Converting an MGF hardtop

[MikeM]

** All credit goes to Ken Read for his work to demonstrate that the MGF hardtop can be made to fit an Elan **

I used to own an Elise as my all weather fun car when the Caterham was off the road (too cold, too wet, too salty, too extreme, too … whatever), and in winter it would have the hardtop put on to make driving it a bit more comfortable.

But my wife always found getting in and out of the Elise too uncomfortable so I thought I’d try an Elan, which then meant I’d want to put a hardtop on it for the colder part of the year. Hence this post to document converting an MGF hardtop to fit the Elan.

First thing is to source a hardtop. I didn’t want to spend hundreds on an old hardtop especially if the conversion didn’t really work, so I waited until a suitable one came up locally at £80 which seemed a reasonable price to pay for an experiment.

So one Heritage (aftermarket) hardtop later and the project begins. The heritage hardtop has a slightly different shape to the roof compared to the standard factory hardtop, more of a 'blood trough' style shape to it. Otherwise either would have worked.

The idea was to use the plans (courtesy of Ken) available on LEC and do a carbon copy. Which is close to what happened, with a few small detail changes along the way.

Step 1 - fitting it onto the Elan

First off, how well does the MGF hardtop fit onto an Elan, what needs changing?

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The rear of the hardtop fits almost perfectly, it's a little close to the boot lid, but there is still enough clearance. The profiles of the MGF and the Elan are almost identical. There are some small detail differences, meaning the hardtop fits slightly closer near the 'corners' at the rear, but it sits on a large rubber seal which takes up the difference.

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The main area that needs modifying is the front, the MGF windscreen rail is almost straight, whereas the Elan has a very pronounced curve to it, so the front of the hardtop needs an infill

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The other part that needs work is around the door windows. The Elan has different sized and shaped windows so the aperture on the hardtop needs both opening in places and closing in others.

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What became apparent is either the hardtop, or the Elan, or probably both, is not quite symmetric form side to side, so unless I'm going to do a lot of modifying, the hardtop will sit slightly higher on one side than the other, only by a few millimetres, but you never see both sides at once, so you'll never see the difference - but you'll know its there

Next step will be modifying the front to fit the Elan windscreen rail.

[dapinky]

Mike,
Have you read Ken Read's write-up on this job? He has all the measurements and angles that need to be adjusted to get a good fit - it is in the Manuals section (link on banner above).

[MikeM]

Step 2 - front infill and front catches

So, the first bit is to make an infill panel to fit the front edge near the windscreen rail. At the same time I wanted to get the catches (front and rear) sorted so that when I started on getting the profile correct I could remove and refit the hardtop in the same place each time.

First trial fit was with a bit of hardboard, to work out what the shape would need to be and to also raise the front of the hardtop slightly to get the correct profile where it would meet the windscreen rail. The windscreen rail has one of Jamie's one-piece seals fitted to it, so this meant I was actually fitting to a rubber seal rather than the hard rail of a standard Elan.

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This gave me an idea of what the infill would need to look like. The original plan was to make an infill from Aluminium sheet (or preferably I'd try and find the front panel from an Elan soft top frame - but this proved 'difficult' to source ), but as an interim I used a piece of ABS floorboard, left over from a bathroom renovation. The ABS board is easy to cut, nice and rigid, and with a bit of heating I could put a bit of curvature into it to get the front profile I wanted.
Knowing that I would be doing a lot of modifying of the hardtop I decided not to worry about hacking it about, so I used wood screws as a temporary measure to fix the ABS boards to the front of the hardtop, plus some urethane adhesive to hold it all in place. At the same time the front corners were removed because they sit far too high with respect to the Elan windscreen profile.

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Before starting any serious reprofiling, the next thing was to sort out the front and rear catches so that every time I removed the hardtop (I didn't want to do too much 'glassing or sanding with it on the car) I could put it back in the same place.
With the ABS front infill in place I sourced a couple of spare front soft top catches and screwed them onto the ABSin the correct positions so that they could use the existing latches on the windscreen rail. To get the angle of the catches correct I needed to cut a bit into the front box section of the hardtop. To put back the strength into the box section I then created a concave profile under the catch to fill the hole I had just cut, but with an indentation into the box section.

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Once the front catches were fitted, next step was to sort out the rear catches.

[MikeM]

Mike,
Have you read Ken Read's write-up on this job? He has all the measurements and angles that need to be adjusted to get a good fit - it is in the Manuals section (link on banner above).

Yes, this write up is based on Ken's design (as I Think I mentioned in the 5th paragraph above ?). I started with his measurements, which were extremely helpful, and then as the fit-up progressed I basically moved away slightly to match the profile I was looking for.

I thought I would go through the steps I used, which differ from Ken's, as an extra example of doing the modifications to an MGF hardtop. All credit goes to Ken for demonstrating that this is possible.

