Yellow Bullet Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
1,305 Posts
Discussion Starter · #1 ·
A 4.375 stroke Eagle crank for BBC says it will clear a 6.385 rod and its rough bob weight is 2300gr.

I want it machined to clear a 6.325 rod.(because I have a nice set of custom pistons allready)

Any idea what knocking .060" off the counterweights would do to the bobweight?

The pistons are heavy Ross custom nitrous pistons and a heavy wrist pin and the rods will be GRP 5300's, but I dont know what the bobweight on them is.
 

·
Registered
Joined
·
13,484 Posts
only a balance guy can tell by looking at it,...and at this time my super infa-red satellite mounted spy camera from above cannot get a clear picture

actually the FLAT SPOT on the counterweights outer diameter is what needs to be altered to clear the underside of piston.

what the detail of the 2300 grams tells you ( if your quoted weight is correct)....
...is that if your actual parts have under the 2300 gram bobweight, then you are going to have to spend more money for the tungsten heavy metal to get it to balance since you want to remove weight from the counterweights.
the weight still has to be there, but you want to remove it to clear the piston due to the fucked up rod length...and so heavy metal will be needed...

...you do not make it easy or simple...
most 4.250 stroke cranks use a 4.385 rod as a MINIMUM.... in a common 9.800 deck height block with a well designed skirt piston..COMMON.....

you will eventually spend more money than the pistons that you are attempting to configure all else around..WHICH IS WRONG..

put the 4.375 stroke crank in a 10.2 tall block and have at it with the better rod length....and proper skirt length piston.
 

·
Registered
Joined
·
4,391 Posts
6.385 as a minimum...not 4.385 I know is a typing mistake but there are some readers that dont know a lot & might think thats correct.
 

·
Registered
Joined
·
1,305 Posts
Discussion Starter · #4 · (Edited)
what the detail of the 2300 grams tells you ( if your quoted weight is correct)....
...is that if your actual parts have under the 2300 gram bobweight, then you are going to have to spend more money for the tungsten heavy metal to get it to balance since you want to remove weight from the counterweights.
...and so heavy metal will be needed...
With all due respect, that seems backwards. If my parts weigh 2100, and assuming I removed less than 200 grams from the counterweight for clearance, would I not TAKE weight out of the counterweights instead of ADDING weight ?


"put the 4.375 stroke crank in a 10.2 tall block and have at it with the better rod length....and proper skirt length piston"

If I had a 10.200 deck, I wouldnt phuck around with anything less than 4.500" stroke.

Im just asking this before I rebuild my 565. Would like it to be a 582, but ima broke dick right now.

....and as a Mfg. Manager for a machine shop, milling .060" off the counter weights is not difficult. We have 4 axis capabilty.
 

·
Registered
Joined
·
13,484 Posts
dont forget that there are four different throws..and depending on the crank shape, there are at least six counterweights...

when you remove .080" thick half radii...

you will have removed a lot more than the 200 or so grams that you have quoted.

the actual bob weight is different than the weight on the counterweight...

it is a factored and computed ratio.

having a 4 axis machine ..

dont mean that you can balance a grank.

because the 4 axis machine does not SPIN the crank to know WHERE it is heavy or lite...

not every counterweight weight has an influence on the next closest rod bearing journal...

you can only use the fancy four axis machine AFTER the balance job is completed, and then you may be able to replicate / copy / make another...with the fancy machine.....but it is still a guess....
the only accurate mannor is to use a spin up machine....

.I know that they are built all the time...but the facts still show that
.....4.375 " stroke in a common 9.800" deck chebby block has some ring and piston wear issues after a long run time..
 
1 - 6 of 6 Posts
Top