Inliners International Forums General Discussion Hi Performance Cadillac 261

Anyone know where I can find the article on to build the Cadillac 261 engine. I looked on Tech Tips but could not view the 261 article.

Thanks
Terry

Dear Terry;

I would contact Tom Langdon directly, as he is the creator of the engine and the article that was in our Magazine a year or so back.

I'm sure there is an 'update' by now, as well as some test data on one he has built etc.

Good luck, John M.....

Thanks John, I forgot about it being in the magazine, I probably have it.

You might also ask Twisted6 - AKA Larry Paige as he is now the Grand Imperial Archiver charged with retaining and distributing the back issues of the 12 Port News. He can send you the issue in which Tom's 261 Caddy article was published.

He has only recently been elevated to that exhaulted position and may still be sorting them out but I'm sure he can dig one up for you.

Mike

Sept/Oct. 2003 issue...

Dear Larry;

I'll take one too.

John M......

I showed the machinist in town the article describing the 261 with modified crank using 292 rods on a modified crank.He is no world famous engine builder but does build winning V-8 types for circle track and drag racing.he didn't like the small shoulders on the crank,his opinion was oil control problems for normal street use.Or at the minimum,excessive drag from too much oil thrown off the crank wasting HP and also heating the oil.But that's his opinion.

Dear Tony;

He's thinking of V-8s that turn 7,000 RPM & higher on those points.

The 261; no matter how you build it is limmited to around 5,500.

Looking at Ton's updates & test date should help you out too.

JM....

PS: I plan on building one next year.

John,it has nothing to do with rpm,but rod side clearance that engine builders spend a lot of time fussing over.The side clearance controls oil spray of the crank and to some degree oil pressure.It was his opinion there isn't material to properly control it.
I'm just a hobbist engine builder,I have no experience to judge it by.
You're right, building one is the best test of performance.

These engines have been around a long long time and were built for truck use. They have been around a lot longer than most engines without major problems. They must be getting oil from somewhere. i realize the rods are different from stock but I don't think they are that different. Tom is a ex GM engineer, I trust his knowledge of these engines.

PS: The 235/261 have a squirt hole in the rods 'big end' that sprays the cyl. wall. So do GMC rods that I have used in the past.

I don't know if the 292 rods do, or what what width they are. The GMC ones have to be narrowed to fit.

This is why we should get the updates before we start.

It's time to bring some light back to this subject. I just got the ball rolling on my 261 project. The block has been cleaned and inspected and is at a shop getting decked. The parts from Langdon are on the way. We will be doing this slow and one step at a time and I don't see being finished before early spring.
So have any of you finished this yet? I'm looking at adding F.I. for novelty's sake but am still leaning on using an Edelbrock 2X1 and rochester carbs. Since I already have them However, I could probably sell them to finance the F.I. :rolleyes:

Dear Bert;

Run what you have first. This way you will have something (equal) to compare your new (EFI) system with.

I would get another (2-carb) manifold & start from there. If you and your Cossin plan this with Tom & Marc helping, it should work A-OK with a minimum of errors.

And always remember to: "keep your potentometers dry"....

John, that sounds like a good plan. I've talked about the F.I. with my neighbor who will be building. He fully understands the F.I., yet prefers the carbs. He sez it's just a personal preference for him. He further elaborated that he has seen guys hide the injectors in stromberg bodies on a 3X1 manifold to make it "look" old school. Just another neat idea.
I will be trying the carbs 1st. Maybe next year I will toy with the F.I. Until then, I'll just try to learn more and maybe keep my eyes open for parts. If anyone has pics of a finished F.I. system, that would be TERRIFIC!!! Thanks for all the input everyone.

I know this thread is old but I just discovered a significant issue with my veniolia pop up 261 pistons/302 rods. The pop ups are apparently not machined correctly and are hitting the head. It will take time to sort out so I am going to put that motor on hold. I need something for the spring and was kicking around the 261 cad thing. Anyone finish one and if so can you tell me how it is working, any pitfalls, advice, anyone race a cad 261? Anyonenknow where cad pistons can be purchased reasonably?

AFAIK it was common for the dome to be supplied oversize, and trimmed to match the actual exhaust pocket.
Is the dome solid?

