one for the engineers

[NewcastleFalcon]

Chris

I thought I had cracked sealing the cylinder/sphere junction with a simple copper washer lying in what remained of the recess, on one the cylinders now donated for further scientific research. The bottom of the recess even on the chewed up rim cylinders remained flat. Probably a lot flatter than able to be achieved with files with the cylinder in situ on the car.

I don't think I pursued this approach to its proper conclusion as I abandoned it, in favour of replacing the cylinder with a better one, and eventually succeeding in getting the pin out to do the job. The washer I used was adapted to be a very good fit in the recess, lying as the normal sphere seal would, however the washer should have been a little bit thicker so that the sphere mating surface bore full square against the washer. This was probably the main reason the repair failed. Intuitively I would guess that to achieve a seal with a copper washer given right dimensions, the sphere would have to be screwed on much more than hand tight to make the seal.

Another thing I thought of in those moments when you think the pin is never going to come out was effectively sealing the threads with the appropriate heavy duty specialist Loctite type product. Probably would prevent any leakage but the sphere has the chance of never being able to be removed from the strut again. Looking at the data sheet for this stuff however the breakaway torque is 15nm which doesn't seem much.


Hope you manage to source an appropriate dowty. You think they would have some samples lying around to help the FCF with this important research. If only there was an on-line equivalent of "Smails" in Morpeth. Its the worlds most old fashioned ironmongery shop, and its no problem at all buying just 1 screw. The new technology amounts to the assistant putting your screws in a paper bag, and writing the price on it, and taking it to the till. Its a gem. I have done a bit of gratuitous Northumberland promotion on the FCF before, but the proper NTB tend to focus on castles, beaches and Hadrian's wall. Ironmongers never get the attention they deserve

regards

Neil

[CitroJim]

Neil, I'm interested in your copper washer idea.

Next week I'm off for the week so will have plenty of time hopefully to look into this a bit further on your donated cylinders...

I'm intending it to be a week of car playing...

[c.morewood]

Neil,
That sounds as though it might work as well...I'm awaiting Jim's results.
10 enquiry E mails and 1 reply so far...plus an atuomated one from a supplier in India ( who would probably want an order of 1000!!!)
Maybe the phone call is the best way to proceed.
Well the MOT examiner wasn't convinced that I had no leak from the repaired cylinder .. although its probably that i had a small tear in the rubber at the piston end and tried to seal it with a bit of inner tube with cable ties round it.. I've got a new rubber seal and will do that next week... but I was hoping to get that, the new LHM, the spheres and Dowty washers done all at the same time!!!

[NewcastleFalcon]

My last foray into the world of engineering was probably making a copper ashtray and turning a brass cannon in metalwork when I was 12 (still pride of place on Mum and Dad's windowsill I might add) so paddling about in a thread entitled "one for the engineers" is probably me out of my depth. So here is a bit of amateurish research.

From "the net"

The connections used in hydraulic circuits can be split into two broad categories:

1. Connections where the screw thread provides both the mechanical join and the hydraulic seal.
2. Where the thread provides the mechanical connection but there is a separate hydraulic seal

I think we are in number 2 territory here for the rear cylinder to sphere joint.

In the second category, where the thread provides the mechanical connection, and a separate seal is required, the most widely used thread connection is the British Standard Pipe Parallel Thread, sometimes known as BSPP or BSPF. This thread has been converted to a metric standard and is commonly known by a G or R designation. (The G stands for gas as the thread was originally designed for use on gas pipes. The R is an abbreviation for Rohr, the German word for Pipe). ½ G (or sometimes G½) is the same as ½" BSPP or ½" BSPF.

Spheres look like they have parallel threads to me.

With BSP Parallel, the hydraulic seal is usually formed at the mouth of the internal thread by using a suitable gasket. This can be a copper or aluminium ring or a lipped seal such as the Dowty seal which is usually rubber bonded to steel.

To get over the damage to the retaining rim at the end of the cylinder, a copper or aluminium seal of a thickness slightly over the normal rim depth may have a reasonable chance of producing a seal. Combine it with the appropriate loctite on the sphere threads leaving enough time for a decent cure and you could have an effective "repair" without removing the cylinder, or having to file the rim to the necessary precision of flatness to possibly get a dowty to sit right for an effective seal.

The dowty probably needs a totally flat surface. Could this possibly be "manufactured" by loctiting a close fitting copper or aluminium ring into the recess in the strut end, or will a simple copper or aluminium ring work well enough so that the dowty would be superfluous.

The proof of the pudding is going to be down to a bit of trial and error, and probably someone of greater engineering credentials than my brass cannon and copper ashtrays. ,

regards

neil

ps other things made..........a cricket spinner........an aluminium after-eights serving dish....a gardeners trowel with british racing green handle.....a shoehorn etc.

[NewcastleFalcon]

In Simon's (mandrake) leaking banjo post
it was mentioned that a proposed temporary fix to his banjo with a copper washer would require the washer to be annealed by heating it up to cherry red then quenching it in cold water. I never even thought of doing that when I tried my adapted copper washer sphere to rear cylinder repair. Probably another reason why the first try didn't prove to be a permanent fix.

regards

Neil