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SAE 20. 20W. Engine/dashpot Oil.


SpitFire6
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Hi,

 Why did Triumph spec SAE 20 & SAE 20W oil for early Heralds, Spitfires & Vitesses?

Only a couple of multigrade oils were mentioned & 20W50 only once. SU Dashpot oil was to be a monograde.

Recommended 20 or 20W monograde in an engine sounds new to me.

Cheers,

Iain.

 

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I suspect multigrade oils were new, and treated with great suspicion. Probably more expensive than multigrades too.

Imagine how thin straight 30 oil gets when hot. OK, it will get as thin (probably thinner) than a modern 5-30 used in the majority of modern vehicles. Suggest using that on here and it would get universal disapproval, and yet the factory specified it!

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I would expect mono-grade oil to work fine in dashpots. It won't get as got in the carbs as the engine oil does, so won't thin very much.

You could argue that mono-grade will work better. When cold and thick it will damp the piston more effectively, giving extra acceleration enrichment. As the engine and carbs warm up, thinner dashpot oil will give less enrichment. So kind of self compensating.

20W50 is too thick for dashpots at any temperature.

Nigel

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7 minutes ago, Nigel Clark said:

I would expect mono-grade oil to work fine in dashpots. It won't get as got in the carbs as the engine oil does, so won't thin very much.

You could argue that mono-grade will work better. When cold and thick it will damp the piston more effectively, giving extra acceleration enrichment. As the engine and carbs warm up, thinner dashpot oil will give less enrichment. So kind of self compensating.

20W50 is too thick for dashpots at any temperature.

Nigel

Nigel, a 20/50 should be the same viscosity as a straight 20 oil when cold, it is just that it doesn't thin as much when hot? so my counter argument is it would be better as give more consistent enrichment during acceleration no matter what the temperature!

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45 minutes ago, clive said:

Nigel, a 20/50 should be the same viscosity as a straight 20 oil when cold, it is just that it doesn't thin as much when hot? so my counter argument is it would be better as give more consistent enrichment during acceleration no matter what the temperature!

Yes I think the cold test is a pour test at -15 or 20 degC so by the time you warm those two oils up to carb temperature there could be quite a difference in viscosity...

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Glad to see this discussion limits itself to OILS.

On US boards, people swear that anything from Automatic Transmission Fluid to Marvo's Magical Mystery Oil will make you dog a racehorse while using less petrol than sailing dinghy.  

My ha'pny?   It depends on your driving style.   Try different oils, although changing it isn't easy!    A syringe with a long needle is best.

 

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8 minutes ago, SpitFire6 said:

Hi,

 I can remember using "3-IN-ONE® Motor Oil is a SAE 20 special blend of high-grade oils" in dashpots.

Cheers,

Iain.

I can remember my dad always using that Iain. even using it on my bike as a kid. Still have a can now somewhere? But i use 20/50 now like most others.

Tony.

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I wonder if service manuals just specify engine oil for carbureters for an easy life. Austin / Morris are just the same with Mini in that early manuals specified 20w/50 but later manuals quote 10w/40 both for engine and carbureter.

Basically I can't find a manual that says anything different than "engine oil" - whatever is being quoted for that.

Personally I use SU Damper oil; works for me.

David

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it justshows how lock down is affecting brain waves ,

for years on these forums its been   Aha, no not  dashpot oils again and here we have chapter  and verse about  what do we put in dashpots   

think i will take up fishing..........nah.....i hate fishing as well

Pete   

 

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A lot of the issue is that as Pete pointed out, thinner oils allow the piston to move faster. The great un- learned thought that was a good thing, must make the car go better. However, for good acceleration you want more enrichment, so a thicker oil is better. Within reason! (not a place for gear oils!)

Is 3in1 oil really 20weight? seems much thinner than any engine oil I have used. (such as a 5-30)

 

 

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Not sure if we have covered this, well in with my big feet anyway.

The function of the dashpot is to stop the piston vibrating and to delay it rise. By delaying its rise it momentarily enriches the mixture so it acts like an accelerator pump.

Thin oil will cause the piston to rise quicker than thick oil. As said winter may call for a thinner oil due to the lower temperatures. However, in the winter generally you need a richer mixture anyway so hence only one type used to be specified. I can remember a Minx, the car, I had in the 1960's where the Solex carb had a winter and summer setting for the accelerator pump. The winter setting gave bigger squirt of fuel. On the SU or Stromberg it's automatic.

I can remember the economy drivers putting in the thinness oil they could find!  

Dave 

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zenith and solex had two ideas the pump stroke lever had two holes you could move the clevis  to change the stroke and there was a simpler version with a rotating stop you twiddled to

give a long or short stoke 

nearest we have is on strom   cds /cdse  there is a winter stop for more choke via a push and turn lever stop.

pete

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