connecting rod big end

[Brandis]

Have you noticed how quiet the Forum is if I'm not begging for beginner level help.  Well, here I go.

I got my steel 2 piece connecting rods which appear to be old new stock. (surprised that there's no oil passage.)  The wrist pin in the new piston is a perfect fit.  The bearing shells at the big end appear to be un-used.  ID is 1.455 with my cheapie calipers.

I know the crank timing side bush needs to cut to .020 undersized and that's no problem. This tells me this shaft has done some hard miles. But the crank pins are a lot smaller than I expected.  1.348.  This will require a seriously undersized bearing shell and then some machining.  That's approx .125

I can't find the standard dimension anywhere.   I remember than in my old Jaguar restoration days, .060 was the limit.  Any words of joy?  Are we talking about custom machining?

[RichardL]

Brandis,

Yes, you've been missing ever since my tugboat joke.

If your small-journal crank pins are 1.348, there is a problem or something very weird. As far as I see, thickest shells were for -0.040 grind. I believe others more knowledgeable than myself will likely confirm that 1.348" pin OD is a risk for putting a rod (or two) through the crankcase. Attached is a page that gives the grinds.

Richard L.

[groily]

https://www.a7a10.net/forum/index.php?topic=11538.0
This thread may help on the dimensions front perhaps? (IKBA, but something's funny there by the looks of, as Richard L says.)

[Swarfcut]

 Standard Size for the small journal crank big end is 1.4600"/1.4595. Regrinds up to 40 Thou undersize shells are available, any smaller and it's metal spraying to restore the journals.

 A pin diameter of 1.348 is something completely out of the ballpark for commercially available undersize shells. So there is something well out of the ordinary here.

 If you are sure it is the correct crank your best scenario is that the measurement is inaccurate, and the true size is 1.448, a worn example of a first 10 thou undersize regrind. Time for a second opinion.

 Old Thumpers website has the service sheet 207 Crankshaft Regrinding, for download. View it also in the Literature section of this very Forum.

 

 Swarfy.

 

[Brandis]

I can get a crank on Ebay that is freshly ground to .030 under.  Will ship to the US.  Reasonable price.  I'v'e never heard of -.030 bearing shells.

[Brandis]

Everyone can relax.  Thanks for hearing me out.  I just pulled the trigger on another crank, -.030 and bearings.  My pile of unusable cranks will puzzle future archaeologists. 
When I bought this bike it looked like it was going to be so simple.

[muskrat]

G'day Brandis.
"When I bought this bike it looked like it was going to be so simple."
Where have I heard that before? Oh yes me a few times 

Don't quote me on this but years ago I was told after all the BSA under-sizes had been used the Trihard shells would give another couple of grinds. Don't remember if it was for the LJ or SJ cranks.
Cheers

[Swarfcut]

 G'day Musky. Triumph Tiger 100/T100A, SpeedTwin/ 5TA and Twenty One/3TA have crank pins of 1.437"/1.4375, and a shell width of 0.755" which is marginally narrower than the BSA Small Journal shell (0.785"). Available  down to 30 Thou undersize.

 So as urban myths go, sure you could grind the pins to suit, but BSA Con Rods would need re-sizing on the big end, or maybe some Triumph rods were used back in the mists of time. Certainly not ideal, but a backyard fix then for those in dire straits. Heresay also hinted that the early BMC Morris Minor A Series Crank had the same size big end journals as the BSA Small Journal Crank, but without a 1953 Bearing Catalogue I can't answer that one.........

 Cheers

 Swarfy.