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Ian Grace
USA
660 Posts |
 Posted - 08/10/2013 : 19:01:31
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Thanks Jeremy.
Here's what I know about the suffix letters for Minor pistons (not the block bores), which might be of interest, and from which it looks like a B piston is 0.25 mm oversize, or about 6 thou, and so on. I have seen some B Minor blocks and one C block, but never a D or E. This was taken from The Morris Owner of June 1932:
"Regarding the markings adopted for Morris pistons, the complete range of pistons comprises five groups, of which "A" is the nominal or standard size. The remainder are considered oversize and the increase in diameter between each group is 0.25 mm. They are designated B, C, D and E, the latter being obtainable only to special order.
Each group is then divided into twenty-four individual piston sized ranging from -13 to +10. These figures refer to hundredths of a millimeter, and not thousandth's of an inch as is commonly supposed. Consequently, the variation in diameter between two consecutive pistons is only 0.01 mm or rather less than half a thousandth of an inch. For example, size A-10 would indicate a standard 57 mm piston with a diameter equal to that of the bore minus 0.1 mm.
In selecting a piston at the works, the following example can be taken: The piston clearance (which incidentally, should always be measured at the skirt) for the Minor is 0.11 mm to 0.12 mm. Assuming that piston A-10 is fitted and as a result of wear the skirt clearance has increased to 0.18 mm, then the following deduction applies:
A-10 piston fitted
Skirt clearance 0.18 mm
Skirt clearance required 0.11 mm
Difference 0.07 mm
Therefore A-10 piston plus 0.07 mm equals A-3 piston needed. Naturally, it is impossible to accurately forecast the piston size which will be needed after reboring, since this is entirely dependent upon the size of the cylinder bore when cleaned up. Careful micrometer readings should be taken of each bore, when after deducting the requisite clearance, you will arrive at the piston size. The letter "P" on the piston crown indicates that the piston is of the Morris parallel type.”"
Going back to the 72J part number, the list below may be of interest. I can't remember where I found this now, but it confirms your data and adds that the engine number switch was at no. 2501AJ.
http://www.vintageminor.co.uk/Forumpix/Product codes.JPG |
Edited by - Ian Grace on 08/10/2013 19:24:02 |
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Ian Grace
USA
660 Posts |
Posted - 08/10/2013 : 19:02:46
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| Hmmm, that space between Product and codes in the link is causing problems. It will work if you type the rest of it in to your browser. |
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