1951 bsa bantam D1

[Mfenech1]

Hi I recently just purchased a 1951 bsa bantam d1 rigid frame and would like to ask for some information. How much 2 stroke oil should I mix with gasoline? And what type of gearbox oil should I use in those small bantams? Thanks for any help and info

[Spaceman]

This seems to be a hotly debated subject with some saying 1:32 by volume is ok but others recommending using 25:1 is safer. I think BSA might well have recommended 1:16 which is what they specified for a D7 that I have info on.

The gearbox needs to run with engine grade oil: SAE 40 or multigrade 20W/50 but it needs to be JASA MA2 spec because of the wet clutch.

[Mfenech1]

Thanks but I also see that on the gas cap it says put 2 measures per gallon gasoline

[BEEZABRYAN]

Two measures are  to one IMPERIAL not US gallon.

[Spaceman]

The D1 instruction manual specifies 2 measures per (British/Imperial) gallon and seems to indicate the ratio by volume should be 1:20. If correct then the capacity of the filler measuring cap should be about 114 cc which is easily checked.

On my D14/4, confusingly, although the filler cap says 4 measures per gallon, the instruction manual specifies 3.5 measures per gallon corresponding to 1:24 by volume. However, the measures for the D1 and D14/4 are different with my D14/4 being only 50 cc - in other words 4 of my D14/4 measures is roughly the equivalent of 2 measures in the D1.

Where there is further confusion in the D14/4 manual is that it says the mixture should be 1:24 for self-mixing oils but should be 1:32 for non self-mixing oils. As far as I can see, many modern 2T oils are self-mixing with non self-mixing 2T oils being relatively rare. That said, the modern recommendation for 2T motorcycle engines appears to be 1:32 or weaker.

Basically, it's probably a question of you pays your money and takes your choice! For peace of mind, use 1:24 and live with clouds of smoke billowing out the exhaust or run cleaner with 1:32 and, possibly, a slightly higher piston/bore wear rate which probably won't matter for the average low mileage classic bike owner

[BEEZABRYAN]

So, basically,  for our friends' D1 the Oil to Gas ratio is 1:20

[Spaceman]

That's what it appears to say in the D1 instruction manual. That said, 2T oil has probably changed a lot in the last 50 years and I would personally go for either 1:24 (158 cc per US Gallon) but, if too smoky, to reduce down to no less than 1:32 (118 cc per US gallon).

[Mike Farmer]

 

the comment that the oil has changed over the 70 or so Bantam years is of course fact. Some of the newer oils you can use at 40:1. However something to consider is that the qty of oill affects the fuel air mixture cos the oil doesnt burn in the same way or at the same rate as the petrol. Therefore the lower the qty of oil the richer the mixture. In truth I have no idea what the differences might be.

Mike

[Mfenech1]

Thanks to all for the help and info

[griffo]

  I run my Bantam on 40/1  and no nipping up or problems.. No I don't go too slow...

[BILL NELSON]

  I run my Bantam on 40/1  and no nipping up or problems.. No I don't go too slow...

My D14 was highly tuned (helped by George Todd) & I had 2 carbs for it. Normal running was somewhere almost 40:1, but for fast work (as certified by Cheshire Police) 83 mph could be sustained at 50:1 using the alternative carb set up to give the right mixture.
BTW, although I ran bigger bikes on Esso 5 star (101 octane) the Bantam ran on 2 star