[Shotimes] knife edge crank

[Mark Mucher]

Haven't we had this conversation before?

I thought the crank NEVER hit a standing sump of oil - in fact there are
baffles to prevent it from doing so...

If the crank was submerged in oil, I can see a benefit to knife edging, but
it's not! 

(Or am I missing something?)

Mark


-----Original Message-----
From: shotimes-admin@autox.team.net [mailto:shotimes-admin@autox.team.net]
On Behalf Of Ron Nottingham
Sent: Sunday, May 09, 2004 8:54 AM
To: shotimes@autox.team.net
Subject: Re: [Shotimes] knife edge crank

What "knife edging" is, quite simply, grinding down the counter weights
some, until they have an edge to them. I used to have a program/formula that
could be used to calculate how much metal could be taken off. The effect of
knife edging is so the crank does not slow any going through the oil, plus
it is supposed to help at higher rpms to keep from aerating the oil. This is
now mostly done to a crank when an engine is balanced and using lighter
pistons and rods.

I could be wrong, but unless you have a lighter rotating assembly, I don't
see any benefit to knife edging the SHO crank, since there is a windage
tray. Sure, you are lightening the crank, and you /may/ gain a couple of hp,
but at what expense? Erratic idle, probably, but that is not major. What you
could end up with is a high speed imbalance.

OK, just looked through the good book on this... Smokey comes really close
diety status, and whatever this man has said, I take like the Gospel. If you
take more than 3 grams of weight off the counter weights, you WILL have to
have the entire reciprocating assembly rebalanced. Wait a sec, that's for an
already balanced engine. If you want to knife edge the crank, you will need
to have the reciprocating assembly "balanced" first (you need to know the
weights of the counter balancers and each corresponding piston/rod combo).
There is a formula that is used to determine the balance needed for the rpm
you want (you can not ever have a "perfectly" balanced engine, there will
always be some different harmonics at different engine speeds). This will
determine how much you can take off. Unless you are building a
balls-to-the-wall maximum hp engine, Smokey doesn't this is too important.

Ron N. - Dalton, GA
90 SHO
89 325i
(OO==00==OO)
"It takes a man to suffer ignorance and smile"


----- Original Message -----
From: "James White" <greensho@crown.net>
To: <shotimes@autox.team.net>
Sent: Sunday, May 09, 2004 2:19 AM
Subject: Re: [Shotimes] knife edge crank


> What is a "knife edge" on a crank?
>
> And how could anything with the crank effect idle?
>
> regards, Jim White - greensho@crown.net
>
> ----- Original Message ----- 
> From: Ian Fisher <dataflash@yahoo.com>
> To: <shotimes@autox.team.net>
> Sent: Sunday, May 09, 2004 12:02 AM
> Subject: [Shotimes] knife edge crank
>
>
> > Has anyone had their V6 SHO crankshaft knife edged
> > during a motor build up? Any thoughts on how it may
> > effect idle or possibly cause other problems?
> > Benefits?
> >
> > TIA
> > Ian