Crank indexing

[Chad D]

With all the attention I see to degree camshafts, does anybody bother indexing the crankshaft?

[jayb]

Do you mean checking that the throws are 90 degrees apart, or checking that the crank key is in the correct position? 

If you go through the cam degreeing process, and check for TDC on number 1 as the first step, you will automatically phase the cam correctly with the crank, and take out any inaccuracies in the crank key position, timing set, etc.

[Heo]

if you mean straightening and indexgrinding the crankshaft
i allways do it .Keyway indiferance is cured when you degree
tha cam as Jay mentioned

[Chad D]

Do you mean checking that the throws are 90 degrees apart... 

Exactly.

I understand that degreeing the cam phases the cam/crank to the #1 throw.  I rarely ever hear mention of checking crank index, or is this machining error so infrequent or insignificant as to not be worth investigating?

[My427stang]

I have never checked one for my own, mostly because I probably dont want to know

However, I have had Lunati provide documentation on some BBC cranks proving they were equally indexed across all throws.

It SHOULD certainly matter, 2 degrees makes a difference in intake centerline, what you are essentially doing is the same thing for each throw. 

With that being said, to be a real indexing animal, after ensuring a crank was perfectly "spaced" at each 90, you'd have to go back and check the cam against each opening point to make sure it was ground perfectly too

[Chad D]

With that being said, to be a real indexing animal, after ensuring a crank was perfectly "spaced" at each 90, you'd have to go back and check the cam against each opening point to make sure it was ground perfectly too

Which was going to be my next question ;-)

[Heo]

The biggest variations i have discovered
is on cranks that have been reground
but yes there is some variations on
factory stock crankshafts to
Like my machinist say this engine
had a bad tailor
And yes camshafts have some variations to
before when i was young and ambitious i used
to check all cylinders and yes i found some cams
that was real bad several degres wrong and
different lift....like you say its better to not know.....

[machoneman]

Indexing is something one can check with the right tool, yet fixing an out-of-index crank as mentioned isn't for the average builder. Very important to check btw on a top runner. Often, cheapo reground cranks suffer from inaccurate machining yet for a grocery getter, it makes little difference.


Having crewed on a supercharged alky dragster and then a supercharged nitro dragster long ago, I found that even big-bucks forged LA Billet, Keith Black and HTC cranks will bends the throws a few degrees, especially when a exhaust rocker breaks and forces a huge spike in pressure in the dropped cylinder. Sad that a pricey $2,000+ crank can be tossed after only a few runs with a bad tuneup! 

[Barry_R]

My crankshaft guy has found variances in both indexing and in stroke variation from throw to throw...

[jayb]

How much variation has he found, Barry?  Go ahead, scare us   

[Barry_R]

Would .005 in stoke variation get your attention?
Twice that?

[jayb]

Sheesh, just from a zero deck perspective and a piston to valve clearance perspective that is pretty substantial.  Sounds like it would be worth checking on a max effort build, that's for sure...