Just curious if there were any differences in the 78.9mm cranks from 78-86? Also were the rods all the same? ANyone know the weight of the rods? crank?

 

Oil channel diameter was increased from 4mm to 5mm at '84 MY. At same time #3 main bearing sides were made taller. This also meant making crank slightly different in area where bearing sides are in contact with it.

 

scot is running the older euro block, bored out, with the newer 84 style crank, which has the bigger rod bearing holes and using the stock older set of main bearings. rod bearings are all the same.
The rods can also be different, interchangeable, but slightly different weights, and thinner at the wrist pin end. we used a mix of them on scots engine, but balanced it all out to within a gram.
His motor is racing now and has been all season!

MK

 

Anyone know the exact weights of some of the different rods? Are all the cranks interchangable between 78 and 86 despite the minor diffs?

 

yes, but the later cranks on the early blocks rub a tiny bit near the outside area of the main bearing. nothing a little dremmel cant fix to give it a .030 clearance.

the weights of the rods are rigth around 850gram, if i remember correctly.

if you mix and match parts, just have the entire assembly balanced. not a big deal, and match all the rods to the same weights and tip and tail balance them too.

mk

 

850g is quite a damn bit... thanks for the advice on mixing up the rods.