The engine: part one

When it comes to the motive power unit of your restoration, there’s only one way to do it – and that’s by doing it properly.

Skimp on parts, reuse components that are worn, cut corners or bodge something and it will end in tears; you can be certain of that. There are no cheap options when it comes to rebuilding an engine, only the ‘right way’ – which is using original parts. That said there are some very good aftermarket components out there, and it’d be remiss not to consider them, however OEM – or Original Equipment Manufacturer – is the preferred route. If you are new to all of this it might be advisable to get an acknowledged expert to carry out the refurbishment to the engine of your first restoration, and for very good reason. Little is more demotivating, more frustrating and more vexatious than having a restored bike that has a duff engine. Just one misplaced circlip, a wrong bolt or bearing in the wrong way can be enough to stop an engine dead; in fact, any of the above and much more besides can mean it might never start!

Fortunately the VJMC has numerous guys who can take rebuild engines almost in their sleep. Seek one of these out and listen to what they have to say as they know more about old Japanese motorcycles than the rest of us put together. If they say ‘such and such is a weak point on this engine’ or ‘you always need to replace that in the gearbox’ then take that advise on board; it will be infinitely cheaper than doing the job twice.

A perfect example are the main bearings of Yamaha two-stroke crankshafts. On any engine that’s sat around for years, unloved and stored in a damp shed the main bearings will almost certainly have picked up a little moisture which can – and often does – lead to corrosion of the ball bearings. With the engine down to its component pieces, it’s tempting to simply replace the outer pair of bearings as it’s a quick and easy fix. Well, it is until the older centre-pair let go! The trouble with centre bearings is that to replace them the crank needs to come apart and this takes more time and parts which, in turn, costs money. You might, just might, get away with it but chances are you won’t. Have the crank broken down, checked and fettled as necessary, then rebuilt as a new unit. When the connecting rod is poking out the bottom of the crank case because you were too mean to replace the big end, you might want to reconsider being parsimonious about new bearings.

Whether you are rebuilding the engine, it’s being done by a friend in the know or it’s being shipped off to an expert, clean it and clean it properly. Yes that may sound patronising but working on a motor that’s thick with grease and corrosion does no one any favours. Neither is it viable to break down a motor when it’s covered in crud. If grit or similar gets into an oil way, a cam carrier or a bearing that’s been passed as being reusable it will cause chaos pretty much instantly. If the engine is still in the frame make sure there are no open plug holes, filler caps etc. then set to with a proper engine degreaser and a stiff brush. Once it’s rinsed off and dry, the engine will be easier to take out of the frame. With it still in one lump any further dirty areas can be cleaned with brake cleaner and a smaller brush. Brake cleaner is almost magic in the way it lifts off grime and dirt to leave a clean surface behind. Work with plenty of ventilation and preferably outside, absorbing the run off with rags.

Now, and only now, are you in a decent position to fully inspect the power unit – and we’ve still not undone a single nut, bolt or screw! With a decent digital camera take shots of the motor from every angle including the underneath – aka, the sump. This will be part of your rebuild reference library and will, without question, be extremely useful. Study the engine, its cases, the cooling fins, various castings and mounting points noting for any signs of damage, corrosion or past butchery. If fins are missing, broken or bent they can be recreated by clever people with specialist welding knowledge. Get such repairs sorted or find replacement parts before committing to the engine’s rebuild. Once you’ve taken stock of what you have it’ll be time to take the engine apart.

So, naturally, our next step will be to go inside the engine.