The difference between MGF and MGF Trophy Hydragas spheres

[Rob Bell]

Thanks to Steve160, I am now in possession of a rear MGF Trophy 160 Hydragas sphere. The plan is to dissect it (Tim has already taken one of his apart) and compare it to a failed standard rear Hydragas sphere

To kick off though, let's play "spot the difference": can you identify which is the Trophy sphere?

[Dell]

Hi Rob

Can we have a top view

[robbie1003]

interesting, wouldnt mind having a go at operating on one, I still think theres a way of putting in a spring within the sphere when they fail. over the weekend I saw some coil kits that are fitted instead of the rubber suspension on the minis, there has to be a way other than swapping subframes from a tf. difficult to tell difference if supposedly one has failed and other hasn't, obviously the bottom one would give lower with the cones bottom not poking out.

[Dell]

interesting, wouldnt mind having a go at operating on one, I still think theres a way of putting in a spring within the sphere when they fail. over the weekend I saw some coil kits that are fitted instead of the rubber suspension on the minis, there has to be a way other than swapping subframes from a tf. difficult to tell difference if supposedly one has failed and other hasn't, obviously the bottom one would give lower with the cones bottom not poking out.

There is the Suplex kit for the f which does exactly what you are talking about but if you do some digging on the web there appears to be problems with it as several people have suffered cracking around the top damper mount after fitting. There is also an Australian version which looks a lot better made but I have read reports of people suffering the same fate with them.

[robbie1003]

interesting, wouldnt mind having a go at operating on one, I still think theres a way of putting in a spring within the sphere when they fail. over the weekend I saw some coil kits that are fitted instead of the rubber suspension on the minis, there has to be a way other than swapping subframes from a tf. difficult to tell difference if supposedly one has failed and other hasn't, obviously the bottom one would give lower with the cones bottom not poking out.

There is the Suplex kit for the f which does exactly what you are talking about but if you do some digging on the web there appears to be problems with it as several people have suffered cracking around the top damper mount after fitting. There is also an Australian version which looks a lot better made but I have read reports of people suffering the same fate with them.

iam aware of the rather expensive suplex kit but im thinking of a spring within the stripped out sphere void.

[Rob Bell]

To let you out of your misery, the two rear 'spheres (standard and Trophy) are outwardly identical. The one on the right (or the upper one, depending on how the image is orientated when you look at it - pesky iPhone picture!) is the Trophy one.

I suspect that there may be differences in the displacer cone/tapered skirt, to provide the difference in spring rate - and this can be transferred from a Trophy sphere to a standard version - and vice versa. The key question is whether there are any difference in the design of the internal damper - and that will require some action with a junior hack saw!

More soon (the weekend I suspect!)

[Rob Bell]

Putting a spring inside a Hydragas sphere would be a challenge, and it depends on exactly what you have in mind - are you replacing just the nitrogen egg with the spring and keeping the fluid interconnection, or are you replacing both media with the spring? In either case, space inside the original casing is at a premium, and designing a spring with the correct properties that will fit and not become coil bound is a real challenge.

If springs designed for minis can be tuned to cope with the additional mass of the MGF (which depending on spec, weighs up to 100% more than the most basic Mini), then that might be an option worth looking at.

But for this thread, we're looking to see whether a standard Hydragas sphere can be turned into Trophy specification...

[quick_spider]

I'm pretty sure the main difference on the metro gti rear hydrogas units is the shape of the aluminium cone rather than an internal difference.

It might be worth comparing the two cones first before doing any destructive tests!

[robbie1003]

Putting a spring inside a Hydragas sphere would be a challenge, and it depends on exactly what you have in mind - are you replacing just the nitrogen egg with the spring and keeping the fluid interconnection, or are you replacing both media with the spring? In either case, space inside the original casing is at a premium, and designing a spring with the correct properties that will fit and not become coil bound is a real challenge.

If springs designed for minis can be tuned to cope with the additional mass of the MGF (which depending on spec, weighs up to 100% more than the most basic Mini), then that might be an option worth looking at.

But for this thread, we're looking to see whether a standard Hydragas sphere can be turned into Trophy specification...

My plan would be remove all internals and use the sphere just to contain the spring,the spring size is determined by the space inside,obviously the weight of vehicle determines the rate and would need replacement shockers.how the bottom of the spring meets the arm would depend if the desplacer cone could be used. Bear in mind I have never pulled one in bits yet. Just a thought.

[Rob Bell]

Tim has sent me some pictures of a Trophy cone he has pulled apart, but Dieter already has pictures of a standard rear cone in pieces: http://www.mgfcar.de/cut_unit/index.htm



To fit inside the standard casing, the spring diameter would need to be extremely small - hence why Suplex went to the trouble of making their own spring capsule.

[Rob Bell]

I'm pretty sure the main difference on the metro gti rear hydrogas units is the shape of the aluminium cone rather than an internal difference.

It might be worth comparing the two cones first before doing any destructive tests!

Sorry Jon - missed your post! Yes, I agree - I strongly suspect that you are right that the sole difference between the two cones is based in the shape of the tapered skirt/displacer cone. But to be definitive about this will require testing and ultimately disassembly of the internal valve to confirm whether or not they are identical...

