The Stovebolt Site Forums The Shop Area Engine Shop New engine project, a 261

I recently purchased an engine from a friend, it came from his '50 3100. We knew it wasn't the original 216, but thought it was a replacement 235.

I got the engine home and unload it the other evening. This afternoon I was finally able to really look at the engine. Of course the first thing I noticed was the valve cover, it's a center hole. That got me wondering, so there just above the starter were the "Captains Bars " ( Ohhhhh Yeah!!!) The numbers cross to a '58-'62 block.

This will be a great start for a engine build for "Thor".

Sweet!

Leave some of the good stuff for the rest of us, Craig…..

I plan on following in Jerry's footsteps,...

Craig, my book says its a '60-'62 block.

You don't want it. You'd better give it to me to get rid of for you. Got the carburetor???

The friend I got it from has it. I'm not sure if it's the correct carburetor or not.

He is the same guy I built a 292 with a lump port head for.

I thought you were already driving Thor around town.

Yep, but this is a "261". This is a future engine build for Thor, a high torque engine with a few more horses.

Thor will be making the trip to the Jamboree in Townsend this year.

The only thing better than a 261 is one with about 40 extra cubic inches, and 3/8 inch more stroke (lots of torque). The one I've got on the drawing board will also have pistons and sleeves from a Toyota Diesel engine, so when it's rebuild time it won't have to be rebored- - - -just slip in a new sleeve.That one might possibly end up with a roller camshaft and lifters and roller rocker arms, as well.
Jerry

What, no 12 port head Jerry?

That's a dfifferent project- - - - -twin overhead cam cross flow head from an Atlas inline six, with a Weber DCOE 50 side draft carburetor, on a 270 cubic inch "235".
LOL!
Jerry

Congrats and a nice find. Thor will be happy!

I have been doing some research on this engine build. While it's possible to bore a 261 .125 over sized I don't think that would be practical. I am thinking of .040 -.060 over with a flat top piston, decking the block to around .020 -.040, hoping for an even 9.1 compression. Doing some head work, larger intake and exhaust valves, unshrouding the valves and some blending. Possibly a lump port on the intake runners, and opening up the exhoust a little. These things are basically a Tractor engine, made to do work and keep going. Having a 261 with around 270 CID and good low/mid range torque is really the goal.

Camshaft selection is key in this build. The factory cam was pretty much the same as the Corvette 235, Jerry as mentioned the Melling CCS-1 cam. The idea on a higher lift cam sound good until you factor in valve clearance, things can get a little tight. While I'm not looking for a full out race engine, some extra ponies would not be bad. As this engine will ultimately find it's way into "Thor" it needs to be able to work. I keep telling myself torque is the goal here, not speed.

I'm open to your ideas and suggestions.

Be careful about "unshrouding" the intake valves- - - -unless you enjoy changing valves every few months. The intake valve is recessed into the cylinder head for a good reason- - - -to shield the edge of it from the flame front as the cylinder fires. I've got a very nice 848 head that was given to me after a couple of milling jobs- - - -because it burned up intake valves frequently. I can fix it, but the machinist who did the milling had his head firmly inserted into a dark, stinky place! Use the 1.94" intakes for a Powerglide-equipped 235 spray oiler engine and pocket port the tulip area of the port above the valve, but be sure to keep the protective lip in place that deflects the flame front away from the edge of the valve.
Jerry

If one shaves too much off of one of these heads, You remove the "quench trench". With not enough room for the air to flow when the Big Bang takes place, much heat is created which will turn what is left of the quench trench gun metal, case hardened blue and cooks the intake valves.
I must say that the added compression from doing this results in a remarkable increase in performance, but at the cost of a perfectly good head in short order.
I have heard of angle milling a head, favoring metal removal on the exhaust side of the head. This preserves the quench trench, while increasing compression ratio. Then you will only have to worry about throwing a rod which likes to break where the clamp bolt for the wrist pin is when the engine gets pushed too hard.

This engine build will be nothing exotic, no custom pistons, no one off valve train. The main idea is to go oversized .110" to add a few cubic inches (276 CID), deck the block around.010 and mill the head .030" - .060" to add some compression. Pistons can be sourced, JE and Ross still have them in production. The cam as many of you have pointed out will be on the "smaller" side with around 210° to 212° Intake and 218° to 220° exhaust duration at .050" lift. I may go smaller as this is a Torque engine, something in the 190/220 duration @ .050 range. The intake and exhaust will most likely remain stock.

With respect to valve and head work, you have to start with the premise that the intake ports and combustion chamber are so terrible in terms of performance that there is little that can really be done to fix it. The short side radius, the flat back wall, there is just nothing that can really fix the issues, including a lump. In fact, some basic porting work on the intake side can actually make the problem worse.

