needs a line bore. Can someone elaborate on whether or not it is a good idea tosleeve something that is already .080 over and if there are concerns with sleeving all 6?

I have heard that the metal used in the new sleeves are superior and would actually function better than stock. Plus the added benefit of going back to the original bore for more life. Two shops that can sleeve and line bore are quoting 1000 for all 6 and the line bore... kinda pricey and the rebuilding is just starting. I have been looking for other 261s but they aren't easy to find.

Thanks !

You posted this over at stovebolt and I wanted to say a little more over there but just was not possible. Here is my take on this. It is possible to run that block to .100. You would want to sonic check the bores. I have a 261 in the back of my garage that I had checked and it would theoretically go to .100. Needed .030 to clean it up. Got to .030, started to see rust staining on the fresh bore from the cylinder itself. That was it, that block would need sleeves to go any further. Myself, I do not like to go any further then .080 which is where you are now. So just from this point, you could bore to .100 and get new pistons, or install three sleeves and use your .080 pistons.

Yes, you can sleave the entire block back to standard. It’s expensive no doubt but it is not an unusual procedure. You would be what they call dry sleeving (overboring the cylinder and installing a sleeve within the overbored cylinder) as opposed to wet sleeving (essentially removing the old cylinder and replacing). No issues in my mind except for the cost. Once done, you have nice round strong correctly machined cylinders with plenty of meat for another couple of rebuilds. I might go for that my self because I agree those blocks can be a bit of a pain to come by but the cost vs. replacement may not balance.

The deal breaker for me is the misalignment issue you apparently have with the mains. These 235/261 motors have their peculiarities. One of which is the fact that each of the mains is a different size. So in order to do the job, you have to set the block up on center, machine some material from each cap, and then machine each main saddle individuallly, hoping that you can take as little material from the block side of the main saddle as possible. The time for set up and machine work is expensive. If the block is in really bad shape, a pretty good amount of metal from the block side will have to be removed. Now, that in it self is not unusual for a lot of other motors but with theses motors it presents a few little issues.

As you know there is no timing chain on these motors, just what Isky used to call immaculate timing, gear to gear. When the crank gets moved more into to the block, the crank also gets closer to the cam. So you run into head long into gear tooth interference with the cam and crank gear, depending on how much the align bore moved the crank toward the cam. For a 235 with a fiber cam gear, ignoring that issue is usually catastrophic. The cam gear disintegrates with the gear teeth shoving too deeply into one another. Once that happens, you promptly bend a couple of push rods and intake valves. With the use of an aluminum cam gear, not so much but you still have the gear teeth meshing and stressing and possible breaking, noisy, metal particles, eventually leading to the same result. So the cam gear/crank gears have to be clearanced.

Now you will need to degree in the cam after you have clearanced the gears. With that kind of movement, the cam timing events may end up being off a bit. So to get it right, you have to sort out where each event, exhaust and intake are happening, sort out where they should be happening, and the send the cam out to a cam grinder for correction.

Then you have to deal with the rear main seal. If it’s an early motor, no issue, you just cut the rope seal a little closer, but if a later motor with a neoprene seal, you have to modify the neoprene seal, and hope you got it right, not to much off the ends of the seal, and not too little, otherwise leaks. The other alternative is to use the rope. So, it’s not just the expense of the machine work to take into consideration lots of other stuff. For me and maybe you too, this is too much work, money, aggravation and potential trouble. Believe me, there is nothing worse then having to pull a motor multiple times to fix or trouble shoot a bunch of problems.

Just as an FYI, I have built a lot of these motors over the years, close to 50 (all as a hobby, not professionally). I have never had a 235/261 block that needed a main bore alignment. Frankly, I am pretty sure if and when I ever do, I will take a pass on doing it. It’s just not worth the trouble, expense and effort. You will be Way ahead time and money wise by hanging in there and finding another block. With a block in better condition, you can do a basic rebore, machine the top of the block, new pistons, and you have your self some good bones to work with.

I apologize for not saying a little more on this to help you figure out which direction to take when you first asked your question over at stovebolt but holy cow, could not get a word in edgewise without getting bazooked, lol. Whew.

That being said, if you look at our classified ads, there is a member who is selling a couple of 261s. Maybe he has one for you!

Nothing wrong with boring the block beyond .080" as long as you sonic check it and have adequate wall thickness. Having to sleeve all 6 cylinder plus a line bore expense is an awful lot to sink into a block. There has been 261's for sale in the classified section recently, so you look to that as an alternative. Since this block is already .080", the shop could bore into the water jacket when boring to install a few sleeves. The sleeve is only as strong as the metal supporting it from behind. And if you expose the water jacket behind the sleeve, it can lead to other problems. Boring it to .100" or even .125" over as long as the cylinders are thick enough is better than re-sleeving with the water jacket exposed to support the sleeve.

mdonohue05 what are your thoughts on using a crank from one block to another block? Think the align bore is a must then? Im in the same boat with one of my 261 blocks also being at 80 over. I know caps are a issue and should never be transplanted from one block to another without a align bore.

I have never had a 55-62 235/261 block that needed an align bore. It’s really pretty rare for these early 6 motors. Yep, no changing the caps. Each block was machined with the cap in place so the caps are specific to the block. No, no need to align bore simply because you are changing cranks. My 59 Canadian 261 block has a crank out of a 56 235 in it. But I was particular when I machined the crank. The crank had been through another motor of mine so it needed a full redo. Ended up .030 on the rods and mains. Had the throws equalized, and the crank was ground at 120 degrees. Drilled the snout for a small block balancer bolt (mr gasket), then balanced. So all the specifications are spot on.

