B50 connecting rod

seattle##gs · May 27, 2022

I just purchased a 1973 B50 with a stuck piston with rust. I removed the piston and discovered the small end of the rod was blue with heat. There is NO OTHER INDICATOR OF EXCESSIVE HEAT. The wrist pin is normal color. Motor turns freely. It looks like the small end was heat treated though I've never seen this before. Did BSA heat treat their rods?

kommando · May 28, 2022

Looked at 3 conrods, no sign of bluing anywhere and also not on any C15 or B40 rods either. That suggests your one blued with a previous piston seizure, new piston and pin used after rebuild so they now look good (except for the rust) but the rod was not cleaned.

baz · May 28, 2022

There was no sign of blue on my b50 con rod

seattle##gs · May 28, 2022

kommando said:
Looked at 3 conrods, no sign of bluing anywhere and also not on any C15 or B40 rods either. That suggests your one blued with a previous piston seizure, new piston and pin used after rebuild so they now look good (except for the rust) but the rod was not cleaned.

That is a reasonable theory though I've never seen a rod blued like this before. This is a standard bore so I would think if a piston had seized hard enough to blue the rod eye it would have destroyed the bore. So the question is...is the rod safe to use? Pin and rod look great.

baz · May 29, 2022

I think it depends on what you are going to do with the bike ?
These rods are known as "gambler" rods on a b50 that's used hard
Normal road use should be fine

kommando · May 29, 2022

This is a standard bore so I would think if a piston had seized hard enough to blue the rod eye it would have destroyed the bore.

No, I have recovered bores from seizures, the aluminium melts and sticks to the bore but the bore is undamaged. You remove the aluminium by using hydrochloric acid and the bore will take the same size piston unless the bore is worn anyway.

So the question is...is the rod safe to use? Pin and rod look great.

The B50 rod is from the B44 so is near or at its limit, the blueing will have made it weaker.

B50 connecting rod

seattle##gs

kommando

baz

seattle##gs

baz

kommando