MotorHead

What would you consider acceptable runout ( crank straigtness ) for a crank in a 650HP, 7500RPM motor, I will tell you what my 4340 Eagle crank is after I get some opinions

4-vettes

I would say about.0007-.0014

A88FXRS

+ /- .0002-.0003. that should be a cnc turned crank

TheSkunkWorks

TimAT

gkull

Here is an article, but i talked to the machinist at the race shop. The least amount is best. Think of it as wobble when the crank is rotating. Lets say that you have .004 bearing to crank clearance. If the crank is perfect you have .004 clearance on every main baring to crank surface with oil pressure. if the crank is bent from end to end. If it was .001 off at "0" degrees one main bearing would have 5 thousand clearance on one side and .003 on the other.

http://books.google.com/books?id=TXE...hl=en#PPA57,M1

MotorHead

I just got back from the machine shop, I was getting .002" when installed in my block, they got .0011" in their fixture, which is much less but still the crank is bent.

I am going to see if they can return it and then I am going to get a Callies Dragonslayer crank, enough of the this Chinese stuff. This is an expensive motor, I want it done right

gkull

less than .002 is acceptable. Did you know that less than .007 was acceptable for big block chevys

You can sit a crank on a shelf for 6 months and chances are if it is not properly supported that it will change the runnout

having it perfectly balanced is a better thing to worry about.

BLOCKMAN

We have used quite a few of the Callies Compstar cranks and so far they have been dead nuts straight and for just under 500 dollars there a real nice peice.

TheSkunkWorks

Back when (I tend to say that too often ) I was drag racing and building my own bullets for the effort, I spent a fair amount of time in Lunati's machine shop. They did cranks for anyone who was anyone in racing, and it was standard procedure to place every crank in a special runout checking fixture and to press any offending piece into submission. Pretty scary to watch that first time, I can assure you, as you wouldn't believe how far you can bend one before they take a new set. An experienced hand on the controls was necessary not to break one, but unless this old school technique has been proven unsound or has been lost to the ages you can just have it straightened if there's a truly competent shop near you.

FWIW from what I observed, as often as not my cranks endured such torture, but we're talking very fine adjustments to achieve on the order of ~0.0005" tolerances, not about salvaging cranks that were out 0.005" or more. However, even the original Buick BB stroker prototype billet crank Moldex manufactured to my specs with Chevy rod journals (read, "$$$", even in 1980 dollars) arrived over 0.002" crooked. IMHO, we've all gotten quite nicely spoiled by the commonality of highly precise parts, so I certainly wouldn't panic or start a petition about inferior quality components over a curable amount of runout. Just thought I'd share...

Solid LT1

Compstar crankshafts are Chinese material too! Get a Howards crank at Competition Products for best bang for the buck. Here's a link: http://www.competitionproducts.com/p...s.asp?dept=543

Solid LT1

Best crank shop in our area will only HAMMER a forged crank back into straightness. Using a press is not a good method of getting crank back straight.

BLOCKMAN

I know thats why there under 500 dollars my cost. But they are machined by Callies and they are straight and round and the journals are sized perfect from journal to journal compared to the other Chinese cranks out there.

MotorHead

I agree they are forged in China but the machining and more importantly the quality control is done in the states. I am looking at either a CompStar or DragonSlayer by Callies.

That's if the shop will take the crank back. Technically it is within spec. On there jig the total dial deflection was just over .001" meaning runout is half that .0005" which is within spec. When I had it in my block I was seeing a .002" deflection, can't understand the discrepancy.

I am building a $10,000 small block here, I want a straight crank, I don't think that is too much to ask. Makes no sense to me to be **** about the bearing oil clearances when the crank isn't straight and every time it rotates the clearances change a thou.

I did not like the looks of that Eagle crank, came with a "Made in China" sticker right on the box. Some of the throws looked like Johnny Wong got tired of grinding and they look terrible

Glensgages

My dad and I both worked in the glass-container industry (mould-shop), and in the '70s, after the Chi-Coms came-over to scope-out our capabilities, they returned a few years later with TERRIBLE-quality moulds (sizes off, capacities wrong, etc.):
all Wong-Fok would say is 'Look, Joe..... shiny!" , as-if a nice polish job made-up for poor quality.