Repainting mild steel pipes
Posted: Mon Apr 23, 2012 8:12 pm
Here's a bit of info with the benefit of my experiences of refreshing OEM mild steel headers. My pipes had just started to corrode slightly so I removed them last winter to respray them before it got any worse. We're talking about a few outbreaks of surface rust towards the tops of the headers, plus a fair covering of rust on the collector box. The pipes were cleaned up with a wire brush and emery paper to get back to clean metal, with the still painted parts thoroughly emeried to provide a good keying surface. This did not get the collector box area shiny metal but there was no loose rust and the only stuff that was left was light discolouration in shallow surface pits.
The pipes were sprayed with several coats of B&Q BBQ paint. This has been recommended in magazines by restorers as being both heat resistant and durable. I found that I needed pretty much the whole can to give a good covering as it is very thin, almost like it's way too thinned down. But it did the job eventually with a good finish. Note that it remains soft and will not resist knocking until it has been cured hard in use by heat, so handle with care.
The bike was then started up this spring and has been used on two runs amounting to roughly 200 miles. The paint on the header pipes cured hard with an excellent finish but that on the underneath of the collector box started to flake off and, having been caught in a shower, the rust has already started to come through the paint. I'm not particularly happy about this as the tin suggests that the paint contains a rust killer so it should have killed off the underlying rust and keyed hard to the remains. IMO if you are going to use this paint then you need to get all rust off and apply to clean metal, if necessary by sending the pipes off to be blasted. On clean metal it seems to do a great job, but it will not stick on even superficial rust.
I have now sanded off the BBQ paint on the collector box area and applied two coats of Finnegans No.1 rust killer paint. I've had that in the garage for years, I think it's now sold as Hammerite No.1. It says resistant to 300C so I'm hoping that will be ok for the collector box area. Then resprayed with Hi-Cote VHT matt black paint. Luckily I could get at all this with the sump / dogbones etc masked off without removing the exhaust again. I'll report back if this holds and is the way to go, although No.1 right along the headers where they get way hotter would seem to be a no-no, so if you've got badly corroded headers looks like they're going to want blasting clean anyways.
HTH boys and girls
The pipes were sprayed with several coats of B&Q BBQ paint. This has been recommended in magazines by restorers as being both heat resistant and durable. I found that I needed pretty much the whole can to give a good covering as it is very thin, almost like it's way too thinned down. But it did the job eventually with a good finish. Note that it remains soft and will not resist knocking until it has been cured hard in use by heat, so handle with care.
The bike was then started up this spring and has been used on two runs amounting to roughly 200 miles. The paint on the header pipes cured hard with an excellent finish but that on the underneath of the collector box started to flake off and, having been caught in a shower, the rust has already started to come through the paint. I'm not particularly happy about this as the tin suggests that the paint contains a rust killer so it should have killed off the underlying rust and keyed hard to the remains. IMO if you are going to use this paint then you need to get all rust off and apply to clean metal, if necessary by sending the pipes off to be blasted. On clean metal it seems to do a great job, but it will not stick on even superficial rust.
I have now sanded off the BBQ paint on the collector box area and applied two coats of Finnegans No.1 rust killer paint. I've had that in the garage for years, I think it's now sold as Hammerite No.1. It says resistant to 300C so I'm hoping that will be ok for the collector box area. Then resprayed with Hi-Cote VHT matt black paint. Luckily I could get at all this with the sump / dogbones etc masked off without removing the exhaust again. I'll report back if this holds and is the way to go, although No.1 right along the headers where they get way hotter would seem to be a no-no, so if you've got badly corroded headers looks like they're going to want blasting clean anyways.
HTH boys and girls