The Stovebolt Site Forums The Shop Area Engine Shop My 261 build and discussion thread!

Found a 56 261 early summer. Got it home and found out under all the crud it had a cracked water jacket from front to rear. Found another fresh 261 block that was on its original bore and already fully cleaned up in the hopes that its all good and has no cracks.

Already took the 848 head off the first 261 and had a shop clean it and check for cracks. Found out today all is good and its ready for machine work.

Any thoughts what i can do other than my list below or anything better i can do to it. Want it to be for a street build.

Here is my current wish list.

Head work:
- Mill face true
- larger intake valves (possibly from Tom L)
- New valve springs (already have new on hand)
- New exhaust valves
- Have brass valve guides installed
- Have the new style of valve stem seals installed
- Hardened valve seat installed
- Check and possibly port match the headers to the head exhaust openings if required.
- New rockers (Im actually missing 6 so I want a full new set)
- New rocker shafts (Im actually missing them also but have the perches)

Block work
- Bore block to .060
- Deck block as much as possible
- New pistons (not sure what to do)
- New rings (not sure what to do)
- Reuse connecting rods / pins
- Machine Crank
- Balance Crank
- Check and possibly replace oil Pump
- New Cam from Delta Camshaft (Same as what im using in my 235)
- New solid lifters
- New Pushrods
- New crank gear and aluminum timing gear
- Leave oil system stock as a bypass system and not go full flow.
- Stick with rope crank seals
- Timing cover bolt modification
- New water pump (old one is damaged)
- need new oil pan (old one has holes)
- Drill the crank for the pulley bolt

External Stuff
-Swap over as many parts form my 235 when its time to change over. Hei, dual intake, headers, pulleys, fuel pump, remote oil filter, and other stuff.

Is the head already drilled for the extra two water passages between each pair of 261 cylinder bores?

People mistakenly call these extra passages "steam holes". You'd only worry about steam if you did not drill the holes.

Yes the head already has the holes installed.

This is the first block I started with. Turned out to have a crack from back to front.

[IMG]http://i96.photobucket.com/albums/l170/mazdacub/1949%20Chev/IMG_3177.jpg[/IMG]

Took it apart and removed the internals. The plan is to reuse the crank and con rods from this block.

[IMG]http://i96.photobucket.com/albums/l170/mazdacub/1949%20Chev/IMG_3178.jpg[/IMG]

This is the 848 head from the damaged block prior to cleaning. Got word back it all perfect and ready to be rebuilt.

[IMG]http://i96.photobucket.com/albums/l170/mazdacub/1949%20Chev/IMG_3199.jpg[/IMG]

This is the other good block i got that I am planning to use if it checks out. #7012. Still measures to be on its original bore.

[IMG]http://i96.photobucket.com/albums/l170/mazdacub/1949%20Chev/IMG_2695.jpg[/IMG]

Strange thing is this block has no provision to select full flow or bypass for the oil. Im just not used to seeing this style of block. I also wish it had the 3 hole mount so i could have used it for a remote filter mount but i will make due.

[IMG]http://i96.photobucket.com/albums/l170/mazdacub/1949%20Chev/IMG_2683.jpg[/IMG]

Why waste nearly 1/16" of bore size for an insignificant increase in cubic inches? The only thing you'll accomplish is eliminating the possibility of two more rebuilds. I'd strongly recommend doing maybe an .020" rebore to straighten out any taper, and don't mess with decking the block more than a very slight cleanup cut. You'll get plenty of increased compression pressure with the 848 head for anything other than a VERY radical camshaft profile that needs an increased compression ratio to get the actual compression pressure back close to stock with a radical valve overlap.
Jerry

Where is your sense of adventure Jerry? live a little.

Good on you Scott! I had plans to build a killer 261 but then bought a C5 Corvette and lost interest in making more power with my truck .Anyway a few things I can share are:

1. You can find 50-52 powerglide intake valves (and guides) locally from Gary auto, ABS engines, etc.

2. The picture of your last block is 55-57 variety. Canadian 58-62 blocks have the boss for the diverter pin/large pipe thread but it is only machined for the small NPT. See here.

3. You are welcome to borrow my torque plate. Boring cylinders with it mounted in place of the head will make for rounder holes/faster ring seating.

4. As for the head I made a flow bench adapter plate and tested several modifications. The exhaust valves are severely shrouded so removing some material where the valve comes close to the wall will help. See here.

