What is the allowable undersize on the crankshaft?
I have a late A+ 1275 crank, and the bigends come in at just on 1.7500 - no less.
May be ½ thou oval but that would be all if that.
The book states between 1.7504 and 1.7509.
Will standard bearings do the job?
The mains are on spec.

Just to check, which Workshop Manual are you working from?

A+ is NOT the same as A! This seems to be a reason why peoples say A+ Cranks, Block and Bearings (like the plain lower slipper in the Mains) are no good. They are very good, when used correctly!

The Factory A+ Workshop Manual shows the Crankpin Diameter (Big Ends) at 1.7497" to 1.7504"

Mains are also different - 2.0011" to 2.0017"

With 0.0005" Ovality, if it were me, I'd have it re-ground.

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GT, thanks for the info.
So my crank appears to be in spec, even though it is up to 1/2 out of round.

Take it to a crank grinder shop, they can probably linish that 1/2 a thou ovality out if there's no scoring.
Pity to take a whole .010" off it with a regrind.

[edit] typo

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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.

Hi Dave,
Take it to Jim @ Crankshaft Grinding Specialists behind Chris Miltons at Prospect.. Good bloke and does a top job and he is tainted by the A-series brush as well on the Sprite side of things.

He has just done my new crank for the race car after my EN40 wizz bank crank was cracked.. and yesterday he crack tested and linished the crank in Beanies motor as well.

Rob F

Guys, thanks for the comments, will get it checked out.

You're welcome. Have fun with your project

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