Dashpot damper

[trekcarbonboy]

Why does my SU dashpot damper continually pop off? I thought it was just because the oil was low but I have been more pro-active about keeping it at the proper level and still have the problem but to a lesser extent. I put on a thinner fiber washer which helped get a little more thread engagement but it still persists. I did replace them thinking the threads where just worn to no avail.

Also how often is the oil supposed to be topped up to the proper level? My carbs seem to go through an awful lot of oil with not a lot of use. Even quite a bit of leakage while sitting.

Any thoughts would be appreciated.

[dursleyman]

You wouldn't expect to top up the oil very often, I rarely need to put any in mine, and I do not understand how it could leak at all. I didn't think there was any route for the oil to go. The SU operates by suction in the piston chamber so its also very weird that your dampers could get forced out. Puzzled.

[skertonman]

Are the screw threads on the Black plastic tops in good order, if they're stripped and the engine "backfires" through the inlet manifold they could push the dampers out of the top of the carbs if the threads are shot.

[Beans]

The actual damper should be fine, they indeed can't loose oil. But the damper's tube also acts as a guide for the pistons movement.
That is why the oil level should be above the top of the damper tube to help lubricate the pistons action.
So if the the car's not used the oil above the damper tube will drain away between damper tube and suction chamber's guide.

p.s I don't understand the original problem. I have never seen the dampers pop off.
To start with they should be tightened by hand only. So check if their thread (plastic!) are damaged.
If so replace maybe the dampers are incorrect (from a Stromberg )

What markings are on top of the dampers?
And check the venting holes are open ...

[trekcarbonboy]

Markings... AUC 8103. Less than 2 years old. Same problem I had with the original set, makes me think the metal female threads are the worn ones.
Car ran fine this morning but when I went out to check those markings the cap was just sitting loosely on top. May have popped loose when I stopped because the car runs pretty poor when they are off. It is typically only the front carb but occasionally the back also.
I don't see a vent hole.
Scratching my head.

[saabfast]

Vent hole is a small hole through the black cap, allows air to flow in and out as the piston moves. The rod is a loose fit in the bore with the oil to damp out rapid movements of the piston. I normally find that, after filling, the first decent rev of the engine ejects some oil through the vent. If you don't have a vent hole in the caps it will probably affect running as there is no pressure release when the piston rises quickly.

[Beans]

As this picture wasn't meant to show the top of the damper it is a bit out of focus.
But the vent hole is quite clear. As is the marking AUC8114. So it might well be you have an incorrect damper fitted

[jeffremj]

Why does my SU dashpot damper continually pop off?

I am not sure, as it happens on my TR7 V8. Only one 'unwinds' itself. I put it down to vibration.

[trekcarbonboy]

Vent holes...Check.
The threads visually seem good. They tighten down nice and solid.
I checked the SU reference Catalogue and it lists AUC8103 and CUD4108 for TR7's.
It has AUC8114 listed for TR4, Spitfire, Dolomite Sprint. etc... I did get these HS6's off of Ebay, so there's no guarantee what they really came from. They did come re-built and mounted to a TR7 intake manifold.
Rimmers has a brass-capped version available. (no part# listed) I might just try that.

[Beans]

There should be an alloy tag with the carburettor number fixed to the float bowls.

[lgray001]

On my MGs, I never had them come off, but there were fiber gaskets in place.

One thing I did that solved the Summer/Winter temperature extremes in St. Louis, MO, USA; I used Caster Oil from the pharmacy. It never lost viscosity in the Summer or became syrup in the Winter.

[Hasbeen]

Not all SUs are the same, even in a particular size. I had a "set" of 1 & 3/4" SUs bought second hand. The size of the brass "piston" on the damper varied by 28 thou.

One was so loose it wouldn't have been doing much, & one was about right.

I'd check yours to see how tight they are in the bore of oil chamber. They may be so tight that they are being forced off.

You could also try a small O ring or rubber band under the plastic nut. it should stop vibration rattling them off, if that is what's happening.

Hasbeen