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Post  ian1954 on Tue Oct 23, 2012 5:10 pm

From some of my previous posts you will gather that I enjoy restoring engines from any condition. Aluminium (Aluminum) of all grades, steel, cast iron etc. are not a problem but the two components in cox engines I have difficulty with (and mixed results) are:-

1. The "delrin" venturi mounts on TDs, Medallions and the little TD tanks.

I can tell you what not to do - Don't put them in a dishwasher, use anything that has chlorine in it (bleach) or anything alkaline (oven cleaner).

Flame polishing can work but I cannot recommend this as the difference between a shiny finish and a burning piece of plastic is a few seconds.

I have several delrin pieces that are dull with a matt finish.

2. Nylon tanks as per Space Bug Jr.

I have had mixed results with "Back to Black" - car bumper and vinyl restorer.


Any advise would be appreciated.

The picture I saw of the spotlessly clean and shiny tanks on the bugs that Mark Boesen (I hope I spelt your name correctly) posted in the engine of the month contest (and I voted for) prompted this. Especially on engines that are almost as old as me.

If anything works I will be happy to post before and after pictures.

Thank you in anticipation.


Last edited by ian1954 on Thu Oct 25, 2012 4:18 pm; edited 1 time in total
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Post  Ken Cook on Tue Oct 23, 2012 5:24 pm

I've tried similar tests as yourself. Truth be told the best way is to just replace it. Your more than likely not going to get the optimum finish you desire. I've seen many of the Tee Dee bodies turn chalky on the deep red. They go from the red and start turning pinkish. I'm sure the sun is more responsible for this. The black goes to a chalky black. What did work for me however was a soft buffing wheel and I used white rouge on the wheel. I had a very nice finish on the plastic. The problem is holding it. If left on the engine, don't buff the aluminum at the same time as it will really foul things up and drag black metal residue and burnish it into the plastic. Ken
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Post  ian1954 on Tue Oct 23, 2012 5:57 pm

Thanks for the quick reponse Ken.

I am very familiar with the chalky finish although not certain that it is entirely sunlight. I have quite a few of these parts which I would describe as faded (pinkish) which I think is sunlight but I put one of these in the dishwasher and it came out "chalky".

I did some research in delrin and it was originally used in "plumbing" systems but after a period of time broke down after exposure to hot water and particularly chlorinated water.

Delrin's resistance to fuel - especially glo and diesel fuel is remarkable but that seems to be the drawback in repairing or cleaning it. I have had qite a bit of success repairing the cracks using hot shim material to melt the two surfaces but you have to be very, very quick swiping the hot shim and squeezing the joint together. I have found one glue that works but it is white and can be seen afterwards - a plastic epoxy adhesive. Easy to trim of the outside but very difficult to remove from the threads inside - even using a tap. The glue is stringer than the delrin and the tap has a habit of ruining the delrin threads preferring to cut the delrin rather than the glue.
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Post  jsesere on Thu Oct 25, 2012 2:38 pm

A friend of mine has had some sucess in polishing Cox plastic parts. Here what he send and before and after pictureThe process is as follows:
Start out with a grit of sandpaper that will sand the scratch out. Work gently with very light pressure on the sandpaper against the plastic. Always wet the plastic part or the sand paper first. I work with the wet-sandpapers usually and you can buy types of wet sandpaper that have a plastic film backing, but the paper backing types work better because it is more flexible which makes it a whole lot easier to sand smoothly around radius's, etc.
The goal is to just barely sand out the scratch or scratches, but no more. Now, change sandpaper to a higher grit count. I usually work my way up to the 600s to 800 grit or more. Remember to use water and very light pressure on the plastic part. When the last grit is used in this process, only the weight of the sandpaper itself, should be applied to the plastic.

Now, two other products come into play:
Meguiar's Mirror Glaze, and an old cotton tee-shirt. Apply the Mirror Glaze (shake bottle very well first) to a small area of the Tee-shirt with the Tee-shirt wrapped around your index finger or thumb kind of tightly. Using your index finger or thumb, rub the Mirror Glaze onto the plastic using back and forth linear motion. Small rapid but consistent motion is required along with even pressure applied to the plastic part. This motion will cause the plastic to heat up (I have burnt my index finger many times before trying to get out stubborn scratches). MAKE SURE THAT THE Tee-shirt STAYS WET WITH THE MIRROR GLAZE, or else the tee-shirt will scratch the plastic. You have to get the plastic to heat up. The heat combined with the Mirror Glaze, combines to form a new surface on the plastic.

