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Discussion Starter · #1 ·
Anybody who has lightened a crank, by knife edging, can you tell me how well it worked out. It is not a good idea to do that to these cranks? How did you do it, and how how much did you take off? How long did it take? Any reliability problems? I was talking to some racers and they did theres using a grinder and it took a long time. I know you have to rebalance the crank when done. Theirs were on fords and chevy's, not Nissan's. Thanks for any help.
Joshua L.
 

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> Anybody who has lightened a crank, by knife
> edging, can you tell me how well it worked
> out. It is not a good idea to do that to
> these cranks? How did you do it, and how how
> much did you take off? How long did it take?
> Any reliability problems? I was talking to
> some racers and they did theres using a
> grinder and it took a long time. I know you
> have to rebalance the crank when done.
> Theirs were on fords and chevy's, not
> Nissan's. Thanks for any help.
> Joshua L.

Knife edging is the way to go for that last ounce of power, very common in the all the ponies you can get world of drag racing. However, this can get expensive, very expensive. You may well get those ponies in another fashion, for less money. If you must, I would think that a well known high performance machine shop can do it. Personally, since I'm in Arlington Texas, I would take it to Reher & Morrison Racing Engines. In fact, I would call them even if I didn't live in Arlington. Their experience in NHRA Pro Stock, Comp, Pro Stock Truck, and Craftsman Truck series speak volumes.

Ken
 

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Re: Don't do it

> Knife edging is the way to go for that last
> ounce of power, very common in the all
> the ponies you can get world of drag
> racing. However, this can get expensive,
> very expensive.

Very well put. It is for that last one or two hp. But the cost far outweighs the benefits. And actually, in some cases, there is no appreciable difference, other than it revs faster. Most of the time, you will not see a power difference. And let me say DO NOT do it yourself, should you decided to do it. BAD Juju.
As Ken said, you can get those ponies in other fashions, and much cheaper. The cost of lightening or knife-edging a crank can run from 500-1000 or more. And for what? MAYBE a hp or two? And that is if you are lucky. I am talking in reference to our L6 motors, and my experience with them. I have no idea if it makes a larger or smaller difference in other motors. These are the results that the race shop that built my 3.1 had with their race L4 and L6 motors. In a few cases, he found the full weighted crank actually was better, and he attributed it to the better harmonics, for you take away some of that natural dampening, etc... when you remove that much weight.
So my vote is an emphatic NO, DON'T DO IT!
-Bob Hanvey
 

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Discussion Starter · #4 ·
Re: Don't do it

Bob,
Thanks for the advice. As I said before, I think, I was very curious as to how this affected things. I will not do it, but I will detail the crank, grind smooth, remove burrs, possibly shot peen, etc. This all came up from talking to a couple friends who race locally and had done this to their chevy cranks. They did it themselves.
Thanks again,
Joshua L.
 

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Re: Don't do it

> Bob,
> Thanks for the advice. As I said before, I
> think, I was very curious as to how this
> affected things. I will not do it, but I
> will detail the crank, grind smooth, remove
> burrs, possibly shot peen, etc. This all
> came up from talking to a couple friends who
> race locally and had done this to their
> chevy cranks. They did it themselves.
> Thanks again,
> Joshua L.

Joshua,
By all means, if you want to do those things, go ahead, but be sure to get the entire assembly balanced when you are finished, for you have changed the characteristics of it. By the entire assy, I mean the crank, rods, pistons, harmonic balancer and flywheel. You can get by w/o the balancer, but you need to do it with the flywheel, and possibly the clutch,(for not all clutchs are balanced right, centerforce are)
-Bob Hanvey
 

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Discussion Starter · #6 ·
Re: Don't do it

Bob,
I guess I just forgot to put that down, I would like to have it all balanced to 7.5K-8K. Just one question, I thought the Z's and most japanese caars had internally balanced crankshafts. Why is it not balanced like that, with only the crankshaft? Either way, I will definitely balance everything after I am done modifying/prepping it.
Thanks a lot for your help,
Joshua L.
 

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Re: Don't do it

> Bob,
> I guess I just forgot to put that down, I
> would like to have it all balanced to
> 7.5K-8K. Just one question, I thought the
> Z's and most japanese caars had internally
> balanced crankshafts. Why is it not balanced
> like that, with only the crankshaft? Either
> way, I will definitely balance everything
> after I am done modifying/prepping it.
> Thanks a lot for your help,
> Joshua L.

You have answered your own question, but might not realize it. Yes, they are internally balanced. That means that the interaction of the pistons, rods, crankshaft, etc.. all contibute to balancing the engine. If it were externally balanced, you have more leeway in how well balanced it must be,(that is a crude comparison, but it works). Anyways, yes, the crank is what balances the engine, ie the couterweights on the crank, vice some engines, that have a huge counterweight on the balancer, hence, externally balanced. But if you change out parts, modify the crank, etc... you have now changed how that crank spins at higher rpms, and the assy. now needs to be re-balanced. the reason you want the flywheel to be included is because it is bolted directly to the flywheel, hence, it acts like it is part of it. Idealy, the flywheel would be perfectly balanced, and wouldn't affect the crank, but that is not the case.
And as for balancing it to 7.5-8k, realize two things. One, the actual machine that does this only spins the crank at 900 rpm, much like a tire balancer only spins the tires at 20-30 mph. where you gain the advantage in the higher rpms, depends on the quality of the shop. Now, second, if you want it balanced for that high, i will assume for a min you want to run it that high. you realize to run it up there, you are looking at a full race cam, that is useless, and i mean useless below about 5-6k? If you just want the extra margin of saftey, and are not worried about driving up there, just have it balanced by a competent shop, then it won't matter.
-Bob Hanvey
 
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