rebuilding an 1973 74". got crank apart, and checking run out on pinion side. got .007 run out at flywheel rim with pinion shaft in lathe on centers. what is typical runout when these cranks are took apart? should be within a thousand i would thunk to be correct. skimmed the manual, but didnt see anything about it.
just checked sprocket side of crank, & its .005 runout on rim. indicated both shafts, zero runout.
The '73 factory service manual states:
Runout (flywheels) 0.003" maximum at the rim
Runout (mainshafts) 0.001" maximum
i got crank apart. checking run out at rim vs pinion & sprocket shafts separately. shafts being perpendicular/true in flywheel half. should be truer than .007, right?
Maximum of 0.003" runout at the rim. But the spec is based on assembled flywheels, not halves.
I've had to replace shafts, or lap the tapers to get the runout right. In some rare cases replace flywheels.
Some left the factory out of spec.
I would be tempted to check on V blocks. Some shaft centres can be off but on V blocks you are indicating as it would be installed and running on the main bearings. If changing shafts it is imperative that the matching tapers are surgically cleaned with a solvent and bone dry. No finger prints allowed. That can skew the fit when being torqued down and seat them too deep.
I would disassemble the shafts from the flywheels,cleane the bores and shafts reassemble and check it again.Shafts can also be checked when apart ,may need new shafts or maybe lapped in :potstir:
When you true up wheels, you try to get your rim spec first before doing it with crank pin assembly. some old wheels may be problematic & you may have to remove shafts & re try, but the main point is getting the shafts true to each other. theoretically, if your close on the rim spec, the shaft spec should follow, but when dealing with old wheels there's no guarantees, so getting your .001 is the end game with a truing stand or dead centers.
i had 2 more 74 in cranks laying around. took them all apart and checked side of flywheel as pictured. closest was .002. begining to believe the side of flywheel isnt machined square with crank pin taper. any expertise info on this? looked up s&s instructions on replacing pinion shaft. they said just torque shaft, assemble rod set& true wheels. no checking wheel runout check while apart.
If the shafts are properly installed in the wheels, and still the sides measure excessive run out, can you not chuck the shafts up in a lathe and machine the wheels to have next to no run out?
-JW
Quote from: JW113 on December 08, 2020, 12:19:13 PM
If the shafts are properly installed in the wheels, and still the sides measure excessive run out, can you not chuck the shafts up in a lathe and machine the wheels to have next to no run out?
-JW
How do you think that will affect the location of the crank pin?
About as much as knife-edging flywheels I suppose?
:nix:
Not being a machinist, what does one do if the tapers & shafts are good, but the flywheel rim out is not within spec?
-JW
I don't think you will ever know until it's fully assembled. The influence of the crank pin will be an important part of the equation.
Quote from: kd on December 08, 2020, 03:52:11 PM
I don't think you will ever know until it's fully assembled. The influence of the crank pin will be an important part of the equation.
:up: Once together, the crank will likely need to be spread, shifted, etc. to get the shafts within 0.001".
.005" runout on the rims isn't going to make any difference if the shafts are true. "Most" cases have more than enough room to accommodate that much, Mock setting up can tell a lot. If shafts are true and the rims of the FW do touch, there's something going on elsewhere.