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Hello all

Became a TF owner in October 2019 of a 44000 mile 52 plate 115 Trophy, with the intension of doing a rolling restoration on it.
So far I have replaced the cooling pipes front to rear and have started replacing the brake pipes, thanks to a brake pipe failing on me.
While doing this I have noticed a lot of surface rust on the front and rear subframes, nothing serious just bad surface rust.

So my question is has anyone carried out a clean up of surface rust on the subframes in place? If so whats the best way to approach it and what are the best materials i.e. primer/paint/underseal ect ect.
Or would it be better to remove the subframes and tackle it that way.

I am considering purchasing a front and rear sub frame for the future anyway, but like to keep this a rolling restoration and have them ready if required.

Cheers Ian
 

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I remember having an original mini with subframes with the same, black, thin, scant paint. The impression then was 'if it rots out we'll put another one in...' I think the attitude prevailed through BL and tho' our subframes are a little 'beefier', they continued to be similarly poorly protected. (In fact I remember Zeibart was THE aftermarket accessory.) If left untreated subframe surface rust is par for the course for us F/TFers, I think.

I've found drill/wire brushing, rust killing fluid then (black) waxoyling has always worked for me. I do a little bit more, or re-do, a bit every time when I'm underneath. Personally I'd rather redo it (if necessary) than cover it over with black paint. - Let's face it our F/TFs all have Special Needs :). Isn't that the fun of it?

Yes, one on the car + the other being done up/powder-coated would be good, too...
 

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I've done almost the same as Arnty: wire brush, rust converter, paint and then a waxoyl-type of coating. Our Fs also sleep indoors and don't see winter anymore.
 

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Can be done in situ. Grind down, wire brush attachment. Oil rig primer paint - glass reinforced top coat.
134511

134512

The paint I use is Coroless from arcrite paints. They do an all in one chassis black that is good but not as good as the two primer and top coat. Easy to put on with no messing about. I have epoxy mastic as well from rust buster. Takes too long to dry. Their fe123 is good but fiddly to put on.
You want a reliable easy to paint good enough to do the job paint. With the primer and top coat there is a long protection period. Something like 10 to 15 years.
 

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mg_tf
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A bit late on this discussion but yes, as has been said, the subframes can be teated in situ. It's a horrible job though. It takes forever as well. I started on my rear subframe and the rust wasn't that bad but I had had an advisory in an MOT about subframe corrosion. I put the car up on blocks/stands and went at the rear subframe with wire brushes, both power and hand. The worst rust on the rear subframe, a dense sort of scale, was on the cross member at the bottom of the frame just behind the fuel tank bulkhead. It was very difficut to see what I was doing so a lot of it involved using a mirror on a stick or touch. I found to get the worst off in that area, tapping the scale with a chisel or something similar was the way to get ahead. Once the worst was off I used a burr tip in a Dremel tool. I couldn't actually see what was happening on the top of that cross member so just did it all by touch and watching the jet of orange rust powder that shot away when the burr was on rust!
The rear subframe area is the worst as there's so much in the way. Once I had the rust removed as far as I could mechanically I used MetalPrep, a sort of phosphoric acid/phosphating derusting treatment on the subframe - several applications. You can't get the pitted rust off (well, you can with muriatic acid but I didn't have any at the time and it's a pain to work with). Then I made sure it was all dry and went over it with POR15, a polyurethane paint that is also terrible to work with. I ran out of time to put the mandatory second coat on within the specified time limits though so then had a problem - so I stippled on two coats of Hammerite-Waxoyl underseal on top.
My experience since with POR15 has not persuaded me to use it again - it initially sticks tenaciously to anything, particularly skin, but after two years in one area where it was exposed it could be peeled off in little strips.
My latest most-favoured underseal type treatment is Dinitrol 4941. It comes in an aerosol can. No brush marks or lengthy brush work and it is a bituminous type of underseal that shouldn't flake or peel. I also injected the sills and the inside of subframe members with Dinitrol ML Cavity Wax while I was at it.
If you don't want to go to the trouble of removing all the rust laboriously, I suspect your best choice would be to remove the worst of it with a wire brush then spray some kind of very thick oil over the subframe members (NOT engine oil - it doesn't cling well enough - and not on anything rubber). 'Project Farm' on Youtube just did a test of some American products for this kind. 'Fluid Film' was one anti-corrosion product that seemed OK. The usual advice otherwise is for some kind of 'Bar and Chain Oil') which again is a US term - I don't know what the equivalent is here. The advantage of this form of protection is that it can't flake or peel. Some of these rubbery sprayed aftermarket coatings can make things worse if not applied correctly as if water gets in behind the coating, it can't get out and the car rusts even faster. The disadvantage is that it needs reapplication every year.
 

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'Fluid Film' does work well, it seems to be similar to Waxoyl.

Bar and chain oil is the oil you add to a chainsaw (special reservoir) that gets fed onto the bar to keep the bar and chain lubricated. It has a tackifier added to it so that it clings. Other than the tackifier, its just pain old oil. It would be a step above engine oil.
 
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