The BSA Workshop > Singles

B44, Bigend, Piston. Bad vibration.

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MICKREEVES:
My B44 vibrates badly on a light throttle opening, opening to accelerate stops the vibration,
closing throttle to overrun stops it as well. This is most noticeable at high RPM.
So bad, bits are dropping off or breaking.

I thought it must be bigend play, or possibly smallend or mains.
I have stripped the top end this morning.
No play to be found at all. I  cant mend something if it aint broke!

I wonder about balance factor?  The piston is 71/798, 1/2 mm oversize. It looks quite normal.
I see bsa part numbers. 41/794 standard, 41/795 + 10 thou, 41/797  + 20 thou (1/2mm)

The engine is not loose in the frame. I cant think what it can be.
I will order a new rocker gasket, and rebuild when it comes.
Any suggestions? Do they ALL have this fault??
Mick

MICKREEVES:
answering my own question!
I checked again.
Gripping the piston with both hands, push up and down, moving around and sideways.
Finally found a point where a very small amount of play was felt. Enough to hear a small click.
Im guessing that that is the answer?? ANY play is not acceptable??

Suggestions for a good supplier for replacement bearing please.
Mick

JulianS:
Just read a contemporary road test of the 1970 441 Shooting Star. The tester reported lots of vibration.

On piston part numbers - the numbers in the BSA parts lists are for a complete piston - including pin and rings - the number you see on the piston is the number for the bare piston.

You could try Alpha Bearings for a bigend .

ANDY HIGHAM:
There is no reason why a B44 should vibrate badly.
Don't assume BSA correctly balanced the crank, they probably balanced the prototype then made all the production ones "similar"
My B31 (400cc) crank/rod/piston assembly was balanced by Phil Pearson and the bike is smooth as silk all the way to 80 + MPH

MICKREEVES:
answering my own question!
I checked again.
Gripping the piston with both hands, push up and down, moving around and sideways.
Finally found a point where a very small amount of play was felt. Enough to hear a small click.
Im guessing that that is the answer?? ANY play is not acceptable??

Suggestions for a good supplier for replacement bearing please.
Mick

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