Aprilia RS125 restoration

Two Stroke on a budget – Aprilia RS125 (Part 5)

Two Stroke on a Budget Part 5 – Polish on, polish off.

Aprilia RS125 alloy swingarmWhile cleaning the ally bits I noticed that there were some rather deep and ugly scratches to the left hand side of the swing arm so I thought I would tackle them to show what can be done for time rather than money. You can be quite aggressive with ally but be careful that you don’t go so far as to structurally weaken anything. As I said last time you can treat it like paint by using wet and dry in ever finer grades, as my frame was quite rough I started with 400 grit followed by 800 grit and then went to the trusty old Autosol to finish the job off. In the past with really deep gouges I have started with a file but you can end up making things worse so go with the least aggressive method first. The results were good though – well worth the 45 minutes it took.


Aprilia RS125 alloy swingarm polishedLess nasty. I think my next job will be to get that back wheel off. It offends me.

So I got the back wheel off and then removed the sprocket and brake disc. The disc is sadly beyond use. I thought I may be able to clean it up but by the time the surfaces would be usable the disc would be below the minimum recommended thickness and any eagle eyed MoT man would tick the “fail” box without hesitation. I started cleaning up the rear wheel with a view to painting it but where the coating had come off there was some quite deep corrosion that made me a bit wary, I have heard of alloys becoming porous and I knew the tyre kept deflating – could be the tyre or wheel at fault. I decided the best bet was to go inside, have a cup of coffee and trawl the bay of e to see what my options were. I first looked for a brake disc -WTF!! people are asking more for a used one than a brand new one – get real folks, it’s not a 1930’s Indian. This put me in a very bad mood so after shouting at the PC for a few minutes I gave myself a check up from the neck up and came to the following conclusions:  I need a replacement tyre, I had budgeted £80 for one. I need a brake disc – £45.

Aprilia RS125 manky wheelThe wheel is nasty, It’s taken me an hour to get about 75% if it sort of stripped, it needs a couple of hours work before any paint goes on it and I don’t have enough etch primer to do it. It will need a tenner’s worth of paint on it, one of the bolts was seized so I had to weld a bolt to it to get it out – another tenner for new bolts. The sprocket is fine – just needs a bit of fettling. So I could sort out my own wheel for about £145 or I could buy the one on ebay for £45 with a nearly new Pirelli on it and save myself 3 or 4 hours work. So that’s what I did. It still needs some work but way less than the one I have. Nice to know some sellers on there are realistic when it comes to prices. Just as a brief aside, I found the same sort of thing while looking for an air box – all the buy it now ones were 30-45 quid, but if you look at completed auctions they rarely go for more than about 15 or 20 quid. People really should do their research before listing stuff, they would sell a lot more.

Dirty cow! Nasty disc, one bolt seized then the head rounded, tyre knackered, wheel itself badly corroded. Shit!

This one. On the other hand, still needs a wee bit of work but altogether a much better proposition.

Aprilia RS125 manky wheelNow seems like a good time to talk about electrolysis – this is a great process for removing rust from heavily rusted parts, I was going to use it on the rear brake disc. On rarer bikes it can be hard to find certain parts, particularly those prone to corrosion – if they are rusted on your bike they probably will be on everybody else’s too. I have built a few cars in the past and have had heavily rusted parts to deal with that no amount off brushing on of phosphoric acid or any other method would deal with. You can use electrolysis in such circumstances. It’s very easy – all you need is a simple battery charger or other DC voltage source – 12 volts is fine, higher is better, some soda crystals to make the electrolyte (current carrying liquid) a suitable container and a piece of steel plate to act as the anode.

Mix about 250 grams of the soda crystals in enough water to cover the part, any old bucket will do, warm water makes the crystals dissolve more easily.

Place the steel sheet in the bucket, connect the positive cable from the charger to it.

Connect the negative to the part to be cleaned

Place the part in the bucket making sure that the part can not touch the steel plate as that would short out your charger.

Turn on the power, leave for about 12 hours. After an hour or so you will see bubbles rising and pieces of rust starting to float and building up on the steel sheet, that’s the rust coming off the part being cleaned. I don’t claim to understand the science fully but I have conclusive proof that it works.

Due to the coronavirus I can’t get any soda crystals at the moment – most old fashioned hardware stores and some supermarkets do them, you can of course get them on line. The flowing pictures are taken from when I built a car a few years back, the hubs are off the Sierra donor car.

You can see from the fine head of scum just how much rust has come off this wheel hub

You can see from the fine head of scum just how much rust has come off this wheel hub

You can see from the fine head of scum just how much rust has come off this wheel hub.

Before and after. A much cheaper and often easier alternative to spending months looking for that illusive and / or expensive part. A quick going over with a wire brush finishes the job nicely.

Anyway, look I was supposed to be doing brakes this episode so I should get on with them really. It’s odd on this bike – usually the pistons are sticky and the seals worn but despite the caliper bodies looking hideous these looked and worked absolutely perfectly. The seals perform 2 functions – the first is obvious – they keep the hydraulic oil from leaking out but the second less obvious function is that they make the pads retract.

Often times older bikes have brakes that bind – you put the brake on and they don’t then release fully – that’s bad seals or dirty seal grooves in the caliper that causes that. These looked like they had been recently serviced and were working perfectly. Not much really needed therefore other than new pads, which I happened to have in stock. They are only about 15 quid for the back and 20 for the fronts so it makes sense to replace them any time the calipers have to come off. As mine were in a sorry state it had to be done anyway. All the minor parts like the pad retaining pin and the fixing bolts were removed and cleaned separately. The caliper body was a   simple clean up, etch prime and paint job, here’s the rear one before:

Aprilia RS125 caliperAnd here it is after together with it’s bracket all nicely cleaned and put back together. It’s not been bled yet, I’m thinking of putting a new hose on it.

The story was similar with the front caliper but there was something worth noting. Usually bleed nipples have a tapered tip that seats in the caliper body, a thin hole drilled in the side of the nipple joins the larger hole out of which the fluid comes when bleeding. On the Aprilia it is different in that a small ball bearing forms the seal. The bottom of the nipple is flat and it pushes the ball in to the seat when it is tightened. Be really careful if you take one apart – the balls look like they could be very easily lost, if you did lose it you would not be able to bleed the system. Oh – just one other thing I thought of – if you need to do the seals make sure you buy the kit that has the small o ring  – it’s to seal the fluid passages between the two caliper halves, if you separate the two halves you must replace that o ring.

Anyway, here’s what the front one looked like:

And here’s what it looks like now.

Aprilia RS125 front brake caliperUnusually it bled up very easily indeed, it has all new fluid in it. Rather pleasingly it had a high quality Goodridge braided hose on it so I need do no more at that end of the bike except to clean up the wheel and get a new tyre. Unless of course a cheaper option comes along. Anyway that’s it for this time I will leave you with a photo I took when I was trying to work out how the fairings fix together. Turns out I have a few bits missing but more of that next time.

Article provided by David Powell of Boston Bike Bits.

Boston Bike Bits