I will soon be stripping my K3 down for a complete rebuild and am collecting bits together. I have a 143 VVC engine and PG1 box to replace the metro 8v carb engine but I am considering changing the rear subframe for an MGTF one with coilovers already fitted and all the relevent mods ie decent rear brakes and handbrake along with the mg gearchange cables. Obviously I will need to replace the front subframe as well to give coilovers on the front. Has anyone done this conversion and if so was there any obvious pitfalls. I am also considering making a bespoke fuel tank to fit in the front to give better weight distribution as I would like to have a go at track days. Is this a daft idea?

I seem to think that the rear suspension is vastly different so may come across some problems may be better off using mg rear subframe to get your rear brakes etc and fit coil overs in place of the hydro gas units.Believe that a company call onyx sportscars did make this conversion for the front of there onyx firefox which used metro front subframe and the coil over upgrade was available may be worth speaking to them as would be far easier.I had the same thoughts as you when I had my K3 before getting a Libra.Contact details here
http://www.onyxsportscars.f9.co.uk/id24.htm
Matty

Can't say for sure about the MGTF rear subframe but can say that the MGF rear subframe is basically the same as the metro front one but with added brackets. I replaced the metro subframe in the back of my K3 (after an accident) with the front subframe from an MGF.
The dims of the MGF and Metro subframes were the same and it looks to me as if MG got hold of a metro frame and modified it to suit their needs as when I ground off the extra brackets I found that the original Metro captive nuts and brackets were still in place.
It was only after I had changed everything that I actually looked at the rear subframe and did some measurements to realise that with a couple of brackets removed it too would have fitted the rear of the K3. I plan to fit this after I rebuild the 1800 engine and then fit all the subframe, brakes, gearbox and gear cables etc. This is a project for a few years time as I am still trying to get the K3 back on the road.
One issue you will have is that if you decide to fit the rear end you will probably also fit the 15" or 16" MGF wheels and they will not fit inside the bodywork as I have found out and am in the process of flaring the arches to suit the wheels and tyres (looks better already to my mind).

Near the end of GTM at Sutton Bonnington I believe Dudley built a K3 and used MGF subframes

You could try ringing Him at Talon and asking?

Thanks for all your replies, certainly food for thought. The car was fitted with 14 inch wheels with the wrong offset which provided entertaining driving especially on the motorway - the car choosing which lane to be in. I have fitted 13 inch metro alloys to the front which has solved the problem but Compomotive will make me a matching pair with the right offset for reasonable money. Nearer the time i will go to a mgf breaker and compare the subframes.

Mgtf's are coil over suspension, rather than hydrolastic. Other than that there isn't anything too major I don't think. As you say though, have a measure up.

If it was me and I had the money I would go with the TF suspension if it will fit as the Hydragas spheres are getting harder and harder to find in good condition and in fact you can't get new original rear units anymore only fronts (you can use fronts on the back but there is a bit of fiddling to do it).

The following link maybe of help www.mgf.ultimatemg.com/group2/suspension/

as there is a folder that compares the F to the TF rear suspensions

Thanks lindiloo, its time to get out the tape measure.

Ok so i've done some research and I have done corner weight calcs to find that as it stands it is a 43/57 split front to rear. Having looked at the tf subframe it seems very heavy so I am now considering making my own rear frame on the lines of the Libra suspension with trailing arm bottom link and top arm as tf. I should then be able to use fairly short coilovers from the top arm instead of the long ones of the Libra. This will allow me to retain the existing track width and avoid widening arches etc. I will think about the front later but possibly go down a similar route. MGF hubs seem to offer the easiest attachment points and give me the requisite handbrake mechanism etc.

I am looking forward to relase of the replacement suspension from Suplex, see note below:

Our SUPLEX SUSPENSION conversion to the MGF is pretty well as described by Roger Parker in the MGOC magazine.
My first involvement with the MGF was assisting in the set up of the Trophy cars with Wynn Mitchell. These cars still running Hydrogas of course were restricted to damper tuning work only. At that time I was Technical Director of Eibach and we had a high tech race damper programme. The MGF race series was the first series to use those dampers.
It wasn’t long before I became heavily involved in the development of the coil sprung MGTF with the development engineers from MG-Rover.
Later I was to be thrown down the challenge of developing this conversion. Having been told it was impossible. I set out to prove that wrong. Also by this time I had set up the business centre of SUPLEX GmbH the German specialist suspension companies UK operation as managing director. I was approached by Caterpillar’s MG-ROVER spares division who were desperately seeking Hydrogas units as the supply was completely at an end to develop an alternative. This prompted the completion of the project which I’d had in embryo state for some time.
Where we are now is having two prototype car sets available. One on our own development car and one which will be fitted as a feature article to come out shortly taking the reader through all the steps in performing the conversion.
Essentially this conversion is designed to salvage a car when the Hydrogas fails and no replacement can be found. Whilst the concept and construction lends it’s self to further tuning work, in its base form that is not the intention. It is designed to replicate as nearly as possible the characteristics of a standard MGF.
It was also intended that the completed design would require no modification work at all and that the conversion could be fitted quickly with simple tools. This we have achieved.
In order to achieve realist costs we are having to produce the parts we need in very large quantities, minimum one thousand pieces at a time. Hence we need to gauge interest at this time.
We are now confident there is a demand and are putting our first volume pieces into product during August 2010. We anticipate having the kit available in November 2010.
Our target retail price for the complete conversion is £850.00 + VAT
Which will include two front and two rear conversion canisters plus two front and two rear dampers. We expect to make these available at this price from recognised MG specialists.

More information on Suplex solution

The sphere is replaced by a canister with a variable rate spring inside. It is a direct replacement that bolts in place of the hydragas sphere. So the advantage is that it is easy to fit, and the ride height will be fixed. You can, presumably still use lowering pins with these units also.
The disadvantage is that you must replace all 4 at the same time.

Very interesting. I have seen this solution used by Watsons Rally in their vtec conversions for the mini by using a modified metro subframe and replacing the sphere with a short coil spring and using a damper bolted to the strengthened flitch plate of the mini shell. In our case we would just need the top arm that takes the damper and make a bracket to fit somewhere on the subframe.