crankshaft cheeks/flywheel

I read in the workshop manual that the flywheel has a certain orientation where the weight is slightly different on the timing side journal, can anybody enlighten me as to the correct way to bolt up this assembly please, David ( 1969 750 S )

fireflake said:

I read in the workshop manual that the flywheel has a certain orientation where the weight is slightly different on the timing side journal,

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Not necessarily 'left-right' but just as importantly, 'fore and aft' (for want of a better way to describe it) balance.
The workshop manuals say to mark the flywheel before dismantling the crankshaft so the flywheel is refitted the same way.

fireflake said:

can anybody enlighten me as to the correct way to bolt up this assembly please,

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I'm not sure anyone can basically tell you which way is correct (which is why the manuals say to mark it) but why are you asking?
Is it because you have a dismantled crankshaft without markings (or you dismantled the crank without marking it first) rather than just asking out of curiosity?

Thanks L.A.B. I had to purchase another flywheel due to damage and I neglected to mark which way it was assembled, Cheers, David

Recently I had a crank apart, I did put witness marks on the assembly before splitting it. I sent the big end cheeks out to Mile High Crankshaft for turning. When I got it back I wondered what would happen if I assembled the pieces with the flywheel the other way round. I did that. The pieces fit fine, but when I put the crank on a set of ball bearings that I use for wheel balance and indicated the drive side and timing side pins I saw almost 3 thou (.003) run out. When I reassembled the flywheel the way I had marked it the run out showed just under a thou (.001).

I suggest that you try both ways and choose the one that has acceptable run out.

If I were to change out to a replacement flywheel I would send it out for a dynamic balance.

I agree Dances - a crank can only be better with dynamic balancing - I think Enfield were the only factory to do this as stock
Maybe because their cranks were so bad if this were not done?
RoadScholar makes a good point though - even dynamic balancing will not correct run-out from an incorrectly assembled crank
So, if you have stuffed up (and we all have) then assemble both ways and pick the truest for run-out then have dynamically balanced to your chosen factor.
Cheers
Rob

I am fortunate to have one of the best balancing companies on the East Coast less than 10 miles from my shop, LIndskogg Balancing of Boxborough, MA. A week to 10 days turn around and under $275, if no Mallory is needed.

robs ss said:

...................assemble both ways and pick the truest for run-out ....................

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I certainly agree with this. I am trying to visualize the two types of misalignment; 1.) where the axis of the two main shafts are parallel but do not share the same centerline, and 2.) where the two axis are not parallel. Any opinions on what is going on? Also, what is the recommended tolerance? I don't recall ever reading about it for the Norton big twins. Obviously 0.001" is better than 0.003" but........

Besides test assembly to find the least run out are there any other remedies?

It would be interesting to know if during manufacture the mainshafts are machined after the crank has been assembled. Also whether the flywheel is balanced independently for every crank - whether if it is reversed, affects the balance of the assembly ?

Dances, during the lead up to the race bike motor build, the crank out of the worn motor (one cam lobe was lower than the other three)needed a -0.010" grind on the big end journals , when we offered it up to the grinding machine we found it was 0.015" out of phase between the journals, so replaced it.
I wonder if the PO timed it off the same side all the time, certainly wouldnt get it right if you used either side to time it.
It still ran, although as there were other issues you would never know until it was wound out and probably shake like a bastard. Glad i only idled it around the block before deciding to strip it to become a race bike.