5. Don't ream/enlarge the intake ports from the manifold side to the intersection. This was shown to reduce incoming velocity and did more harm than good. Frank McGurk did it in a hop up article but I assume his other mods "masked" what a flowbench proved detrimental.

6. We'll chew the fat over a few beers sometime to get into further details.

"Strange thing is this block has no provision to select full flow or bypass for the oil. Im just not used to seeing this style of block. I also wish it had the 3 hole mount so i could have used it for a remote filter mount but i will make due."

Only the 1958-1963 USA 261 truck blocks were set-up from the factory to allow:
- no oil filter
- by-pass oil filter
- full-flow oil filter

Once a full-flow oil filter was properly installed, you could not "go back" (I think).

Yes Curt a beer would be great.

Do you have a top down pic of what you did around the exhaust valve? Looks like you might have just removed the shroud all together to get a vertical wall.

From previous posts and research I gained an impression that drilling the vent (steam) holes in the 848 head, to match a 261 block was not critical or, would not hurt a 261 after reassembly and running it. Comments?

Tom,

It would be nice/helpful to hear from someone who ran/runs a 261/848 engine with that set-up (an undrilled head).

If the vent holes were not necessary on the 261 head, why did GM choose to go to the effort to drill them in the first place? I love it when self-appointed experts try to explain why they're smarter than the engineers who designed these engines. Small block 400 V8's have the same type of holes drilled in the heads for the same reason- - - -to allow coolant to flow past the siamesed cylinders and prevent hot spots from forming due to low/no coolant circulation. The quickest way to create a boil-over problem on a 400 is to run a set of 350 heads without drilling them.
Jerry

Yeah, it's necessary alright. I haven't seen a post here on The Stovebolt that ever said that. Maybe I wasn't looking close enough. There is even a correct and incorrect way to drill them.

http://devestechnet.com/Home/TheVenerable261

thanks for clarifying this. -tom

Got word today the second block i had is good to go. It still on its original bore and has 6 thou of wear. It was all cleaned and read for me to take back home. I want to clean up a few things on the block prior to having the machine work completed. The lower side of the block at the oil pan lip is very sharp and i want that beveled and cleaned up. Also want to take the extra time and just ensure all the passages are thoroughly cleaned using a rifle brush and such.

Are you planning on painting the engine yourself? If so, you might want to tell them not to paint it. Most of them are engine builders, but not detail painters. They worry about flash rust after cleaning it.
I don't worry about that, since I always treat mine with Ospho, wait a day, wipe any residue (byproduct of the chemical reaction) with a rag soaked in Ospho (works as a solvent and doesn't cause any more reaction to the metal), wipe with auto paint thinner and wipe clean with a clean rag, prime with extreme heat engine primer, and paint with engine enamel.
Carl

Carl,

I wish I had known last summer what you stated above.

I am not ready this exact second to have it fully rebuilt all at the same time. Im going to have the block and head down to bare metal as they were just both tanked and shot blasted. I don't want them painted yet because i know they will be all damaged when it time to do all the machine work. When it all said and done im going to do this build gloss black black like the one in my truck now or possibly a dark gunmetal.

I like black as it so easy to touch up and you never see where you did it. Also it always looks clean with no possible dark oil stains or other stuff showing. Any minor oil on it just helps it shine when you wipe it down lol. Just dust shown on it if i dont wash it down every few weeks.

The original engine paint on 235s was like that. You can't tell where the painted surface stops and the oil soaked bare cast iron starts.

So on the weekend i ran into a random guy and we started talking about inlines. He mentioned to me doing a 261 was a waste of time. Granted it just one guys opinion but he said if my 235 was running correctly going to a 261 is pointless. The gains are so minimal and not work the effort and money he said. He had one in a old car he had a long time ago.

This swap over from my 235 to the 261 really worth my time and money? I have never had the chance to feel what a 261 go like so im going into this build blind.

All things considered, more inches is more power. More power is more heat. In the world of inline 6 engines, that is as true as ever. You can put split headers on a 235. They sound good. You can put 2 or 3 carbs on if you want. They look good. You can put a hot cam in a 235. It will make tuning a fun and everlasting project. A stock 261 will probably make more HP than any of the options listed above. And, you will still be able to drive it. Stock 216 90 @ 3300 RPM. Stock 235 Powerglide: 136 @ 4200 RPM( best of all years) And for the 261 150 gross hp at 4000rpm. So cubic inches still the best way to make power. There are ways to get power out of these engines. Most involve a lot of work. Many will make the engine suitable for "Track" only driving. Most will show small gains and higher RPM. These are torque motors. Not spinners. Clean, working mid-range power for work is what they do best.

