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Old 03-15-2013, 09:07 PM   #21
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Yeah that makes no sense to me. Take it a step further a 185 vs a 275 of the same compound. Same overall traction?
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Old 03-15-2013, 09:09 PM   #22
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Part of it is also that tire manufacturers can use a softer compound on a wider set of tires and still get the same wear because the load is more distributed.

Softer tires = more grip.

Also:
http://en.wikipedia.org/wiki/Tire_load_sensitivity
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Old 03-15-2013, 09:11 PM   #23
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Well no we're not changing that, we want the same coefficient of friction, just one tire is fatter than the other one.
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Old 03-15-2013, 09:17 PM   #24
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Old 03-15-2013, 09:19 PM   #25
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Old 03-15-2013, 09:21 PM   #26
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Owner said he meausered 1.965 on main journanls and 1.737 on rod journals. Any thoughts?
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Old 03-15-2013, 10:21 PM   #27
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Quote:
Originally Posted by Hot_Wheels View Post
Owner said he meausered 1.965 on main journanls and 1.737 on rod journals. Any thoughts?
With the mains you can run a standard bearing with race motor clearance.

The rods on the otherhand, that is a.0330 difference (according to the solomiata website). You need to see if you can find a bearing that will fit it. The nitriding would have most certainly been lost at that depth.

Depending on who you talk to, you will want a .0018-.0025 clearance on a race motor. If you can get the bearing to meet your proper clearance, that is great. However, if you damage the crank on the rod journals in any way, it will be a boat anchor unless you are willing to pay to have it welded and possibly nitrided. I do not know what it costs to do the knife edging like that or what it costs to have them rewelded. You will have to weigh whether it is worth having fixed if it is damaged.

My opinion is that whom ever cut that crank knew full well that it was a one shot deal. Buyer beware.
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Old 03-15-2013, 10:28 PM   #28
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How hard is the crank to be cut on a lathe?
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Old 03-15-2013, 10:33 PM   #29
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Knife edging? I do not know how long it takes or how much it costs. There is considerable amount of balancing work involved.
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Old 03-15-2013, 10:54 PM   #30
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That crank was done by a properly equipped shop that knew what they were doing. The lathe required to make that cut is quite specialized.

On the friction. I need to open, Norton's Design of Machinery. I know the relationship between surface area and friction is in there. Its one of the advance concepts of friction. With simple friction we assume that surface area doesnt matter, but thats a simplification of whats actually going on. Unfortunately my copy of the book where I know this is, is at my apartment and I'm at my house. I also know that surface speed, which reduces when when you reduce the diameter of the pin, also effects hydrodynamic bearings.
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Old 03-16-2013, 02:12 AM   #31
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well i guess books are good for something! i busted out my book that someone on this site donated to me (thanks!) and from the specs he provided as mentioned the crank is below the recommended specs. He was asking $300, it may still be use able but i just couldn't sleep at night with how much i will have in my bottom end to trust a questionable crank.


Im very curious how much he paid for the work to be done, from what he told me is the machine shop sent the crank out for the work.
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Old 03-16-2013, 06:21 AM   #32
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Quote:
Originally Posted by miata2fast View Post
I like how that crank has been knife edged. How much has been taken off the journals?

There is an advantage of removing material off the journals. If you take it down, you reduce the amount of surface area that the bearing contacts. This creates less friction, and also makes it a tad lighter. It was a known tactic to take big block cranks and turn them down to small bock size to make more power. The only downside is if you hurt the crank, you have little or no room for repairs. You will have to get the crank rewelded, or source another crank. I guess this is ok for the higher budget racers, but not so good for the Joe Shmoe.

If you do decide to take the crankshaft down further, find out what size bearings are available from the supplier of your choice. You should be safe to make as much power as you desire from a crank that has been turned down to what a bearing supplier like ACL has to offer for your crank.

As far as the nitriding, you can typically take it down to 10/10 size and still have the nitride hardness. However if you want to take it further, there are nitriding services available. It depends on what you can afford.

I found this operation that does various hardness services of many types.
IBC Coatings: ION Plasma Nitriding | Boriding | TD | Vacuum Heat Treat | ION Nitriding


Most good V8 crank companies will offer a "honda" rod jurnal option, allowing V8's to use honda bearings for the rods. this gives them a very good selection as well as a smaller and narrower bearing.
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Old 03-16-2013, 12:06 PM   #33
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Quote:
Originally Posted by ctdrftna View Post
Most good V8 crank companies will offer a "honda" rod jurnal option, allowing V8's to use honda bearings for the rods. this gives them a very good selection as well as a smaller and narrower bearing.
I was hoping you would join this discussion. It would be nice if BogusSVO would drop by.
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Old 03-16-2013, 12:45 PM   #34
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RE: friction

You guys are right about the total friction force being about the same at the bearing surface. The difference is that we're talking about rotation here so we need to also consider the length of the lever arm. With a smaller journal the friction force is acting closer to the axis of rotation, so it has less leverage and consequently a smaller effect.

Think of it in terms a work if you want. Here I mean the physics definition of work = force x distance. The force is more or less constant, but with a smaller journal the distance all the way around is smaller, so the work (loss of energy) is smaller per revolution.

EDIT: Consider the fact that larger diameter brake rotors work better because the pads are farther from the axle, even though the friction force at the pads remains the same.

Last edited by DaveC; 03-16-2013 at 01:55 PM.
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Old 03-17-2013, 04:21 AM   #35
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You couldn't pay me $300 to put that crank in my motor. Leave the crankshaft alone.
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Old 03-17-2013, 05:16 AM   #36
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You only like Hustlers cranks dont ya.
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Old 04-05-2013, 09:50 AM   #37
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I am standing by on this thread, Just DO IT! and come back with results.

+1, leave it alone, stock crankshaft all day.
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