1930 Small End Bush

[tony.barnett]

Afternoon
Before I make one, does anyone have a source for a replacement small end bush for my 1930 Model B in the UK? The bush is turning in the conrod eye. Its got a 1" gudgeon pin. I can't see anything like it listed on Single Spares.

I'm assuming that I need a solid bronze bush, and Oilite wouldn't work in that application...?

[tony.barnett]

As a supplementary comment - I have a piece of SAE660 phosphor bronze - is that a suitable material for a little end bush?

[cmfalco]

SAE660 phosphor bronze - is that a suitable material for a little end bush?

SAE660 is a good bronze to use for a wide variety of medium-strength applications, but might not be up to the pounding it will take in a connecting rod. I used PB1 to make the small-end bush for my 1928 Ariel and it performed flawlessly for the 3000 miles of the Cannonball Rally, showing no sign of wear or eccentricity when I re-rebuilt the engine afterwards.

Depending on how the 660 you have was made, it could have a yield strength at little as 56% that of PB1, and no more than 82%.

[nevhunter]

You often find the bush has come loose on the rod eye in any makes of older bikes I think the heat has a lot to do with this and you need a good bronze for sure. A "soft" one will lose it's size on the OD and tighten up on the pin at the same time. 1" is a generous size for that application. Later models didn't use it. Most of the extruded bars are low tensile and not up to it at all. Nev

[cmfalco]

For what it's worth, making the bush from PB1 and subsequently balancing the crankshaft for the greater weight of it and the replacement piston are described in detail in: https://www.amazon.com/Ariel-Chronicles ... B0BN61Z6H1

[tony.barnett]

Thanks for the replies. As Mallard Metals are now gone, where do people buy metal stock from in the UK?

[paul.jameson]

I have been using M - Machine in Darlington. Full details on the web.

[tony.barnett]

Can anyone advise the fit I need for a little end bush in the conrod eye please? The bush OD is 1 3/16 (1.1875"). Half a thou? 1 thou?

[cmfalco]

Based on the thermal expansion coefficients of PB1 bronze and generic steel, the bush needs a press fit of 0.002" to be sure it won't come loose in operation. Also, since that press fit will reduce the ID by ~0.001", final sizing of the ID has to take place after installation of the bush to achieve the necessary 0.0005" clearance. Since the gudgeon pins for the aftermarket Gardini and Omega pistons I bought differed in diameter by 0.0003", that sizing has to be based on measurement of the actual pin for your piston, not by assuming it has the nominal 13/16" diameter.

[tony.barnett]

Excellent. Thanks.