SU Carburettor Damper Cap

[SV_Minor]

Hi, I've just been tinkering around with my 1932 Minor and noticed the damper cap is missing! I have had the car back on the road since last month and I've done around 150 miles in that time, with the last trip being to the supermarket last Friday, and the car has appeared to be running well. I can't say when the cap went missing, as it's only something I've noticed today. Are these brass caps prone to unscrewing and dropping off? The only other explanation is that it wasn't refitted when the car was being recommissioned in December. Advice gratefully received.

[Ian Grace]

Yes, they are! I have lost a couple this way and since then I have made sure they are really tight!

Luckily, you should be able to get a shiny new one from SU - as I did!

[SV_Minor]

Thanks Ian, I've already taken a look at Burlen's SU webshop, they're around £15. So how will it affect the running with it missing? I'm just trying to figure out if it's been a recent loss or whether it's been missing for the last 100+ miles.

[Ian Grace]

I guess you could run without one as long as no dirt gets in and prevents free movement of the piston. These caps are very common so you may be able to pick up a used one. More recent ones were black plastic, but fit the same and do the same job. You won't notice the difference at 60 mph!

[SV_Minor]

I've only managed a max of 46mph..... and that was 'interesting' for a newbie to pre-war/vintage motoring

[SV_Minor]

Good news, I've found a black plastic vented cap in my small collection of spares

[Ian Grace]

Well done!

[SV_Minor]

Thanks Ian. As a follow-up, do forum members use a splash of light oil in the top of the dash-pot, or do they keep the inside clean, dry, and polished? Mine is currently the latter, after advice given by an old-school mechanic and friend who has looked after my old cars over the years. I do have a small bottle of SU light oil in the car.

[Ian Grace]

I believe that the SU light oil (or any light oil - like 3-in-1) is appropriate. The original Minor manual calls for a few drops of good quality thin oil, such as sewing machine oil. Don't leave it dry. It is easy enough to slip a finger in the intake and lift the piston and feel if it is binding at all. Again, from the manual, "The piston should come up quite freely and return to its seat with a click as soon as it is released".

I have had a few problems in the past where the piston was lifting and falling with no problem - until I tightened down the two dashpot screws, whereupon the piston seized solid. With two screws, there are two ways to fit the dashpot. Turning it 180 degrees and refitting it solved the problem.

[SV_Minor]

Thanks again Ian, I'll try a few drops in the top and see if it makes a difference.