Stroked to 80"

Well, I have come to a momentous decision...  Because of my flywheel troubles (see previous post), it was recommended to me that I would be better off replacing the old flywheels with new ones.  Since the primary cost of upgrading from 74 cubic inches to 80 cubic inches is the flywheels, this caused some serious reflection...

The stock 74" has a bore and stroke of 3.25" x 4.4375".  The 80" (Indian's last ditch attempt to resurrect flagging Chief sales against the Panhead) came out in 1950.  Applying creativity in place of development $$$, Indian achieved the 80" by stroking the 74" by 3/8", to 4.8125".  This necessitated three (or maybe four) relatively simple changes:

1) Replace the flywheels
2) Shorten the piston skirts 1/4 inch to keep them from hitting the case at BDC

When I compared my new 74" pistons to the old pistons that came out, I was curious as to why the old skirts were shorter...  Turns out they were 80" pistons!  Just for the record, the old (80") pistons have a total height of just under 3" (2.995").  The new 74" pistons have a total height of just over 3.25" (3.255"). 

I'm not sure I have the guts to throw the new 74" pistons on the lathe with my remedial machinist skills.  I think I will try to exchange them for 80" instead.

3) Cut a recess into the heads to accomodate the piston at TDC, now sticking up 3/16"

This is my stock 74" head.  note the lower part of the combustion chamber is flush with the gasket surface.

This is an 80" head.  Note the cutout at the bottom, to accommodate the "pop-up" piston.












I may also need to relieve the cases at the cylinder bases to clear the rods a little bit, not sure yet.  I am told the stock cams and followers will work just fine in the 80", although  several different "hot" cams are available, with names like Bonneville, Shunk, and Ollie.

I took the plunge.  I ordered 80" Kiwi Flywheels (manufactured by Truett and Osborn) today, and also sent my heads off to be machined.  Hope I don't regret this!