[robbie1003]

ok, pie in sky though until I get my hands on one but, if you were to remove the displacer and remove whats in lower chamber, cut into the top chamber (obviously discharge nitrogen first) as far as you can to the to chambers connecting welds to access the space in the top sphere surely the space is large enough for a coilover type spring to fit in? (spring rate obviously needs working out), possibly use displacer into the bottom of the coil (or convert slightly) as the normal connection to suspension arm. looking at the mini rubber type suspension the coils are not long, how far does the f suspension travel to accommodate a spring without coilbounding. like I say its just a thought.

[Rob Bell]

If you want to fit conventional suspension, then in my opinion the best solution by far would be to retro fit TF subframes and suspension, which already have the strut towers built in. With TFs being broken for parts at the moment, complete replacement assemblies need not cost you a great deal (and probably less than attempting to engineer your own solution).

There again, if you enjoy the challenge, then go for it (which is kind of what I tend to do! )

[Uncletone]

I've been monitoring Tim's thread on the other forum and he's trying to engineer a solution. Unfortunately he doesn't want to get involved on a commercial business and I guess I can understand that.

With that in mind, and obviously great minds think alike, because another forum member thought of it, I contacted Pleiades @ Sawtry. They refurbish Citroen Hydraulic Spheres, same principle higher pressures.

They are willing to look into this because of the captive market.

http://forums.mg-rover.org/showthread.php?t=669178

If he comes back to me I'll let you know.

Tone

[Rob Bell]

Nice one Tone

I am planning to disassemble the spheres this weekend - commitments permitting!

[Rich in Vancouver]

I think that the reason that both Suplex and Sydney MG Centre went with the spring in a can solution is mainly due to the height of a proper coil-over setup.
I haven't done any proper measurements but you would be looking at least 10" vertical space to fit a coil-over. If you used an adjustable shock in the stock position it would be possible to construct a coil-over less shock to fit in the space occupied by the sphere. This would just have to accomodate the spring travel. (This is basically what Suplex has done, but it seems the "can" is a big part of the issues they are running into.) A sturdy bracket would replace the removable portion of the sphere mount to create a place for the top to mount. (And take the place of the can) The top could be located by a typical stud-type mount with the bottom seating in the suspension knuckle. The spring could be supported by a coil over adaptor as shown. The suspension cone could be machined down to fit inside the adaptor and welded or bolted into place. There are hundreds of different springs available, but of course it would be challenging to find the correct combination of spring rate and shock setting.

Coil-over adaptor (E-bay photo)

[160steve]

Get on with it Rob

[robbie1003]

I think that the reason that both Suplex and Sydney MG Centre went with the spring in a can solution is mainly due to the height of a proper coil-over setup.
I haven't done any proper measurements but you would be looking at least 10" vertical space to fit a coil-over. If you used an adjustable shock in the stock position it would be possible to construct a coil-over less shock to fit in the space occupied by the sphere. This would just have to accomodate the spring travel. (This is basically what Suplex has done, but it seems the "can" is a big part of the issues they are running into.) A sturdy bracket would replace the removable portion of the sphere mount to create a place for the top to mount. (And take the place of the can) The top could be located by a typical stud-type mount with the bottom seating in the suspension knuckle. The spring could be supported by a coil over adaptor as shown. The suspension cone could be machined down to fit inside the adaptor and welded or bolted into place. There are hundreds of different springs available, but of course it would be challenging to find the correct combination of spring rate and shock setting.

Coil-over adaptor (E-bay photo)

i do believe there is a cheaper option for a replacement setup on coils other than the overpriced stuff that's available, one reason for the coilover spring use is because they are easily available in the length and multiple rate at a reasonable cost.my idea of useing the sphere body would mean theres no need for any change in brackets, you could even cut top off the sphere top and put a spacer band in and reweld it back on if space for the coil was a issue. my advantage over most people is i have the garage,space, tackle and engineering brain to have a go,just don't have broken spheres and time atmo to have serious go at it. Its good to throw the ideas about, be boring otherwise.

[Rich in Vancouver]

Exactly Robbie, at this point, other than one sphere showing signs of weeping my Hydragas is holding up OK. The more ideas we have going and the more people that are working on an eventual solution the better the odds that practical solutions will be found by the time they are needed.

[Rob Bell]

Made a start over the weekend to undertake the autopsy of the Trophy rear hydragas unit (part number RPJ000010). It is taking quite a lot longer that I had initially imagined because I am using a junior hacksaw, and the containment cannister is made from 2mm thick steel (understandable given that the dynamic pressure range probably exceeds 600psi)... and I didn't want to use Mr Angry (aka the angle grinder) because I didn't want to destroy by accident the internals of the sphere!

Removing the displacer cones (tapered pistons, or tapered skirts - what ever you want to call them) revealed the first surprise:

Bar for the length of the piston itself, the shape of the cone that displaces the lower rubber membrane is exactly the same compared to the displacer cone from a standard rear Hydragas sphere. I had imagined that the Trophy displacer cones would have a different profile to provide a stiffer springing characteristic. As it happens, it doesn't.

Here's a slightly superfluous image of the rubber membrane that these displacers abut against:

Now started the hard work (wasn't it a hot weekend? jeepers, I needed a cold beer after eventually cutting through the flange!!!

After much sawing, and an attack with a bolster chisel, the nitrogen egg was released from the assembly (I'd discharged the nitrogen first, drilling a 1.5mm diameter hole through the top rivet as Tim Guy had done for his project):

And here is the top part of the internal damper assembly: