The Stovebolt Site Forums The Shop Area Engine Shop sick 261 vs. healthy 235

This will be long. My 1 ton panel (Ruby) is now powered by a 261 bored .080, 848 rebuilt head, HEI,T5, 4.10 rear. When I put the 261 in, 18,000 miles ago, I knew there were some problems, namely cyl. #4,5,6 were badly scored but not knowing better I just re- ringed along with bearings and ran it. Rear 3 cyls. burned oil some so I used plug extenders on them and that helped.
Compression at that time was (from cyl 1 to 6) 115, 112,115 105,100,98.
Now the last three are 102,95,96.
Not good; hard to time and set the valves.
I have a good rebuilt 235, .040 as a spare. (My wife has wondered why would anyone have a SPARE engine?) Anyway, this engine was in a local Vol. FD truck that rolled. Supposed to have about a 1000 miles on it. No cyl. ridges, hyd. lifters; looks fresh. (Has a funky external oil line from the block to the head).
I haven't checked the compression on this engine but assuming it is good, Would it make more sense to swap in the 235 for the 261 or try to do something to fix(?) the 261.
Would there be much difference in driving feel between a sick 261 and a healthy 235? I guess that is my question.

Blacksmithdon,


My two cents. I think the best bet would be on the 261. BUT, this would be dependent on the cylinders cleaning up. I don't think they usually sleeve one of these engines, so if the bad cylinders wouldn't clean up without a life threatening overbore, you might have a boat anchor and the decision would be moot.

Would a donor 261 block be a reality? The condition of the existing scored block would make the decision for you. Good luck

Stuart

I say be patient and find a new 261 block if you have to. I'm going the other way. I will soon be swapping my perfectly fine 235 for a 261 stroker. I'm doing it because I want the truck to be all it can be and still "look" stock with period accessories and speed parts.

"I don't think they usually sleeve one of these engines, so if the bad cylinders wouldn't clean up without a life threatening overbore, you might have a boat anchor and the decision would be moot."
From what i read it is already life threatening overbored , unless the .080 is a typo.

.080 is right. I'm really wondering if there will be that much difference between a sick 261 and "fresh" 235.

'52motorhead,

I evidently didn't read the post well enough. I agree with you. If it is already .080 over and now has scored cylinders, it sounds terminal.

Blacksmithdon,

I don't think your question has an true answer...sort of like the apples and oranges deal. If one were to tell you there would be little difference, would you leave the 261 in?

There is probably a 'right' answer, but it isn't in the comparison between a worn out engine and a engine of unknown condition.

Stuart

080.is a substancal overbore for shur,some are only good for 030. at best. But some will go 125. without trouble. With this much of an overbore you must also consitter what is happening to the compresion ratio. If the new pistons don't have added chamer volume built in the added displacement could send the C/R through the roof.

I thought compression ratio was the difference between the cylinder volume at BDC and TDC, or something along those lines. I wasn't under the impression changing the bore size would change compression ratio.

Stuart

Don't throw the 261 in the lake just yet. Here's a thread where sleeves were found locally. Good luck.

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=22;t=002072#000003


Curt B.

Awh yes atomarc you are 100% right. when you bore the cylinder it's volume gets bigger at BDC but not so mutch at TDC. Most overbore pistons will compensate for this by sitting a little lower in the bore increasing the chamber size. But they don't always do thi so the mech. will have to.

a 261 can be bored .125 without any trouble...

Hey Darin how big dose a .125 overbore make a 261
A .125 over 454 is 482 ci.