Main bearing replacement 1957 AJS single

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glynnbarham
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Posts: 16
Joined: Mon Jan 01, 2001 12:00 am
Location: FLINTSHIRE UK

Main bearing replacement 1957 AJS single

Post by glynnbarham »

Hello, I am rebuilding a worn out 16MS 350 of 1957 vintage. when I removed the plain bush bearing from the oil pump side of the engine a small pin also fell out which, as far as I can tell is to prevent the bearing from rotating in use.
the replacement, new bearing, is a tight fit, probably press fit, it may even need the casing heated up, in the housing. my question is should I replace the small pin which I still have (the crankcase will require drilling to suit)?
I ask this as, although the pin is shown in one of my old catalogues (Jampot Spares Limited - PARTS 08/09 page 7, part number 012233), it is not listed in the catalogue as far as I can see.
the pin appears to be undamaged and, I believe, has been in the engine since new, this its first rebuild I think as I have had it since 1967 and I haven't done any work of this nature since I bought it then. thank you in anticipation Glynn. :?
Andy51
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Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Re: Main bearing replacement 1957 AJS single

Post by Andy51 »

Ken de Groome recommends drilling and tapping for a 2BA grub screw to do the same job - the hole should be half in the bearing, half in the crankcase, parallel to the mainshaft. Andy
glynnbarham
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Posts: 16
Joined: Mon Jan 01, 2001 12:00 am
Location: FLINTSHIRE UK

Re: Main bearing replacement 1957 AJS single

Post by glynnbarham »

Thank you Andy, that's along similar lines to my thoughts. I was after other people's thoughts on the situation. I also suspect I may need to warm the crank case in the oven to fit the bearing. Glynn
Dixter
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Joined: Mon Oct 02, 2017 8:27 pm
Location: Seattle area, WA USA

Re: Main bearing replacement 1957 AJS single

Post by Dixter »

Hi Glynn, you will find this reference manual quite handy. It was produced by the British Army for rebuilding the military's pool of AMC Motorcycles.

http://archives.jampot.dk/book/Workshop ... ndards.pdf

Specifics concerning clearances and fits for the bushing and mating bore in the crankcase begin on Page 5. Please ensure that you properly ‘back-up' the crankcase when pressing in the bushing. I've seen more than one disaster at this stage.

As to the pin, yes, it is to restrict rotation. Either the old pin or a tapped screw will suffice, AMC found the pin sufficient, simply find a fresh position, drill a new hole, and ensure you stake the opening to trap the pin. You do not want it working it's way out of the hole and into the timing pinion gear train.

Ciao, DC
Dick Casey
The RideNut
glynnbarham
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Posts: 16
Joined: Mon Jan 01, 2001 12:00 am
Location: FLINTSHIRE UK

Re: Main bearing replacement 1957 AJS single

Post by glynnbarham »

Good morning Dixter, that link is certainly very helpful. I shall be having a go at the task in the next few days and progressing the work on the engine.
I assume by "backup-up" the engine you mean ensure it is well supported.
The original was simply pushed not pressed in place so was only finger tight.
Many thanks and enjoy your day
Glynn :P
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