Technical Off set ground Hemi crank

Any one offset ground a 354 crank down to BBC small rod dia. of 2.1"seems this would be easier and cheaper than welding the journals to increase stroke. Several rod manufactures make the 2.1" rod in various lengths. any reason the crank if ground and nitrated would not be strong enough.

 

The crank would probably be OK, I wonder if you could find rods with big ends wide enough to fill the gap? Maybe big block chevy rods?

 

I'm not an expert but have looked into this also, they offset grind a lot of cranks to increase stroke. Oldsmobile is done all the time. Things that need to be considered are the width of rods, where the oil hole comes out since it is on an angle, how much you can offset grind it. What is the dia. of the stock hemi journal?

Pat

 

i run a billet 392 crank in my 354.. the mains were cut down to 354 specs. .050 was added to the thrust. the rods were cut to 2.1 so i can run cheap readily available bearings. i switched over to alum rods so it would have been hard to get pinned narrow 354 bearings. mile high crankshaft in colorado did the work. ask for dave 1-303-781-6764

 

a 354 block .030 overbored with a 392 crank gets 389 cubes. .060 gives 392 i use bbc rods it all fits just fine. no need to offset grind you can build a stroker with out it using readily available parts.

 

Racer-X I was thinking that I had heard BBC rods but was not sure thanks for clearing that up.

 

when i ran the steel h-beams i had about .055 between the rods. with the alum chevies its a much more reasonable .035

 

The 331/354 Chryslers rod journal is 2.250 stock BBC is 2.20 and they make an after market BBC rod that is 2.10
331/354 and BBC have a .990 pin.

 

The way I see it you can only offset grind that crank approx. .035" hardly worth the cost of doing. That is of course without welding it up. On our Oldsmobile we offset it .250" which is quite a bit. I like what racer x suggests.

Pat

 

If you ran the BBC rods at 2.10" wouldn't that be off set grind .135"

 

i made a error i ground the rods to 2.20. that way if the crank needs grinding again it can be done. remember there are water jackets were the rod clearancing needs to be done. offsetting the crank may put you into them depending on the size of the big end and bolts used. caution needs to be taken when grinding down there. stay with proven combinations. reinventing the wheel may have negative effects like a junk block. you can also use the stock length h-beams hot heads sells. if you go this route get the rods with the tang on the other side then the muuuch cheaper big block pontiac bearings can be used. this setup uses the stock 354 journal. i have used this setup for years.

 

I have one sitting right here. Offset ground to 3.775 stroke. Using MGP 2.1 journal rods. You can also get bbc rods with a 2.0 journal.
Offset grinding is THE least expensive way to build a stroker. You do one thing.... grind the rod journals. Far cheaper than 1: buying ANY 392 crank, 2: having the mains cut, 3: the counterweights cut, 4: the rear seal cut, and 5: welding and cutting the thrust.

 

I was looking for around 3.75 stoke so no clearance issues there

 

Are rod bearing readily available for the 2.10" rod journal

 

yes its a chevy size. but why grind it that far if you don't need to the counter weights don't need to be cut. the crank fits the block. like i said i have one in my car. call mile high. these are the guys that attend all the nhra races. they pick up all the pros hurt cranks and fix them. they then return them at the next race. this is no small operation. talk to dave he will set you straight. i think the last time i had one done it cost around 550 you have to grind the rods thats a given. and most likely the mains on a used crank. so really the only added cost is the thrust work. the benefits far out weigh the cost on going the 392 way. the crank can be cut several times down the road. taking it down to 2.0 or 2.1 leaves little room for future repairs. then you get to spend your money again buying another crank. there is obviously several ways to do this with various opinions. go with what fits your budget. talk to a crank specialist like dave . good luck on the build.

 

Is

My idea was to offset grind the crank to increase the stroke, using BBC 2.10" rods allow you to add stoke to the crank in my case .125" yielding a 3.75 final stroke with out welding up the journals, I'm just throwing ideas out there to see what others think, see if anyone else has used this method, thanks for your imput.

