Project Katmandu: GS rebuild

[pete.keys]

one step forward two steps back

Got the rear wheel back from shot blasting the hub. It came up really clean but the finish is quite rough. I thought it would be smoother.

I thought the spoke were stainless, they were to perfect on a tatty bike to be anything else. Shot blasting i thought wouldn't be an issue. They would go a bit dull but then I'd polish them back up when I polished the rim. .. wrong .. they must have been chrome as the chrome has been blasted back to the copper :-(. So now I **have** to get the wheel rebuilt rather than it being just an option :-(

There is still a lip on the steel rim, so will have to get it machined off.

 

[fayeslane]

Shot/bead blasting can be done in different grades just like sandpaper. Glass bead gives the best finish on airheads IMO. Perhaps the blokes who did yours can redo it with a finer grade.

Bummer about the spokes, one of the downsides of not doing stuff yourself is getting others to understand what you are tryig to achieve and the consequences of their actions.

 

[Rob Farmer]

As Fayrelane says shot blasting is far too course for aluminium.

I get the guys at work to use a bead blaster on my aluminium bits, it gives a nice smooth finish.

You need to get that wheel redone with bead, unfortunately it will never be the same again and will get dirty very quickly.

The BMW spokes are chrome as standard, are propely plated with copper as a base coat and will last for years if you look after them and of course are much stronger than stainless spokes.

 

[pete.keys]

As Fayrelane says shot blasting is far too course for aluminium.

You need to get that wheel redone with bead, unfortunately it will never be the same again and will get dirty very quickly.

Shot/bead blasting can be done in different grades just like sandpaper. Glass bead gives the best finish on airheads IMO. Perhaps the blokes who did yours can redo it with a finer grade.

oh dear. So you reckon that even if done again with a finer grit its still spoilt? In that case maybe I'll get it powder coated in silver when I get the frame done. Or do you think i need to get a new hub?

 

[MattW]

Bead will knock some of the bigger corners off but unfortunately you'll still end up with a very 'textured' coarse finish. Perhaps as you say, bead then powder might be the best way to go (but then you might find you want to do the front as well so they 'match')...

 

[Rob Farmer]

oh dear. So you reckon that even if done again with a finer grit its still spoilt? In that case maybe I'll get it powder coated in silver when I get the frame done. Or do you think i need to get a new hub?

Powder coatings an option but try the bead blasting. Hubs are hard to find so I'd make the most of yours. Try the bead, if it looks ok work some clear silicone grease into it, leave it for a while and then work the grease in with a soft cloth, this will make the ally far less likely to pick up dirt. obviously you need to decide if it's going to be powder coating before you work the silicone in.

The hubs get very hot in normal use and dissipate the heat from the discs. I've seen powder coating lifting from rear hubs caused by heat from the drums.

I was messing about with our thermal imaging camera. You can see just how much heats generated through the hubs. This is with gentle braking

It's a bit nerdy I know and you may well have no issues at all but nothing looks worse than blistered and lifted powder coating.

 

[(RIP) Kaister]

The BMW spokes are chrome as standard, are propely plated with copper as a base coat and will last for years if you look after them and of course are much stronger than stainless spokes.

st st is stronger than mild steel, you say ??

define stronger ?

less likely to stretch ? nope

less likely to bend? nope

less likely to crack ? minute possibly depending on grades of SS

 

[MattW]

It's a bit nerdy I know and you may well have no issues at all but nothing looks worse than blistered and lifted powder coating.

Agreed.
My 1100's rear hub being a case in point

 

[Dogbytes]

I'd be very surprised if all powder-coating was the same. Steel isn't simply steel, paint isn't simply paint, I could go on. I think it would be worth approaching a couple of powder-coaters and explaining the application and what material it's going onto. They may be able to recommend a suitable application - or tell you it isn't possible. I have someone I can talk to about this in aircraft undercarriage applications and I'll get back to you although I have a nagging thought in my mind that they just inspect it regularly and re-apply it when necessary.

 

[Rob Farmer]

I'd be very surprised if all powder-coating was the same. Steel isn't simply steel, paint isn't simply paint,

Exactly and thats why I posted there may not be an issue. Most powder coaters simply blast the ally and then coat straight onto it

To do it propely, as they do for aircraft, there should be a at least 5 process including phosphating or chromating. it's this process that provides a proper key for the powder.

 

[Rob Farmer]

st st is stronger than mild steel, you say ??

define stronger ?

less likely to stretch ? nope

less likely to bend? nope

less likely to crack ? minute possibly depending on grades of SS

Depending on the grade I know stainless can have similar properties to steel, personally I have mine done in stainless but I have had problems in the past with stainless spokes. I had a Laverda 3c wheel that snapped them so often the wheel had to be relaced with steel spokes. I suspect that most stainless spokes have a high chrome content to make them look good. How do you select spokes of the right quality in stainless when you have to rely on whats available. Pete is building his bike for a Trip to Africa at least the standard spokes are a known quantity.

 

[Kenny]

And at the end of the day, it is a GS..so now leave the hub as it is and get a trusted wheel builder to respoke in either OE spokes or ( my favourite ) stainless spokes It ain't a Harley D !!

 

[pete.keys]

I was messing about with our thermal imaging camera. You can see just how much heats generated through the hubs. This is with gentle braking

It's a bit nerdy I know and you may well have no issues at all but nothing looks worse than blistered and lifted powder coating.

Wow - totally and uterly nerdy - "just messy about with our thermal imaging camera" ... I love it

At least I'm learning from my FU's

 

[AliBaba]

And at the end of the day, it is a GS..so now leave the hub as it is and get a trusted wheel builder to respoke in either OE spokes or ( my favourite ) stainless spokes

Yes, isn't the intension to make a travelers bike? Who cares if the hub has wrong texture.

 

[Padmei]

Yes, isn't the intension to make a travelers bike? Who cares if the hub has wrong texture.

Thank God - I don't have to feel guilty about not cleaning mine now

 

[MikeP]

Great thread.

Got the rear wheel back from shot blasting the hub. It came up really clean but the finish is quite rough. I thought it would be smoother.

Paint the hub. That surface looks perfect for a good key. Any enamel paint will cope with the heat generated in use.

Painted will be easier to clean and unlike powder-coat can be touched-in very simply.

It also has the advantage of not letting corrosion work its wicked way under the coating only to finally burst-out like something from a Sci-Fi horror film.

 

[Beemerboff]

I read somewhere that one of the aluminum based anti corrosion paints worked into the pores with a rag works well - never tried it myself but the pics looked good.

 

[pete.keys]

I read somewhere that one of the aluminum based anti corrosion paints worked into the pores with a rag works well - never tried it myself but the pics looked good.

Lots of good advice from everyone on the rear hub i've "ruined". I'll get the machining done and then decide what to do. We might wreck it machining it - then I'll have to get another one anyway

 

[Rob Farmer]

You haven't ruined it Pete. At least you knocked the shit off it

 

[Dogbytes]

It'll be fine. At least it got blasted - none of mine has made it that far yet!