Repairing CT90 Plastic Covers and Air Filter Assemblies

Most of the time when you pick up an old CT90 the plastic covers or air cleaner housings are either missing or in need of repair. If you have the money new plastic's are readily available, but if you're cheap like me and not to picky you can possibly repair these parts to a serviceable condition.

I'll describe the process I followed and hopefully it will enable you to salvage some of your old plastic parts.

With this approach I use I need a seperate plastic cover or air filter assembly that has an undamaged section that is the same as the section I am trying to repair on the damaged plastic.  This usually isn't a problem for me as I have several CT90's, but you may have to borrow a good part from a buddy.

For this example I was trying to repair part of the air cleaner on one of my 1971 CT90's and the picture below shows the part to be repaired on the left and a good part on the right.

The next step is to make a casting of the external surface on the good part that you are trying to repair on the damaged part using Durham's water putty which you can pick up at Lowe's for just a few bucks.  This is actually really neat stuff and when it drys it is very hard and feels like a ceramic material.

I will apply some car wax to the surface of the good part and then mix up some of the Durham's to a thick paste consistency and then apply it to the good part and let it dry.

Once it is dry I will gently pry it off and you now have a nice casting of that external surface.

You next apply car wax to the surface of the dry casting you just made that will rest on the exterior of your damaged part. and then tape the casting to the damaged part.

So if you look on the inside of your part to be repaired you now have a surface where plastic was missing.

You would next rough up the interior surfaces of your damaged part and apply fiberglass and resin to the area to be repaired.

Once the fiberglass is cured, remove you casting from the outside of the part you are repairing.

You may have a few pockets or divers to fill in with some resin and then once thats done and dry, sand the part and paint as desired.

Here is a picture of a down tube cover where I have a casting that I will be using to repair this cover on the corner by the carb that always seems to be busted away on old CT90's

This isn't the quickest repair process, but if you like to work on your bike this will end up providing you very serviceable parts.

An Alternative Repair Method
I plan on trying out the method described at this link which uses MEK (Methyl Ethel Ketone) and Styrene which may be better then using an epoxy/fibre glass approach.  I'll do another post after I try that method if it works out well.

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