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MG MGB Technical - Damper cup function

What is the function of the small cup that slides up and down on the rod attached to my damper/dashpot cap on my ZS carb? I assume that when one is filling the tube that this cup is slid up the shaft and then seated into the piston tube or is it simply allowed to slide back down and float/gently sink into the damper oil. My reference manuals are a little unclear about this. Thanks!
Frank

Frank,

http://www.team.net/www/morgan/tech/carbs/cd-carbs.html
Dan Masters

Dan,
Thanks for the reference...I am still a little unclear about the function of the small metal cup that is above (towards the damper cap) the check valve plunger you describe in your article. It has a flared upper lip such that it will not go any deeper into the guide tube than its overall length. This lip is also notched (? reason). This slides freely up and down on the metal rod to which the check valve is attached. Are these present on the SU carbs as well?
Frank

Thats a good question Frank.When I bought my 79,the cup was seated firmly in the piston tube.It took a good yank to pull it out for a rebuild. I didnt want to press the cup back into the tube(with a narrow tool of some sort) for fear of damage. Now the only time it seats itself is when I drive the car fairly hard for a while.And still it only fully seats sometimes! The other thing I wonder is how do you check the mixture without the cup seated firmly in the tube? Theres no way I can get a hold of the tube to raise it without the cup in tight. Hopefully,there are some (more) ZS experts out there!
Michael E

In order to get the cap back on, you have to
remove the air filter housing, and lift the
air piston. The cap seats onto the top of
the damper.

The cap will come off when you lift the damper
piston to check the oil level.

All that said, I have no idea what the real
purpose of the cap is. I run my 79 with the
cap unseated, without any ill effects or loss
of damper oil.
Ronald

Later SUs with ball bearing suction chambers were fitted with small clips in the same way - later still the clips were replaced by circlips on the outside of the piston tube.

The circlips stopped the piston falling out when the suction chamber was removed - helping to ensure the piston and chambers were not so easily mixed up (they are matched pairs).

I assume the clip was an early attempt to do the same thing.

Perhaps they "stole " the idea from Zenith??
Chris Betson

I think know this one because i've done the thing it's designed to prevent....

I noticed the engine in my B wasn't picking up as smoothly as it should and diagnosed a sticking damper, why is it that the air filters never seem to stop those tiny particles that get ino you dashpots and gum them up? Anyway I digress. So I undid the three screws and took the dashpot off. Now because the dashpot was sticking the piston/needle assembly came off too; then it miraculously unstuck itself and fell out onto the garage floor bending the needle (much olde anglo saxon spoken at this point)

The little clip is to hold the piston in place so that idiots like me don't have to remove the needle, straighten it, check it by rolling it on a piece of glass, and refit.

Happy MGing

Phil

P.S. Michael if you don't reseat the clips when you reassemble, your carbs wont be able to open fully.
Philip Shingler

This thread was discussed between 14/11/2002 and 16/11/2002

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