What piston

[trophy]

Hello all.  I have several items relating to the B single series that I need to shift.  One of the items is a very usable piston but I don't know for which model its for.  The top of the piston is marked 65/1693   and   3/55.  Its diameter is 84.93mm and the distance from the top of the piston to the centre of the gudgeon pin is 42mm.  Can anyone tell me what it will fit so I can advertise the items as a job lot?  Thanks in advance.

[Derek996]

It would seem to be a B33 piston but I can't see where 65-1693 fits into the series, unless there was ever a +10 oversize. 65-1692 is B33 std, 65-1694 is B33 +20, 65-1696 is B33 +40.

[JulianS]

The stamped number will mean the part number for the bare piston, 65 1692 is the number for the piston complete with rings pin and circlips.

[chaz]

as far as I was aware original oversize pistons were done in 10 thou increments, original thoughts were lower speeds so less chance of damage to the bore caught quicker also wear found quicker due to regular checking. stocking/production stopped as stock levels of not needed sizes on shelves being used took up space and more wear could be tolerated.

[trophy]

It would seem to be a B33 piston but I can't see where 65-1693 fits into the series, unless there was ever a +10 oversize. 65-1692 is B33 std, 65-1694 is B33 +20, 65-1696 is B33 +40.
/quote]
Hello Derek, and all other correspondents:- I don't think it's a 10 thou oversize size piston as its dia is 3.34" (84.84mm).  Cannot find 65-1693 to 1696 in any of the literature I have, and I have a lot.  I must assume it to be for the STD bore B33.  Is the 42mm from the top of the piston to the centre of the gudgeon pin correct?

[JulianS]

It is a standard size piston. Add rings pin and circlip to bare piston 65 1693 and it becomes 65 1692, the complete assembly, common BSA practice to include the complete assembly number in the parts lists and not the bare piston number.

It fits the B33 M33 engines with 6 7/8 conrod.

[trophy]

Many thanks JulianS.  That's cleared that little conumdrum thanks to your knowledge.  Isn't that what forums are for?  Thanks again.  Ride safe all.