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Crankshaft spec's

bobbo

Gold Level Sponsor
The WSM refers to the diameter of main journals and crankpins as either "A" or "B" with different sizes for the A and B. Can anyone let me know what the "A" and "B" designations refer to? I'll be ordering bearings and need to know the correct sizing for my Series V 1725.
Noted on page 17 of the WSM general data.
Thanks Bob
 

puff4

Platinum Level Sponsor
These are standard size and standard undersize as supplied by the factory. You’ll note they 0.010” different.

As for what YOUR crank is, I strongly suggest you remove it, measure it, and then get whatever needs doing first (cutting, or just polishing) and then measure it again before purchasing bearings. I say this because you need to know than actual final size of the journals before buying bearings, and machine shops don’t always get it right. Also, a word of caution - not all bearings are now made to spec - you’ll find that there are variations in sizing, with some shells being thicker or thinner than advertised on the box. Initially measure each bearing shell and put them in mix-matched pairs such that the combined thickness of each pair is reasonably consistent. Then once installed, use Plastigauge to ensure you got it right.
 

mikephillips

Donation Time
And in using plastigauge I always measure twice rotating the crank 90 degrees from the first one just in case there is a slight oval to the bearing surfaces.
 

bobbo

Gold Level Sponsor
So pistons are out, and I'll be removing the crank. Thanks Kevin, for the tip on mix matching the bearings. The ones I've removed from the con rods haven't shown even wear but loads of miles on since I bought the car in 2011. Will see what the mains show once I get the harmonic off.
 
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