offset grinding crank

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OUTLAW

OUTLAW

Master of All Mopars
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Here is an odd idea that I think might work but I want your input incase I missed something.

What I have is a stone stock 74 - 360 short block that is in near perfect condition. This is a low compression motor with flat top pistons in it that are .080 below deck heigth. rather than buying new pistons and rebalancing the motor I thought about having the crank offset ground .080 to end up with a zero deck motor with high compression. To my figuring, since this is a Detroit balance motor and nothing is changing weight from the rods out. With the crank already balanced for these rods and pistons nothing changes there, with the .080 stroke change the same amount of metal will be welded on the journals and ground down back to stock diameter it shouldnt need to be rebalanced. The extra weight( if there is any)would be equal on all planes. Along with this idea is if you have a crank turned down .030 on the rods you don't rebalance so I wouldn't think you would have to this way either. Did I miss something?
 
You forgot to figure on that the weight is now .080 further out. This will affect balance. Also, this is a much more expensive operation than to buy some new pistons, figuring on welding the crank and regrinding the crank. Unless you can do it yourself it'll cost.
 
You will need to rebalance. The amount of weight "hasnt changed", but the placement of that weight has. You need to think 3 dimensionally. Pistons and boring/honing for me ($600+ depending on pistons) are about $100 cheaper than welding and offset grinding, and the balancing work is the same after either. And you can install better pistons, and have a straight, perfect bore. You'll make better power from better ring seal than loose stock pistons and .160 more stroke.
 
my reasoning is that yes the weight being changed is .080 further out but it is being changed radially the same amount all the way around. And since you don't rebalance after grinding to make the rods .030 undersize that you shouldn't have to re bal;ance when offset grinding .Also this is a Detroit Balance engine which can be as much as 7 grams off from the factory.

But yes I agree this is not the optimum way to go about this but it looks to be a feasible way. To weld the crank up is about $200 and to offset grind it will be about $120. (A plus side is my crank is -.010 now and this will also bring it back to stock).
pistons...$240
bore... $160
balance..$250
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$650 vs $350

this seems like a feasible way to go from a 8.4 compression motor to a 10.7 aprox without getting too deep into it. Remember there isnt anyone locally who can balance worth a damn.So this would probably be a better balance job than a bad balance job with the extra expense
 
You don't have to re-balance to put new pistons in also. What the guys are saying is that you should balance if you change the weight amount or the weight placement even if it is the same. I balance all of my motors whether stock or race. Just something I like to do. As far as the 7 grams thing, it's your motor if you want to run as high as 20 grams off it up to you. Another thing to consider, 7 grams on a stock low-comp motor, not that big of a deal. Start added horsepower to the 7 grams and it starts to become a bigger issue. I assume you are looking for more power otherwise you wouldn't be trying to add compression.

How about this for cheap have the dish in your pistons welded up. Weight them before this is done then after you weld them remove material from the bottom to get the same weight.

There are all kinds of things you can do, but it might not be the best route, but that's why the call it hot rodding. People over the years have done some weird things to save money and make more power, some things work some don't.
 
You cant hinkt of it as radially. A V 8 is balanced by putting wieght 180° from the reciprocating assembly, or as close as possible to that point. Picture each rod as it's own, not the 4 throws roataing around the same point. It's the imbalance of each rod and the power stroke that adds the twist forces on the crank. Not one set of rods balancing the other. That's why most straight 6s, 8s, and 4cyls have the counterweights spread out more, opposing each rod throw. Same reason one internally balances. To get the weight as close to directly opposite the direction of force of the piston as possible. You are comparing taking .015 off the circumference of the journal, vs adding metal, and then removing .080 from one side, and 0 from the other. You've move the center of mass of that journal out by .040 as opposed to keeping it in the same spot and just making the overall mass less. Plus, running heavier rods vs heavier crank throws, the heavier crank throws is the better of the two evils. The resulting imbalance is the mass of the weld times the distance you move it, or .040, times rpm IIRC. So the mass the crank "feels" is more, because it's further out from the crank centerline by .040". The rod throw of the crank is part of the total mass the counterweight is reacting against. You may need mallory to get it in balance too, althought it depends if you can lighten the small ends of the rods a little, you could probably get it close enough. If it's worth a try for you, go for it. I dont think I'd try to make it that complicated, but that's one guys opinion.
 
The factory balance job isnt great to begin with. I think you would be better off with a set of new KB107 pistons.
 
Is the crank not a "Cast Crank" - upon which welding is not practical at all.
 
Just for giggles, how much can you off set the cranks stroke without adding a weld job to it?
 
rumblefish360 said:
Just for giggles, how much can you off set the cranks stroke without adding a weld job to it?
Click to expand...

