Primary shaft question

Good afternoon folks. 
I'm wanting to to put a later crank into my earlier cases but the primary chain gears are different width. 
Is the gear in the idler interchangeable or will I need a different shaft?
Thank you for any advice. 
Charlie. 

simoncharlton8@gmail.com wrote:

Good afternoon folks. 
I'm wanting to to put a later crank into my earlier cases but the primary chain gears are different width. 
Is the gear in the idler interchangeable or will I need a different shaft?
Thank you for any advice. 
Charlie. 

This is the crankshaft of my Z13 A1, it has more counterweights than an endocrinologist's scale.

As you can see, the width of the primary chain sprocket doesn't match the crankshaft sprocket you showed in your message.


However, it does seem to match the crankshaft you showed without counterweights at the bottom of the photo.
 

The lesser weighted crank was in my engine, It bent a rod.
I've got another crank with all the rods (the multi weighted one) which has a much smaller drive gear but my chain is too wide for it.

Am I to replace the whole idler shaft, or is the driven gear replaceable?

 

I've been working on this site for  11 years now and I can honestly say that there has been maybe a handful of members who have actually split the engine. Only one member (StanG) has actually split both the early engine and the later engine but he is no longer on this site.
I tend to look at Partzilla when I need to dive into parts diagrams for information because I can then see what models part # XXXX-XXX is used on. I had a look this morning and I see that the primary driven gear on the secondary shaft that is driven by the primary chain, was changed on the A3 model. The A1, A2 primary driven sprocket appears to be a 25 tooth gear where as the A3 is a 35 tooth gear? Now the A1, A2 models drive the timing of the pulser coils off of a timing chain that's driven off of the secondary shaft, where as the A3 times the ignition off of the left side of the crankshaft. So the relationship for the primary drive is critical in the A1, A2 models.
I didn't dive into the primary chain to see if there's a length difference but I'm sure there is.

Very interesting to see the physical difference between the 2 crankshafts. The later model crank looks to be significantly less mass then the early crankshaft.

You bent a rod on the early engine and you need to change out the crank?? Begs the question "Why?" Damage to the crank throw? Quite a few bent rods from engines that got hydraullically locked but never heard of a need to change out the crank.

As much as I like the look of the lighter crank, the fact that it runs a narrower drive chain concerns me. Quite a few bikes out there running primary / secondary chains that are out of service limits. My engine has 37K kilometers on it and I found the 2 drive chain beyond the limits so I bought new chains and changed them out. Scotch hasa bike with over 100K on the engine and still hasn't found the need to change out the chains.

I think you are on your own here. I doubt that anyone here can answer your question, but we'd like to hear how you make out.

good luck,

KB
 

Thank you for that, I had a complete 'spare' crank and I thought it would swap over, I was going to machine the gear on the idler shaft but if the teething is different I'm snookered.
Thanks for your info, it's saved me some time.

I'll try find a rod for my original crank now, which means I've a crank and rods spare if anyone needs one.