I pulled the main cap (knew it had a problem) off one of my spare 1275 motors tonight and it's spun the center main , I'm wondering how far under sized it can be ground before it becomes a doorstop , it's a 12G1288 I think (hard to read stamps) and is already at 20 thou .

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I know of a crank that went to 060 under

Doogie

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I won Hay once, here's the pic to prove it..


Hay, it's not about the car, it's not about the venue, it's about the people that come here. Peter Dwyer, Mayor of Hay NSW.

Yeah for road use -.060", if you can still get the bearings.
My S crank was at -.020" when it almost spun the centre main- it cleaned up at -.030" with .001" to spare..

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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.

I have a -.060" crank.

Do you need to get the cranks re-heat treated after going more than .020" under?

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68 Deluxe.... it's shiny..... I like shiny!!

Depends on the crank. When Spiro reground my S crank's mains to .030" under he said it was still hard as, so no need.
An Oz big journal 1275 crank, or an 850, 998 or 1098 one, are all EN16 material and non- heat treated so are soft anyway.
Mk1 S cranks are EN40B, nitrided. If you re-nitride it there is a real good chance it will bend, as an ausmini member found out a year or so ago..
Most Mk2 S cranks and small journal 1100S cranks were tuftrided EN16. Good luck finding anybody who will do this process in Oz now, the EPA pretty much closed down the process due to environmental and health concerns. GR says there is 1 place, in Melbourne- they do mainly stuff for the aircraft 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.