Front damper valve bolts.

[RobThomas]

Front damper valve bolts.
Right, I have several sets of front dampers and there are some with large (approx 23mm across) nuts/bolts/whatevers holding the valve in and some with small (approx 18mm) ones. None of the arms show any signs of the mythical green paint, so, how do I know which ones are MM and which are M1000? The larger head ones also have RXP cast into the body of the damper.
Also, does anyone know how the shims in the valve are arranged and what effect this has? There are several under the spring on the dampers with the larger diameter valve fastener.

[RobThomas]

I think I MAY have got an answer to at least one part. The big spring in the valve can be shimmed to increase the bump damping and the short spring can be compressed by turning the nut on the valve piston to increase the rebound damping. You'd need to have one apart on the bench to see what I mean?

[bmcecosse]

I've tried all that - it didn't make any discernible difference - to me anyway! The big improvement is by using more viscous oil - SAE 30 is good or SAE 40 for best result. That's NOT 10W40 - it must be straight grade oil. 30 from Tesco gardening - 40 from motorcycle place - don't let them talk you into 'fork oil'.

[RobThomas]

Yup! I've got some of that Tesco £3:50 per litre stuff in there. I've flushed the dampers out and have used 1/2 litre for the 4 shocks but have noticed quite a lot of congealed oily crud wrapped round the structure of the internals. It took quite a while to get the air out and then, when topping up, I noticed that there will be an air space above and around the periphery of the filler neck which is presumably there to account for expansion. I assume, therefore, that the filling up to 3/8inch from the top of the neck is not quite so critical. The height of the fluid seems slightly dependent on the angle of the damper arm.

So, has anyone got a M 1000 with front dampers on it where they could measure the diameter of the nut at the dottom of the body. Also the same for an original early car?

Oh, and the reason for asking about the shims on the spring is that I dropped one of the valves before I could see what order the bits came in. I'm now fairly sure that it doesn't matter which order the springs and shims go in so long as they are all replaced and none left out.

Cheers

[bmcecosse]

As long as it's straight oil - and not multigrade - it should be fine. I added more shims - to compress the spring more - and screwed up the little nut - but by far the biggest improvement is the more viscous oil. Yes - leave an air space - but you will likely need to keep topping up for a week or two in use - as the last air gets squished up to the top.

[RobThomas]

Like this...[frame][/frame]

[bmcecosse]

Crikey! I'm guessing the smaller ones are an earlier version.......

[RobThomas]

Does "RXP" have any significance?

[RobThomas]

Aaaaaaaaaaaaaaaaaaaaaaaand the answer IS....


Peter Caldwell, Wisconsin, USA, nosimport@mailbag.com
Rob,
The RXP are the later. The valves are different. Two distinct valve springs in the later vs. very similar springs in the earlier. Also, the pistons and their bores are larger. Armstrong made a "running change" and I believe the RXP indicates the different casting. The smaller valve ones may be correct for your vintage, but I think the ride and handling will benefit from the later. There's some verbiage in an old Sunbeam Talbot factory repair book about the changeover, and how reliability and ride quality was much better with the later shocks. The only reason to use the early shocks would be for originality sake, I would think.

Peter

[bmcecosse]

Interesting! Checked on my 64 car - and my spares that came from a 71 car - and they are both the smaller version you show with no RXP markings.