258 crank

which is better for a 4.6L stroker the earlier 12 counterweight CS or the later 8 counterweight (it is 8 isn't it? :huh: )CS?

the add for the CS i found reads...

"This is a cast AMC American Motors Jeep 258 4.2 Liter crankshaft casting number 3217423. This crank is the early style (12) counterweight type. This crank is for engines from 1972-1986 with a flywheel centering ring on the rear flange. This crank has been freshly ground to Mains .010 Rods .010. There are no welded journals. A complete set of Clevite 77 rod and main bearings is included."


also what's the going price? they're asking $225 plus shipping, should i just go to a boneyard and get the crank out of an old 258 and have it reground?

i spent 150 for crank/rods. that's unturned and without bearings. that's not a bad price to get both bearing sets and the machining done already imo.

$225 is a bit steep for a reground crank. You shouldn't have to pay much more than $100 for one, so keep looking.
The '72-'80 cranks have 12 counterweights and weigh 66lb, while the '81-'90 cranks have only 4 counterweights and weigh 46lb. The lighter cranks have slightly more HP potential because the windage losses are less, but the engine doesn't run quite as smoothly and the harmonics at higher rpm are greater.

If you have a manual tranny, I'd suggest going with the 12 counterweight crank since it's heavier. The extra weight will enhance the feel of the extra torque, since it has more inertia. It'll crawl better at idle, you can set a slightly lower idle speed, and it will be smoother.

If you have an automatic, go for the 6 weight crank. The reduction in rotating weight will allow slightly better performance since the engine will rev a hair quicker and get up to converter stall speed sooner. Being an auto, you don't have to worry about stalling the motor or lugging it, so the extra weight is of no use.

The only issue with a 12 weight crank is that it won't be "drop in", since the snout is a bit too long - you'll have to get it turned down to use with a serpentine belt system. The six weight cranks are this way as well, unless you get one from '87-'88 onward (the exact year escapes me now...)

The windage losses and harmonics issue are all valid points, but I wouldn't think they'd be "real" issues in a low stress, sub 5000rpm motor. You might only get 200K miles out of a bottom end instead of 275K...

There IS NO 6-counterweight 258 crank! They came with either 12 or 4 counterweights. Even the 4.0 crank has 8 counterweights, not 6.
The '81-'86 4-counterweight cranks also have a longer snout (64mm) like their 12-counterweight cousins. Only the '87-'90 258 cranks share the 54mm snout of the 4.0 crank. There's no problem using a longer snout crank in a stroker. Just make a 10mm thick spacer out of an old crank pulley and put it in front of the new crank pulley to keep it in proper alignment, just as I did on my stroker:

http://www.angelfire.com/my/fan/stroker.html

You'll also find other useful bits of info. there too.

Hey, I have a newer style 258 crank if you're interested. I bought it with the intentions of building up a stroker motor but decided against it. It is sitting in my room right now, unground, but in very, very good condition. I will sell it to you for $50 plus shipping (whatever that may be)

Dr. Dino,

Since the harmonic balancer for the 99' Jeep 4.0 (242) is to be fit with it's 8 counterweight crankshaft.. from you your experience, can I still use the same balancer along with 258 crank (# 3235477) that has only 4 counterweights? the last thing I need is vibration.. thanks!

The 4.0 harmonic balancer will work fine with any 258 crank in a stroker. If you have the long nose crank, just remember to put a 10mm keyed spacer in front of the balancer to stop it "walking" forwards.

It was a simple decision of economics for me to decide which crank. The cheapest anyone around would let one go was about $50 and they all needed to be turned. Since there are only three shops in the area that I know of that do crank grinding and the cheapest was $90. In addition I would have to buy the bearings as well, it all ended about the same as the crankshaft I bought refurbished.

I paid $240 for my 4 counter-weight crankshaft with all the bearings and that also included the core charge. It seems like everyone in my area is trying to make money on the stroked 4.0s. Seen an ad in the classified for a 4.2 crank only, needs grinding.. for $100!

Here is a question, how many of you that have strokers have cranks with the 4 c/w setup? And would you get the 12 c/w if you had to do it again? I know that there is a difference, however I am just curious what poeple think about the the 2 different cranks.

Thanks,
Silent

You will never know the difference!
85 4cwt with long snout (that had to be turned down).