02-08-2021, 05:47 AM
(This post was last modified: 02-08-2021, 05:55 AM by Tony Press.)
Thanks Ian,
From Austin works blueprint drawing 1 1/8” Crankshaft XL 145 from the A7CA archive (I assume this is BB1, A1 55)
Front bearing seating 1.124” to 1.125 “
Rear bearing seating 1.124” to 1.125”
1 1/8” to minus 1 thou.
From the early SKF Manual the Bearing Bore tolerance for an 1 1/8” bore bearing is
- 0.0003” to + 0.0002”
1.1247” to 1.1252” (Minus three tenths of a thou to plus two tenths of a thou)
This indicates Austin were using quite a broad tolerance range which would give from a 3 tenths interference fit to a 12 tenths clearance fit– a sliding fit.
(SKF recommended fit for an 1 1/8” bore Roller Bearing on a Crankshaft is K5i : + 0.0005 to + 0.0002 : 1.1255” to 1.252”)
I don’t know if the 1 ¼” rear bearing had the same fit on the Crankshaft but I would assume that it was similar.
Checking the bearing list from the A7CA Index Cards (C.B.K. 17th November 49) shows Crankshaft Roller Bearings R&M MRJ 1 1/8, MRJ 1 ¼, Hoffman RMS 11, RMS 12 with no suffix such as 2 dot or 3 dot, indicating all these bearings would have normal internal clearance.
The SKF equivalents are: CRM 9 and CRM 10. SKF uses suffix markings: C2 clearance less than normal, no marking clearance normal, C3 clearance greater than normal.
As an aside:
I am not sure why the booklet ‘List of Production Changes’ does not mention the Crankshaft changes from BB 1 to BB 67 in October 1929 (from Light Shaft to Heavy Shaft) on Page 32.
From Austin works blueprint drawing 1 1/8” Crankshaft XL 145 from the A7CA archive (I assume this is BB1, A1 55)
Front bearing seating 1.124” to 1.125 “
Rear bearing seating 1.124” to 1.125”
1 1/8” to minus 1 thou.
From the early SKF Manual the Bearing Bore tolerance for an 1 1/8” bore bearing is
- 0.0003” to + 0.0002”
1.1247” to 1.1252” (Minus three tenths of a thou to plus two tenths of a thou)
This indicates Austin were using quite a broad tolerance range which would give from a 3 tenths interference fit to a 12 tenths clearance fit– a sliding fit.
(SKF recommended fit for an 1 1/8” bore Roller Bearing on a Crankshaft is K5i : + 0.0005 to + 0.0002 : 1.1255” to 1.252”)
I don’t know if the 1 ¼” rear bearing had the same fit on the Crankshaft but I would assume that it was similar.
Checking the bearing list from the A7CA Index Cards (C.B.K. 17th November 49) shows Crankshaft Roller Bearings R&M MRJ 1 1/8, MRJ 1 ¼, Hoffman RMS 11, RMS 12 with no suffix such as 2 dot or 3 dot, indicating all these bearings would have normal internal clearance.
The SKF equivalents are: CRM 9 and CRM 10. SKF uses suffix markings: C2 clearance less than normal, no marking clearance normal, C3 clearance greater than normal.
As an aside:
I am not sure why the booklet ‘List of Production Changes’ does not mention the Crankshaft changes from BB 1 to BB 67 in October 1929 (from Light Shaft to Heavy Shaft) on Page 32.