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Dashpot Oil

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AUSMHLY

AUSMHLY

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I have HD8 carbs. What is the proper/appropriate dashpot oil?

I believe the SU dashpot oil is 20W. Is it non detergent? (About $16.00 +)
3-IN-ONE sells a 20w oil. I don't think it's non-detergent. (About $7.00)
TrueValue sells a brand called Super S. SAE20 Non-Detergent motor oil, Qt. (About $8.00)

Should the 20w be detergent or non-detergent?

I found this 3-IN-ONE description on the net.
Electric Motor Oil, Series Motor Oil, Container Size 3 fl oz, Base Formulation Conventional, SAE Viscosity Grade 20, Additives Included Corrosion Inhibitors, Color Amber, Compatible Engine Type Low HP Engines, Container Type Bottle, Features Anti-Wear, Flash Point 315 Degrees F, Maximum Operating Temperature 212 Degrees F, Minimum Operating Temperature 25 Degrees F, Odor Threshold, Pour Point 21 Degrees F, Specific Gravity 0.90 at 59 Degrees F, Viscosity @ 40 Deg C 68 cSt, Viscosity Index 95
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When I got My '65 3000 back from the resto, I was told any 20w or ATF or Dashpot oil. I use the dashpot oil because it's apparent the tiny bottle will last years. 5 so far as it only takes a dribble at the beginning of driving season.
 
I had my SUā€™s rebushed by a Thomas Bryant who knows his stuff. He recommends using Mobile 1 15W50 oil in the dash pots. I followed his advice.
 
I have used the damper oil sold by Moss for the past ten years and have never had any issues. The little bottle of SU oil will last a long time. I think there's about 1/3 of the bottle left. PJ
 
I've tried them all over the decades, and don't recall much of a difference. The oil is there mostly to prevent a rapid rise of the pistons when you floor it, so as to create more vacuum over the throat bridge to offset wall-wetting (and, presumably, to damp piston motion). When oil is low you'll get a slight stumble on acceleration; I suppose 20W-50 may give a slightly richer mixture.

I use the SU bottled oil, mostly for the convenience. On long road trips, I kept a little can of 3-in-1 oil by my seat to top up the carbs every couple thousand miles. Detergent or not shouldn't make any difference, the oil shouldn't be getting contaminated.
 
The oil acts as a damper on the piston. If you are low on oil and you give it the gas, the piston will rise too quickly which will create a temporary lean situation that will cause the engine to stumble.
 
I think it depends on how much richening you need/want when you accelerate - higher viscosity will slow piston rise more giving a briefly richer mix, lower viscosity will slow piston rise less giving a briefly leaner mixture on acceleration. For most of us it doesn't matter, as long as there is oil of some sort in place. With wide band AF meters installed, I have been able to see a slight, brief difference in mixture using different viscosity oils when suddenly accelerating, but the difference is too subtle to feel/hear when driving.... So I quit worrying about it and just make sure there is some oil in there.
 
A chap on the MG forum with a supercharged B did a lot of testing with the wide band AF meter and concluded that damper oil/piston spring fiddling didn't make it run any richer on acceleration, just less lean.

Danny
;)
 
Most British car owner manuals from back in the dark ages recommend using the same viscosity oil as was being recommended for the crankcase. I personally find nothing wrong with using SU Damper Oil. I have just replaced the first bottle which lasted me only 45 years,
 
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