Powder coating produces a surface which is very durable and tough. Surfaces which have been powder coated also tend to look good for years. Powder coated surfaces are easily cleaned, making it especially popular for that reason.
However, there is a growing list of indications that powder coating is not the cure-all that it might appear to be.
What I am going to say here is cautionary. I do not yet have enough data that would allow me to say definitively that a person never should use powder coating on his vintage vehicle.
I have watched powder coating become increasingly popular over the years—especially with the vintage vehicle crowd. Chassis, engine tins, rims and seat frames and more. What’s not to like about a coating which protects and which looks so good!
My first indication of a problem came when a company powder coated a friend’s VW engine tins, including the crank and generator pulleys. The coating company failed to mask the shaft orifices, resulting in reduced shaft hole diameters in both pulleys. The coating had to be reamed from orifices so that the pulleys could be installed. This was not an easy task! And, it is difficult to remove the coating without doing some damage to the steel during the process.
Shortly, we noticed that fan belts were being chewed up at a rapid rate. After examination, this deterioration was found to be due to the powder coating in the Vs of both pulleys. Powder coating is not a paint—it often is described as “plastic”. Powder coatings are based on polymer resin systems. Under certain conditions, such as the chafing of the V belt in our illustration, enough friction can result to destroy the belt. In short order, my friend was replacing V belts, having to keep a keen eye to avoid getting caught with a destroyed belt. I rescued him on one occasion when he was caught out on the road at night in his Beetle.
The next time I heard about a powder coating problem was from the owner of a ’67 Beetle. Walter complained of stripped threads in the brake drums. At first he blamed the “cheap” Brazilian brake drums. But, the VW Community has been using Brazilian drums for many, many years without significant problems. Walter’s mechanic even blamed VW rims as being defective, which is unfounded, of course.
Then, it was revealed that Walter had had his rims powder coated.
An Internet search revealed a similar problem with powder-coated steel wheels on a particular model of farm machinery. The report talked about the need for metal-to-metal contact. The torquing of the securing bolts on powder coated surfaces, according to the report, “… is like using a plastic washer under the nut. Plastics creep under load and the nut will loosen”.
Walter and I discussed how he could rectify the problem with his rims. He used a Dremel tool fitted with a grinder to remove the powder coating. This allowed the lug bolt shoulders to torque against raw metal. Later, Walter wrote this: “Since we last spoke I did a more thorough job of removing the powder coating from the bolt holes using a power drill and conical grinder. This was a definite improvement over the Dremel I used first. I then took several trips of 40+ miles, each time following up with a check of the bolts with a torque wrench. So far there has been no loosening of the bolts.”
Not long following Walter’s incident, I received notice from a second person who had a wheel come completely off his 1962 Convertible Beetle. When I asked if the rims had been powder coated, the immediate and emphatic reply was “Yes”. The owner discovered that lug bolts on the other wheels also had loosened. In a follow-up message, the owner revealed that he had removed all wheels and had removed the powder coating where each lug bolt seats.
With these cases under my belt, I decided to interview a powder coating expert. The owner of the company took time to explain the process. He showed me special tape which is used to cover areas where powder coating should not be applied. He also explained that bolt holes, for example, should be plugged so that threads would not be compromised with the coating. He showed me special plugs for the purpose. He indicated that a knowledgeable powder coating company will take necessary precautions to protect areas of concern.
The same day, I spoke with a professional who owns a Volkswagen Formula V fabrication and machine shop. He told me of further concerns about the use of powder coating on vintage vehicles. Since each part which has been coated must pass through an oven during the process, certain parts, such as bearings, bushings, rubber parts, etc., must be removed in order that they not be damaged. Temperatures can reach 400 degreesF and higher, depending upon the application.
This professional told me that VW front axle beams are especially vulnerable to the heating process. He said that the bushings can loosen, resulting in the need to machine special bushings with set screws to hold them in place.
He then told me that should there be a necessary repair to a powder coated chassis, it is very difficult to remove the coating so that welding can be accomplished.