I never saw the Inliner article, but I did read a version similar to it on the EGGE site (not there anymore). In their article, they fixed up the crank two different ways, the first seems to be the same as the Inliner's version in that they had no "shoulder" at some points around the rod journal. In the second version they welded a good tall bead all around the journal on both sides, when they did their offset grinding to suit the 292 rod in diameter and width the welded up "cheeks" provided a nice fillet and "shoulder" all trhe way around the journal.

Instead of Caddy pistons, they used some of their own custom pistons. This appears to be an expensive way to go, but where else can you get a 3/16" stroker for your ol' 235/261. I like the second crank method the most. Using the 292 rods provides you with a well designed rod without the pinch bolted wristpin.

Hopes that helps someone.

It's a lot of money with a pretty small return.
The 3/16" stroke increase is less than 5% added displacement.

If I remember correctly, this crank mod, along with a .125" overbore you can make your own four main bearing 292. And I know a 194 head definately wont work well on it. (either?)

The venolia's were supposed to be Fully machined and ready to install. That was what I understood I was paying for and to be honest they were not cheap. The lump is not too high, and not as high as some of the Jahns pop ups I have seen. I think the problem is that the lumps are machined right to the edge of the piston and the other lumps that I have seen are set in from the edge a little bit. I have to make a sheet metal template of the combustion chambers to bolt on the head and sort out what has to be done. The lumps are not that big so my fear is that to fix it will require taking so much off the lump off from the edge that there will be nothing left. The other problem is that I would have to find someone who has a lather or mill that can do the remachining, I may just call venolia's and see if they would be willing to do it. it is times like this I really wish Jahns was still in business

It goes right to the edge because the exhaust overhangs the bore. We'd like to see a picture?

If you will indulge me, I want to bump this up. I would really really like to hear from anyone who has actually done this conversion. I have to make a decision whether to just go with stock 261 rods and pistons or give the cad 292 combo a try. I already have a race prepped set of 292 rods so it's just pistons and crank grinding but I don't want to go down that path if it does not really work or is not durable.

I have never done this particular conversion, but I have hand profiled several hundred custom race pistons to fit combustion chambers on many different types of racing engines. Most of them were for very common engines that have been raced for 20 or 30 years, so you would think that by now they could make a piston dome that would fit the chamber. Since the Stovebolt engines aren't your average run of the mill engine anymore, its not a surprise(at least to me with my background)that you are having this issue. One quick method of finding out how bad the piston dome interference is, is to get a stock flat-top piston and put a bunch of modeling clay on top of it and rotate it to let it form its own dome and impression of the chamber relative to the piston, then compare to the new Venolia's you have. Put a light coating of oil on the top of the clay so it won't stick to the head. You will then see really how much massaging needs to be done to actually make it fit the chambers.

What you might find is that the real culprit is a really poorly machined head or cylinder bores relative to the head, compared to a set of pistons that are machined with much tighter and closer tolerances than a 50+ year old block or head.

Not to belabor a point, but have you talked to Tom Langdon? He's the Inliner who built the engine and wrote the original article.
This is his web site.

http://www.stoveboltengineco.com/

I know Tom. Have bought parts and usually look forward to running into him at the AAA fall meet at Hershey pa. Sent Tom an email on this but I think he may be away. I will try to call him. Yes, I know it's not a lot of extra displacement but it's a cool project anyway. If it does not work out, I can always just do a stock rod piston combo. As for the other motor, I am going to trace the entire bottom side of the head using pressure sensitive paper. Then transfer the tracing onto something more substantial, aluminum sheet, plexiglass, something, then bolt it to the block and see what's up. In the meantime, I have a couple of other unrebuilt heads that I might clean up, put on and clay up the dome like you suggested and see if its a casting issue or a machining issue. Still burns my butt that the pop ups hit.

Resurrecting an old thread...
Here's the article:
http://www.angelfire.com/nv/conv/stovebolt.html

Looks like the Cadillac 368 is so reviled that nobody is making pistons for it anymore. I've found a couple of pairs, and a set of four, but can't nail down 6 the same, except for a $700 auction listing on the unmentionable website.

