Fitting an external canister oil filter

Like many projects, this one started with just one small part of the complete machine. The small part on mine was the battery/tool box lid. It was a bit 'battered' to say the least!

It had always been like that and was the sort of thing perhaps not many noticed (or at least didn't say they'd noticed). But I knew it was there and to me, it stood out like a Henry VIII codpiece. Something finally had to be done to remedy it, but what?

It's fair to say my Tiger Cub isn't a standard 'as it left the factory' Cub. According to the log book and the matching frame and engine numbers, it's a T20 originally registered on the 6th of April 1966 in London. But at sometime in its life, heavyweight Cub forks, Sports Cub wheels, alloy mudguards and a host of other cycle and engine parts have been added.


I have no idea when, but it suits me just fine, it's part of its history and I wouldn't have it any other way.

Having seen new battery/tool box lids for sale and available, I had toyed with the idea of buying one, spraying it up and fitting it. But after removing the compete box, I found the whole thing would need far more fettling than just a new coat of paint to 'bring it up' a bit.

Years of leaky batteries had obviously taken their toll, and what would once have been metal was now fresh air!

I had also been toying with the idea of putting an exterior oil filter assembly on the bike, as like many older Triumph machines, the standard Tiger Cub oil filter design can definitely be improved on. Not only that, an exterior canister oil filter would add some welcome extra oil capacity to the system. Around 350cc extra. But where to put it - easier on one of the bigger Triumph machines, but on a much smaller Tiger Cub?

The space once occupied by the now missing battery/tool box gave me the inspiration. Would the oil filter assembly fit there? Time for some serious measuring. But if there was to be no battery box to hold a battery, where would a battery go?

In fact it was to go altogether along with a change from a positive earth 6v to a negative earth 12v system, the fitting of a new regulator rectifier and Lucas type-2MC capacitor and spring holder - more on that later.

Measuring over, drawing complete, it was time to fabricate a mounting for the oil filter inlet/outlet assembly to bolt to. One that would also bolt to the same flat metal crosspiece between the top frame tubes under the seat the ignition coil is bolted to.

A couple of things quickly became clear though.

One: the inlet/outlet tubes of the oil filter holder were too large a diameter and stuck out too far.

Two: an indentation would have to be pressed into the lower section of the rear mudguard to enable the oil filter to be screwed on and off once the complete assembly was in place.

Number Two was easy, but number One required a little more work. First off was to measure the outside diameter of the tubes and luckily, if they were sawn off and the remainder carefully drilled out of the housing, it would be possible to tap them to take 1/8 BSP fittings with 90 degree swivel hosetails for the 1/4 inch oil hose necessary to connect to the Tiger Cub oil return and then to the tank.

Once the complete assembly had been built up and the ignition coil, etc. removed from its mounting place on the steel crosspiece under the seat, it was bolted in place using bolts that protruded enough to enable the ignition coil to be remounted on top.

Time to fit new extended oil lines, taking one from the steel return pipe from the engine to the new oil filter assembly and a return from there to the oil tank.

Now as the rockers shafts are fed with oil from the oil return line from the engine, the final thing to do was to fill the new filter with oil before screwing it in place to the holder.

Thereby negating any delay in getting oil to the rockers, as would happen if an empty filter body would have to be filled with returning oil from the engine before being able to be delivered to the rockers.

Earlier on in this article I mentioned altering the electrics to run negative earth 12 volt and battery-less, and this was achieved by joining the green/black and green/yellow wires together from the alternator and connecting them along with the separate white/green wire to an Electrex RR2 single phase 12v regulator rectifier that I mounted on the rear mudguard.


This was then linked to a Lucas type-2MC capacitor replacing the battery. A change to 12v bulbs completed the conversion.

Finally I fitted a slim trials-type alloy air filter on the left side of my Cub, which ideally hid the new oil filter assembly behind it.

Job done!