Well... the 12G1505 (late Morris 1100S, 1275LS, etc) cranks are only EN16 material, and are not tufftrided (hardened) like the small journal 1100S ones (and some Mk2 S cranks) used before them.
Also, many have had a hard life by now and are cracked- do get them crack tested before doing any work.
They are poorly counterweighted compared to other A series cranks, ie the sides of the crank are parallel- so they can tend to whip at high rpm and wear one side of the mains more than the other.
This can be improved heaps by wedging the crank- basically making the crankpin journal side of the webs narrower.
Here's a pic of my 12G1505 crank after stroking and wedging- before cleanup and balancing.
As they have 1.750" crankpins, it is common to offset grind them to 1.625" which increases the stroke by around 3.0mm. You then use Cooper S or MG Midget rods.
After either of the above steps you will need to get the crank dynamically balanced.
As for tufftriding, most heat treatment places in Oz that used to do this work no longer do. It's a molten arsenic salt bath process... not exactly good for the operator's health.
Rumour has it there's still one place in Melbourne that does it for the aero industry.
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
