Ok.............. tore down my 78 FXS shovel today. It is a 74" that has .70 over pistons installed which would put it a little over 80 inches. I am not liking the shape the cylinders are in. Nothing major but you can barely feel a little scoring on one cylinder. Better to take care of that right now while I am rebuilding the bike. Also the wrist pins feel like they are a little sloppy in the pistons.

What I am looking to do is buy new cylinders and pistons and just make it an 80 inch.

My question is this:

Is the flywheel the same in the 74 and 80 inch motors? From looking at different catalogs I have, it shows the connecting rods and outer cases to be the same. Can I just buy 80 inch cylinders and pistons and be good to go?

Thanks in advance for your answers.

 

The 74 has a 4" stroke and the 80 has a 4 1/4 " stroke with .030 more bore than the 74. Your 74 with the .070 overbore is not a 80. To go to 80" you need new wheels, and you will need new cylinders and pistons, since you are past the max the cylinders will go for stock 80 + a .030 overbore. And while you are there, replace the rods, crankpin, and all of the bearings. S$S sells excellent stroker products. There is no "Big Bore" cylinder kit that will make a 74 a 80.

 

A78 bored 70? are you sure that's not a 80 ci already

 

If my memory serves me correct, the 74 will go .090 over, and the 80 will go .030 over. Someone flame me if I'm wrong.

 

Thanks for the reply Al.

I definitely am planning on replacing the cylinders and pistons. I was thinking of using stock 80 inch cylinders and pistons if the bottom end was the same on the 74 and 80 inch motors. So you are telling that I have to have new flywheels in order to do this? When I looked up rods in the catalogs, it showed the same rod for both motors.

 

The Rods are the same. It's the flywheels that make the difference. The crankpin offset is different. The pistons are also different, they are larger and there is a 1/4" difference in the wristpin offset in the piston.

 

Got you ................ sometimes I have a thick head but it makes sense now. Appreciate the info. You saved me some headaches.