Pre-unit T100 Cam Timing Advice Please.

Some months ago I acquired a fully restored Tribsa with an all-alloy c1952 Triumph T100 engine. It is similar to a machine I owned in my youth and I wanted to experience riding one again before I get too decrepit!

I bought it knowing that the engine wasn't running right but figured it wouldn't be too difficult to sort out, as the engine sounded mechanically quiet. Just a few minor adjustments needed. Easy-peasy. A nice little project.

The engine runs, just about, but it misfires and spits back, runs unevenly and only on choke, and is extremely difficult to start. I checked valve clearances (at 2 and 4 thou), contact breaker gap, and spark plugs. All look okay. Likewise, the carb was stripped (a brand new Concentric 626 Mark 1) and all seems fine and dandy, although I have no idea whether the jetting is even close to being correct (190 main jet, 106 needle jet).

So, with plenty of time on my hands due to the present 'lock-in' situation, I started to check everything over, starting with valve timing and ignition timing, before looking at carb settings.

With the timing case off, it was clear that the cam timing marks on the pinions are not as depicted according to Haynes manual or the official Triumph 1946-55 manual, and extra marks have been added using a punch and white paint marker. Not very helpful.

When I pulled gently on the cam idler gear to see how easy it would be to remove, it slipped straight off in my hand! Well, that's one way to lose the existing cam timing. What a numpty! Okay, so not really a problem. I just need to set the valve timing from scratch. And the magneto timing. Bo**ocks!

But here's the thing: I can't find what the correct valve timing should be for this engine.

It's an all-alloy T100 from about 1952 with no 'wheel' mark after the engine number. This apparently means that it doesn't have the ramp type cams. I cannot for the life of me find the valve timing figures for a non-ramp cam T100.

The official Triumph workshop manual No 11 (for 1945-55 Twins) states that the Tiger T100 and the 5T Speed Twin has valve timing 26.5/69.5/61.5/35.5 with 10 thou clearances. BUT it also states that these models have ramp type cams. With no 'wheel' mark by the engine number, my engine does not have ramp type cams.

The Triumph manual gives valve timing figures for the Trophy TR5 model as 27/48/48/27 with 2 and 4 thou clearance. This does NOT have the ramp type cams. So is this right for my T100 engine?

Just to add further confusion, Haynes says that the T100 has 27/48/48/27 timing with 2 and 4 thou clearance, and also contradicts the Triumph manual as listing the Trophy TR5 with 26.5/69.5/61.5/35.5 (10 thou clearance) and yet the 5T is apparently the same as the TR5's 26.5/69.5/61.5/35.5 timing but with 2 and 4 thou clearances!

With all this contradictory information, I could really do with some sage advice. The problem is that none of the above information relates specifically to a T100 without ramp type cams.

My thinking (tentatively) is that the early T100 without ramp cams possibly has 27/48/48/27 timing, but this is little better than guesswork. And if the guess is wrong, I could end up with valves hitting pistons.

Can anyone with knowledge of pre-unit Triumph twins please shed some light on the murky subject of T100 cam timing?

Any advice welcomed...

 

Just realised that I'm assuming that it has the same cams as originally fitted 60-odd years ago. Reckon I'll have to pull off the head and cylinder barrel to check what's in there before going any further.

Hey-ho. Just as well I've got plenty of time on my hands.

 

Couldn't use the existing timing marks as there are too many. On the exhaust pinion there are two punch marks in different places, plus a white paint mark in addition to the original timing mark. Could be any of those.