I used to know this question, but forgot and can't find the answer myself!

What all does it take to drop a "J" crankshaft into a 900 motor? For clarity- If the J crankshaft has already been modified, do you have to and is there a way to modify the Z1 case to accept it? Would it be easier at this time to also run a "J" head?

A little help? 87 views!

Without having a J crank in front of me, with cases, it was a tough memory builder. Well, of course- the J crank, if already welded with the J pin- won't work in the Z cases.

CR, I know a drag racer in town that has a J crank in Z1 cases - so it's possible, but I don't know how it's done. Sure you know this already, but the reason for using the J crank would be weight (supposedly lighther than Z1 cranks) and strength (supposedly stronger than the heavy MK 2 cranks). APE might be able to assist with a conversion "kit", or perhaps there is some unavoidable machining that has to be done. Also, the rods are different lenght between the J and the other cranks, so you'll probably end up looking to mix and match pistons to end up with the right stroke and compression...:S

I guess if you're looking for a strong and light crank you might be better off going all the way with the J - cases, frame and all, or getting a MK2 crank sent off to APE, Schnitz, Falicon etc to have it lightened. Used to know someone who did this in Denver, CO as well, but they have fallen off the planet:S

When I changed out the MKll crank to an 84 GPZ crank we had to have .032 removed from the surface of the block to compensate for the shorter rods. Other than converting the hyvo centrepin to a Falicon big pin with 16 teeth,no machining or other mods required.Hope this helps.