The Stovebolt Site Forums The Shop Area Engine Shop teach me more about the 261............

i was reading wizzerick's post on the "new" 261 that he got ahold of, congragulations by the way, and now im really curious about this rare engine. i was wondering what makes it so saught after? is it more similar to the 235 or the later 230 and 250's? also whats all this about a 848 head? what makes it so special? any other interesting facts you guys want to add in would be appreciated. thanks

Here is my 2 cents...
I think there MAY be a bit of hype surrounding that motor...

It's little more than a 235 with added bore and stroke, but the internals (like the connecting rods) are in fact 'beefier' than the 235.
Of course, there IS an increase in horsepower there, but more importantly it's the possibilities it affords as far as 'hopping up' an inline 6...

In my case, I would have been happy with any 'newer' 235 (with oiling and insert bearings) because I'd like to replace my babbit, splash oiling '53 235, the 261 was a nice surprise.

They are certainly rarer in the USA than Canada, as our Pontiacs came with 261's.
Though judging from the serial #, the 261 I bought, was rebuilt and installed in a Pontiac sedan but came from a truck...

The 848 head is not a rare head 'per se', it has a smaller combustion chamber and therefore more compression...

Any input from the Stovebolt gurus?

I forgot to add the most important aspect:
the 235 is still a great engine... for little GIRLS!!! HAHAHAHA!!

Just one small correction to wizzerick's post. The 261 has the same stroke as a 235, in fact it uses the same crank.

http://www.oldchevytrucks.com

Technical Articles

1955-66

Forgotten 261 Six Cylinder

text, difference in 235, 261 - some pictures. Good Information.

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This is the link to the article, but sometimes linking directly to pages on that site doesnt' work out good, hence why I wrote out where to find it, in case:

http://www.oldchevytrucks.com/cgi/htmlos.exe/002286.2.4428693807700005274

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Read all about it.

-W

The 261 has beefier rods and thicker wrist pins (rods and pistons will not interchange with 235), siamesed cylinders (due to the larger bore), extra water jacket holes between the block and head, a somewhat more aggressive camshaft, and the '58- ups have built in full flow oil through the filter ports (which are 1/2" NPT). In addition some of them have a bypass thermostat, which is interchangeable with the 235 thermostat, except you may want to drill a hole in the thermostat to let steam and air out of the head on warmup. 261's are sensitive to steam pockets in the head because of the siamesed cylinders and require extra measures to eliminate them: the extra holes in the block, and a bypass thermostat on heavier duty applications.

The head is similar to the 235, but the 848 head has slighly smaller combustion chambers for a few extra compression points. The 261's came with Stellite valves in all years, but I'm not sure if the 235 did or not. The ports are exactly the same.

Distributors, water pumps, fuel pumps, intake and exhaust manifolds, and valve covers all interchange, as well as crankshafts. The cam bearings are the same too. The stock carburator is a Rochester B with larger power piston passages and #57 or #58 main jets.

I got my 261 out of a '62 suburban. It came with an 11" clutch and a bypass thermostat. It runs great although it needs new valve seals. It has been running cleaner since I started using Delo 400 oil in it.

Well, I guess its official...I'm a little girl. I have but a lowly '57 235 in the '51. Maybe someday when I grow up...LOL

I don't know about the 261's, but the 235's 848 head is the most common. It ran in production from '56 thru '62. As was stated, it has a smaller combustion chamber for a higher compression ratio. The cast iron also had a higher nickel content to reduce warpage/cracking than the older castings.

Now, correct me if I'm wrong, but somewhere I read the horsepower ratings for the 235 and the 261. It seems to me that the 235 was rated at 140 horse, and the 261 was rated at 145. Does that sound right?

hehehehehehehe! :p

148... Hence my comment about the hype...
Again, it just lends itself well to some 'soupin' up'...

I think the thing I love about old trucks the most is all the lore...which motor had which head, which fuel pump interchanges with which, what year the Rochester Q carbojet as introduced...nobody knows the answers for sure because people have been tinkering and fooling with all this old iron for 50 years. Who knows if GM engineers even ever knew the truth.

I would have been happy with rebuilding my FP 235 two years ago but my engine man said he had a FP, FF 261. Last week, I took a spare 848 head to him for magnafluxing. He was talking to an old fellow and he told him "Here's the guy who has your 261." I talked with him a long time about the old Chevy six'es.