3 cyl forged or cast crank

[johnsonracer]

I rebuilt a fishing engine last week. Was a 1980 70hp johnson. Originaly with the small cast crank. I fitted a newer forged crank. (only one we had) I had to slighlty modify the inside of the piston skirts as the crank was hitting because the Webs are bigger. Much bigger.

Has anyone played with putting the smaller crank shaft in a late model 920cc 70? Is the lighter smaller crank better or does the loss of crank case compression make it worse?

[ultrafast30]

I am in the process of building a brand new skiff to get to the beach. We put a 9 inch pad and stepped chines in the hull. laid it up light Came out of the mold at 290 lbs. I am building a 60 hp twin . 15 inch mid , finger ports, big bore carbs, etc. I am considering dry stacking the exhaust. Does this work on this motor
Questions are: Props available- i am considering going to 1.87 gears I will surface the prop?
Which tuner works best? Exhaust relief! I will relieve the mid.
I have lots of experience with the big loopers, none with these little ones. Appreciate help!!
Thanks

[Ron Hill]

Need to let some water out or you'll burn the plastic water pump housing...I've seen this happen with a dry 45 SS pipe!

Why use a two banger, when a three is about the same price and I'd think a ton more torque and power....

I've gott various props that might "Blow Your Dress Up"....

[formeone]

i always run cast crank in my v-rudes ,, look ugly and need abetter balanceing done to them but never as prob..cheyney

[formeone]

i built a full circle crank for a engine years ago lots and lots of hours into it,,, when we finally tested it,,, wasnt faster,,, all for not,,,ugg..cheyney

[johnsonracer]

I looked at making a full round crank. Does the full crank not block the main transfer port?

[Bill Gohr]

The Forged crank hitting the inside of the piston on 49 cubers was a common problem back then, so common there was a service bulletin on it, we actually told people to take the crank to a belt sander and touch off the crank wheel for clearance, the real issue was a manufacturing tolerance on the inside bevel of the piston.

[formeone]

no dont think it blocks at al... it was deff a waste of time remeber this engine is alot of volume and does not have alot of velosity in there so work with that and you will be better off,,, if you prop right and find right boatwill be way ahead of game... give ya one hint,,, dont run newer carbs on the motor..,, kills the motor...

[johnsonracer]

I running twin throat one inch carbs. I dont think there is much I havent done to motor. I running 195psi with 21thou squish. Getting 8700 with 4 blade dewald prop. Prop awesome on track. But for kilo i think 3 blade is better. Anyone have 3 blade prop to suit the cc gearbox? I think thats what it is. The hydraulic jacking midsection one.