The Stovebolt Site Forums The Shop Area The HiPo Shop Stroking 235 engine

Hello fellow bolters. Need some wisdom about the possibility of stroking the 235 engine by using 292 crank, rods, pistons etc. I read some where quite a long time ago that this is possible. Has anyone have any experience doing this? John

I have been wrong before, but I would not think it would be possible to use the 7 main bearing 292 crankshaft in the 4 main bearing 235.

It would be simpler to pay a good machinist to offset-grind the 235 crankshaft, and find some smaller-diameter rods that are slightly shorter than the originals. We used to do that with flathead Fords, by using 85 HP rods in the 100+ HP engines. It was possible to increase the 4" stroke 49-53 Mercury crank to 4 1/8" without doing any welding, and a 4 1/4" welded stroker was a popular size. Of course, racing parts were much more available for the Ford engine, special bore & stroke pistons, cams, etc.

The Chevy V-8 3.48" stroke crank can be reground to a 3 9/16" stroke by using the 265/283/early 327 rods with the 2" diameter rod bearings. Stock 350 rod journals are 3.100".
Jerry

Thanks Lonnie,
That is the best info yet that I have seen that sounds most practical on stroking the 235 to get more cubes to give the engine some pep. Now I am getting real excited about getting my 56 short block that I recently purchased and get that crank reground and get the rear seal modification done to reduce rear main seal leak to a very minor drip! I am getting excited now
John

Goggle:Sissel Automotive,they just about all there is in modifying a GM 6cyl.

Boyd,
Thanks for the tip, I will definately google the site. You stovebolters are creating an info junkie here. I am new to all this and just can't seem to get enough input! But i'd rather research all this before I spend the money on building up my drivetrain. I would like to keep my hydramatic original tranny so I need to find someone in the southwest who can go over and make sure all is well with this old classic transmission. So far I have acquired a rebuilt head, 56 235 rebuilt short block that came out of a powerglide equiped car so it is a block that has the lifter galaries drilled for hydraulic lifters should I desire to go that route. I have HEI distributor, split exhaust, and Offenhauser dual carb intake. I would like to hear about the best setup as far as carbs go for this intake and engine. I also have a 12 V starter and generator. I noticed that my stock 235 carb from my 54 truck does not fit on the Offy intake, the spacing on the mounting flange is narrower on the Offy intake. What are the correct carbs then? I would like to have the crank re-ground to stroke the engine and use the stronger yet lighter connecting rods from the Chevy 292 engine and maybe go with 60 over pistons to increase the CI displacement as much as possible. I understand that the compression can be bumped to about 9.5 using the right components to come up with 170-200 HP engine depending on component mix. Is that too optomistic? I am planning on switching to 3.55 or 3.28 rear end from the existing 3.90 ratio for better highway crusing performance. Here in SW it seems if you are not doing at least 70 MPH you are relegated to the right lane. The 3.55 conversion is quite expansive. What about switching to a late model Chevy Blazer rear axle? I read something to the effect that it is almost a straight bolt in with more modern brake setup? Is it cheaper to go that route? local junk yard quoted me $400 for complete rear axle from a late model low milage vehicle with rear brakes and standard chevy 6 lug pattern wheels! What is the ratio on those rear ends? what is the wise thing to do here? All suggestions are welcome. Thanks in advance, I know that this is a quite an ambitious project in the way I am heading but I believe in doing things right the first time so I do not need to be redoing something for the second time. Life is to short for that. John

Thanks Jerry,
After doing a lot of reading after all the tips on this site, I am also leaning towards re-grinding the crank and using 292 connecting rods and pistons.
John

B&M used to modify the Hydamatic.I had one for drag racing in an altered back in the 60's.A 4 speed auto behind a 6cyl what a great idea.You would want at least a 3 thou stall speed however

John, I got my 235 up to about 9 1/2:1 compression by shaving the head as much as it would go. So it is possible. I did not notice a huge bonanza in power improvement though. In fact, I don't think it was noticeable to me at all.
Weak is weak, maybe just a lesser degree.

The biggest improvement I saw was in carburetion. Put some better carb or carbs on it, with a split exhaust, and that is power improvement that you can feel. All that the rise in compression did for me was just to require a higher octane gas. So I don't think that was enough to justify the cost of machine work to do that. But let's see what others think...

LSV, you have a 216 intake, if the 54 carb will not fit. This is better anyway for a mild engine upgrade.

BC52, there is no "stall" in a hydro. They do not have a torque converter like a modern auto. They have a fluid coupler, that allows little slippage. They are nearly one to one in the fluid connection.

this is my first thought ALSO !!!!!!!!!!!!!!!!!!!!!!!!!!!!

I have been wrong before, but I would not think it would be possible
to use the 7 main bearing 292 crankshaft in the 4 main bearing 235.

Lonnie,the B&M Hydro I had,they modified the vanes in the fluid coupler,to give a higher stall

BC52, I understand, I was just referring to stock. Thanks for the info.

LSV...I don't know if it was a typo in your description...but no 235 short blocks mfg'd after 1961.

Thanks Steve for pointing out the typo that I fat fingered on the 235. Yes it is a 56 and I have corrected the post. John

Thanks for your input on the experience of upping the CR. I agree that we do not need to go that high that it will require premium gas. Give me more cubes! 261 block and stroking it?

