Author Topic: Restoration 1  (Read 4951 times)

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Offline richson

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Restoration 1
« on: 12 Nov 2006 at 16:52 »
A couple of weeks into the restortion of my  51 competition, I realise that I have let myself in for a bit more than I bargained for. Working through the half dozen layers of paint, it is clear that all this paint was added after the bike had been neglected for some time as all the bare metal is badly corroded on just about everything. Question now is that getting down to that bare metal what finishes do I now choose? For example, the wheel hubs are now after all weekend with abrasives, in a state where they would look good chrome plated or painted. The plating would be very pretty, and hard plating would give a durable surface after refacing the badly scored internals. Painting would be more akin to the original factory finish. I don't want to create a christmas tree edition, but where do you draw the line between modern day finishing and originality?
Thankfully at least, there was plenty of grease where it should be when all the nipples got painted over!

Neil.


Questions regarding identification and photos of Neil's competition model appear here.
Alwyn
« Last Edit: 12 Nov 2006 at 19:42 by alwyn »

Offline Doug

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Re: Restoration 1
« Reply #1 on: 13 Nov 2006 at 00:41 »
Chromium plating is hardly a 'modern day' finish, indeed the few bits of britework on the Comp models were chrome plated. But not the hubs. If anything has improved, it is the durability and choice in paints. Chrome plating itself is not a durable finish, being rather porous to moisture unless underplated by nickle. And too, the preparation before plating needs to be perfect, as plating does not permit covering up of blemishes, unless a layer of copper plate is laid down for the purpose of polishing. Beyond that, the only option is to grind away at the base metal to create a satisfactory surface for plating.

At least with ambient temperature cured paint, you have the option of filling in the pitting, though if severe, some thought should be given to the soundness of the component for continued service. I do not like grinding away of the parent metal; I like to conserve what is there. After removal of the rust, I like to use an epoxy primer, as it can be laid on heavy and cut back to fill in the pits, and once cured does not shrink any further.

All in all, beside spending a lot of time preparing, and expense with the electroplater, chrome plating items that were not originally finished as such is not restoration but 'tarting it up' or individualizing it to suit one's tastes in style. And with the paints availible now, there is no need to compromise performance or durability.

If you go ahead and plate the brake drums, keep in mind one of the properties of chromium electroplate is a very low coefficient of friction...  Also parts under significant stress need to be baked immediately after plating to prevent hydrogen embrittlment.

-Doug

Offline richson

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Re: Restoration 1
« Reply #2 on: 13 Nov 2006 at 15:31 »
Thanks, Doug, I admit I had not even considered the frictional properties. I'm not going to plate the hubs - I think it will look out of place, and as you say, it will be difficult to get a perfect finish.
After you have removed rust, do you use any inhibitor or go straight to primer?

Offline Doug

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Re: Restoration 1
« Reply #3 on: 14 Nov 2006 at 03:09 »
Quote
After you have removed rust, do you use any inhibitor or go straight to primer?

Depends on what I removed the rust with. Small stuff I like to glass bead blast. Then if the surface is rough and needs filling, I like to go with an two-part epoxy primer like Dupont Corlar, as mentioned earlier.  But it is a pain to mix up the solids, once mixed it must be used, and the vapours are carcinogenic. So it is a bit of a chore to use; particularly on small jobs. But it is impervious, so no more moisture or oxygen is going to reach the surface of the metal once it cures. It also hangs on to bare metal exceptionally well, so if you do scratch through you do not get rust bleeding under the primer.

If the metal has never rusted, or has been striped exceptionally clean and I do not think re-rusting is going to be a problem, then I have been using a self etching primer. Automotive, or aerosols for small jobs. I am not sure if the aerosols are as effective, as one brand I tried was not very tenacious during wet sanding.

If the de-rusting is with wire brushes, sandpaper, etc, and traces of rust may remain in pits or crevices, then I like to use a conversion paint, lately POR-15 is the favorite. I use to use the waterbased product Extend from Loctite, but I found it was not holding up well and I was getting rust under it. Both need a topcoat to protect the primer, but POR-15 seems to tolerate the lack of such better than Extend. Besides being a conversion paint, POR-15 is also a moisture cure ureathane. So it tends to desiccate the surface under the paint, and dries pretty darn hard and impervious to future moisture penetration. In fact it tends to cure a little too fast on damp days! Also, once you open the can the moisture in the air will kick off the cure, so buy it in small tins or use it all up. More than likely when you open the tin a few weeks later you will find just a solid puck in the bottom of the can! Usually whenever there is any left over from a job I brush it on a convenient rusty spot under my car, of which there are no lack of. It is then left to fend for itself, and it seems to hold up well.

-Doug