Commando crankshaft deflections?

Does anyone have idea of how much crankshaft ends deflect by 7000 red line?

Does anyone have idea how much crank end run out is tolerable acceptable?

Does .008" on drive end sound too far out to accept?

Factory cranks can be within .001" and new Maney cranks .002".

Does anyone know if Commando cranks can be straightened to true
from a .008" defect?

Does anyone know if engine size makes much difference
as compared to rpm induced deflections?

Does anyone know if there is a preferred direction of crank
end bend that nullifies some of the piston inertia loads?

hobot

Does anyone have idea of how much crankshaft ends deflect by 7000 red line? No but it was enough to destroy normal main bearings.

Does anyone have idea how much crank end run out is tolerable acceptable? Single cylinder cranks are looking for .001" run out, as this is between 2 close points a twin would be .002" due to the greater distance between the main bearing journals

Does .008" on drive end sound too far out to accept? Yes

Factory cranks can be within .001" and new Maney cranks .002".

Does anyone know if Commando cranks can be straightened to true
from a .008" defect? Yes using a press with a controlled pressure and measurement of the defection as the press works, you will need to say deflect the crank .012" and it will return close to the required .002" due to the elasticity of the steel.

Does anyone know if engine size makes much difference
as compared to rpm induced deflections? More likely the distance between the main bearing journals plus the weight of the rods and pistons, the lightweight pistons and rods recently avaialble would be a good start along with a straight crank.

Does anyone know if there is a preferred direction of crank
end bend that nullifies some of the piston inertia loads? I think the result would be moving the vibrations to the lower revs but only guessing

hobot said:

Does anyone have idea of how much crankshaft ends deflect by 7000 red line?

Does anyone have idea how much crank end run out is tolerable acceptable?

Does .008" on drive end sound too far out to accept?

Factory cranks can be within .001" and new Maney cranks .002".

Does anyone know if Commando cranks can be straightened to true
from a .008" defect?

Does anyone know if engine size makes much difference
as compared to rpm induced deflections?

Does anyone know if there is a preferred direction of crank
end bend that nullifies some of the piston inertia loads?

hobot

Click to expand...

How did you measure the error and is just a shaft bent ? using a press to retrue is 100% not the way...you will could be bending something that could already be true! All cranks flex...works Bsa Rocket threes would flex thirty thou at 9000 rpm.. infact John Coopers pistons clipped the head when beating Ago's mv. that was .030 ! He did rev it "Flat out" on the home straight!!
Light pistons reduce the effect.....gram's at 8000 rpm add up the many newtons. double the piston speed and square the Force!!

This is how the runout was measured on Steve's crank. The total indicated runout on the DS was .013", and on the TS .008". Measurement on the same fixture for a good used (ex-racer) stock crank was .001" on both ends.



High spots on the two sides are 180 degrees apart, and at right angles to the plane of the rod journals, so putting ends in v-blocks and using press on center will not work.

Ken

Do a trace on the flywheel, if this is centered then grip the main bearing journals in a large lathe chuck and bend the thinner diameters true, suspect the bend is not a bend but the flywheel welding has distorted the whole crank.

Hi. I havre used roller vee's with some errors ..A far better method is to hone a collet in a good lathe...i had a special honed one that is the same size as the timing side bearing dia...i have a ground silver steel mandril that will clock .0002 .i then grip the crank shaft in this collet and clock the other side.. produce's a differant reading, i managed to get a harley crank to one thou...that was the combinded errors in the original machining.

Thanks for the feedback as I was scratching at straws for some hope.
Kommando is 3rd to suggest a more central problem with the flywheel
faces and welding than just the long shafts. Also long shafts don't
bend in one plane but twist coil corkscrew for stages of unwrapping.

Kurt's shop http://www.marinecrankshaftinc.com/motorcycles.html
also thought the end run out in opposite directions implied flywheel cheek
not true to start with. He'll judge it for free but says usual run out
they need to correct is 002" so mine is very far off > nil hope to fix.

I have seen the witness marks and damage extreme end flex
from jump rope crank to see the ends point forward and down
most trying to jerk pistons from TDC. Just wishful thinking the
existing bends would nullify that flex at speed as in example of
the BSA .030" jump rope clash. Middle bows up, ends downward.

