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Painting motorcycle parts
Whether you're just touching up the paintwork on your motorbike or repainting entire parts yourself, spray paints are certainly up to the job. Provided you work carefully and with the necessary preparations, you can get great results that are barely distinguishable from the original paintwork.
Things worth knowing about paint and painting
Ready-to-use spray paints that you can buy in the shops are either acrylic or synthetic resin-based. Modern automotive spray paints are almost exclusively acrylic-based, while hobby spray paints (and of course brushing paints) from DIY stores may also use a synthetic resin-based formula.
Acrylic-based paints (car paints) have the following advantages:
- Quick drying (touch-dry in 10-30 minutes)
- Recoating possible any time (whereas synthetic resin paints: within 2 hrs or after 24 hrs)
- Better corrosion protection
- Greater resistance to cleaners; harder surface finish
Synthetic resin paints
Synthetic resin-based paints, by comparison, have better filling properties and often spread more homogeneously over larger areas. They are less expensive than acrylic paints, and popular for hobby and craft use but they are less suitable for painting motorbike parts.
As well as the single-component paints referred to above, two-component paints are also available in spray cans. They are harder wearing. The ColorMatic clear lacquer, for example, is ideal for overcoating normal single-component automotive sprays to create a high-gloss finish with greater resistance to petrol, UV rays and weathering.
And if you're after a special shade, automotive paint retailers offer a huge range of original colours, which can be mixed and put in a spray can. However, we recommend finishing these paints with a top coat of two-component clear lacquer. For further details on the best method of application, ask your local specialist retailer.
Important: Not all original paintwork is compatible with spray paints; particularly in the case of older US import vehicles, you may run up against problems (wrinkling, etc.). Synthetic resin paints cannot be overcoated with acrylic paint. You MUST use a synthetic resin paint again. And if you're not sure what sort of paint is on your motorbike is, then apply a small test patch that is out of sight. If the paint "wrinkles", cracks or turns matt grey, then the new top coat you are using is not compatible with the existing paintwork, in which case you would need to sand it off completely before repainting. If your substrate is thermoplastic (ABS, but not GRP laminates), you will need to use a special plastic primer.
Painting step by step
The primary function of paintwork is to protect against corrosion. To achieve this, it is essential to first mechanically eradicate all traces of rust.
For this job you can use coarse sandpaper and wire brush attachments for your power drill or angle grinder. Sandpaper is good for removing surface corrosion, and wire brushes for power tools are then able to penetrate deeper into the rust pockets, helping to eradicate them completely. The deeper the rust goes, the harder it is to remove all traces.
If you feel you've done all you can with your wire brushes and you can still see rust, apply a rust converter (follow the instructions for use on the packaging). Your only other alternative is to take the part to a specialist workshop that does sand or glass bead blasting – this method produces near perfect results.
Preparing for painting
Mudguard with dent and rust spot
Dented, uneven surfaces (see Fig.1) can be repaired with a two-component filler.
Reduce the dent with a rubber mallet
Large dents can be gently hammered or pressed out using a rubber mallet (see Fig.2) so that you don't have to apply the filler too thickly. You can repair any rust holes by welding, or bridging them with glass fibre mats or a two-component product containing glass fibres.
Sand in and around the dent and rust spot
Apply filler and sand smooth
Smoothing surfaces using filler
Important: Two-component fillers will only adhere reliably to bare metal (see Fig.3+4)! Sand down a wide area around the actual rust, or strip completely, as the edges of the original paint can sometimes show through the repair paint. It is a good idea to extend the repair as far as a "natural boundary", such as a ridge or trim. Mix the filler on a largish surface following the instructions on the packaging, and take extra care to avoid air pockets during application, as these would result in bumps in the filled area later, or even cause the filler to come away! You need to ensure that the surface is absolutely free of grease and dirt, so you should clean the whole area extremely thoroughly using silicone remover, thinners or brake cleaner!
