Jeep Strokers

Given the Weight of a 12 cwt crankshaft & inherent dynamic balance
how much can the counterweights be trimmed to reduce overall weight ?

I like the idea of uniform balancing via counterweights just not
the some 20 extra pounds of cast iron to spin up .

Not sure anyone here has gone as far as knife edging a crank for these motors. The extra weight does help with the harmonics.
Honestly though, it would be way more cost effective and lighter for you to just go with a 4 cwt crank then to have your 12 cwt crank knife edged then balanced. Unless you plan on racing and spinning up to 7000 rpms you won't be gaining anything but a lighter wallet. Even then you wouldnt even notice a difference.

milnersXcoupe wrote:Given the Weight of a 12 cwt crankshaft & inherent dynamic balance
how much can the counterweights be trimmed to reduce overall weight ?

I like the idea of uniform balancing via counterweights just not
the some 20 extra pounds of cast iron to spin up .

On an engine that's rev limited to a modest 5250rpm, why bother?

Trade your 12CW crank for a 4CW crank.
Properly balanced, I don't believe its been proven that a 4CW crank will spin up any faster than a 12CW crank?

I agree with everybody statements up to this point.

Knife edging cast Crankshaft in a low RPM tractor engine is a waste of time and money.

The 20# lighter 4-weight will absolutely spin up(and down) faster than the 12-weight. I was even contemplating a 10# lighter fidanza flywheel at one time. Even 5# lighter makes a noticable difference in the rotating assembly(I'm in the BMW world too with my '95 M3--there are many lighter flywheel and clutch assembly options). The bottom line is if you are off-roading you want the 12-weight and if not, you want the 4-weight.

My brother Nick just told me his knife-edged(or semi-knife 'cause I thought it could be more aggresive), offset-ground(4.060" stroke) 12-weight 505 crankshaft weighs 60#, so that'll give you a clue how much you can lose.

I guess another question that needs to be asked is what is the application of your stroker project?

I ask because sometimes the purpose and budget of the build will help to determine the practicality of a upgrade.

For example. If you had a budget of less then 5K to build your stroker, knife edging a crankshaft would be a waste of money because you'd receive better gains or benifits if you applied your budget and other areas

There is definitely pros and cons to both 12 and 4 counterweight Crankshafts.

A lighter flywheel will give more benefit than a lighter crank, the mass is at a greater distance of the radius.
On our race car we cut a 199 9" clutch flywheel right down to the pressure plate bolts and carved it a lot more than that too, and used a flex plate to start it with, it really spins up fast!

gradon wrote:The 20# lighter 4-weight will absolutely spin up(and down) faster than the 12-weight.

I used to think that as well. The crank is pretty much center mass so the extra 20# is negligible on spining up n down. Only a larger stroke could add rotational mass. The advantage that the 12cwt crank brings to the table is that it softens the harmonics at higher rpms and thats about it. Honestly a 4cwt crank would probably be more benificial for 95% of the people running 12cwt cranks. All for the simple reason that it would drop 20# off the nose of the jeep.

IH 392 wrote:A lighter flywheel will give more benefit than a lighter crank, the mass is at a greater distance of the radius.

Agree.

Russ Pottenger wrote:knife edging a crankshaft would be a waste of money because you'd receive better gains or benefits if you applied your budget in other areas

Like adding a crank scraper, welding an extra baffle inside the oil pan, adding a "kickout" to the sump to increase its capacity, and swapping in a HV oil pump. Perhaps an oil cooler too if you do a lot of offroading.

Darn it.
Wrote a long explanation on the physics of rotational mass. Musta pushed the wrong button 'cause it anit in the thread.

Let's just say the guy with a bad haircut knew a few things way back when.

You cannot beat physics. You might think you can but it isn't gonna happen.

My brother told me the wrong weight. His scale might be off, but he weighed it to be:

Did your brother mention how much or how involved it was to rebalance the crank?