The intake ports are large enough to support a bigger motor so more than enough for a 261 motor. Enlarging them may help a high rpm motor but can only hurt a street motor or a motor designed to run at lower rpm. Kills the velocity. So if you want to tinker a bit, grind out any casting flash in the three intake ports, and smooth it out. Don't polish it, you want just a little roughness to help atomize the fuel, just get the heavy roughness (if any) knocked down. Same for the bowl area. Don't go crazy here, little smoothing, and don't make a cone out of the valve guide. It will not help the flow in this head and leaves the guide less than able to support the valve.

Same for the exhaust, grind out the casting flash, little smoothing.

On the valves, if you want to install a larger intake valve, you can use an intake (1 15/16) for a 50-52 power glide equipped 235. To make use of this valve, you have to hog out the bowls a little, and use a cartridge' roll to smooth out and blend the cut. GM used the larger valve in 1950 to help build a little more power because the newly introduced power glide used up some power.

On the exhaust side, if you want to use a larger valve, you can use a stainless one piece 1.5 exhaust valve for a small block chevy. I like Manley street flow valves for this. Same deal though as the intake. The larger valve will need some clearance on one side of the combustion chamber wall/pocket. So you will need to have the machinist massage the wall a bit. Then you have to hog out the bowl, and blend.

Milling the head and block, more than what is necessary to get a flat surface on each, I am not so sure I would do that. The stock 261 pistons sit further down the cylinder at TDC then a 235. So you are really trying to get to where a 235 would be, and then some. Now, lets say you mill the block .010 and the head .040, that is .050 combined. With that amount of milling you will likely have to sink the intake valves that amount, and then shim the rocker shafts the same amount, and then add lash caps to the exhaust valves or obtain valves with longer stems, just to keep the rocker arm geometry correct. I think the better call, albiet the more expensive call, is to bite the bullet and get some pistons ordered that are pretty close to being the same compression height as a 235 piston or even tighter, maybe 0 deck, maybe even with a lump to raise compression even more, maybe with a valve relief. Its a one and done thing. Then you don't have to sink the valves, shim the stands or use lash caps. Using custom pistons will get you the 9.0 CR you want and it makes a difference.

Then you can use a cam grind that is designed to take advantage of the 9.0 cr and low rpm torque (call Scheneider cams and they will sort out a grind). Another alternative for the cam is Tom Lowe at 12bolt.com. Tom has the specifications for Tom Langdon's Bulldog cam that Tom sold for a good number of years. Way way better then the stock 261 cam.

https://www.12bolt.com/store/p545/235_261_BullDog_solid_Camshaft.html

Just some food for thought.

That’s a LOT of food!

Sounds like you’ve worked on a few of these before. 😊

Two old adages that come to mind regardless of what kind of engine you're working with- - - - -

"There's no replacement for displacement"- - - - -

and

"Horsepower is to brag about- - - - -Torque wins races!"

With the right piston/rod/bearing combination, it's possible to get 3/8" more stroke from a 235/261 crankshaft. That can be massaged into a gain of around 40 cubic inches, whether the starting point is a 216, 235, or 261 engine. It requires some serious metal butchery, but it's doable- - - -without altering the outward appearance of any of those engines. A 258 cubic inch "216" with close to 9:1 compression can turn some heads at the top of a long hill, leading a pack of other "stock appearing" stovebolt trucks!
Jerry

Just a few lol. A good number of years ago I milled an 848 head .125. Sounded great on paper, looked impressive in person, ran fine, but what a mess getting the rocker arm geometry back in order. .050 .060 is half that but still likely to require sinking of valves, lash caps, valve spring shims, shaft shims. Like I noted, get some really good pistons. I know they can be expensive, but in the end, you will be much happier with the torque and power then you would be cobbling up the valve train to get a bit of compression (which does wonders for these motors by the way).

I'm doing the research now. Egge Machine has pistons and a complete rebuild kit, just north of $2000.00. Talking with cam grinders, giving them the weight of the truck, the gearing and overall use. I did manage to locate an NV4500 transmission, so now I will have overdrive. The 261 will no doubt be a fall and winter project this year. I don't want to cut corners, but I also don't want to do any unnecessary work either. As I said I want a solid, strong hard pulling engine with good low to mid range torque.

Does Egge provide a quart of personal lubricant in that kit price? They should! That's at least twice what parts for a rebuild should cost.
Jerry

Well it's not quite in the 'Cadillac Tax' territory of what it costs to pay Cadco for hop up parts for a 500 Cadi V8.. but hey, whenever you're getting into modern day engineering time and manufacturing effort for a 50 or 60 or 70 (OK, pushing a century now for the Stovebolts) year old engine, then you'll have to pay for the small batch runs and large engineering hours required to make them.