No more than the biggest under size bearing that is available.
 
dgc333 said:
No more than the biggest under size bearing that is available.
Click to expand...
Not exactly..More like "depends on the smallest journal that has both the following: Enough strength for the job at hand, and a rod that can be procured that has a bearing to fit that size." In big blocks, we routinely use the big block chevy rod journal size in B block strokers, because a smaller diameter rod needs less clearancing arounf the oil pickup boss. I know some small block chevies running Honda rods and bearings, but things like side clearances and radiuses become critical. The less weight, the less frictional drag, and the less cost, the better. That last one ruins things for Mopars...lol. With good oil control, good materials, and very good machining, a typical V8 is way over built on the bottom end.
 
Well, thats what I was thinking. A Chevy S/B rod has a smaller journal. If you can offset the cranks throw and fit it to the chevy rod, you can do something different while adding inchs. How much is the question. And that amount may or maynot be worth it, but just the fact that it is doable is worth a thought.
 
Here is an example for you guys Paul Rossi back in late 80's
would offset grind a stock 360 crank to 2" chevy rod journals.
The stroke would increase to 3.685 (382 CI), he would use
off the shelf Diamond pistons for a 355 NASCAR motor and shave
the domes down to get 12.6-1 compression. With econo w2 heads,
a 800 cfm Thermo-quad carburator, 904 trans and a 2300# Rampage
pickup he would turn in the 9.30's at 153. When he started out, he
was building to run 9.90's. Combo ended up better then he thought it
would be.

So I guess you could offset grind the crank with out welding
but it would still take new chevy rods and different pistons.
 
cudaj380 said:
Here is an example for you guys Paul Rossi back in late 80's
would offset grind a stock 360 crank to 2" chevy rod journals.
The stroke would increase to 3.685 (382 CI), he would use
off the shelf Diamond pistons for a 355 NASCAR motor and shave
the domes down to get 12.6-1 compression. With econo w2 heads,
a 800 cfm Thermo-quad carburator, 904 trans and a 2300# Rampage
pickup he would turn in the 9.30's at 153. When he started out, he
was building to run 9.90's. Combo ended up better then he thought it
would be.

So I guess you could offset grind the crank with out welding
but it would still take new chevy rods and different pistons.
Click to expand...
Would you have anymore information on this motor? I just purchased it from Ron Kissner. I also purchased the rampage. Thanks all information appreciated.
 
I have offset ground bb cranks approx .060. But .060 bearings r getting hard to find. I say approx because there is always some wear on the journals. U will not get to 10.7 from 8.4 as u need .100 thou to gain 2 points unless of course ur milling heads or getting smaller chamber heads. Yes, re balancing is mandatory..... Kim
 
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you can off set grind the crank all ya want to build compression but a better, lighter piston with the thinner rings would still be needed to make a decent engine...im all for more stroke,if its smart and affordable...building for power always requires balancing,just good business man!
 
When off set grinding a crank another factor needs to be considered. In the original post (which is rather old) OUTLAW mentions that he wants to remove the .080 below deck piston clearance by off set grinding the crank .080,after a weld job. In my opinion there is not enough clearance between the counter weights and the under side of the piston (at the wrist pin area),using a .080 change. Besides the math doesn't add up, to gain .080 higher of a piston you will need .080 lower of a piston at BDC, in effect changing the stroke .160. So it shouldn't be called off set stroking .080 it should be called off set stroking .160.
Clearance could be gained back by: cut the counter weights (rebalance needed) Or use a longer rod (wasn't his original plan)
In this day and age, just go buy the right piston and have the block decked (it needs it, just to correct Mopars fabulous factory deck heights)
 
You offset grind the journal you will need a different rod with a smaller diameter crank end so you will have to re-balance the thing anyway. You can't grind metal off the journal and keep it the same size.
 
Keep in mind the original poster stated he was going to weld up for off set

toolmanmike said:
You offset grind the journal you will need a different rod with a smaller diameter crank end so you will have to re-balance the thing anyway. You can't grind metal off the journal and keep it the same size.
Click to expand...
 
if it hasen't been said you will need to cut some deep valve reliefs into pistons and need to rebalance them again, been there tried it and that was with a stock cam with .445 lift.
 
teringer said:
if it hasen't been said you will need to cut some deep valve reliefs into pistons and need to rebalance them again, been there tried it and that was with a stock cam with .445 lift.
Click to expand...
We don`t even have anyone around here that can offset grind a crank, I don`t think !
 
Great discussions on a revived thread from 2006.
Some of these topics are still relevant and timeless...........
 
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