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## Crankshaft Offset grind

Grinding the crankshaft is a relatively straight-forward process. The crankshaft nose is placed into the head stock chuck and the crankshaft flange (in some cases the crankshaft seal surface) is secured in the tail stock chuck. At which point the main journals can be ground. The rod journals are ground after the machine is set to the proper stroke and after the counter weights are set. After the crankshaft is ground, the oil holes are chamfered and deburred. Then, the crankshaft is polished with a fine grit belt to achieve a satisfactory micro finish.
The above process can be used to add more stroke or remove crankshaft stroke. This has been done for years. The 12 o'clock and 6 o'clock positions are offset ground.

My question is - Is there a benefit to offset grinding the 3 o'clock or 9 o'clock position?
Would there be an advantage regarding timing?
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 Recognitions: Gold Member Science Advisor Not sure I follow. Grinding the pins at 12 and 6 o'clock add/remove stroke; I assume 12 o'clock is pointing back towards TDC? So grinding at 3 or 9 o'clock would change the TDC position with respect to crank angle, and could upset the balance of the engine (as well as buggering up valve timing). So no, no inherent advantage that I see. What were you thinking?
 Any deviation from the correct indexing will cause problems. If you feel the need to change something to optimize each cylinder, I'd start with adjusting the individual spark timing; after that, custom grind a cam with different lobes for each cylinder. As brewnog said, what are you after?

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## Crankshaft Offset grind

lets just say I am looking for optimum performance with in the limits of a restricted class. Engine limited to stock lift cam shaft, displacement, valve size, compression ration can be changed, stock size piston but weight is open as is any piston rings, ignition must be by engine actuated timing intake and card must be stock appearance, exhaust is open, after market connecting rod is ok. stock size crank
am looking for an advantage...
I am having trouble seeing effect of the 3 oclock offset grind on the crank??
Would this modification make the engine think it had a longer con rod and make more power?
 Recognitions: Gold Member Science Advisor No, it would just alter the TDC position with respect to crank angle. If you did it by the same amount to all cylinders, all you might see is a change in compression ratio.
 How would altering the TDC position wrt crank angle alter compression ratio if the stroke is the same? Wouldn't it only reduce CR if there was a change? This is all beyond what i've ever done before. Is this for your open wheel car Mike?

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 Quote by xxChrisxx How would altering the TDC position wrt crank angle alter compression ratio if the stroke is the same? Wouldn't it only reduce CR if there was a change? This is all beyond what i've ever done before. Is this for your open wheel car Mike?
Far be it for me to look for an advantage in a highly restricted racing class...

what ? me take liberties with the Written Word of the sanctioning organization..I am shocked!!

 Quote by Ranger Mike lets just say I am looking for optimum performance with in the limits of a restricted class. Engine limited to stock lift cam shaft, displacement, valve size, compression ration can be changed, stock size piston but weight is open as is any piston rings, ignition must be by engine actuated timing intake and card must be stock appearance, exhaust is open, after market connecting rod is ok. stock size crank am looking for an advantage... I am having trouble seeing effect of the 3 oclock offset grind on the crank?? Would this modification make the engine think it had a longer con rod and make more power?
Offsetting the piston pin in the piston will change the piston motion in a way that can mimic a longer or shorter rod after TDC. But first you need to decide what the engine will respond to.

http://victorylibrary.com/mopar/rod-tech-c.htm

Your rules appear to allow a change in rod length, true? If not, can you use a "stock" rod length from a related engine family (Ford 2.3 rod in a 2.0 for example)?

As usual, there are ways to improve performance with things that are hard to measure and aren't specifically noted in most rules. Is that cheating?

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 Quote by mender Offsetting the piston pin in the piston will change the piston motion in a way that can mimic a longer or shorter rod after TDC. But first you need to decide what the engine will respond to. http://victorylibrary.com/mopar/rod-tech-c.htm Your rules appear to allow a change in rod length, true? If not, can you use a "stock" rod length from a related engine family (Ford 2.3 rod in a 2.0 for example)? As usual, there are ways to improve performance with things that are hard to measure and aren't specifically noted in most rules. Is that cheating?
rules say you can use after market con rod but must be stock length..we already did the piston pin offset thing...lightened flywheel, use 4 inch diameter clutch /pplate package
cold air scoop. CD ignition, thin piston ring package ( we used zero gap rings and too much drag...sucked HP) we run redline oil at \$10 per quart..dry sump oiling system...electric fuel pump and water pump to gain a few HP...it would be a lot simpler to bore it .125 over and go long con rod but that is obvious cheating..
 Is it OHC or pushrod? Sometimes you can change the motion ratio without altering the cam lobe profile and total lift. Is porting allowed? Valve stem size? Spring and retainer weight? How much vacuum in the crankcase? Oil scraper for the crank? Min quench and max compression? Angle milled the head and manifolds? Offset the head on the block to unshroud the intakes? Is this an open forum?
 Recognitions: Gold Member Science Advisor overhead cam , porting allowed, valve size must be stock, cam lift is measured on the head at race course and on top of cam follower, dont know about crankcase vacuum.. there is a combustion chamber min cc regulation as is head gasket spec dry sump has crank scraper open forum? i guess??
 Just wondering if you want everyone to know what you're up to! I'm getting the idea that you're running in FC, right?
 Recognitions: Gold Member Science Advisor No not FC...nice try though...
 Well, what then? Hard to give tips without knowing which engine you're using!

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