The cheap way is small block Chevy, the modern way is LS.. but some of us think outside that box :-)

I'm in the process of building a long stroke 261 using Nissan connecting rods, and Toyota Diesel forklift pistons and sleeves. It's going to be close to 300 cubic inches, with slip-fit flanged sleeves that can be replaced without reboring the engine ever again.
Jerry

The factory 261 piston has a compression height of 2.029" and .927" offset pin. How far down does the top of the piston set in the bore at TDC? How much can the block be decked "Safely"? I have 2 "848" heads that could be used on this engine to increase the compression without milling the head and dealing with valve train issues.

There are several pistons available in 3.875" bore, with a .9310" offset pin. The issue seems to be the compression height, most are around 1.58 to 1.68. Sil-O-lite has a AMC 2.5L piston (P/N: 3243HC) with a 3.875" bore, .9310" pin diameter, 1.592" compression height. This piston has a .116" deep "D" shaped head recess, it also has coated skirts and uses standard 3/16" and 5/64" rings.

Doing more research, the standard bore 292" piston is 3.875", with a .9273" pin diameter and a 2.009" compression height. The Silv-o-lite P/N 1429 has a "D' shaped head recess @ .300 deep. It was rated at 8:1 compression. It uses standard rings and a set is around $160.00.

Has anyone had any experience with the "Bull Dog" cam designed by Tom Langdon?

No direct experience, but some people I've spoken with comment that it gives a somewhat lumpy idle, and low manifold vacuum at idle. "Valve open" duration (discounting clearance ramps at both ends of the lobe) of anything over the mid-260 degree level tend to kill low end torque and produce a choppy idle. That's true, no matter what engine we're discussing. The Elgin clone of the 261 cam (E-323S, I believe) lists a total duration of "300 degrees"- - - -but they include the total deviation from the base circle of the lobe, including clearance ramps on both ends, when the valve isn't actually open. The actual valve open time is in the high 250s or low 260s, IIRC. That's the cam we put into John's 261, and I degreed it during that engine buildup session. He's very pleased with it. Elgin isn't producing that cam at the moment, but I've got a brand new one that I'm planning to send to Schneider Cams so they can make a master cam from it. Then they can grind as many of them as they want as long as the have a good core to regrind- - - -solid or hydraulic cores don't make any difference- - - -the finished product will use solid lifters.

Boring a 261 to 3 7/8" would result in some paper thin cylinder walls, in my decidedly biased opinion!
Jerry

These pistons, and the slip-fit flanged sleeves that work with them can be adapted to a 261 engine. The wrist pin hole can be bushed down to fit the 292 or 261 wrist pin
I have six of them, with sleeves, on hand, and a 261 block they're going into. It's also getting 3/8" extra stroke for around 300 cubic inches.

The same piston/sleeve setup can be fitted to a GMC 270 block, IMHO.

www.ebay.com/itm/195096233829?

Jerry

The stock 261 cam has a lift nearly identical to the 56-62 235 cam of .404 (some books have it as .405). There are slight differences in the duration and ramps (hydraulic vs solid applications) but in all a pretty mild cam. Power and torque begins at about 1700/1800 and runs up through 3800 or so. If you want a basic truck cam, no fuss or muss, that is the baby.

Tom Langdon's cam is similar in specification to the cams offered by Clifford, Isky, Howards from back in the day. Clifford's cam was .444 lift 264 degree duration and was advertised as a high torque cam with a smooth idle that started its curve just a speck higher at 2000 rpm and made power through 4000 rpm. So not overly aggressive by any means. Langdon's cam, which Tom Lowe at 12bolt.com now sells, is similar at .435 lift.

On a 235, the motor will see that cam as a larger cam, the 261 smaller. Tom used that grind because it was not over aggressive, sounded good, and did not require clearance the pistons. Install it and go.

For comparison, what does an aggressive street cam for a 261 look like, well in one of my 261 motors I have a schneider cam that is .492 lift and 284 duration.

Mike - enjoyed the reading.

Would you be able to provide a similar commentary on hydraulic cam options?

