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One problem which most of us have faced from time to time is how to repair cracks and broken lugs on plastic parts.� I was faced with this task again recently, on a 400/4 right hand side panel.� There was a crack starting at the cutaway near to the seat lock and finishing near to the middle of the panel.� Another was about halfway down the rear facing edge, finishing again on the outer panel surface.� In addition to this, the front slot, which hangs over the tongue on the frame, was missing altogether.� Common sense should really have told me to bin it and buy another, but what about when these become obsolete items, as many others already have?
I have tried, like many of us, the various lotions and potions with wonderful claims for glueing ABS, but I have yet to find one, which does the job for an extended period of time.� The main problem seems to be that they rely on mechanical bonding, rather than specific bonding which solvent based adhesives employ.� I asked a chemist friend of mine if he could find a solvent for a piece of ABS, which I had given him.� He came up with two - Diethyl Ether and Dimethyl Ketone (acetone).� I chose acetone on the grounds that I already had some, for cleaning glass-fibre resin from lay up brushes.
I cleaned all of the paint from the panel and went down the cracks with an Abrafile (a fine blade with teeth all the way around, great for cutting out shapes).� Next, I chopped some broken parts from an old Gold Wing fairing lower (well, only the best will do!), into very small pieces, and gradually dissolved these in the acetone.� It took quite a few hours of revisiting for occasional stirring before I had a nice syrupy concoction.� I then brushed neat acetone into the cracks to soften the surfaces to be bonded, this being followed by the dissolved ABS, dripping it from the end of a small screwdriver blade and kind of �puddling� it in with the same implement.� If you are patient and repeat this several times, you will be amazed at the final result, but you will need to leave it to dry thoroughly for a week or so, until no further chemical action takes place, otherwise it might react with the painting processes.�
When making the lug piece, you must consider how to get the largest surface area of contact for your repair.� I did mine by making it rather larger than the damaged part.� Any finishing to size can be done when it is all cured and saves messing with small fiddly bits.� As a belt and braces exercise, I filled up at the back of all repairs with the �glue� to strengthen the whole thing and left the extra thickness untouched, wherever it would not cause any problems.�
From here on it becomes a normal filling, rubbing down and painting exercise, with perhaps a little extra caution in paint thickness when wet.� A heavy build up might cause further chemical reaction beneath, depending upon which type of paint you use.� One important point about the rubbing down process, is that you cannot hope to get good shape to a surface by holding the abrasive paper in your hand � you will just follow the original contours and leave grooves where your finger ends have been; the best way is to use a block, which in the old days would have been cork.� I find that dense foam is a good substitute and can be cut to any shape with a craft knife.� Occasionally I resort to applying a film of spray adhesive to the paper and block to hold everything in place.� Finger ends are still the best though, for the little fiddly bits in corners and also for blend radii.
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