Crank Question

[dagr8tim]

I've been playing with the idea of stroking for a year or two. Today I found a 75 258 from a CJ for a really good price for carb to oil pan. Based on the FAQ, it should be a 12 counter weight 64mm crank. Will I need that turned down to 54mm?

[Muad'Dib]

Nope not necessarily. You can always purchase or make a spacer for the longer snout cranks.

[honkysXJ]

Yes or a spacer,hesco sells them I think its part # hesbs,505 sells them also not sure of the part #! There's another write up on here about it somewhere, I've got a 4 counterweight long nose crank and am going the spacer route,seems people are running them without any issues

[dagr8tim]

To follow up on my previous question, what is the pros & cons of using the 12 counterweight crank instead of the 4?

I know that the 12 weighs about 20 pounds heavier, and can prevent the engine from stalling in low idle situations. But I'm going to be running an auto, so that shouldn't be much of an issue. Also, I was reading something about inertia plates for 2.5's and they said for every pound to the rotating mass, you can expect a 5HP drop. Would the same hold true for a heavier crank?

I'm not looking to build a race engine, and would prefer torque over HP. But I still want to be able to drive this on the street and be able to run on the highway without scattering parts on the road.

[Muad'Dib]

The only benefit 12 vs 4 that I have heard of is for those low idle / rock crawling situations when using a manual transmission. I don't think there really is anything else out there that is real.

I run the 4cw and I have no issues with it. I chose this crank because I like the thought of it being lighter \ less rotating mass (may not be real), and I got it for free out of a junk 258.

If I were to do it all again I would specifically look for a 4cw because I like it just fine.

[dagr8tim]

The only benefit 12 vs 4 that I have heard of is for those low idle / rock crawling situations when using a manual transmission. I don't think there really is anything else out there that is real.

I run the 4cw and I have no issues with it. I chose this crank because I like the thought of it being lighter \ less rotating mass (may not be real), and I got it for free out of a junk 258.

If I were to do it all again I would specifically look for a 4cw because I like it just fine.

Thanks, I have a line on a 12cw crank 258 and I'm considering if I want to find a 4cw crank.

[IH 392]

The one and ONLY MAYBE!!????? advantage that I can see of a 4 over a 12 is in straight up off the line acceleration, maybe???, the 12 run smoother and I have NEVER seen ANYTHING that says a heavier crank makes LESS HP!!????, PROVE IT!, the only reason I can think of why AMC went to the 4 over the 12 is because it provides acceptable drivability and COST LESS to produce!?