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MG MGF Technical - Hydragas queries

Dr Moulton wasn't the biggest fan of the K series Metro GTi with its additional dampers.

I vaguely remember him saying that a better solution to achieve a more sporting repsonse would have been to use smaller diameter interconnecting pipes.

Has anybody gone down this route on the F?

Another thing that strikes me as ripe for experiment is the interconnecting fluid itself. It's only a water/alcohol solution, of course, but what would be the effect of using fluids with different viscosities?
Jerry Reynolds

I think Techspeed did something like you say. (restricted fluid flow by using a washer with small hole... IMO)

On the other hand I've only heard of drivers who just threw out the interconnection and use the units as independent single springs. (Techspeed supplies or DIY)

Another option discussed years ago was replacing the fluid with 'thicker' stuff like oil. The problem with it is lack of knowledge about disintegration of the inner units rubber spheres.
Standard hydraulic oil or brake fluid definately kills them.

Regards
Dieter
Dieter K.

Best thing is to junk the hydrogas system all together. If you have a gti spec metro you can get a coil over kit from roverdose.co.uk. Replaces the front hydrogas.

A set of coilovers is cheaper than one hydrogas unit so it makes sense. I had a front displacer blow and didnt fancy the £170 rover asked me for for just the one unit

It fits where the damper goes. Only downfall is you have to check on the bolt everynow and then just to make sure it isnt getting bent by pot holes etc.

Give awesome road handling. I have to get my rear hydro units changed as they ve given up the ghost. MGF ones are better. Pump up to a higher pressure and machine a few parts and it will give you a nice stiff ride.

mark forrester

Fair enough, but I don't want to junk the Hydragas units or get rid of interconnection.

I have a secret fetish for the interconnected system, and like to ponder about how it can be developed.

Jerry Reynolds

Mark,

interesting. Excuse my ignorance, but which make year was the GTI Metro ?
Post 1990 ?
If so, and if the mentioned coil fits to a 1990 made Metro front, then it should fit to the MGF front AND rear.
Load force is another question. MGF is a lot heavier then the Metro.

Jerry,
>I have a secret fetish for the interconnected system, and like to ponder about how it can be developed.

:)) I learned to like it too :)

Shouldn't be to difficult to add adjustable restrictor valves in line with them, but notice pressure of 400psi ++ inside the system.
A needle valve from pressed air parts shop should do it.
Dieter K.

I run my 4 units as seperate units. In addition I have modified the upper spheres so that I can pump in the nitrogen to whatever pressure I desire. This gives me adjustable "spring" rates and independence which is what I need as I race the car in our local series. I have also fitted adjustable ride height fixings.

Overall it works well and to date has proved reliable.

David Mottram
d mottram

David - have you any pictures of your mods?

I'd be grateful if you could tell me more about the mods to the upper spheres too.
Jerry Reynolds

Jerry, i think this is what you look for.

http://www.dpr-racing.co.uk/tech_hydrolastic.htm

Notice, the rear displacer at the Metro is different rod design.

And don't get the idea to swap Metro displacers from any Metro over to the MGF !!

The lower spheres and piston cone and also the diameter of the lower sphere cover is different to the MGF.

By coincendece, I'm currently working at a comparison of the standard displacers of both, MGF and post 1990 Metro.
See http://www.lame-delegation.de/mgfcar.de/hydragas/compare.htm

BTW, I'd be greatful pleased for any help on getting hands on a broken Metro REAR displacer.
Recommend getting MGR tool # 18G1743 (connection pipe) for easy individual HG unit connection :)
The pipe on top of this pic http://www.mgfcar.de/hydragas/metro_fr_02636.jpg

And absolute nitrogen pressures in the upper spheres.

Anyone ?


Cheers
Dieter
PS. posted the same call at the Metro subject the other day
Dieter K.

Jerry, I made adapters for each sphere that screwed onto the existing fittings. I used the existing male barb and nut and silver-soldered a high pressure fitting suitable for appropriately rated high pressure hard nylon lines. Each of these ran to another fabricated (lathe) bulkhead fitting which took the nylon line on one side and a schraeder valve on the other side. Thus each lower sphere has its own schraeder valve for the hydogas fluid. The pattern was repeated for the upper sphere but of course I needed to weld the fitting onto the sphere. I welded them on the upper curved surface of the upper sphere in line with the lower fitting. The route for the hard nylon line followed the same path as the lower line and agian it finished at a schraeder valve. The conventional hydrogas pump is used for the lower sphere and I always pump it to 400psi after setting the upper nitrogen pressure. For the nitrogen I have a small bottle of compressed gas and an appropriate fitting between the regulator on the bottle and the schraeder valve. My overall procedure is to set the upper pressure, then the lower pressure and finaly adjust the ride height with my adjuster which fits in place of the hydrogas pushrod or knuckle.

