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Repaint rocker (valve) cover and exhaust manifold

Posted: Mon 06 Nov, 2017 8:13 pm
by dhaigh
After repainting my rocker cover and exhaust manifold on my W124 1988 300CE, I wanted to share my experiences – good and bad – in case you are thinking of the same thing. This is a job that anyone can do, no specialist knowledge or tools required, and the results are very satisfactory.
The old rocker cover in factory black was showing signs of age, with a bad case of flakey paint and bubbling, and the magnesium alloy of the rocker cover showing through. The reason apparently is that the magnesium alloy is porous and oil gets underneath the paint; a common curse of the M102, M103 and M104 engines. The exhaust manifold was burnt, pitted, and discoloured. So, they definitely will look better with a fresh coat of engine enamel. I used Dupli-Color High Heat aerosol spray in 340g cans, cost $15.95 from Repco or Bursons, and good for up to 2000F degrees.
A couple of things to note before we get started. The correct way to paint the rocker cover is to take it off the car, give it a thorough clean and a proper respray. I didn’t do that because of the time and effort involved.
I decided I would do the job with the rocker cover on the car, and I think the results are pretty good, although there are some things that are not perfect which I will share with you later. In my opinion, you don’t need to take the exhaust manifold off the car since the cast iron lends itself quite well to being painted on the car and no one will know the underside has not been painted (unless they want to look from underneath the car!) I think the overall results are quite pleasing as the pictures show.
Step 1 was to get as much of the old flakey paint off the rocker cover as possible. I used a small scraper for this to ensure there was no loose material left behind (paint thinner and steel wool could also be effective). Most of the old paint was very easy to get off after years of abuse from oil and other contaminants. However, in retrospect, I would ensure that ALL the old pint was removed off the top section as the new paint will NOT hide the fact you have been lazy. The overall affect is a sort of rough texture but you will not get the glass-like finish from new. You don’t need to remove the plug leads, or the plastic cover over the leads (who really looks under there apart from your mechanic).
I then used sandpaper (240 grit), to smooth it all off and key the surface, followed by cleaning the whole area religiously with methylated spirits to remove all traces of contaminants and dust, followed by a wipe down with a damp rag and allowed to dry. During the scraping and sanding, it’s important to use a vacuum cleaner at the SAME time, to suck up all the loose flakey paint, as you don’t want that falling down into impossible to reach places in your engine bay.
Step 2 was to cover all areas with rags and to use masking tape on the plastic plug lead cover. Although I had decided to brush the engine enamel onto the cover, rather than spray paint, I wanted to avoid any chance of splatter or ‘paint-flick’!
I then commenced to use a small flat paint brush, about 10mm in width. This is quite adequate if you use long smooth strokes, and the paint goes on quite easily without streaking. To achieve this, I sprayed a quantity of paint into a china cup to give me about 5-10ml of paint to use, and topped up the cup as I needed more paint. The paint remains wet and usable for about 15 mins in the coolness of a garage (about 18-21C).
I followed instructions for the paint and used 4-5 coats of Black Dupli-Color, with about 1 hour between coats for drying. The final result is quite pleasing, but using a paint brush will not give a glass-like finish no matter what.
The result of using High Heat Black was a matt finish, so to get a shiny appearance, the final step was to paint the rocker cover with a couple of coats of High Heat Clear. This gave a suitably shiny appearance, although not a glassy effect, but I think it’s adequate (see photos).
The finishing touch was to hand paint (very carefully with the finest brush) the 3-pointed Star on the top of the rocker cover, at the back, with High Heat Aluminium. It’s also possible to paint the 3 parallel ridges along the top of the cover with Aluminium, but I thought that would be too difficult to get a perfect result by hand.
After 2 years, the paint is still looking good. It hasn’t started to flake off (touch wood), but if it does I will just touch up using the paint I have left over. I have heard of a member that did a professional job (rocker cover off; proper respray) and still experienced For King and country after about 12 months. And a professional job (also expensive) is no guarantee of success!
300CE rocker cover.jpg
I then turned to the exhaust manifold.
To be honest, I was not too religious about prepping these. Since they are rough cast iron, they are not going to look like glass and, in my opinion, a rough appearance can enhance the overall effect. I wiped the exhaust manifold with methylated spirits beforehand to ensure they were clean, but did not sand them smooth or try and remove all the roughness. Again, I decided to hand brush the paint onto the exhaust manifold since, with a steady hand, this was the easiest way to get a clean finish where it joins the block and to reach the hard to get areas at the back of the engine.
Step 1 was therefore easy – spray a small quantity into my china cup and apply 2-3 coats of Dupli-Color High Heat Aluminium by hand, leaving about 1 hour between coats for drying. The small flat paint brush (as above) left a few streaks on the larger curves of the exhaust manifold, so the final step was to use a slightly wider brush for a final coat, using smooth strokes – no streaks! It wasn’t necessary to use Clear on the exhaust manifold as the Aluminium was quite glossy.
Don’t forget to use old towels or rags to cover all surrounding areas to avoid any brush ‘splatter’.
Finally, I cleaned the copper nuts securing the exhaust manifold to the block with a small chisel and scraper and then highlighted them with some suitable woodstain to give a rich dark texture. These highlighted items give it a very professional look.
IMG_5295 (2).JPG
Any downside to the above procedure? I can only think of two issues. Firstly, the rocker cover isn’t a glassy finish like new, but more of a shiny appearance – see the photos – but this doesn’t concern me unduly. Secondly, the paint did not immediately cure on the rocker cover, and as a result was a little tacky when hot (after a run). This is probably because the High Heat paint requires very high temperatures to cure – up to 200C – and the engine bay just doesn’t get that hot. When the engine is cold, the ‘tackyness’ disappears. Slowly, the ‘tackyness’ has diminished. It just means you can’t wipe it down with a cloth until the engine is cold. When it is cold, the cover responds well to a clean with a lint-free cloth and some methylated spirits to remove any oil or dirt, and bring up the shine again.
In summary, the approach I used would not suit purists, or those intent on a professional restoration. Some may say, it’s cheating to touch up the visible areas with new paint without removing the engine and doing a complete and professional job; however, for someone looking for an overall pleasant affect, I can say that I am very satisfied with the overall result. If you want to tidy up your W124 and make it a pleasure to ‘pop that lid’ and show off the engine bay, then the above could suit your needs.
Materials you will need:
Scraper and sandpaper (240 grit). Vacuum cleaner.
Methylated spirits to remove oil and grease.
1 x can of Dupli-Color High Heat 340g in Black, Aluminium and Clear
Selection of small painter’s brushes from your local Art shop.
Masking tape.
Lots of rags (for cover-up and to remove any paint ‘splatter’).
Paint thinners for brush clean-up (careful to keep away from car duco).