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!

Crank woes

I apologize in advance to the casual lurkers.  This post will be pretty esoteric.  I am trying to solve a couple of flywheel problems and want to share some pictures:

Problem 1: The crankpin does not pull through as much on the drive side as the pinion side, which appears to cause excessive side play at the rods when assembled with .067" thrust washers.

This picture below shows the pinion side of the crankpin, torqued.  Crankpin end is about .033" below the nut face, not too bad:

This picture shows the problem end, the drive side crankpin end.  Crankpin end is about .067" below the nut face, fully torqued.  Note exposed threads on nut...

By reversing the pin, I concluded that the problem seems to be in the drive side flywheel, and not asymmetry in the crankpin itself.  The taper (hole) in the drive side flywheel seems to be of too small diameter.  This would also explain why the wheels seem too far apart, and very thick thrust washers would be required to get the proper .020" side play on the rods.  Might also explain why I found that the last rebulder ground down the drive side case race on the inner surface with an angle grinder (to try to get proper crank end-play with a too-wide crank, I would guess).

Here is a photo of the outer surface of the drive-side wheel.  Note the "Z-metal" mark and that there is no stamped timing mark.

Below is the outer surface of the pinion side wheel.  This one has a problem too.  When I insert and torque the new pinion shaft, and then mount it in the lathe to check that the wheel is true to the pin, I get about .015" wobble at the outer diameter. 

Note the Z marking and the "84" casting tag.  Note also that the balancing hole at the top of the picture is the only hole on this wheel, and the other crank has no balance holes drilled anywhere.  The lack of drilled balance on one side makes me wonder if the wheeled are mismatched.

Close-up of the crooked pinion shaft taper.  I hope I can lap the new pinion shaft with a carefully indexed Bridgeport and straighten this taper...

Pinion side wheel, inner surface:

Drive side wheel, inner surface:

 Close-up of casting marks on pinion side wheel

Another close-up of the pinion shaft taper, Note wear on lower right, although the pinion shaft pulls in tight, just not quite true.