Triumph Bonneville

Roger Smeeton's high-performance, 1966 T120 Bonnie


My 1966 T120 came to me in the 1980s as a basket case having been in a bike shop cellar for some years. It was in a tea chest, a baby's basket and a baby's plastic bath.

It's a bit of a mongrel, and doesn't have matching engine & frame numbers. In 1966, the engine was supplied to one shop, and the frame was supplied to another. It was, however, all genuine 1966 T120 Bonneville.

I started by having the frame shot-blasted, then checked over and stove enamelled. I rebuilt the forks with stainless steel stanchions, and I sorted out the shuttle valve operation. Both wheel rims are 18-inch alloy. The front rim is an original Dunlop fitted with an 8-inch twin-leading shoe brake.

I like it.

The rear wheel was built with a later conical hub (I have the original still). I also fitted new Hagon shocks, new bearings including a new swinging arm spindle, etc. All the nuts, bolts, spindles are stainless steel supplied by Andy & Kim Molnar.

The engine I stripped, shot-blasted, then bead blasted. That includes the crankcases, the cylinder head, and the barrel. It was then blown out with high pressure air, and then it all went in the wife's dishwasher a couple of times while she was out.

Then it was more air again.

After that, new bronze cam bushes were fitted & reamed, New main bearings, new gearbox bearings, new bushes and so on went in.

The barrel was bored even though it was within tolerance. The crank, rods, and lightened pistons were all balanced by Dave Nourish. The cams, incidentally, were ground to Thruxton profiles. George Hopwood, THE Triumph Thruxton guru, helped with the exhausts, silencers, footrests, and pedals, and he offered no end of advice.


Kirby Rowbotham, a great & knowledgeable precision engineer, modified my timing cover and fitted the pressure fed oil filter and breather modifications.

A Hayward belt drive & clutch was installed.

Standard I don't like, so I fitted mouth organ tank badges, and I painted the tank similar to the 1962 colours (which I never could afford at that time). I also fitted a standard seat and straight bars.

Ambition realised, I then made it look more like I really wanted with more of George's Thruxton bits and repainted it to present colours which I like much better.

A racing mate calculated the primary gearing, final gearing, wheel rolling diameter, and fitted a Krober racing rev counter. We checked it out at 7,300rpm in top gear (which equates to 123mph). It revved to over 8,000rpm in lower gears, and (with these cams and the balancing) it did it quite easily and smoothly.

More lately, I fitted Mikuni carburettors and Ikon adjustable rear shocks. A mate borrowed the Thruxton silencers, so I presently have standard Burgess silencers fitted.

I think it looks okay, and it goes well—although I don't rev it too much now.

But I still hit a ton now and then, which both the bike and me enjoys ( I have a Honda CBR 600 if I wanna go a bit daft). That screams quite nicely and is enjoyable.

Both bikes are over-indulged with care and attention, servicing, oil & filters, etc.


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