Now, after this process, get a "real cloth" baby diaper. The are very soft and finely woven. Cut a piece of the diaper away and use it as a small rag. Again use the same technique as described above, and you will literally get a "mirrored finish". It really can be amazing depending on how much work you put into it.

All this said, it's very much practice make perfect on this process.

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Post  ian1954 on Thu Oct 25, 2012 2:58 pm

Jesere,

Thank you for the excellent response and before and after pictures. My order for Meguirs Mirror Glaze went off 2 minutes ago. Immediately after reading your response and seeing the pictures.
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Post  jsesere on Thu Oct 25, 2012 3:14 pm

Have fun with it and keep us posted. If you would edit the title of your post to show it has been updated others who have read the post will see the additional info.
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Post  jsesere on Wed Jan 16, 2013 8:19 pm

Ian How did this work out for you?
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Post  ian1954 on Thu Jan 17, 2013 2:30 pm

jsesere wrote:Ian How did this work out for you?
Joe

I found that the black delrin polished up nicely, just by using the Megulars that you recommended.

[solved]Cox "Plastic" cleaning Forum_26

but the red is troublesome

[solved]Cox "Plastic" cleaning Forum_27

The black staining goes deep and fine sanding starts to remove too much delrin. In places it works fine but for some reason the black oil has penetrated the delrin quite deeply. The powdery finish comes off swiftly with your recommendation and fine paper but the oil stains???????? Still working on that one!

[solved]Cox "Plastic" cleaning Forum_28

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Post  Mark Boesen on Thu Jan 17, 2013 3:21 pm

i haven't tried it, but i wonder if you couldn't use Dawn or like product, antifreeze, sonic cleaner, etc. maybe get it hot, short of boiling to get as clean as possible and the re-dye red?
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Post  ian1954 on Thu Jan 17, 2013 3:44 pm

Mark Boesen wrote:i haven't tried it, but i wonder if you couldn't use Dawn or like product, antifreeze, sonic cleaner, etc. maybe get it hot, short of boiling to get as clean as possible and the re-dye red?

Dawn is a product I am not familiar with - but I have tried ultrasonic, soaking in alcohol, turpentine, "back to black", swarfega and detergents to no avail. Water and detergent to boiling (must use pure water as delrin reacts to chlorine). Chlorine and alkaline cleaners destroy the delrin and so does putting them in the dishwasher.
I keep experimenting with the cracked 051 carb holders I have.

Thanks for the suggestions though.

This is another example - I have got the shine back but the staining is still there. You can also see a black line where the two parts join - sanding would spoil the fit.

[solved]Cox "Plastic" cleaning Gmark_12
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Post  fredvon4 on Thu Jan 17, 2013 4:13 pm

I fully understand the refurb of many unobtainable or expensive Cox Delrin parts but you keep showing the grief with medallion carb bodies...brand new they are way too inexpensive for me to screw with clean n polish labor.

Am I missing something?
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Post  jsesere on Thu Jan 17, 2013 4:30 pm

This might work just as well with other plastic parts. Wings etc.
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Post  ian1954 on Thu Jan 17, 2013 4:31 pm

fredvon4 wrote:I fully understand the refurb of many unobtainable or expensive Cox Delrin parts but you keep showing the grief with medallion carb bodies...brand new they are way too inexpensive for me to screw with clean n polish labor.

Am I missing something?

They are my practise pieces - it doesn't matter if I spoil them.
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Post  Mark Boesen on Fri Jan 18, 2013 4:54 pm

ian1954 wrote:
Mark Boesen wrote:i haven't tried it, but i wonder if you couldn't use Dawn or like product, antifreeze, sonic cleaner, etc. maybe get it hot, short of boiling to get as clean as possible and the re-dye red?

I would never try to sand them, i've had good luck with BRASSO metal polish

Dawn is a product I am not familiar with - but I have tried ultrasonic, soaking in alcohol, turpentine, "back to black", swarfega and detergents to no avail. Water and detergent to boiling (must use pure water as delrin reacts to chlorine). Chlorine and alkaline cleaners destroy the delrin and so does putting them in the dishwasher.
I keep experimenting with the cracked 051 carb holders I have.

Dawn is really strong cleaner, designed for cleaning baked on crud, on pans, etc. its probably a alkaline type product
you could always dye it a darker color?

Thanks for the suggestions though.

This is another example - I have got the shine back but the staining is still there. You can also see a black line where the two parts join - sanding would spoil the fit.

[solved]Cox "Plastic" cleaning Gmark_12
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Post  ian1954 on Fri Jan 18, 2013 5:15 pm

I'll definitely try brasso - never thought of that one. I will have to look at oven cleaners - never used one (an oven) in anger! So I've never had to clean one!
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