A hydraulic cam in a stovebolt engine is a solution in search of a problem. The oiling system is far too primitive to make a juice cam a reliable choice, and the design of the lifter that's commonly available is stone age technology. It's possible to make the situation somewhat better by using a different lifter design, but the diameter of the lifter bores has to be reduced by putting sleeves into them, using a lifter designed for a MOPAR or AMC V8 engine, and altering the design of the pushrods.
Jerry

There were never very many performance hydraulic cams for the Stovebolt. Clifford only had like three of them in his catalog, the most radical of which was only .449 lift. That was about as much as the hydraulic lifters would take in terms of ramp speed and spring pressures. That cam was advertised to make power from 2200 to 4800. If you did not know to adjust a mechanical cam and did not want to learn, this was your cam. Now Clifford was not a cam grinder. He had cams reground. Erson was his source for a good many years. Schneider will grind a hydraulic cam still. But most grinders only offered solid grinds for the 235/261.

And make no mistake, I am with Jerry on this, a hydraulic performance cam for a 235/261 is not that great. Which is why you did not see many offered, even back in the day. If you want the convenience of a hydraulic cam, use a mild cam grind. The other issue, lifters. The new lifters are terrible. So you have to dig really really hard to find nos gm.

The solid cams on the other hand can have faster ramps, can be ground with higher lifts. Generally better performing cams, both in terms of power and/or torque, and in my opinion, reliable. Setting the valves is not a big deal. You just need to get through your first adjustment and then you know how to do it. Frankly, they don’t need all that much maintenance. They hold the adjustment pretty well. Everyone who ground cams ground solid lifter cams for the inline six. My first performance cam was a Chet Herbert regrind. He use to advertise in hot rod and car craft 39.95 any cam any grind. Howard, Isky, Schneider, Erson, Weber, McGurk, Racer Brown, Clay Smith, all would grind a cam but generally a solid cam.

I have run Howard, Isky, Erson, Herbert, Clifford and Schneider. Herbert, Clifford and Schneider were the better cams.

All of this is great information. I have no intention of building a full on race engine for this Truck. The cam choice will be a solid lifter design, good torque and mid range power.

As for the block, I will look at custom pistons with a bore of .060 - .080 . The block will be decked enough to make it straight and flat. Just a good basic rebuild with balancing of the rotating assembly.

The will be one of the "848"'s I have. I may mill it slightly, no more the .020 - .030 at max. The valves will be larger with some clean up in the runners and bowls, nothing extreme.

I don't want go away from the stock intake and exhaust manifolds. I may use a larger exhaust pipe and muffler to aid in breathing.

Overall I want a solid, period correct 261 with a little more grunt and good drivability.

Here's some info on my 261 setup that I hope helps in cam choice. I have run this setup round trip from Canada to Mexico twice carrying a camper for 9,000 lbs. gross and it has proven itself well on the road.

I have a Crower cam in my 261 that came out of my 235 along with that 848 head, so about 9:1 compression. Head is not milled except enough to ensure it's flat. Here are the specs from the cam card:
- Solid lifter,
- Advertised duration - in & ex 252 deg.
-Duration @ 0.050 - 220 deg.
- lift 0.450
Clearance IN 0.016 Exh 0.020
Split overlap but ground 4 deg. advanced.

Minimum Valve-to-piston clearance when in the 235 was 0.055 at 8 deg BTC. 261 deck height is a little more so that figure is probably higher but I saw no reason to measure it.
Valve action is a bit noisy but valve guide life is good. Bronze guides.
Pulls from about 1300 RPM in town but the real on-the-road power band is from about 2500 up. I down-shift at 2400 unless I see that the upcoming hill is steep, then 2600. I never found the top of the range. Never tried. Sweet spot on the road is about 2800 or 65MPH in overdrive. Idle is a bit lumpy if the carbs' idle screws are set too lean. Runs about 10" vacuum on a level road at 2600RPM at 2500Ft. elevation.

Exhaust valve opens 0.050 at 44 deg BBDC. I'd like to see this closer to BDC because the of exhaust noise and manifold and pipe heat.

Close ratio trans setup with about 300 RPM between gears. This probably would not work well with a straight 4-speed where you lose 50% between shifts. I lose about 20%.

Out of curiosity one ton Tommy what rear end ratio are you running?

John

We were discussing lifters. Anyone familiar with this sealed power lifter design for the 235? This looks like a fairly recent manufacture date, but there are others on eBay that appear to be much older, with the same “necked down” area in the middle.

I suppose that a solid lifter may not need all that material in the middle, just looks weird.


https://www.ebay.com/itm/186076678081

Nathan, the dating I can see on the packaging in your ad indicates copyright 2000. Here is what I think is an earlier Sealed Power AT-274 that looks more like a normal lifter we are used to seeing. Can't say that I have seen the lifter design your ad shows before, but it has been a long time since I purchased any.

This one looks older to me:
https://www.ebay.com/itm/256502722873

Rear Ratio is 4.57. with 265/70 X16 tires. Previous was 5.13. I think 4.88 would be the sweet spot.