I keep seeing a lot of folk on various forums that are attempting to restore or rebuild a motorbike for the first time and see the same easily avoided mistakes made repeatedly so thought it was time to do a bit about some of the pitfalls and how to avoid them.
First thing I always do is check the oil - not only to make sure it is there but to see what colour it is and whether it is contaminated with anything. You would be amazed how often I see bikes with half a gallon of petrol in the sump, running an engine like that will do it no good at all. It will be obvious, the smell is a dead give away as is a higher then normal reading on the dipstick. Usual suspect is ethanol damage to seals in the petrol stop cock and in the carbs - it's not typically a problem with injected engines. The ethanol in modern fuels eats just about anything rubbery and causes all sorts of havoc - I have seen many engines destroyed where fuel has diluted the oil and the owner hasn't realised. Always make that you first check, also check to see if the oil is clean, any doubts change it and don't forget to do the filter at the same time. Always check the drained oil to see if there are any metallic or other particles in there, if it looks sparkly the engine needs a strip and rebuild.
Next drain some fuel off, preferably from the carb bowl, you don't need a lot, put it in a see through container, check for water droplets, another side effect of the devil's piss known as ethanol. It absorbs water from the atmosphere, which sinks to the bottom of the carb bowls, good luck starting an engine on water. On injected bikes you will need to pump some fuel out, if you find any water drain the tank and refill with clean fuel.
Check for spark but don't assume that if the plug sparks outside of the engine that it will spark inside it in the moist atmosphere of compressed mixture. I had a bike a while back looked like it had a great spark but it just would not run, I found out what was going on by using a timing strobe, it would flash with the plug out but not with the plug in. I closed the gap from 20 to 10 thou and it has worked perfectly ever since. Moral of the story is that a good spark is not always as good as it looks.
Carb cleaning should always be undertaken early in the process, repair kits are usually available and are quite cheap these days. Beware of using too much carb cleaner on rubber seals, they absorb it, expand and then you can't get them back where they belong, only remove cv vacuum boots if really necessary, the chances of getting them back in place again is pretty remote. Once again they expand as a result of absorbing fuel, if you must take them out, use a heat gun very carefully to drive the absorbed fuel back out, they will hopefully shrink back to a point where they will fit back in. This has to be done really carefully, is it's hot and sunny just leave them in the sun all day, that should do it as well.
Older bikes nearly always need the points cleaning, if you have no spark it's always the first place to start, 99 per cent of the time they are the only component in the ignition system to cause trouble. Sometimes the charge coils go, if you have a rare one and the charge coil has gone it's often better to go over to a battery system unless you really value originality.
Some manufacturers like to make their tanks out of the same steel Lancia used in the mid 1970's to make their infamous Beta model out of. You were lucky if you bought one of them and it lasted 6 months. There are numerous ways of de-rusting a tank, I prefer electrolysis, followed by chemical treatment and a liner such as POR15 to stop it rotting again, it all depends on how bad your one is and how hard it is to get another one, sometimes it's a lot easier to go the replacement route. There are lots of videos showing how to do electrolysis so I won't go in to detail here, it really does work brilliantly but you have to be patient - it takes hours rather than minutes.
Fork seals - don't bodge them. I have seen all sorts of temporary fixes designed to stop fork seals from leaking, from filling the voids between the seal and the dust cap with silicon to emptying the oil out altogether. There is only one way to fix them - replace them with new decent quality ones. Don't be tempted to buy the cheap Chinese crap ones for a fiver, you will be doing the job again in 3 months time. Check the condition of the forks first, any pitting in the travel area and replacing the seals is a waste of time, they won't seal and frustration is guaranteed. Save your money by not wasting it on ridiculously expensive oil, it's no better than the cheap stuff, use the cash you save to buy better seals, you will thank me in the end. Always use the manufacturer's recommended way of putting the right amount of oil in there, sometimes they state it by cc quantity , sometimes it's by the level it comes up to.
Paints - modern paints are shit. they react with old paints, they tend to be quite watery and nothing seems to be petrol resistant, except for 2 pack paints, which require breathing apparatus to apply. There is nothing worse than spending hours getting a lovely finish only for it to be destroyed because a tiny splash of fuel got on it - it's the ethanol that does the damage. You can get lacquer in aerosols now that are proper 2 pack, they coat about twice as much as a standard lacquer but they are the only truly petrol proof solution I have found. Ideal if you don't want to go the full air compressor / spray gun route. Even supposedly petrol resistant lacquers often aren't. Ask me how I know. When putting new paint over old I always use an isolating primer, I have had really good results with it, you can then go over with a high build primer or whatever followed by the basecoat. I have never had a problem with reactions after using isolator.
Anybody got any other ideas / thoughts to share with others? Please let me know and I will add to this so it becomes a useful resource for anybody wanting to have a go. Cheers.
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