DIY Manifold and Exhaust polishing - using blending disc

[vertew]

I've had a few attempts at polishing up the stainless steel exhaust and 4:1 manifold on my 7, aiming for something close to a mirror finish.  I tried some of the advice in the forums - a combination of wet / dry papers / fine wire wool, then sisal drill polishers + metal polishes such as autosol to finish.  Nothing seemed to work that well + it was all really hard, slow work. 

I came across this youtube vid (

) a while back which looked like a whole lot less work, using a blending / finishing disc in an angle grinder to very quickly cut the steel surface back to shiny metal.  I gave it a shot over Christmas hols and it certainly was much, much quicker.  See pics below for before / after.  I've also added more info on the process after the pics.

Before ...

After ...

Assuming your pipes are all off the car, the process is in two parts:

• Stage 1: Fine 'brushed metal' appearance - Use a fine 'blending disc' in an angle grinder.  This very quickly creates a surface that looks highly polished, with a very fine 'brushed' appearance.  If you're not looking for something close to a mirror finish you're done.
  There'll be a few small areas you may not be able to polish with the angle grinder, due to (eg) tight bends near cyl head flanges.  Use a polishing wheel in a dremel to get to these.
• Stage 2: Mirror finish - use a polishing disc in an angle grinder (same low speed) and a 'finishing paste' for stainless steel which come in hard blocks as shown in video from 4'35''.  How close you get to a mirror finish depends on how much time you put into this stage.

I was only intending to polish up the front pipes, but ended up doing the entire exhaust + silencer as it was so much easier than I expected, not to say rather satisfying!

A few more points on the parts I used:

Stage 1 polishing

I used these finishing discs which do most of the work - obviously, you can get these from other sources ...

• Product info: Norton Finishing Abrasives
• Buy: Coventry Grinders (go for the softer 2SF version)
• I only needed one disc for my entire exhaust + manifold and is only part worn
• These discs are rated to 12,000 RPM, but product info suggests that they're best used at around 6,000 RPM.  Note that many angle grinders are fixed speed.
• For the few small areas that the angle grinder may not be able to reach, use a polishing wheel in a dremel tool - Abrasive Wheel Buffing Polishing Wheel Set (or similar)

Stage 2 polishing / finishing

• Buy: Polishing disc for angle grinders
• Buy: Polishing compound - Silverline 107874 for Stainless Steel
• I only needed much less than one bar for the entire exhaust

Hope that's useful + Happy 2020 !!

cheers, Andrew.

(Edit 1st Jan: added note about use of dremel for difficult to access areas on the pipe.)

[TANGO7]

Results look fantastic. Did you polish all the pipes in situ or take them off the car to do them. (I was wondering if there is much “splashing” of paste or scattering of debris during the polishing process and if you can get access to all surfaces of pipes whilst they are still in place).

[TANGO7]

Another query - can you recommend a low speed (or variable speed) angle grinder. Mine runs at at 11000rpm and this seems a similar speed to any I can source at Screwfix etc.

[vertew]

Hi Ian,

Thanks, yep, I'm pleased with the results.  It's possible to see very fine brush marks if you look closely - I could have got rid of these too, but was on a bit of tight schedule to get done before Christmas.

Re. your Qs ...

Did you polish all the pipes in situ or take them off the car to do them ...
I took the pipes off the and I suggest this is best.  Don't think it would be possible to get a good result with pipes fitted to the car.  I used the blending disc in the angle grinder to work up and down each pipe in ~6" strokes,  working around the circumference, rotating the pipe in my hand, then moving up the pipe to continue.  On my CSR (Duratec based) pipe removal didn't require anything else to be removed from the car, just a bit of a logic puzzle, threading the pipes out of the engine bay, either through the top, out from under the car, or out of the manifold exit on side panel.

One more point I didn't mention above and I'll need to edit the post to include this.  Even with the pipes off, there a few areas that the angle grinder can't reach, eg, where the manifold / cyl head mounting flanges get in the way.  During 'stage 1', I used a dremel with a small polishing wheel to get to these areas, which worked fine.

Is [there] much “splashing” of paste or scattering of debris during the polishing process ...
There is quite a lot of debris produced, small black particles rather than dust. In fact a job for today is to clean my garage floor.  Probably not a job to be done in the kitchen ...

Can you recommend a low speed (or variable speed) angle grinder ...
I got a new angle grinder too as mine was single speed.  The one I went for was the Makita GA4540C, which seems excellent and has as wide range of variable speeds.  Pricey, but I reasoned it was a good investment to have a polishing / brushing / finishing capability, which does require lower speeds.

tks, Andrew.