Jacking points pads plates - time to sort!

Well Dear Reader- you may recall the dismay with which I first viewed my jacking points. 3 were damaged or absent and only one remained. This was before I had given them much thought and realized that damage here isn't that problematic. This is firstly because there are plenty of other ways to raise the car and  secondly I suspect the use of the original points is probably not wise. This isn't because I doubt the strength of the body, I'm sure that it was and is perfectly strong enough- but to my mind letting the weight of the chassis, motor, gearbox, differential and suspension hang from the body through 40 year-old bobbins is probably not such a great idea. Fine when everything was new, but it may now be an unwise added stress to put on an aged classic! However, the main reason I stopped worrying was because these are not automatic MOT failures- whew!

However, this situation isn't great, and even though I don't intend to use these points for their intended purpose, I don't like damaged GFRP potentially admitting road muck into the box sections of the car and anyway; if they are supposed to be there, then for originality they should still be there- OK a bit OCD I know.

My front jack points are the best preserved. Front left is intact and I don't need to do anything to it. Front right has a missing plate but there is no damage to the body. The outline of the missing plate is preserved in the adhesive.

Front RHS  jacking point

The pop rivets aren't visible though. I cleaned off the old adhesive with a sharp chisel. This restored the under body profile and revealed the remnants of the pop rivets.

Adhesive removed, rivet heads visible

I drilled these out using a 2.5mm drill

Pop rivets drilled out

The plates are fitted using countersunk pop rivets. I don't have any of these. The rivet hole in the plate is 3.5mm in diameter, and the plate itself is 2mm thick. I gently displaced the red body plug so I could see how thick the body is here and I measured  this as 3.5mm.

Bung displaced-thickness of the body material is visible

This means I need a 3.5 diameter rivet to grip over a 5.5mm depth. The nearest rivet size is 3.2mm but the depth requirement places it at the upper extreme for an 8mm rivet or the lower extreme for a 10mm. I ordered both lengths and will see which works best.

Whilst the red plug was out I compared it with a new one and its apparent that it has been trimmed to provide a flush surface against the underbody.

Old bung left- new bung right, obviously the old bung was trimmed to fit flush.

The LHS rear point is similar in condition and this plus the front points should repair perfectly.  I expect them to be as functional as 40 year old jacking points could be expected to be even though I won't use them. 

All the new jack plates were treated with Metal Morphosis rust converter/preventer and then sprayed in zinc primer and black paint.

Chemical treatment of new jack plates.

Zinc primer before black satin top coat

 I fitted two new plates to the front right and rear left jacking point positions. I used Araldite Rapid generously to bed the plates onto the body and secured through them with the countersunk pop rivets- the 10mm length was the best. I hadn't needed to fit new red inserts into the points as they weren't damaged, just filled with road crud. After a clean I could reuse both. However I wasn't happy about them being a simple push fit in the foam so I glued them in with silicone to help weatherproof the joins.

Rear LHS jacking plate fitted

This gives me 3 pretty much original plates.

However, the rear RHS point was more badly damaged. Its clear that at some point someone has used an un-shielded trolley jack directly on the body here and the round cup of the jack has broken up the body material.

RHS rear jack point. The position of the pad is again outlined in old adhesive but the round  scar left by the trolley jack is clear. 

A section of the body has been pushed in and another actually broken off revealing the foam infilling the box section. The damage covers the entire location surface for the jacking plate. Excess adhesive was again removed with the chisel and the damage was cleaned up before attempting a repair.

Adhesive cleaned off

Frankly I'm not sure how to fix this- I had hoped that Miles of Fibreglass Services would do it while he had the car, but his retirement meant his availability (and patience) was somewhat limited. My thoughts are as follows:
The foam itself is not strong- it can be poked about with a fingernail, Strength is derived from its role in preventing the box section from flexing, the strength of the composite being greater than that of either component individually. At Lotus the body sections were made by the VARI vacuum assisted resin injection process. - Basically top and bottom of the moulds were coated with paint and gelcoat and allowed to harden. Random fibre glass matting was layered in and the foam block beams (pre-wrapped in unidirectional fibre matting) placed in position with more matting as needed. The mould was closed and resin/catalyst mix injected with a vacuum assist to help draw it in and around the matting and eliminate air bubbles.

