Custom Crankshafts ?

[10sec rx7]

$5500 is not bad for a custom crank.. This owes $5350 and its not custom lol

[BigMuz]

$5350 and they had to cable tie it together. Ripoff.

[10sec rx7]

came back from balancing yesterday.. they had to drill in some metal...

[333pg333]

Excuse my ignorance but how do 'they' balance reciprocating parts? I've heard that they will spin cranks out to about 2000rpm and are able to determine (and influence?) where harmonics come in, but how can they take the crank, rods, pistons and clutch parts and truly balance these parts without actually having an assembled long block within which to spin up parts?

[Dogsballs]

Weigh them and match

[333pg333]

Ok. So then if you're saying you just weigh up e.g. the rods and pistons to get that pairing as even as possible to the others then wouldn't you want to supply these parts to the manufacturers of a custom crank before they build it? Can't imagine that you'd want some other party to start carving bits off a custom $6k crank when balancing all the parts? I'm sure I am being a simpleton here but I'm just trying to visualise the sequence of events.

Also, as we've gone into a new page I'll ask the question again. Has anyone heard or used these guys in Melbourne for parts?

http://www.pureperformancemotorsport.com/

[10sec rx7]

Yeh you get the bob weights from the rod, pistons, pin, rings weight, then the bob is applied to the crank and its spun up and balanced

[Dogsballs]

$5500 is not bad for a custom crank.. This owes $5350 and its not custom lol

which ls crank is that?

[10sec rx7]

Callies ccw billet

[Rdyno]

Yeh you get the bob weights from the rod, pistons, pin, rings weight, then the bob is applied to the crank and its spun up and balanced

There is actually a bob weight division number or some shit I will have to get my engine book out you divide or multiply by a certain number that you get from the piston and rod and you get your bob. My mate built engines for over 10 years when he starts talking about balancing my brain starts to hurt lol.

[10sec rx7]

Yep mine too I can't work it out lol

[profi]

+1 Crankshaft rebuilders, don't compromise on such an important component.

[Rdyno]

Ok just reading my engine book most machinists will add 50% of the total reciprocating mass to the bob which is the weight of the piston rod pin and retaining pins. It seems this is done for dynamic reasons but all engines are different "the formula used to compute the bob weight for a 90deg chev v6, for example, calls for adding 46% of the reciprocating mass" That was straight from my book.

[10sec rx7]

LS1 making 1500hp is done between 51 and 52%

[333pg333]

So...they spin the crank up on whatever device they have and then merely add or subtract with these bobs based on the paired weights of the pistons/rods/hardware ?