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Block markings - darcher121 - 23-06-2021
Also, adjacent to each bore is a diamond with a 1 in; what could this mean?
RE: Block markings - Colin Reed - 23-06-2021
Hi,
1/64 seems an odd size .o156 th
normally over size bores go in .010 th increments in imperial measurements
unusual to stamp the block face
Colin
NZ
RE: Block markings - JonE - 23-06-2021
what do the bores measure now, and what size pistons are in?
I had stamps in the same place, for a (fully dated!) 1953 rebuild. It wasn't great...
RE: Block markings - Bob Culver - 23-06-2021
The original Austin branded pistons in my car, reconditoned about 1939, had the marking1/32
RE: Block markings - Parazine - 24-06-2021
It was common, in the pre-war era to bore blocks oversize by 64ths.
By the end of World war 2, we had become Americanised to some extent; the Americans had "decimalised" the inch. Rulers became available with 1/10 inch divisions and the the thousandth became the standard base unit. Somewhere I have a pair of Vernier callipers, calibrated in 1/64" increments - very difficult to read!
My set of drills however, remains in 64th increments!
RE: Block markings - Tony Betts - 24-06-2021
as suggested austins pistons originally went up in 1/64ths.
its not until we got into post war aftermarket things changed to 10thou at a time.
the 1/64 stamp on the block would have been done by austins. it may be that the block didnt clean up at standard. and had to be taken out to 1/64. or the engine was used on a test bed or in a car on the test track. then rebored when it came back so it could be refitted and sold. so it left the factory at 1/64
sorry i dont know what the diamond stamp dictates, but again its an original factory stamp. it could be test department it has been through??
tony
RE: Block markings - darcher121 - 24-06-2021
For interest, the pistons have the same markings.
It will need a rebore and new pistons as the pistons can be “wobbled” in the bore
with my thumb.
I will decide on a new size after careful measurement.
The crank seems remarkably unworn; no discernible wobble or end float, and the big ends are the same. But more investigation before I decide to leave it as it is as I can’t believe it won’t need at least big end bearings renewed.
RE: Block markings - andrew34ruby - 24-06-2021
A30 piston.jpg (Size: 41.12 KB / Downloads: 175)
The number in a diamond. Pictured is a piston from a 1955 Austin A30. Standard size. In 1962 it was explained to me that pistons were made, then measured, and graded according to the exact measured size. The grade number was stamped on the piston in a diamond. Bores were similarly bored, measured, graded and stamped.
The pistons were then selected such that a number two piston goes in a number two bore etc.
Effectively this gave closer tolerances than they could manufacture.
So I'm guessing this was used in the 1930s too.
I've remembered all this, and kept the piston, since 1962. I was eight.
RE: Block markings - darcher121 - 24-06-2021
Very interesting!
I will be keeping these original Austin pistons,
maybe as some kind of mantelpiece ornament
if management allows it.
RE: Block markings - Chris Garner - 24-06-2021
Just to expand a little more on Andrew's graded number in the diamond.
The Austin Service Journal, dated April 1934, states:
Each grade covers a limit in diameter of 0.0005" only. When built the same grade number is stamped both on the block face and the respective piston so ensuring correct clearance.
Where oversize, fractions such as +1/64, +1/32, + 1/16 etc will be stamped, subdivided into grades as per the standard sizes above. Where the + figure is a plain number. eg +5, this indicates the oversize in thousandth of an inch. +5 thus being + 0.005". All oversize stamping appear on both piston and cylinder block face.
Prior to '34 the nominal oversize figure of a bored out block was stamped on the valve cover facing.