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How much dashpot oil leakage is normal


Country flag
My rear carb dashpot seems to be leaking oil. How often do guys top up your dashpots?

FYI - I'm using 20w50 motor oil


Jedi Knight
I rebuilt my carbs 3 years ago and have not had to add oil yet. I have only driven about 2000 miles though on the rebuild.


Great Pumpkin - R.I.P
I consider any leakage at all to be abnormal; but I do top them up at every major service. The excess oil runs down the shaft and lubricates it.

There's an O-ring inside the piston that fails and causes the leak. To replace it, you basically remove the needle and it's carrier (unscrew the mixture adjustment and remove the retaining screw on the side), then use a pencil or similar object through the hole to drive the mixture adjustment screw and it's retaining clip out the top of the shaft. The process is covered in detail in one of the carb articles at Buckeye Triumphs


Jedi Knight
I tend to fill mine up about two or three times a year. I suspect that they are a little worn.


Country flag
I had one that tended to go down. I emptied both dampers and went back with Bars Rear Main Seal Repair. Seems to be the same viscosity as 30 or 40w oil.
It must have swollen the o-ring enough to stop the leak.


Great Pumpkin
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Uh oh...[/QUOTE]

Ahhhh, Tom???

What the heck does that mean??


Luke Skywalker
Country flag
Tom, BTDT. Follow Randall's advice and check out the Buckeye Triumph /Nelson Reidel 3 part carb-rebuild PDF. It's so good, I had my printout bound at Kinko's. Use Randall's tip of using the pencil to push the needle/o-ring assembly out. This is also a good time for the ZS carb tool you have in your toolbox.....


Luke Skywalker
That's pretty heavy oil for dashpots ain't it..20/50? I use a 30 weight in the summer and auto tranny fluid in the winter.
Oh no, another oil thread....


Moss used to have the orings for this leakage available. Probably still do.. I found similar size at my well stocked auto parts house, in their oring supply drawer... Might also check a plumbing supply store or well stocked hardware store.


Senior Member
The O-ring comes in the carb rebuild kit, which is how I got a new one. Even with my new O-ring, I still top up my oil about once a month. On my old Midget 1500, I used to top its damper oil up about twice a year. Victoria British has the O-ring as a separate part; that's where I got my rebuild kit, new metering needle, and my adjusting screw.



Great Pumpkin - R.I.P
tdskip said:
Yeah, you guys are (of course and as usual) right. I'll do it properly.
It's easy and quick; but if it's keeping you off the road I'd just live with the leak for awhile. It's not like it gets any harder because the carbs are mounted or have been driven.

The seal sweller is an interesting idea ... never thought of that.

Not sure I understand the comment about 30 weight vs 20W50. Remember that 20W50 acts like 20 weight @ -10C and 50 weight @ 100C. Since the carbs are much cooler than 100C (boiling point of water), the effective weight will be somewhere between those two numbers. If we assume the change is linear, and the carbs are around 40C, the effective weight of 20W50 comes out almost exactly 30.

That said, I found that straight 20 weight seemed to work best for me in my TR3A. Haven't repeated the experiment with the Stag yet, though.


Hi There tdskip,

I have never had the need to top up the dash pots.

I bought from Moss Motors their "Damper Oil" which is specially designed for SUs & Strombergs. What the mix is ???

I bought it just to have it & have virtually never used it.

Its not cheap but you`ll never have to worry about the mixture.

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