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Painting inside gearbox casings


agmerlin

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Hello All,

 

has as anyone every painted the inside of their gearbox? A friend of mine is restoring a truck and mentioned he had done this with a special paint inside the gearbox and wondered if it was any good on a motorcycle gearbox?

 

any views?

 

all the best

Andy

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Hello All,

 

has as anyone every painted the inside of their gearbox? A friend of mine is restoring a truck and mentioned he had done this with a special paint inside the gearbox and wondered if it was any good on a motorcycle gearbox?

 

any views?

 

all the best

Andy

 

Andy,

Gearbox casings that are usually painted inside are cast iron, as most motorcycle gearbox casings are alloy, I see no reason why it would need painting.

 

regards, Richard

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Andy,

Gearbox casings that are usually painted inside are cast iron, as most motorcycle gearbox casings are alloy, I see no reason why it would need painting.

 

regards, Richard

 

Hi Richard,

 

thanks for for the reply, I sort of thought that might be the case but nice to get that confirmed by someone else.

 

cheers

andy

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  • 2 weeks later...

The inside of my Harley Davidson wla crankcase, cam case and gearbox had traces of red paint, when is rebuilt them I applied glyptol paint which is supposed to prevent any leaks from any porosity in the aluminium castings.

 

i used to work for Toyota and they used to dip their aluminium blocks in a liquid adhesive for the same reasons!!

 

Dave

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On some of our race bikes we have actually polished the inside of the engine cases and covers to make the oil circulate more quickly, and dissipate the heat easily

 

 

Tim

 

I have never seen that done, though it is worth bearing in mind that a rough surface can allow things to flow faster and will have a greater surface area to absorb heat from a hot fluid.

 

As to painting gearbox interiors, I could see that as being very useful for old, porous castings, especially if you didn't want to paint the exterior surface for originality's sake. Does anyone know what Toyota uses to dip the castings in?

 

trevor

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A friend of mine builds a lot of engines for racing Jaguar XKs and E Types and he paints the inside of the crankcases and sump pans for the reasons already stated.

 

I've also been told that painting the casting helps ensure that any residue sand from the casting process is sealed in and can't find its way into the lubricant...

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Some time ago there was some discussion on another thread about the effects of galvanic action on aluminium top and bottom radiator tanks. I was wondering whether a paint might protect the internal surfaces from severe pitting.

 

Kind of like what you do to protect the inside of a fuel tank?

 

trevor

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One of the Pinzgauer experts came back with this response.

 

"As regards your question re painting the inside of the housings, below are the reasons;

Stops weeping/permeating through the castings.

Helps with oil drainage.

Seals any stray material/media after blasting etc."

Some time ago there was some discussion on another thread about the effects of galvanic action on aluminium top and bottom radiator tanks. I was wondering whether a paint might protect the internal surfaces from severe pitting.

 

You have to be very careful with this concept. Logic would say to paint the aluminium as it is the anodic part......... But it would be a great deal more effective if you coat the surfaces of the cathode i.e. the brass or copper bits.

 

Ok basic corrosion we know the anode corrodes..... so my method appears odd. The bit most, even industry forget about is size matters.

 

The bigger the cathode to a smaller anode the faster the corrosion. If you coat the aluminium and there is one tiny pinhole then you have a massive cathode and a ting anode, so corrosion will be extremely fast. If you coat the copper brass and there is a pinhole you have a tiny cathode and a massive anode so corrosion will be almost negligible.

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It would be difficult to coat the cathode in the radiator case. However, suppose you wanted to reuse an original but very heavily pitted aluminium bottom tank. Could you clean it up, fill, and paint, and then place a small slab of zinc inside the the tank connecting it to the copper base plate. Robert

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It would be difficult to coat the cathode in the radiator case. However, suppose you wanted to reuse an original but very heavily pitted aluminium bottom tank. Could you clean it up, fill, and paint, and then place a small slab of zinc inside the the tank connecting it to the copper base plate. Robert

 

Coating is never perfect, but I guess a pinhole is better than the whole thing corroding. If it has a drain plug in it you could attach a bit of zinc to it and take it out every now and again and look for wastage.

 

It has had me intrigued since this topic came up in another thread a while back as aluminium and brass/copper is a really bad combo but who would have thought of the lifespans we are talking about. You can get some very fancy types of coatings they use offshore which they check using holiday testers. But unless you got a mate in a oil and gas paint shop its expensive. I can find out what the coatings were this guy used on his Pinz as he is based in Melbourne?

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