TOPIC:

What's the benefit of the M2 crank over a welded 900 crank...?

Biggest gain is the 16 tooth over the 15 tooth, larger center pin is much stronger.

Les

Still a ratio of 2 between different combos so still not sure I'm following the performance gains.

What about the connecting rods, do they need to be swapped as well...?

Main bearing cap work out the same...?

And Les, not trying to bust your balls or anyone else for that matter for I'm seriously asking to understand/learn something new here.

Example, next KZ1000 build I need a new crank and will be following this thread...

Larger center pin, more surface area where pressed together and larger diameter is much stronger. Really not necessary till big power. Overall weight is in between the 900 cranks and the kz1000 cranks. Im sure Larry C. can give you even more reasons it's used than I can.

Les

Old Man Rock wrote: Still a ratio of 2 between different combos so still not sure I'm following the performance gains.

What about the connecting rods, do they need to be swapped as well...?

Main bearing cap work out the same...?

And Les, not trying to bust your balls or anyone else for that matter for I'm seriously asking to understand/learn something new here.

Example, next KZ1000 build I need a new crank and will be following this thread...

The Mk II crank has a mix of flywheel weights - some full circle some pork chop. This puts it in the middle of the range with the Z1 the lightest crank and the 77-78 crank the heaviest (as it has all full circle weights). The Z1 crank will spin up the quickest. It tends to have a little more vibration and not as much inertia when cruising - so it's not as smooth. The 77/78 KZ1000 crank is great for a cruiser - the heavy crank is smoother, but much slower spinning up. The MkII is probably the best compromise and the strongest crank. THey will interchange, but you need the later stator/rotor and the alternator cover to match the crank.

John Pearson also told me the 900's and the MK2's are better for welding than the 1000's, the 1000's get brittle when welded. My motor always had a buzz that drove me crazy so when I started putting it back together last night I dug out a 1000 crank and welded it up, I'm done beating on this motor for the most part so I decided to tame it down a little.

Les

Now that explanation makes perfect sense to me... Thanks Jeff!

i put a MK11 in my 76.
the z1 and 76 cranks r known for spinning the stator off the end. this can damage the end of the crank in the process,been there.
the z1 stator is held on with a 6mm bolt that is torqued at something like 16ftlbs. the kz/MK11 have a larger bolt that takes 100ftlbs.
i beleive the MK11/kz stators put out more amps than the z1 as well.

i had a z1 crank with a close ratio trany. it spun up so fast i bent the valves. lol

Lots of great info here. I was curious as I too have spoken to John Pearson about which crank to weld up, 900 or 1000 for my build. My question: is it possible and even advantageous to drill out and tap the 900 crank end to take the larger alternator bolt and thus a greater holding strength of 100 ft/lbs? Seems to me that would help with the common problem of spinning alternator and broken woodruff key etc etc. I have one of each crank and there is no difference in the dimension of the tapered end so in theory it should work. Any thoughts?

If i remember correctly they just cut or press the end off the cranks and weld the mk11s on the 900's or 1000's