Once the filler has hardened, sand it down until you have a smooth finish. To do this, wrap a piece of wet sandpaper (approx. 100 - 240 grit) around a sanding block or a piece of wood (if you don't use a sanding block you can easily end up with slight depressions over a larger area) – only small repairs on curved surfaces are best sanded without a block. When sanding down curved surfaces, always follow the shape of the part so that you don't end up with flat areas or depressions. Wet sanding will keep the dust down considerably while you work. After sanding, dry and clean the surface, then run your finger tip over it to see if it feels smooth. If it's not 100%, de-grease again, apply some more filler and then sand down again. Any remaining fine pores and/or minor grooves can be filled using fine or spray putty.
Step by step painting instructions
Now you can finally start painting. Never apply the top coat straight onto the substrate – or straight onto the original paintwork (sole exceptions: you have already used the same spray top coat before or you are painting an engine with thermal paint), as it would easily peel off and also doesn't offer the required corrosion protection on its own. If you are painting over original paintwork, first sand down with a 400 grit wet sandpaper, clean thoroughly with silicone remover and then spray on a "primer" or "filler" (see Fig.5). This promotes adhesion of the top coat and fills any minor sanding marks.
High-quality two-component primer fillers produce outstanding adhesion and particularly robust paintwork. You will have to dig a bit deeper in your pocket but the reward will be a very professional result. If you're looking at a slightly uneven substrate that you don't really want to completely cover with filler, you can also apply a layer of spray putty and sand down – this gives a thicker layer than an ordinary filler. However, you will still achieve the best adhesion and resilience on exposed parts using a two-component filler and two-component primer.
If you intend to paint plastic, it is essential to first apply a thin coat of plastic primer before applying the base and top coats! If you are primarily working on bare steel sheet, a fairly thin coat of zinc spray acts as an excellent rust protection. After allowing it to dry and sanding down, overpaint with a filler (if you apply the top coat directly onto the zinc spray, the finish may turn matt). Zinc sprays are generally very temperature-resistant (approx. 600°C) and are therefore ideal for protecting exhaust systems (in this case you can overpaint directly with a matt high-temperature top coat).
Applying the top coat
Prior to application, allow the spray can to reach room temperature (approx. 20-25°C is ideal), then shake it very thoroughly (approx. 2 minutes). Do not work in a very cold place. Cover the surrounding area with dust sheets, and mask off the parts that you are not painting. Bear in mind that the spray mist drifts quite a long way! So make sure that all shelves and stored items in the work area are properly protected! The room should be as clean and dust-free as possible – it's best to give the floor a wipe with a damp cloth or mop. You will only be able to paint outdoors if there is no wind at all. The part you are painting must not be damp (e.g. due to condensation caused by temperature differences).
First spray a piece of newspaper to check that the can is working properly – and you will also be able to see how strong the spray jet is. Spray larger items crosswise to ensure even, all-over coverage. Hold the can approx. 20-30 cm from the surface. The distance and speed of application will of course depend on the part you are spraying, the can pressure and the room temperature. The slower you move the can, the thicker the coat and the more likely you are to have drips (particularly when working on vertical surfaces). If your paint looks "grainy", you are probably holding the can too far away from the surface, spraying too fast, or the room temperature may be too high, so the paint is drying in the air before it reaches the surface. Your first coat should ideally just be a light "mist" layer to create a key for the next coat. Apply another 2 or 3 thin but covering coats, allowing approx. 5 minutes' drying time between coats. If you want to apply more coats, allow the paintwork to dry for 24 hrs. before continuing.
Sand the primer coat …
Allow the primer to dry properly and then go over it with 600 grit sandpaper (see Fig.6). making sure to remove any dust inclusions and imperfections. Carefully remove any dust from the surface (using a lint-free T-shirt or special tack cloth from a specialist retailer). Do not touch the surface (to avoid leaving traces of grease from your skin)!! – if necessary, wipe with silicone remover, but not with thinners, which would dissolve the base coat).