The other issue is 7" blower pulley wobble to keep flat
belt on and not jerk the snot out of the impeller shaft support.

Today I'm forced to accept the crank is scrap and search for
an optimal replacement.

hobot

If you think the crank is scrap try peening it around the big end and draw the bend out .

lcrken said:

This is how the runout was measured on Steve's crank. The total indicated runout on the DS was .013", and on the TS .008". Measurement on the same fixture for a good used (ex-racer) stock crank was .001" on both ends.

High spots on the two sides are 180 degrees apart, and at right angles to the plane of the rod journals, so putting ends in v-blocks and using press on center will not work.

Ken

Click to expand...

welding is good to stop the whole assembly flying apart, early gsx cranks where done , but the whole assembly should be heated to remove any stress ,,then the crank should be ground...could this still apply to your crank? the drive shaft can be turned down and pressed sleeves fitted , with a out rigger bearing....? huge loading from wide belt pulleys will bend the shaft easly...out rigger is a defo....regards J

Thanks for some encouragement John and splatt, [ugh as biker name]
Ken will send crank to the Marine/M/c shop for an opinion on
what can be done or not and where the distortion is coming form
and what else it may be miss aligning and learn something.

Here's how it was prepped plus some gearhead back ground.
So a mystery how it got tweaked. Saw reference cranks should
never be stored on side, don't know if applies to Nortons.
= = = = = = = = = = = = = =

A crank grinder uses a set of adjustable three-jaw checks that are offset according the the stroke of the crank. A dial indicator is used on the big-end journal to check that the offset is correct before grinding assuming that the big-end journal is not damaged. On Triumph and BSA cranks you can see large centres and the sludge-trap plug hole that may allow these cranks to be mounted for grinding between centres during original production.

The difficulty with most Norton cranks is that the shafts are soft. Most people use a hammer on the end of the crank to separate the crankcases. If you look at the end of a Norton crank under a magnifying glass you can see how the end has been damaged. This bends the drive side end by up to .030" depending on how hard someone hits the shaft. The timing side can be off too. Even some cranks that show no damage to the drive end show a .003-.005 bend that may of may not be original. The worst cranks are the 1975 electric-start cranks because of the longer drive-side shaft. Every second crank I get from one of these bikes is not usable even from a running engine; the ends of the cranks must wobble alot!

I have also found cranks where the drive-side taper was not machined concentric to the bearing journal before I even touch them; same on the timing side with the timing gear journal not concentric to the end where the oil feed seal sits.

Of note, I never see this problem with BSA or Triumph cranks. The shafts are shorter and the material they are made from is harder. I can also understand why people like machined-from-billet cranks because they are perfectly aligned from side-to-side and made from better material. There are limits to the strength of these cranks because they cut through the grain structure of the material; forged components will always be stronger. Like stock cranks, these cranks break where the drive shaft meets the crank cheek. I still can't figure out why Norton made the radius from the drive side shaft to the cheek .030 when the radius on the Superblend inner race would allow it to have a larger, and stronger, .090" radius - I have modified cranks to do this.

When I weld the cranks together the journals are mounted in spring collets mounted in a cast iron fixture. They are aligned when I start the process. This fixture is also used for heat treating to maintain the alignment; through both the stress relieving and nitriding.

Geoff
= = = = = = = = == hobot = = = = =

hobot said:

Saw reference cranks should
never be stored on side, don't know if applies to Nortons.

Click to expand...

Wasn't recomended due to the fact longer cranks could start to bend under their own weight.
I supose now it's been stress relieved and nitrided you have very few options, I don't really see what you are doing, probably can't get my narrow mind past all the welding on the crank.

Ugh rider splatt,
Got what I needed from experts, Ms Peel needs new crank : (

I feel a bit like camel sticking nose in nice pub discussion.
Just trying to build my final dream machine as most powerful
Commando like bike ever fielded and that dose not see other
bikes as any competition in handling only 4 wd drive rally cars
and race Karts that can steer from either or both ends at once
all the time harshly accelerating. I'm considered a nut case
but my point of view is no one else yet knows what they are
missing out on w/o a low rear Helms rod end linkage.
As good as the other rod reports are, merely comfort items
to me that will not stop the hinged handling onset, only raise
its speed and frequency to more dangerous surprises level.

Safe Journeys.
hobot