I would not stop at 117". You will spend $500 to have the crank T/B/W and still have the cheesy rods unless you replace them. With the money you will be spending and this one time that you will have the lower unit out, throw another $500-$600 at the project and build a 124" motor. Talk to Kirby at VeeTwin Performance; sometimes he offers a very reasonably priced 124" package. You have made the commitment, why pull up short?

 

djl, I think I'm going to start calling you little devil. You seem to jump in these build threads and whisper into the builders ear "Why stop there?"

 

Exactly what I was thinking... I've got to stop somewhere. I think the 117" build I have planned will more than exceed my performance goals, and keep a smile on my face for years to come.

I will check out Kirbys 124" though. Just for fun.

 

I learned the hard way. Built a strong all bore 107" only to regret later how much more fun I would be having if I had spent another $500 on the crank for 124". Of course, an easy fix, right? Just pull the lower unit and replace the crank. Lots of work and down time and it is now very hard to justify tearing down a happy (124TQ/110HP) all bore 107" motor. Sometimes I wish it would develop a problem to provide the justification but it just keeps running flawlessly. If going after more displacement, it just makes sense to get all that is available.....

 

Stopping point should be 124"; stopping at 117" is stopping short........

 

It's a little more than just a crank, Going 124 will need longer cylinders and depending on how it goes pistons.. Currently owning a 116 and 131 (4 5/8 stroke), I'm preferring 4 3/8.. When the crank in my 116 dies, It will go to 117 as it's hard to get long 4 inch bore cylinders and it's easier to fit manifolds to the heads. I like the 117.. It will be interesting to see what displacement you can get out of the new M8 with the 4 3/8 stroke.. The nice thing about the shorter stroke is that there will be slightly less vibes.. (about 6%)

 

Right, but the OP has to buy cylinders/pistons anyway and I wouldn't think there would be a big difference in price but could be mistaken since my build experience has been limited to 98" and all bore 107" configurations.

Good to know about the difference in vibration between the two strokes; I had not anticipated more vibrations from the longer stroke. How did you arrive at the 6% variance? I will have to take that into consideration before deciding what to do if/when I pull the trigger on more displacement. I will be faced with the cylinder/piston issue if/when I pull the trigger on more displacement; cheaper in my case to stop at 117"......