You are right, I must have remembered it wrong. It was a long time ago and I am definately not drinking enough beer so I am not getting any smarter. :mad: All the suggestions I received about regrinding the crank make a lot more sense but it is costly. The simplest solution would be to go to a 261 block (I found one for around $100) for more cubes and a lot cheaper unless there are fitment problems with it in 54 chevy 3100 but I am sure you stovebolters will keep me on the straight and narrow. I guess I am going thru all the "New guy to stovebolts" education process, bare with me and I promise to get a little wiser. John

The 261, with its thicker cylinder walls and different water jacket will handle a considerable amount of overbore. It's probably possible to get close to 300 cubic inches with a combination of a radical overbore and the stroker crankshaft that's described in the tech article. Since the 292 rods only partially solve the deck height problem created by stroking, it's going to be necessary to have a set of custom-built pistons made, so why not just include a 1/8" overbore while we're at it? Just ran the numbers- - - - - - -a 3 7/8" bore with a 4 1/8" stroke gives us a 292 cubic inch displacement with an original-looking engine. How's that for building a real sleeper? That's one that might actually benefit from the added carburetion lots of folks like to hang on a stovebolt.
Jerry

Edit: After a bit more research- - - - - -the 292 piston can be made to fit this setup with just a bit of machining! If the 261 block is bored to accept the 292 piston, it will stick out the top of the block .073" when assembled onto the stroked crankshaft with a standard-length 292 rod. There are two 292 pistons listed by Sealed Power that might work, a low-compression hypereutectic cast piston with a .312" recess in the crown, and a LP gas engine piston with a .150" recess. Either one could be machined down .073" to give a zero deck clearance without compromizing the strength of the piston crown. The LPG piston has no offset on the wrist pin, which would result in a somewhat noisy engine due to piston slap, but it would have higher compression with the smaller dish in the crown. (good for racing, IMHO) The lower-compression piston with the .312" dish would be better for street use, since it has a .060" offset, close to original equipment specifications for the 261 piston.

It looks like we can build a stovebolt-looking 292 engine with stock parts! How cool is that?
Jerry

Although the 292 rod method has been used successfully, this is high precision work and cannot be safely entrusted to any shop that is not familiar with the engine ("what do you mean, they have different size main bearings?").
The change in compression is a nice plus, of course.
The displacement change isn't really a big improvement - less than 5% (which is generally considered to be the low limit of human sensory perception - you can't detect changes below 5% easily). This makes regrinding just for stroke ineffective as to cost.
The rod angle is slightly worse, but which, while still a fairly reasonable figure (drops from 1.73:1 to 1.64:1) is definitely going the wrong way. A larger engine "works" its ports harder and a larger rod ratio helps slightly here. Unfortunately, even getting the original ratio is very tough: 1.73:1 with the new stroke is 7.14", which requires an expensive (custom) rod and aifferent piston.
There is a potential cam interference problem here as well, where the rod will strike the cam core. I'm not sure at what stroke increment this will occur, but it's very close now and relieving the cam is dangerous due to length and torsional stress.
There are also rods from older engines with even smaller journals which will permit a larger stroke increase by the same off-set grinding method but obviously:
1. this weakens the crank even more (less journal overlap)
2. requires an even longer rod for a good ratio
3. more chance of hitting the cam

Has anyone any data or links for longer strokes?

Most of the well-established machine shops around Nashville are 3rd. or 4th. generation businesses, with a long history of doing real craftsman-quality work. The one where I worked for several years would have no problem at all with the modifications described in the tech article. They were regrinding flathead Ford cams in the 40's and 50's, duplicating the latest offerings from places like Iskenderian and Clay Smith within weeks of their roll-out on the national market. One of the projects I got personally involved in some time ago was a 5/8" stroke increase on a John Deere 2-cylinder tractor engine for antique tractor pulling. That job involved cutting out the crankcase wall between the engine and transmission for connecting rod clearance. They share a common oil sump now.

One modification we did regularly in the 50's was a 1/4" stroke increase on a 4" stroke Mercury crankshaft. It was necessary to offset-grind the crankshaft way below the rod journal diameter for the smaller 85-HP engine, then build the journal back up by welding and do a finish grind to standard 85 HP diameter for the smaller rod. Thousands of dirt track racers and illegal whiskey runners used those crankshafts. There's a long tradition of precision engine building in the southeast, and lots of it was for quasi-legal purposes.
Jerry

good info

BTW: the math comes out nicely.
235 stroke 3.9375" ÷ 2 = 1.96875"
235 rod 6.8125"
Total deck - CD = 8.78125"
New stroke 4.125 ÷ 2 = 2.0625"
292 rod 6.76"
Total deck - CD = 8.8225", or only .041" taller than the original.
This is probably do-able with a slightly modified stock piston using a new .927" pin bushing.

I should clarify:
1. the compression distance change is very low (.041") because the 2 changes in opposite directions almost zero out: longer stroke and shorter rod. Since both must be done, the "new" piston includes both changes. However, that's not the largest stroke that can be made from a 235/261 crank, or even the largest one using the 292 rod, it's just the most common. The journal size difference dictates a maximum change (if everything were new) of .211", which yields a maximum stroke of 4.1485" and would make the piston even taller.
The stroke could also be slightly less than 4.125" and put the piston exactly where it was originally, but you still need to change the pin size because the 292 rod uses .927" (SBC V8 and Gen-3 L6 size) pins.
Before everyone rushes right down to their machine shop: this is less than 5% larger than the original engine, and that's about $100 per horsepower. The only reason it was ever done is because there's very little that can be done to these motors. "Cost effective" is not a reason.

Another approach to the pin size difference would be to install a thicker bushing in the 292 rod and bring the wrist pin size in the rod down to 235 wrist pin diameter. It would be necessary to machine the pin bosses for Tru-Arc snap rings, because the clamp bolt in the stock 235 rod would be lost in the rod change, and the wrist pin would have to be shortened slightly. Doing the same stroke change to a 261, plus a healthy overbore, would be a better approach. There's no substitute for cubic inches, or cubic dollars!
Jerry

Another source to tap for information on this topic.

Inliners

More than a few "Bolters" are members.

John