Exhaust refurb

[Chris152]

We removed the exhaust from my lad's Aprilia rs125 and want to sort it out a bit before it goes back on. Cosmetics aren't the issue, but I'm wondering how far back we take the rust before we spray with high-temperature paint. So far it's just had a quick going over with a hand-held wire brush, and I'm thinking one on a drill next. Is there anything else we should do before painting? Sand blasting etc would probably do more harm than good, and there's probably little point in using solutions or electrolysis as it'll just get rusty again anyway. It's pitted, pic shows the worst of it. At some point he'll try to make a replacement.

Thanks for any thoughts, Chris



ps The silencer is apart, ready for re-packing.

 

[Noel]

Hard to know, can you feel/tell how much metal there is left under the rust? Good rust converter (once you are finished with the wire brush) might be an option although no idea on how it will behave once hot.

 

[Chris152]

Hard to know, can you feel/tell how much metal there is left under the rust? Good rust converter (once you are finished with the wire brush) might be an option although no idea on how it will behave once hot.

In my mind, heat is the issue - as far as I'm aware, heat-resistant paint is the only thing that'll cope. It seems like there's enough metal left for the foreseeable, and of course repairs are possible tho maybe not desirable?

 

[Spectric]

That is verging on being a tetley tea bag, I would get it lightly sandblasted and then see what you have got. Yes there will be some holes but then with it clean you can do some repairs. The other issue is how much crud inside, here we used to block one end and fill with caustic soda and leave overnight and rinse out but again I think you might spring some leaks. Have you taken all the required dimensions so you could make a new one ?

You can of course just buy a new one

https://www.jl-exhausts.com/jollymoto-aprilia-exhausts-911-c.asp

 

[Hypnotic Chimera]

A mate of mine used to design, build and dyno test replacements for these for racing and tuned them to optimise bhp. He started by welding but I think he graduated to hydro forming.

I'll ask if he still does this or still has the gear, because I think he supplied a couple and was very inexpensive.

 

[BillK]

A strip & clean disc aka poly strip disc on an angle grinder or drill would take most off and quickly, brass wheel brush for the bits around the seams and suchlike that the fat discs can't get at. Strip discs are meant for the job without taking off lots of metal, but still go with a lighter touch. A drill is a softer touch if more awkward to hold. They don't last too long especially if you have to use the edge of them vs the flat, so a lighter touch helps there too.
They're fast and leave a nice clean surface for paint.

Rattle can heat paint for speed, or wood burner paint brushed on, flows out well with a nice flat brush - I used a flat artist type brush on our burner.

 

[Chris152]

Thanks all, I'll have a go at further cleaning up today and see where we get to (Tho ideally I'd be doing it outside but it's tipping down, still dark and for some reason, much warmer than in the house.)

 

[Chris152]

ps I just had a quick go with a small poly disc on a drill (wire brush on a drill just seemed to polish the rust!) on the worst bit, it does look better than it did, and tapping it makes a sound and feel that suggests solidity - not sure what that's based on tho!

 

[Fergie 307]

Grit or bead blasting is really the only way to get right into the pits if you don't want to use chemicals.
Or maybe from where you are now use a strong citric acid solution and just brush it on? Never tried it but might work.
Bead/grit definitely the best as leaves no chemical residue to wash off, just a quick rinse with thinners to remove any remaining dust.
If he intends to keep it then we'll worth the extra money to get a stainless replacement when the time comes.

 

[Chris152]

Grit or bead blasting is really the only way to get right into the pits if you don't want to use chemicals.
Or maybe from where you are now use a strong citric acid solution and just brush it on? Never tried it but might work.
Bead/grit definitely the best as leaves no chemical residue to wash off, just a quick rinse with thinners to remove any remaining dust.
If he intends to keep it then we'll worth the extra money to get a stainless replacement when the time comes.

Sadly our air compressor isn't up to working a sand blaster - 11cfm (about 6 cfm output, according to Hyundai). We could definitely use one...

 

[okeydokey]

You mention that cosmetics aren't an issue - in which case as you have pretty well cleaned all the junk and surface rust off so now hot surface primer and hot surface black/top coat should do.
The more you metal you rub off the quicker the exhaust will fail

 

[Chris152]

You mention that cosmetics aren't an issue - in which case as you have pretty well cleaned all the junk and surface rust off so now hot surface primer and hot surface black/top coat should do.
The more you metal you rub off the quicker the exhaust will fail

I think that's the route we'll most likely go down, I'm pretty sure there's at least another season in it.

We used a high-temp black exhaust paint from Halfords on another exhaust that's used regularly and it seems to have held up fine, tho that one wasn't rusty. Will a primer make any difference compared to a straight-to-metal paint? Something like this?
https://www.carbuilder.com/products...mSXAa8l7mcVbPHT5P5DON_uQT7TLqjcp0ayeDllXhOxXp

 

[Amplidyne]

Well the more you clean it, the thinner the metal will get. It ain't going to get no "less rust pitted" So I'd clean it up the best you can with whatever you have that works, and then I'd paint it with a good thick coat of paint brushed on. Preferably primed first with a suitable primer.

 

[okeydokey]

The link went to primer so yes to that then whatever hot paint colour afterwards
A primer does just that it prepares a surface maybe fills in a few dings for a final coat

 

[Homeless Squirrel]

Primer needs to be heat stabilised also though or will cook and peel

One of the best thing for rust removals are Zipp wheels they do a few types and work on angle grinders and they also do a flat one that fits in a drill it's a sort of plastic impregnated with wire and for dealing with seams