SU problem on standard set-up

[Ian F]

Just been for a longish run with the BGT and have a minor issue which has occurred both out and back. Speeds of circa 70 mph on motorway, standard carbs but with K&N filters, but probably totally irrelevant to this issue! SUs filled with Castrol 20/50.

The issue: after each run the damper on the front SU has been found to be unscrewed. Didn't appear to affect the running but obviously not right somewhere!

The questions:
a) why does this happen despite being screwed down tight?
b) what do I need to do to cure it?

Never had this problem before in 39 years of ownership!!

IanF

[Vic Butler]

Evening Ian.
A very strange problem. Try swapping the dampers around and see which carburettor the damper comes undone. That should indicate whether the fault is in the damper or carburettor.
I use automatic transmission fluid in my SU's. It has a constant viscosity regardless of temperature.
. Vic Butler

[Ian F]

Thanks Vic. I've swopped the dampers over and will see what happens on the next long run. These are the original 1972 SUs and have been refurbished by me, but the damper/piston assembly isn't touched during refurbishment. I've never been sure which oil to use in the dashpots, the lubrication chart in the Leyland workshop manual states use 20/50 (same as engine etc.) but in the text it also states "under no circumstances should a heavy bodied lubricant be used". Seems a bit of a contradiction? I do recall that in the '70's the "racers" suggested using a light oil as this allowed quicker enrichment as the piston could rise more easily in response to the throttle opening. I've never noticed much difference in whatever oil I've tried!

IanF

[David Wicks]

I've had these loosen before on other BL cars and Jags but never unscrew completely or leak. I would give them a dab of locktight if you are really worried. As for the oil I have been putting sae 30 or 20/50 in SU's for over 50 years and never had any problems.