Apply top coat …
Now apply the top coat (see Fig.7). As previously described, apply a mist layer and then 2-3 covering layers crosswise, avoiding drips (see above). If you do see a drip forming, you may be able to smooth it out by turning the part around quickly.
Mask off section for second colour …
and spray …
If you are working on a two-tone paint job (see Fig.9), allow the first top coat layer to dry at least overnight and mask off ready for the second colour with a special curve masking tape from a specialist paint shop (see Fig.8). This tape is ideal for applying around curves on your bike's bodywork, ensures a clean edge and doesn't leave any adhesive residue on the surface. Do not use normal masking tape, as you will end up with rough edges! Fine-sand the surface and remove any spray mist that lands on the first top coat layer.
Clear lacquer for protection and lustre
Clear lacquer ensures a mirror finish.
Allow metallic paint to dry for approx. 30 mins. (or longer) and then apply a clear lacquer to protect it against environmental influences and achieve a mirror finish. Non-metallic paints also have a more attractive high-gloss finish and better protection if you apply a final clear coat – the best option is a two-component lacquer (Fig.10). Important: You will need to work extra carefully with clear lacquer, as it tends to drip easily, so do not spray the coats too thickly. Once mixed together, two-component lacquer will not keep for much longer than a day – so gather all the painted parts together and try to do as many as you can in this time so as not to waste any of your can. If the paint surface is not 100% smooth and free of spray mist, it requires a final finish after a few days.
Smooth away larger imperfections using 1000 grit wet sandpaper. Fine spray mist and the sanded area are then fine-polished with a special polishing paste. This will produce a beautiful finish that looks as good as the original paintwork. However, single-component paint is always slightly sensitive – so try and avoid scratches and keep well clear of DOT 4 brake fluid. While the paint is theoretically petrol-resistant, petrol spillage does tend to leave the paintwork matt, so it will need to be buffed up again. Finally, protect the paint by applying a layer of hard wax in order to seal it and ensure a lasting shine.
- Heat-resistant Dupli-Color spray paints are highly durable and specially formulated to restore engine parts to their original appearance. However, it is essential to ensure that the surface is absolutely clean, grease-free and slightly roughened. Individual parts, such as a valve cover (rocker box), can be removed and carefully de-greased using silicone remover, thinners or brake cleaner and then lightly sanded down (600 grit). "Rust bloom" must be thoroughly removed prior to application, as otherwise it will very quickly show through again. The many nooks and crannies on cylinders and cylinder blocks make them quite hard to prepare for painting – nevertheless it is still crucial to be very thorough! You can clean up a rusty engine case by blasting with glass beads.
Important: Do not allow blasting material to infiltrate the engine, as this can cause irreparable damage to the bearings, and the resulting friction will slowly but surely wear out the engine. Therefore if you are planning to bead-blast the entire engine, you need to dismantle it first, rebuild the empty case with the gaskets, seal off all openings and, after blasting, make sure that you carefully wash all the individual parts from the inside out on a part washing table! That is the only way to ensure that you do not cause your engine lasting damage! Alternatively, some specialised workshops also now offer blasting with dry ice. As there is no risk of damage to the engine using this method, you can blast the whole engine.
- If you want to freshen up the paintwork on your engine, it's always best to stick with the original colour. The best spray can option is silver-coloured thermal paint, which is particularly durable and is the best paint for camouflaging any rust spots. Do not use primer. Clean, degrease and lightly roughen the bare metal surface and spray direct with the heat-resistant paint. The thinner the layer of thermal paint, the more heat-resistant it is
- And if you feel so inclined, you can also bake individual parts in the oven – this hardens the thermal paint even before the engine is warmed up when you take your motorbike out on the road.
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The Louis Technical Centre
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These tips for DIY mechanics contain general recommendations that may not apply to all vehicles or all individual components. As local conditions may vary considerably, we are unable to guarantee the correctness of information in these tips for DIY mechanics.
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