However at the time my Excel was made, Lotus were also using the RRIM technique- certainly for the front bumper at least. This uses two reactive resins which are injected under pressure and simultaneously mixed in the mould. I find it difficult to tell the two materials apart, and although I think its unlikely Lotus re-tooled all the body moulds for RRIM I guess its possible. If the body is RRIM then I believe effective (structural) repair would be difficult if not impossible using GFRP alone. 

The foam used by Lotus was polyurethane, and although its not the same stuff, builders expanding foam is also polyurethane and therefore should be chemically compatible. This foam also expands after spraying and this should allow it to fill any hidden cavities in inside the beam.  I removed the plug and cleaned the cavity out. To prevent foam from also filling the bung hole I refitted a new plug wrapped in clingfilm to protect it from the sticky foam. I'm working on the basis that if ever anyone does wish to refit a plate in this position it will be fitted higher then the original owing to the new fibreglass and so a longer bung should be preferable.

Plug removed and cleaned out

I then  filled the cavity with expanding foam, trying to get it in behind the folded down body section in the hope that it will push that back down to restore the original profile. To prevent the foam from simply bulging out of the cavity I sealed it in using a piece of wood covered in clingfilm and held against the body using a trolley jack.

I will attempt to make a laminated repair with GFRP across this area but I'm not sure that this will restore any strength to the jack point. There are two reasons for this; firstly I suspect that this body section is actually made from RRIM rather than GFRP, and as has been noted when dealing with the bumper, this material cannot be properly repaired using GFRP. Secondly, and as noted above, the entire locating surface for the metal plate has been damaged, and any new plate would need to be fitted to my new GFRP laminations. Jacking here would presumably still be possible provided that the weight is spread widely and evenly. However, a jacking plate would actually prevent that and concentrate the load onto the weaker, new GFRP - which may or may not be well attached to the body material proper. I think for these reasons I will not fit a plate here. This should mean that its always clear that this point should be used with care (if at all). Consequently I will treat this  as a cosmetic repair only, and performed mainly to keep the road spray out of the bodywork.

The next day the foam had cured well

 ...and rubbing it down blended well with the surrounding bodywork.

 I roughened up the area around the infill using a DA sander and a wire brush

The first point is that I had a problem with the instructions!  U-Pol managers if you are reading this please credit your customers with some intelligence. The instructions say mix 10 ml of resin (nice precise value) with a "pea-sized lump of hardener.... PEA SIZED??? What sort of SI unit is that? ... And are we talking about  petits pois or marrowfats???  ...Yes it makes one Hell of a difference because the volume of a sphere alters with the CUBE of its radius so this particular vegetable fixation actually covers an 8-fold range in the amount that might be specified!! So what do you mean??? If you mean X ml or Y grams for God's sake say so!!... Why is it 10ml of hardener and not a cocktail gherkin-sized amount??? ... And while I'm at it why not state the  temperature at which the 30 min hardening time is derived. At least then I would stand a chance of getting something approaching a predictable setting time.
I have a fear of the stuff going off before I'm ready so I suspect I use too little hardener- and given that today is only about 14 deg C its bound to be slower anyway.

This is an inverted repair and so not the most accessible. I opted to lay up the sheets of matting on a clingfilm covered support. I wetted each thoroughly with mixed resin using a combination of brushing, rolling and immersion and assembled the pile  of matting decreasing in size on the support. I wetted the area around the damage with mixed resin and was then able to apply the stack of soaked matting as a unit, bedding it into the resin on the body, persuading it into position with my hand beneath the cling film layer and easing the sides which I had cut as "wings" around the back and side of the sill.

It took two attempts, but I did get a repair that wrapped the end of the sill under the car and covered the jackpoint damage with good adhesion. This should keep the muck out. Gravity interfered again and I do have an unsightly bulge but at least its solid and rock hard... Sorry double entendres not intended. I will probably add a few extra sheets as I have a paranoia about strength in the body.

New fibreglass up to edge of sill

... and folded around the back and side of sill.

Finally in order to avoid this sort if damage again I ordered so "Do not jack" stickers for the sills. I got these from Isaydingdong a seller on Ebay. They weren't listed as a ready-made product but they are very easily made, just find a font, size and layout you like and send them the details.