Crankshaft Questions

[Bodo]

Ok gang. I am able to get a used 3235477 (that's the 4CW) crank for free. The shop I work at has one out in the shed. The engine builder took a look at it and said that I should really use the 12CW (3214723) crank.

Is there really a difference between the 12CW and 4CW cranks for a DD with occasional offroad use with regard to longevity?

[Muad'Dib]

I may get flamed for this, but but it hasn't actually been proven that the 12CW is better / worse than the 4CW. Most people say to go with a 12CW. More because they think the 12CW is stronger.

Logic tells you that a 12CW is going to be heavier (which it is), and have more rotating mass. It has been said that this extra mass is good for low RPM rock crawling for instance.

The 4CW is lighter, and logic tells you that it would "spool" (for lack of a better term) up faster.

However, this is theory, not fact. I don't think anyone has any factual information on the subject .. its speculation. However, one fact is that so far no one (unless they haven't spoken up) who has built a stroker with a 4cw or 12cw has complained that they should have gone one way or the other.

A lot of people also say that if you are building a stroker for an automatic that a 4cw will be fine, but if you have a manual, than you should go with a 12cw.

I personally feel it doesn't really matter. I also think that when choosing a crank, you should just get what you can get your hands on as cheap as possible. My preference is towards a 4cw (which i am going to use for my stroker build).

If i was to advise someone to choose i would tell them to pick the 4cw, or pick one based on what transmission they are going to use like outlined above.


Hope that helps.

[RAPTORFAN85]

I run a 4cw crank. Never had any problems and can't tell a difference from a 12cw stroker that I have driven FWIW...

[5-90]

The differences between a 4cw and 12cw crank have nothing to do with longevity - just reaction.

The 12cw has more rotational inertia, and suits a manual transmission (especially in towing/hauling applications) rather better. The filled torque converter assembly used in an automatic is rather heavier than the clutch/flywheel in a manual, so the 4cw is just fine. Also, in cases where absolute throttle response is critical, the 4cw will suit you better.

I want a 12cw when I finally do my stroker - but that's because it's going into a work truck with a five-speed, and a reasonable amount of towing and hauling is to be expected (you'd be surprised at some of the things I've moved with my XJ...)

But, if it doesn't really matter to you and you've already got the 4cw, go ahead and use it.

[Bodo]

Thanks Ya'll. I'll take it and have it ground.

[SilverXJ]

What was the engine builder's reason?

[Bodo]

It looks wimpy. I think was the actual quote.

I think he's been spending too much time building 600ci BB Chevy's...But that's Bob for ya.

[yuppiexj]

All else being equal (price, availability, condition)
I'd take the 20lb weight savings of the 4cw.
It will spin up and down the RPM range more quickly than the heavier crank.

Newtons 1st law and all that.

Free crankshaft, I'm glad you took it.

[SilverXJ]

Well, it does "look" wimpy. You go over to the machine shop I use and you see all these beefy looking V8 cranks. Then you saw my 4wt crank and it looks kind of sickly compared the the V8s. However, my machinist said that he would rather use the 4wt over the 12wt.

-Chris

[seanyb505]

You cant argue with weight saving. I havent experienced any issues with the 4wt and 5sp setup.