The offset grind in the Cadillac article results in a 3/16" stroke increase, only half of which (3/32" = 0.09375") needs to be accommodated at the top. The "Cadillac" piston has a .029" short compression height, and the 292 rod is .053" shorter, leaving the pistons about 0.045" in the hole on an unmolested block, very similar to the stock configuration. This gives roughly 9:1 with an 848 (79cc) head. Note that the Cadillac piston pins are larger than both the 261 and 292, requiring that the rod ends be opened up to accept the larger pin.

I'm wondering why I couldn't just offset grind the crank and use the 292 rod, but mate it with a 261 piston, which would end up about 0.016" in the hole. Compression would be about 9.5:1, without decking the block or milling the head. And, since both the 261 and the 292 use a 0.927" piston pin, shouldn't they mate without modification? Or is there another difference I'm not aware of?

Any other reasons this wouldn't work? (Rod to piston skirt clearance?)

Thanks for any insight.

261 Caddy 261 stroked 261
Bore 3.75 3.80 3.78 (+30 Pistons)
Stroke 3.938 4.125 4.125
CID 261 281 278

Head Volume cc 95 79 79 (848 head)
Swept cc / cyl 712.7 766.6 758.6
Compression 7.13 9.08 9.49

Piston comp height 2.036 2.007 2.036
rod length 6.813 6.76 6.76
1/2 stroke 1.969 2.0625 2.0625
total 10.818 10.8295 10.8585
block height 10.875 10.875 10.875
piston below deck0.057 0.0455 0.0165

The problem that you would encounter in trying to use a 261 piston with a 292 rod is one of wrist pin retention.

The wrist pin in a 261 is retained by the clamp on the small end of the connecting rod. The pin in a 292 is retained in the piston by locking rings. The fact that the 292 rod is not split on the small end is a major reason that it is stronger.

To use the 261 piston with a 292 rod you probably would have to shorten the wrist pin and have the piston grooved for pin retention clips or you would have to use buttons to hold the pin in the proper place.

The 292 rod does not use a floating pin with locking clips, it is a press fit rod as are all of the 194-292 connecting rods, and is actually the rod that is used in the Cadillac 261 article. The Cadillac 261 mods are being featured in the last section of the Stovebolt Performance book.

You may be thinking of the GMC rod swap for the Stovebolt that does require a piston with circlips or spirolocs as those rods are floating and uses that form of piston design.

I stand corrected. I have limited experience with the 292, having only built one, over forty years ago. I have done a lot of 235/261's though.

I certainly plan on giving the 292 rod option another look when building a competition engine. I will have to see what the net weight savings between using a narrowed GMC rod and a 292 rod actually is. It may not be enough to justify the crank machining cost even though there would be a bearing speed advantage.

We are only talking about a 6,000+ rpm engine so the bearing speed is not really an advantage.

Roy, I'm after stroke, not bearing speed.
3/16" more stroke, with the shorter 292 rod, would put the pistons about .016" down in the hole without decking the block.

CNC-Dude, if I read your post right, both the 292 and 261 use the same "type" of pin retention, so they should be compatible?

Well, they're similar in that the wrist pin doesn't move in the S/E of the rod. The Stovebolt uses a "pinch bolt" that tightens up and closes the S/E of the rod around the wrist pin, while the 250/292 style rods have an interference fit in the S/E of the rod.

Both the 292 and the 261 (but not the 235) use a .927" pin, same size as V8 SBC, but they can't use the same piston because of the rod length difference.
For increased stroke the new rod journal must be substantially smaller than 2.311" (the 235/261 size). The 292 is at 2.100", but the G.M.C. isn't.
The maximum stroke change (up or down) is slightly less than the difference in journal ODs: 2.311" - 2.100" = .211" or 4.1485", generally rounded down to 4.125" (3/16" increase).

Is the Stovebolt Performance Book referenced above the one by Jeffrey Diamond? I did not know that had been released yet.

I didn't know Jeff Diamond, aka panic, was doing one also. But no, I am not refering to his. I am publishing one along with many others.

Goes to show you what I know, I did not know panic was Jeffrey Diamond. Victory Press on the internet. Anyhow, is your book done and available for purchase? I must not be paying attention as I had no idea that others were writing also. I love to read and there is always something to learn!

I have had it ready to print several times but keep finding things relevant to keep adding to it. I have already published one book this year and am trying to finish the Stovebolt book up as well so I can start off 2015 with more of them. Here's the link to my publishing company. Here