Wanted: Undersized Big End Shells.

[Gavin]

Hi, not sure if they exist, but none the less I'm searching for a set of small journal big end shells that are 60thou undersized. for a 51 Plunger A10.

If you know of any in captivity, or of someone who supplies such, i'd appreciate a heads up. Thanks.

Gavin.

[RDfella]

Not sure about this, but try checking the crankpin sizes of Triumph twins of that era.
Best of luck

[CheeserBeezer]

I wouldn't recommend going to -060. That would make the crank quite weak and, because of the reduced surface area, they won't last very long. Small journal cranks aren't that expensive, if you can get hold of one.

[Gavin]

"Not sure about this, but try checking the crankpin sizes of Triumph twins of that era."

Thanks RD. Had a look at the techno stuff and it seems that I could get Triumph shells that will fit, if I get the crank reground to 1.4165. However before venturing into that process, would you know if Triumph shells are compatable with BSA Rods? Outer circumfrence of the shell and width of the shell?

Alternatively, would Triumph Rods, and pistons etc, fit into the heart of an A10?

Andrew, if Triumph journals can be trimmed a further 10thou from 1.4165 then  I think the trim required on the BSA journals should be safe given that this will be a low compression, soft cam job and hopefully won't get a hammering later in it's life.

[RDfella]

would you know if Triumph shells are compatable with BSA Rods? Outer circumfrence of the shell and width of the shell?

In a word - no. Most BE's seem to be 1" wide, so I'd be fairly confident there, but BE dia of rods???  Triumph rods had same 3/4" SE and were 6 1/2" c to c (same as A10) so might interchange (later 750cc T140 rods were 6" c to c). They also had steel caps - better than BSA's alloy ones. Triumph tended to use the same crankpin sizes across several years. If I remember, I'll see if A10 shells will fit a Triumph rod I have.

UPDATE - just checked sizes.
Triumph, inside of rod c/w bearing shell  1.615"
BSA A10 - 1.777". and rod minus shells 1.863"
Beware - all above sizes taken with dial calipers (not known to be very accurate)

And from my records:
BSA small journal is 1.460"
Triumph 500 '59-'74 is 1.438"

So maybe a .040" U/S Triumph (possibly with rod too?) might suit a BSA .060" U/S.

[JulianS]

Some information on big end shell dimensions in the AE 1981 catalogue here

https://bsa-info.nz/other-brands/#AEHepolite

Also shows the bearing housing diameters.

I think you will struggle to find a suitable shell.

[Gavin]

Thanks for the link Julian. I have a couple of leads to follow up, and if they can't help / don't reply I'll contact our Kiwi friends across the ditch. They look like they will have the info I need. The page you suggested didn't cover the small journal crankshaft, but I am confident they will have more specific info when I set out the measurements that I know

Gavin.

[JulianS]

The small journal is at the bottom of page numbered 49.

[KiwiGF]

Years ago I was told one could get more regrinds (beyond -040) on a small journal crank by fitting triumph rods and shells, my A10 is on -040 and I also have a spare sj crank on -040 that needs a regrind, hence my interest in this topic.

The triumph info I have found is “confusing” leading me to think there is some duff info on part numbers circulating.

From what I can see glacier shells ref B2047M or B2026M might suit, but there is differing info on the dimensions on B2026M so that needs clarifying. Owners of early triumphs fit later cranks with different shells so that may be the cause of some confusing info on the net.

I have yet to find a definitive source that says there is a triumph rod 6.5” long that suits B2047M, but there is a 6,5” rod that fits B2026M.

See http://www.mapcycle.com/categories/engine-top-bottom-end/connecting-rods.html

If Triumph rods are used then the width (big end) probably needs to be the same as the bsa rods (to l8mit side movement), or at least larger so it could be machined down.

Aftermarket Triumph rods seem to be readily available from carillo, thunder etc

Some pics attached.

[trevinoz]

I think that Triumph rods are slightly longer than A10.

[RichardL]

Some information on big end shell dimensions in the AE 1981 catalogue here

https://bsa-info.nz/other-brands/#AEHepolite

Also shows the bearing housing diameters.

I think you will struggle to find a suitable shell.

Julian,

That, there, is an awesome link to myriad useful information, in addition to pistons, shells, rings, etc. Thanks for posting that. I think it's the first time I've seen the BE housing diameter stated anywhere.

Richard L.

[KiwiGF]

I think that Triumph rods are slightly longer than A10.

BSA is 6.469” long from memory, so the triumph rod at 6.5” is some 031’ longer so might need a plate under the barrel?

[Gavin]

Thanks for all the help. It really is a minefiled of minute detail. REally appreciate the way others here share the fine print with many of us novices who simply want to get, or keep, another BSA on the road.

So I have resolved the issue for myself by finding another small jounal crank. We shall see how this one measures up.

[muskrat]

G'day Fellas.
A bit off topic but have a look at the 2nd picture in KiwiGF reply. Crankbuster's avatar, I've never seen a rod break like that!
Cheers