Dieter, AFAIK the upper spheres had an initial pressure of 250 psi with the Racing spheres having a lower pressure (200psi?). I am currently running at 165 psi in the front and 180 psi in the rear. This gives a stiffer front spring rate. Of course they both assume a working pressure of 400 psi once I pressurise the lower sphere. As you would expect I find that different circuits require different pressures and I am still on the learning/testing curve in that regard. Certainly those pressures work for our two fast open circuits but I have yet to optimise them for the small twisty circuits. I will do that this season as we use those circuits.

The machining needed for the adapters is not rocket science. I went to an hydaulics fluid transfer hose shop and sought their assistance WRT the nylon lines and push in fittings. It is all common stuff in that industry. Getting the nylon line with adequate working pressure was not difficult. All the fittings and line for eight hoses cost less than 100 australian dollars ( about 50 euro and 40 pounds stg).

The adapters were made on the lathe from hex brass and cost a couple of bucks. What worried me most was the welding of the fittings onto the upper sphere. What I did was to immerse the sphere in water with just the site of the weld exposed. I used a TIG welder which kept the heat local but enabled a quality leak free weld. Once welded I then drilled through the centre of the fitting to release the existing nitrogen and to blow outwards any swarf from the drilling. The diaphragm in the upper spheres was thus not exposed to heat and remained undamaged. They are working well now some 8 months and 10 race meetings later so I reckon they will be OK.

Hope this is of some help.

Regards......David
d mottram

Dieter, I went to the dpr site and was amazed to see that they run only 50 psi for the nitrogen in their MGF spheres. They also 50% fill the upper chamber with water to prevent overstressing the diaphragm with such a low pressure. I will try the same between the next two race meetings. The car would be very very stiff with only 50 psi.

Regards.....David
d mottram

It'll be interesting to hear how you get on David! :o)

>> I vaguely remember him saying that a better solution to achieve a more sporting repsonse would have been to use smaller diameter interconnecting pipes.
Has anybody gone down this route on the F? <<

Yup - this is what MG did themselves for the MGF Trophy 160! There is a fluid restrictor in the interconnector pipe. I don't know the part number though? Anyone help?
Rob Bell

Mines a K reg Metro Gti. Ive just found in the past that the hydrogas system is more grief than its worth.

If you look at all the guys who race in the MG metro cup you will see fabricated suspension turrets on the rear for coil overs. Metro's are known for bouncy rear ends. If i could get a spring kit for the rear i would put it on.

Theres a hill climb with this set up and its a gti and he has no hydrogas. Lots of welding required and turns it into a race car not suitable for day to day driving.

I did like the hydrogas system when it was running properly but after jacking up my car one day and getting a face full of green hydro fluid i decided i had had enough :O)

mark forrester

Mark - one day I may need to chat to you and discuss metros! I may be 'inhereting' a 16v GTa model in a year or two ;o)
Rob Bell

no problem mate if you ever want help just have a look at the forum on

http://www.performancemetro.com

loads of people with loads of knowledge
mark forrester

From the responses thus far (thanks by the way) I am thinking of getting my F modified in this manner:

Lowering knuckles and the Trophy restrictor thingummy.

Any downsides?

And Rob, just what is that part number?
Jerry Reynolds

Thanks for the mention of the DPR-Racing site.

We did experiment with the hydrolastic set-up as can be seen:

http://www.dpr-racing.co.uk/tech_hydrolastic.htm


We filled the air space with hydrolastic fluid not water!

Although we only pressurised the air chamber to 50 psi without any fluid pressure, when the fluid is pressurised, the fluid & air pressures equalise - hence the reason to add fluid to stop the rubber diaphragm bursting.

We did also put a hydrolastic unit in to a test rig to
look at the stiffness with different initial air pressure, fluid pressures, and chamber volume to get to the 50% fluid/50 psi initial pressure that we felt gave the best spring rate.

Bear in mind this was for the front of a Metro that carries the engine weight - The MGF is a very different set-up.
Derrick Rowe

Cheers Mark :o)

Jerry - looks as though you have to buy the interconnector pipes complete (http://www.mgf.ultimatemg.com/model_specific_suspension.htm) - RPN 000060 and RPN 000070
Rob Bell

Chaps

The MGCC race championship Trophy cars use the pipe restrictor. You will need one per corner and of course access to a Hydragas pump and some spare fluid. Try MG Sport & Racing on 0121 475 6217 or I'm quite sure Brown & Gammons or Techspeed could oblige with a supply and fit service.
Richard Jones 1

This thread was discussed between 07/02/2004 and 10/02/2004

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