Mike

[MikeM]

Step 3 - rear catches

The rear catches make use of the existing hardware from the MGF. The modifications necessary are to mount the static U-shaped catch onto the B pillar so that the adjustable latches on the hardtop can interface to them. This is where I made some (small) irreversible changes to the plastic covers over the B pillars, which can always be hidden underneath plastic grommets.

I made up a couple of fixings that would mount to the B pillar underneath the plastic cover, with nuts welded to them to mount the MGF catch to from the inside of the cabin. Essentially a piece of flat steel welded to a bit of box section, and a couple of nuts (either M8 or M10 from memory), to create a T-shape, that mounts where the top seatbelt mounting goes.
I did some hand-calcs which suggested that the extra load of the hardtop (~18kg) during a crash would still be within the peak load that the bolts can take. I'm sure others maybe cautious about using this mounting point, but essentially me+hardtop weighs less than an equivalent 100kg driver, so I was happy with using this feature.

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The plastic B pillar cover fits over this and the U-catch (after flattening with a lump hammer) bolts on top of that.

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The later MGF hardtops have an adjustment feature to allow the sides of the hardtop, where they latch, to be set to the desired height above the bodywork - so that there is less rubbing between hardtop and bodywork. These can be used to get the hardtop just where it needs to be on either side.

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So now the front and rear of the hardtop can be fixed in place, repeatably, which allows the front profiling to begin.

[MikeM]

Step 4 - front profile

Now that the hardtop is fixed to the Elan, and I can remove and refit it easily to allow any messy work to happen off the car, the front profile needs to be modified.

This is where the best place to start is with the dimensions that Ken has provided in his write up. Essentially the two sides of the front profile need to be sanded down and the centre needs to be built up. Depending upon how the hardtop has been aligned, and also somewhat down to the individual nature of the hardtops themselves, the values in the write up may need some changes, but they should be extremely close to where you need to be.

I mentioned at the start that the ABS boards were intended to be temporary, but at this point I decided to bite the bullet and leave them in place and rely on fully encapsulating them with glass fibre to make up for the poor adhesion between resin and ABS plastic ( a year and a half later this seems to be justified ). So I used a combination of chopped strand mat and Isopon P40 to add material where it was needed and to strengthen parts where I had to remove some of the original hardtop.

This was the repetitive part where I would be continuously 'glassing, fitting, removing and sanding until I reached something I was happy with.

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Lots more fitting, sanding, removing and filling !

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Eventually I reached a profile that I was reasonably happy with. The hardest part being to get a good transition between the angle of the windscreen and the shape of the top of the hardtop. I ended up taking the front edge down to quite a shallow angle otherwise it would look too much that the hardtop didn't go with the car, almost like it had a 'fringe' at the front
It really is a case of spending time at this stage to get a profile you are happy with. I probably spent several months adding material and then removing material until I was happy. But this was only having an hour or two hear or there to spend on the project. In total I could probably have down it over a long weekend.

Next, onto the door window aperture.

[MikeM]

Step 5 - window aperture

The Elan door windows are a different shape from those on the MGF. So the profile of the hardtop around the glass has to be modified. This also means that the rubber seals need to be modified to seal effectively against the glass.

Unfortunately this is where I seem to have lost a number of photos due to some IT issues. Essentially it is the same approach as with the front profile. Grinding away the GRP of the hardtop where it is too high and filling in the gaps with P40 where the clearance is too large.

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One thing I did make use of was sheets of stainless steel mesh. This provides an easy way of creating a 3D template of the required shape which can then be impregnated by pressing P40 into the mesh. This creates a light weight, but strong profile, especially where large gaps need to be filled. Using this approach I brought the large clearances down to something more manageable to allow me to then create a rubber seal for the windows to press against.

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Ken's plans propose the re-use of the MGF window seals. I'm sure this should be possible, but I couldn't work out a good way of using them to give a good seal. So instead I built up the GRP profile around the windows and made some custom seals using Ebay sourced EPDM round door seals. To account for the shapes required at the corners I them created mouldings using CT1 sealant, which sticks well to EPDM and stays flexible under UV light. This allowed me to create a near (not quite perfect yet) 100% seal around the windows.

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The disadvantage of the CT1 approach is that it is quite stiff, so unless it is applied 'just so' you can end up with a slightly stiff seal that doesn't quite conform to small changes in weather, so what seals perfectly one day might be marginal the next.

Designing better seals is on the cards, mostly be relying on the EPDM and less on filling gaps with CT1.

[MikeM]

Job Done

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Well nearly, still to do is a good paint job, better seals (100% instead of 99%) and getting the rear window heater working.

Living with it is great, it's quiet, almost completely water tight and makes the car feel slightly more refined.

[cyber_drought]

What thickness of ABS plastic did you use for this please?

I like the upgrade on the design to be able to use this alongside the soft top.

Thank you.

Scott