Quite a few years ago, probably back in the middle 80s, Charlie Baker described his procedure for installing the crank. I was pretty young then, and I use to call Charlie, buy parts, and have him learn me on building these motors his way. So here is a little extrapolation from my notes and an article he wrote for the TPN all those years ago.

When he had his cranks ready for install, he like to install the main bearing shells in the block and light oil on them - do not install the rear main seal yet. Lay the crank in and rotate it a few times, it should rotate nice and smooth.

Bolt the main caps and bearings on (light oil on the bearings) on and torque to 30-40 pounds, rotate. Repeat the process in 10 pound increments until 80-90 pounds. If all spins free, disassemble, remove the crank.

Clean the bearings, caps and block saddles one more time. Insert the upper bearings back in the block. Install the rear main seal. Light oil on the bearings, install the crank. Install bearings in caps, oil, install caps, torque to 30-40, rotate, repeat in 10 pound increments until 80-90 pounds. Crank should spin smoothly but with a little more force.

Remove no. 1 cap, wipe oil from journal and shell. Apply plasticguage, retorque to 80-90, no rotating. Dissemble, Read to confirm clearance is within specification. If it is, clean the journal and cap bearing, coat the cap bearing with assembly lube. Reinstall cap and torque, rotate the crank. Repeat the process for the remaking three caps.

For the rear main seal, offset it if it’s a neoprene seal, little dab of silicone on the ends, smear the rear seal with assembly lube.

Spin crank, should spin smooth but with the same force as before with the main seal installed. If so, last thing is to put a dial indicator on the crank flange and move crank back and forth. Should be .003-.008. If so, you are done!

I have used charlie’s Procedure on every 235/261 I have built since probably 1984 or so, nearly 50 of them, purely as a hobbyist. Not one single failure. Not one time was an align bore required. My motors have hung in there for years. One in my garage was the first one I did using Charlie’s procedure, and other things he liked to do to these motors. I beat that motor unmercifully for years. Still ran great when I took it out for the bigger 261 a couple of years ago. The new 261, no issues (even with the gmc truck rods) and over twenty runs down the dragstrip at the trifive nationals over the last couple of years - it’s a street car and street motor.

Mike

Not from personal experience, but I would think that unless you have reason to suspect the quality/condition of the other crank (seizure, overheating, leaning against a wall for 30 years) it should be OK.

I agree. Those 235/261 blocks are pretty good castings, not much core shift at least in my experience. Others may have a different experience with these motors, mine is that they are good reliable castings capable of multiple rebuilds. The cranks are generally cast steel. Not a forging but not terrible either, but they are old castings. Those motors were meant for low rpm reliable use and that is how they were machined by GM. So its not uncommon to find the balance off just a little, or the throws a tad bit unequal. Other cranks are spot on. Because I am a hobby builder, I like to redo them so that they are essentially blueprinted. I have not yet had a failure so I tend to stick with what works. I agree though, that unless the crank has seized, overheated, I generally presume it can be rebuilt. In fact, I have no issues whatsoever grinding a 235.261 crank to as much as .060 over. So if a crank passes the visual inspection, off it goes for magnaflux, and if it passes, machining.

Dongray, You may not need sleeving. Depends where the pits are. They may be in an area that's not crucial. The bore center can also be shifted to minimize the next oversize. All these Chev & GMCs get heavy #1 cyl wear at water pump area. Shifting bore ctr toward pump often allows .030 bore instead of .040-.060 bore. $ 1000 for the mentioned work is a good price. Would cost more in my area. I agree that you should seek another block,as suggested.
On lineboring: Usually only a thou or is all that comes out of block. The cam is off at about 45 deg. Not like many engs like a flathead Ford where the cam in directly above the crank. Chevs don't have problem with mesh or timing change in my experience.
David

True.
The cylinder wall above the highest point of ring position (about 1/4" from the top of the piston) can look like concrete without penalty.
The range of piston ring position in which gas pressure is high is the only important area.

Im going to squeeze in another question about the 261 quickly as we are talking about it. The block i have at home that i planned to use for my new build has already been cleaned and inspected. When I got the block it was bare with only the crank caps. The front and rear are caps are stamped with codes that also have a code stamped in the block so i know they are the right caps or the block and im going to have to assume the 2 center ones are also but.....the front center cap when installed either way does not perfectly line up flush with the block casting below. is it possible the center caps are not off of that block originally?

Any chance the center caps have an F or an R on the top of each respective cap? If you shoot me an email address I can shoot you a couple of photos. They are not perfect but will do the trick I think. I have not figured out how to post photos here but if you can, maybe you would lost them for others to see.

Mike

There's no mixing up the center caps on the earlier engines. The center-rear cap has a tapped boss for mounting the oil sump. Did that persist into the later 235/261 design?

Also, both center caps have part numbers in the casting. The correct orientation is when the part numbers are readable when viewed while standing at the flywheel end of the block.

Do your caps have part numbers on them?

yes both have the part numbers and i do have them installed in the correct place and flipped the correct way. The front middle cap is still about 1/16 of a inch to the rear of the engine when compared to the block casting below

Just back from a week of hiking in the Smokies . . . hence the delay in responding.

The crank journals are huge in comparison to the saddles and caps:

Inliners post circa '14

Do you have the bearing shells handy? If so, see if the staking in the block and the cap are aligned by installing the shells without the crank. If the shell halves are aligned I'd venture to say it came from the factory that way.

It's really only the wrap-around thrust bearing shells that need to align perfectly centered front-to-back - which positions the crank. The rest of the journals then lay&run where they will. Have a look at my posting from '14 - in some cases the shells are much narrower than the saddle and cap. That said the front-middle cap of my 216 block is fairly well centered but by no means perfect.