 

TR,Would that crank be for-sale

 

Journal Hardness: Another thing to think about is journal hardness. In a typical billet crankshaft, the journals have been nitrided - and the hardness only goes down into the material about .020 or so (depends on the process, manufacturer, etc). Typical OEM forged cranks are induction hardened. One thing to think about is to have the crankshaft nitrided again (after the offset grind) - this will restore the hardness and should give you extra journal life. The cost can vary, but it is usually a couple hundred $$$ when you're all said and done.

Journal Sizes and Overlap: One of the things that makes a crankshaft strong is the amount of journal overlap between the mains and the throws/rods. When you dramatically reduce the rod-journal diameters, you reduce the overlap and this does weaken the crank. Here is a picture that I found that shows what I'm talking about:

This is probably not a big deal for a typical street Hemi build, but one does need to think about it on a full-on blown motor (especially competition, high HP levels, high boost, etc). If you regularly check the motor, have the crank magged during re-freshening, etc . . . probably not a big deal. But, when I start to hear of 2.000 rod journals and blown motors, I start to ponder what can happen on a crank failure . . . you can lose a lot more than a few hundred $$$ of work.

Just some things to discuss with your crank suppliers.

B&S

 

Thanks for the info, I am considering running a blower at around 4-5psi of boost, street car, most likely a 32 style roadster, no competition racing, street use only I would have the crank nitride for sure. Just looking for interesting engine combinations, I know Hemi's are already unique but doesn't hurt to try something different if the cost is reasonable and the engine reliable.

 

The Early Chrysler cranks are plenty strong and many have 2.2 journals. As mentioned, not a big deal on a street engine and IMO, not a big deal up to 8psi or so when the 'rules' start to change. To go one step farther, a slight weld-up in addition to the smaller journal can yield some bonus inches and not be a strength issue.
Although there were some spectacular failures of long stroke 392s back in the days of F/A and such, there were plenty more 4½" cranks spinning at ridiculous rpms every weekend and putting big smiles on drivers faces.
The obvious also needs to be mentioned. Crank work should be done by a competent welder/grinder who can ensure that the journals remain indexed at 90°. Being off just a little bit can wreak havoc on the runability of the package and could cause damage.

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Thanks a lot for the added info.

 

Gary, does your shop do offset grinding?

 

I think we're on the same page - and agree with what you're saying. A lot of those 4.5" cranks were originally welded strokers (guys like Joe Reath did a ton of them). But, they weren't running 2" rod journals in most cases, had large bearing clearances, grooved mains, hard-chromed journals . . . stuff to 'hopefully' keep the crank alive. Of course, when you grenade a motor - is hard to know "what went first"!

Good thread guys - lots of cool options to get some cubes and not have to call Crower for a new $3000 billet crank! I've been jonesing about a 4 3/8 billet crank for awhile - may just have to order one soon . . .

B&S

 

Yup, same page.
$3000 for a billet is pretty cheap these days. A Winberg runs $4k+

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Pat,
I actually built a B/RB in the '90s for a fella that was racing in an oddball stock class that allowed up to .010 offset grind on the crank. It would not increase your displacement much but it does change the rod angle ever so slightly which could free up some torque, even ever so slightly. Was it worth it? I don't even know if you could measure it with a dyno but evidently the fellas that wrote the rules thought it would give some advantage.

Bored and Stroked

You are going to love this, I was reading the thread from the bottom to the top and when I saw your post I saw B&S first. My brain said B.S. and I read your post 3 times trying to figure out what you were calling BS on. LOL

 

i bought a used billet 392 crank from a fuel racer. the crank had a roughed up journal. it was of no real use to them. but for my blown gas street application it was perfect. i figured i was going to cut the rods any way so i bought it. there are lots of these cranks around. nitro racers rotate out parts all the time. they may not be capable of a load of nitro but in a street application will live fore ever. a stock crank is a good piece the billet is obviously better. i paid 250 bucks for mine. i have had it in the car for seven years now. i beat he crap out of the car racing it and street driving it. i have taken it on drag week the last two years. just another option.

 

Sorry Bob, somehow missed your query in all of the excitement...
We no longer do any custom crank work. For us it just did not pencil out but there must be a shop somewhere in the NW that is capable. Seattle is a big town, maybe start asking at all of the local parts shops.

.

 

No problem Gary, there is a shop in Vancouver I'm going to check out,
Thanks for the help.

 

Wayne Harry????