2002 M750 Crankshaft Runout Spec

[Jordan1234]

Hello!

I just put my crankcase together with new main bearings, and the crank has zero end play (i.e. axial movement). I can turn it by hand, but its stiff.

The manual says: "Check that the drive shaft rotates with a certain interference on the main bearing." Not terribly helpful.

Does anyone know if I should expect 0 play and stiffness on a rebuild?

Thanks!!
-Jordan

[Speeddog]

There is a spec on crank preload, IIRC the factory one is a bit tight.

Don't remember the number off hand, I'll have to dig a bit to find it.

[bond0087]

I'm not 100% sure that I know which measurement you're looking for, but if the '02 is the same as the '01, then pages 141-143 in my scanned 2001 M750 Factory Service Manual should give the specs (or they should be somewhere else in that manual if it's something that Ducati provides).

It says "Maximum oval: .01mm =.0004in, maximum taper = .01mm = .0004in" but I think looking at the pictures and reading the context would be more insightful than just those numbers.

Hope that helps.

[brad black]

preload is the term you're looking for.  runout implies something rotating out of round.  taper and oval are usually to do with cylinders or big end journals

0.15mm preload, increased in later models to 0.20mm (998) and 0.30mm (1098).  0.30mm is quite tight.  lots of motors used to come around 0.40mm ime, and you could hardly turn the crank by hand when grabbing the lh snout.

[Jordan1234]

Runout is the wrong term - sorry about that.

I had no idea I should "pre-load" the crank... I guess the crankcase flexes around the crankshaft, which is crazy to me.  Thanks for the advice - now i just have to figure out how to measure my pre-load.

-Jordan

[ducpainter]

Runout is the wrong term - sorry about that.

I had no idea I should "pre-load" the crank... I guess the crankcase flexes around the crankshaft, which is crazy to me.  Thanks for the advice - now i just have to figure out how to measure my pre-load.

-Jordan

It's more an issue of thermal expansion than flex.

[WTSDS]

>> It's more an issue of thermal expansion than flex.

Yep, alloy has a greater co-eff of expansion than steel.

To get yer preload right a dial gauge is needed, and a way to mount it so you can measure endfloat when the cases and crank are bolted together with the correct torques for the crankcase bolts.

If, say, you have 1.00 mm of endfloat without shims you will need to get shim/s which total 1.15 mm for a 0.15 mm preload.

Scrupulous cleanliness is essential, a speck of grunge can affect the measurements.

Getting the preload set correctly is of the utmost importance, and of course make sure you have the right bearings, there are different grades.



 

[brad black]

from the manwell and how i do it, altho i do push the crank both ways to get the full travel.  my set up here - http://3.bp.blogspot.com/-yHoVTzC75Ys/T50NftJm5PI/AAAAAAAAAL4/XhDymz13gHI/s320/ss3.jpg
http://bradthebikeboy.blogspot.com.au/2012/05/crank-shimming-info-for-monster-forum.html
http://bradthebikeboy.blogspot.com.au/2012/04/998s-motor-showing-its-bits.html

i only use 0.15mm preload.  0.30mm is a lot:

Practical shimming procedure
for the crankshaft
Below is a practical shimming
procedure allowing to correctly
calculate crankshaft shims.
Install a shim (9) of minimum
thickness (1.90 mm) on each side of
the crankshaft to avoid contact
between crank web and engine block.
Fit crankshaft into casing and close
engine block.
Fit three M8 screws into the holes
shown in the figure and tighten to the
specified torque (Sect. C 3).

Place a dial gauge (F) with magnetic
base on a support plate fixed to
crankcase.
Bring stylus in contact with
crankshaft end and set dial gauge to
zero with the stylus touching the
crankshaft.
Place a lever (R) between casing and
crank web and lever crankshaft
pushing towards dial gauge.
Note dial gauge reading. This will be
crankshaft axial play. Add pre-load
(0.30 mm) and total size of shims
used (1.90x2=2.8 mm).
Divide by two and you have obtained
the shimming required for each
casing.
Note
After closing the casings,
crankshaft must turn with some
interference in the new bearings.