C15 flywheel width

[rhyatt]

The engineer , who is rebuilding my crank , has asked me if there is a nominated width of the flywheels.
He is squeezing them together onto the new crankpin and wonders if there is a set "distance apart to allow any con rod waggle
Thank you

[limeyrob]

Print off BSA Service Sheet 424 and hand him that.
It includes the flywheel assembly instructions.  Its a free download.

[rhyatt]

Thank you, I have 424 already and there are no dimensions other than "fully home".
I wonder if there is a dimension between the big end cheek and the inside edge of the flywheel?

[limeyrob]

My reading of 424 is that "fully home" refers to a shoulder on the big end pin so that fixes the distance, then the run out means that the shafts are true at that distance.  The crank shims then adjust for the final size.

[rhyatt]

Thank you.
Again, there is no mention of shimming in any of the service sheets.
Just place flywheels in this crankcase etc

[limeyrob]

OK, The parts book lists shims on the timing side: 40-0064 and 40-0066.
I've not rebuilt a C15 bottom end, I had a B40 and I've long forgotten how it went together!

[DAVE BRADY]

Hi,

I think the important thing is that the flywheels are parallel to each other and exactly lined up on the. Service sheet 424 has illustrations show this along with some measurements and how to measure the flywheels with dial gauges for concentricity.  fig. C17A and C18A

Dave.
 

[Rupert]

All the big end assemblies made by bsa for the C15 have a shouldered crankpin so the flywheels are fitted tight against the shoulders. Truing the flywheels is done after that.
The Alpha bearings replacement roller bearing big ends to go into the 40-48 and 41-55 rods have plain crankpins with no shoulder so with those it is important to position the flywheels on the crankpin to give the correct conrod side clearance - I believe 10 thou side clearance.
If you are fitting one of those bearing assemblies maybe measure the width of the crank before it is taken apart to give a width to aim for.
Crankshaft shims on all C15 and B40 engines with a timing side main bush are fitted on the drive side between the flywheel and the main bearing.

[limeyrob]

Interesting about the shims. Between the drive side bearing and the flywheel is where I'd expect them, but parts book confusingly shows them on the timing side.  Drive side makes more sense.
The run out for the TS shaft is tight - .0005" but it makes no ref to alignment.  I would be wanting to get the run out in limits at several places on the shaft, that would likely put the flywheels well inside the .005 alignment.

[rhyatt]

Thank you all.
The replacement big end I have is the non shouldered type.
Equally interesting is the placement of the shims.
The draganfly exploded drawings show the shims on the timing side between the flywheel and the main bearing sleeve (dare I assume , apart from end float, it also keeps the oil holes on the sleeve in line with the oil groove in the bush).
So , Rupert , I shim the drive side mainshaft.
Finally please, what end float of the crankshaft am I aiming for.
I've looked in the service sheets and can find nothing indicated

[limeyrob]

If you take the A10 as an example the book setting is (if I recall) 0.002 - 0.003 but the reality is that its hard to be sure all the bearings are pressed fully home and won't settle after the first hot run so there's a school of thought that 0.000 to 0.001 better so long as the crank spins freely.  Since the ally case will expand more than the crank a 0 - 0.001 cold clearance will be more once hot.  I set my A10 to 0.001 and its running very smooth and quiet. I've not checked it now its done some miles - perhaps because ignorance is bliss if its increased too much 

[Rupert]

It's not endfloat as such as the crank is locked in the driveside bearing. In effect it is clearance between the timing side flywheel and the inside of the timing side bush.
In theory the less clearance the better, BUT -
In use when the engine runs both the cases and crank heat up pretty much together. The cases being Ali will expand relatively more than the steel crank and the clearance between them will increase; no problem.
When the engine stops the Ali cases being in contact with the relatively cold air around them will lose heat faster than the hot steel crank inside them. Hence the cases will contract faster than the crank. To prevent the contracting cases pinching the crank there has to be sufficient clearance to cope with the differing rates of contraction, hence 4 thou or so is needed.
The shim seen behind the timing side crank sleeve in the parts books is misleading. I've never found one fitted in engines which were undisturbed since bsa put them together. Might have been intended when the model was first introduced, hence drawn, but not fitted for long if at all.

[rhyatt]

Now I understand entirely and all the reasoning is very clear.
Many thanks
I'll shim the drive side bearing to crank to give me .004" or so between the timing side inner bush face and the flywheel face.
As you say, the shim location in the parts diagram doesn't help things.