Offset grinding crank ?
 

In general, what's the guideline for finished journal sizes on a .013 stroked stocker crank?

Can one that's .010 and not stroked finish at .020?

Thanks! -Al

Re: Offset grinding crank ?
 

It all depends on a few things. Is the stroke on long side or short side of spec. How close is the index, 90*, 90*, 90*, 90*. The size of crankpin. We have made a +.013 crank and it be 10/10.

Re: Offset grinding crank ?
 

No, one that's already .010 would finish at .030. You can't take .013 off one side of the throw when there's only .010 to offset grind with.

Re: Offset grinding crank ?
 

Aren't you only taking .0065" off one side?

Re: Offset grinding crank ?
 

I savvy math but we're talking .0065 per side. ;)

Re: Offset grinding crank ?
 

If you take .010 off ONE side, you've moved the centerline .005, increasing the stroke by .010.
If you grind .0065 off one side, where do you remove the remaining .0035? bearings usually come in undersizes of .010, with plus or minus .001
You need to move the centerline .0065 to achieve .013 offset

Re: Offset grinding crank ?
 

The center-line of the crank pin is moved .0065 away from center-line of mains. If stroke on stock crank is 3.483'' instead 3.480'' and the pin is on the high side of tolerance it will make a stroke of 3.493'' grinding it .010'' under to the low side. But usually it takes a .030'' under on the rods to get .013'' stroke. If the index is good why not make it .014'' long?

Re: Offset grinding crank ?
 

Larry has it correct , it is a math exercise. The one thing that you also must realize is that indexing can not be fixed much by grinding. As an example, a 3" stroke crank would take a move of .026 for each degree it is off. to move it that much, it would need to be ground a minimum of .052 under.

Re: Offset grinding crank ?
 

Would you then have the rod journals chrome plated to build back to a std bearing? Or some other method. And would it be worth offsetting to a shorter stroke, if allowable to gain piston to valve clearance so as not to sink the valve job,in a piston without valve reliefs?

Re: Offset grinding crank ?
 

I never heard of anyone hard chroming a crankshaft to bring up a surface thickness. I thought it was like nitriding, to give a harder surface so the bearings doesn't bite into the journal.

Re: Offset grinding crank ?
 

Maybe for both.About ten years ago I had picked up a crank from a still active today Stock/super stock mopar racer and it was offset ground and hard chromed journals to standard bearing size.

Re: Offset grinding crank ?
 

I once did a back to back on a bracket car. 355 vs 383 sbc everything equal. 355 ran 6.80 - 383 ran 6.80. 1/4" made no difference.

Re: Offset grinding crank ?
 

I did that in 74 with a 426 street wedge and a 383, same heads, cam, carb and the 383 Torker instead of the 440 Tarantula, the 383 was used after I spun a bearing in the 426 so I could still bracket race every week while I built a new engine. The 383 had almost a point less comp. and about 80k miles on the shortblock, it ran within a tenth and a mph of the average of the 426.

Re: Offset grinding crank ?
 

You can weld and regrind the journals to get the stroke you want and keep the standard size. Also we were chroming crank journals back in the sixties.

Re: Offset grinding crank ?
 

Take it to a smaller journal size.2.100 to 2" Ect..
I have built many BBC with a 2.100 J instead of 2.2

Re: Offset grinding crank ?
 

The .013 Offset only adds a very small amount of displacement!

Re: Offset grinding crank ?
 

Anyone know the origin or purpose of the .013 rule? (Is it actually .015, .002 to be safe?)
As John implied, the small amount of cubic inches (inch?) gained seems, even though every little bit counts, hardly worth it, unless there's an ulterior motive.

Re: Offset grinding crank ?
 

Dave, Years ago , some crank strokes turned up short in teardown. NHRA decided there might be an advantage in altering the b/s ratio. They decided the limit would be + or - .015.
Of course come crank companies began to offer "rules rider " cranks at + .013..So it began..
Not a lot there, but you might as well take it. Plus, a smaller crank pin can't hurt, can it?

Re: Offset grinding crank ?
 

Some makes get to grind crank pin from 2.437 to 2.200 in stock to "fit" the rod.

Re: Offset grinding crank ?
 

Thanks Mark. Still trying to learn something new every day.
IIRC, it was the early 90's? At the time, I remember my partner and I wondering what was up with it. When we ran a car in the mid 90's, if definitely wasn't fast enough to warrant being looked at. lol It was a 440, maybe we were bogus and didn't know it. I know we never checked the stroke. Figured a stock crank was just that.

Re: Offset grinding crank ?
 

The impact is a bit more compression from the added stroke.
Draws .013 more air and then compresses .013 a differential of .026
Plus slightly smaller diameter crank diameter, less parasitic drag.
Most engines it is about 1.5 cuin increase.

Re: Offset grinding crank ?
 

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Re: Offset grinding crank ?
 

Excuse me!?! Stroke is measured from BDC to TDC so the "differential" is .013", not .026".

Re: Offset grinding crank ?
 

This may be a stupid question but just because you are allowed a little extra stroke does that mean the piston can come out of the that much more than the spec?

Re: Offset grinding crank ?
 

No, no more than spec. You just don't have to deck the block as much.

Re: Offset grinding crank ?
 

Yes. And max compression is dictated by spec limits. Adding stroke does not increase compression except for the additional displacement added to the mix.

Re: Offset grinding crank ?
 

Yes. There are comp. calculators all over the 'net. One can run the numbers and see if you think it's worth the extra effort.
To me, the indexing and smaller pin size are at least equal in value.

BTW, thank you to to Dwight for what you do for racers....Appreciated by 98% of them ,and called names by those who are Left.

Re: Offset grinding crank ?
 

Gasket thickness (A) and deck (B) can vary, but total of A+B has to same as or greater than NHRA spec. .000 deck and .040 gasket = -005 deck and .035 gasket or +005 deck and.045 gasket. Give yourself a few extra thousandth to the good side so you can be fearless in tear down.