Oil for SU carbs; reminder

[SwallownAmazon]

I use ATF in the rally car - tried engine oil but ATF is more consistent. Never have to top it up and dashpots don't stick so lubrication OK.
I think someone said earlier that ATF doesn't lubricate - so why don't automatic transmissions seize up?

.

[Ron Kwas]

V21;

In the SU, Damping Oil both dampens the rise of Dashpot AND lubricates its action (I've zero experience with, nor interest in, Strombergs, but I expect since the design is similar in this respect, their oil likely serves similar functions...)

...vacuum in the Dome liberates droplets from the Damping Valve and Reservoir as Dashpot continuously rises and falls, and these droplets get into precision clearance between Dashpot and Dome Tubes, lubricating this joint and its continuous action in this way...and since the relocation of the droplets is driven by vacuum, it also leads to a drop in oil level, as oil is (exceedingly) slowly consumed (through vacuum holes in bottom of Dashpot).

See also: http://www.sw-em.com/su_carbs.htm#Da...20of%20Dashpot
Note that precision clearance between Dashpot and Dome Tubes is not shown in the Damping Valve Assembly and Function sketch...I may have to add that to sketch...

Cheers

[jimbo1593]

good info as always, Ron

[Ron Kwas]

Forum;

I was not able to add the Damping Oil simply to the existing sketch, but I found another SU drawing to add it to...here's the result:


Simplified SU carb showing Damping Oil Reservoir (1) with Damping Valve (2), lubrication of Dashpot Shaft (3) and path for Consumption (4).

Cheers