And you never know, maybe he was using that old choked down 235
carb on that 261 because it fit the same base. Maybe that 261
was an old tired truck engine that had seen better days.
That engine will put out more hp & torque than the 235 or they
wouldn't have used them in trucks buses and cars for a decade
even after the advent of the small block.

dg

Im all over the torque aspect. After i spent last and this summer playing with carb settings, timing and changing the cam im very happy with the way the 235 behaves now, but being your typical guy I want more torque. Im 90% city driving and love to have the get up and go when just cruising in the city. when putting around in second, third, fourth and then punching it i just want it to get up and go faster.

Almost 11% more displacement, without increasing piston speed, is always worth having. Is it worth building an engine to obtain? The answer is money.

I don't think it going to cost all that much actually. I already have all the " performance and aftermarket parts " lol from my 235 I will swap over. Basically I am going to have them do the head fully, the lower block I would like to have them assemble it to the point it has the crank, cam, pistons, and rods installed so i know the important clearances are correct and i can do the rest. I have spent $300 cad to date with the cleaning and inspection for the head and block.

wolffcub,

Will you be drilling the extra coolant passages in the 848 head?

What two carbs will you be using on the 261?
Most likely, they will be better on the 261 than on a 235?

The head already had the holes drilled stock. The carbs i currently have on the 235 are 2 of the Weber 32DFT with 32/32 mm throttle bores. From day one i had some issues with these carbs only to find out the first set were both bad. The second set i installed worked 1000 times better out of the box and have gotten better as time goes on with me tweaking them. Still i have got some feedback from others that they feel that they are still slightly over carbing the engine at low speed thus why im always whining about the acceleration. I'm thinking that the 261 might be better suited for them and hoping they work well without me having to possibly switch to a set of Weber 32/36 units. Im not sure if the top end will need the larger 34 bores. I do hear however the 32/36 units are way easier to tune and rejet if required.

Going to get around to do some minor head cleaning soon but i have a question about rockers. The 2 spare engines i now have (55 235 and a 56 261) have rocker assemblies but they are worn. The rocker shaft is very badly worn on one and the other is fair. I want to just replace the assembly with a new setup for the 261 build. The only place i can find that lists new rockers is Jim Carter. His rockers are listed as being for 59-62. I was wondering what the difference in rockers was thru the years and if his would work.

Rocker web page

Here is a good place to start.
I can answer almost any further questions on this subject.

Thanks for the link. I did review that prior to my post. So im going to assume if i get the new rocker set and it has the offset groove in the rockers I should then just pinch off the overflow tube to add the pressure to the rocker shafts. Then the next ting is that the 1/16 restriction at the start of the tube down by the cam bearing still stays and needs no modification right?

One thing i just noticed is now the oil moves from the block to the head. I thought the head had another hole almost aligned with the block top outlet oil hole. I never knew it only relied on the gasket thickness to allow the oil to pass and flow around the head bolt to the gallery in the head.

Can this possibly explain how some people say they have little oil flow to the head. Maybe the head gaskets have been reused too many times and are crushed thin?

I see in my 55 engine book that i currently use for my installed 235 there are 2 different number for the rockers between the 235 and 261. What was the difference? Strength? valve lift?

Wolf, if you read Dave's Blog, he covers the differences. The rockers oil grooves are offset on some later years and there are other differences as well outlined there. It's pretty important to keep the parts together in some years. If you have the correct rocker shaft/rockers and the connector that distributes the oil in the center, all will work fine.

Oh and a side question......other than the casting number in my 261 block that says 3837012 (55-57 year 261) i have W86502 stamped in 2 places. One next to the distributor and one on the side cover gasket face. I cant find a code description for that number.

That is not the GM engine serial number format for a 1955-57 261.
A code was not stamped on the side cover.

You might have a replacement engine and the installer put those codes on the engine?

Find and post the head and block date casting codes.

What did i miss? i see the stated difference between rockers of different years with the offset oil groves but dont see anything about the 235 vs 261 rockers of the same year that have different part numbers. Am i going blind?

There might have been some different 235/261 rocker arm parts in some years.

ID the year and people can check the parts.

The block has only the 2 numbers on it on the distributor side. Nothing like what you see in picture 2 of the link you just posed. Only has pic 1 and pic 3. No sign of anything being ground off either. Would a replacement engine still not have the plant and date codes on it? strange bit i cant find that info anywhere.