Author Topic: BS 350 Crank Rebuild  (Read 161 times)

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Offline rwgibbon

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BS 350 Crank Rebuild
« on: July 15, 2021, 04:25:53 PM »

A friend of mine sent me this question regarding a BS 350 crank he is rebuilding.

Randy , got a funny thing with the 350 crank I'm playing with.

This is the crank I got in 4 pieces and went through Hell trying to align it at 180 degrees.
I have not assembled it at this time as I am still trying to source the spacer shims 30x0.3 that fit between the bearing and the crank cheek.
I thought I could get them lazered but $50 min for 2 , 0.012" shims don't make sense.

The assembly looks simple enough as its just a male shaft that press fits into a bore location , BUT when I measure the stack up of the 2 inner bearings and the labyrinth seal then when i measure the 2 mating crank parts it does not compute as the dimensional stack up of bearing seal etc is larger than the assembled inner crank cheeks.

Never mind I have not included the 2 shims that the parts drawing shows between the bearing and the crank in the equation ?.

If I assemble it then install into the casing not sure if the locating holes that prevent fretting will line up, if it does great if not , I got to pull the crank apart .

My other cranks I checked for 180 degs before i pinned the inner cheeks ensuring correct 180 degrees on re assembly.

Just wondered if anyone out there has had similar experience ?

Bert

Offline czmike

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Re: BS 350 Crank Rebuild
« Reply #1 on: July 16, 2021, 02:35:36 AM »

Hi Randy,

Your friend Bert didn't provide the dimensions of his centre bearing parts "stack up" or of the space he has between the assembled inner crank cheeks. As far as I am aware Bridgestone have not provided us with these dimensions either.

So I measured two used, spare 350 cranks I have. One of which is still in its, partly dismantled, engine.
These engines were modified & raced so measurement of them could be misleading but I think they would be indicative of the Factory assembled dimensions.

The total length of the removed crank measures 163.5mm from flywheel outer edge-flange to flywheel outer edge-flange.
The dimension between the inner cheeks of this crank is 53.0mm.
The bearings, shims & labyrinth seal measure a total of 50.0mm.
So there is a total of 3.0mm clearance in the centre section.

For the crank still in the motor the dimension between the inner crank cheeks measures 51.0mm.
Probably there is a total clearance of 1.0mm in the centre for this crank assuming the same centre section parts are in there.

Maybe Bert has the wrong parts combination for his centre section?

Best Regards,
Mike

Offline rwgibbon

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Re: BS 350 Crank Rebuild
« Reply #2 on: July 17, 2021, 08:05:50 AM »
Thank you Mike I will send your response to Bert.

Randy

Offline rwgibbon

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Re: BS 350 Crank Rebuild
« Reply #3 on: July 17, 2021, 01:07:46 PM »
These are from Bert:

Hi Mike, I appreciate your feedback it great information.     my bearings and labyrinth -49.5
Inner cheeks 49.2
Measuring with digital calibers
I will get onto my surface plate with height gage and dial indicator to be more accurate 
Bert

A picture of the surface plate is attached.

 


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