Triumph Valve issues

Bertie Simmonds
April 25, 2017

Q: I have two valves out of a classic motorcycle (a Triumph) one and the other are the same size in all respects. The parts book gives a different parts numbers for each valve (inlet and exhaust). The problem is knowing which is which. I have looked in all my service books but cannot find any reference to this matter, Which is the inlet and which is the exhaust? As I have said they are in all respects identical! In normal circumstances, even allowing for an exhaust valve being more ‘burnt’ etc than the inlet, the inlet is normally on engines (generally) larger. The only thing that may help is that one is ‘ferrous’ i.e., a magnet sticks to one valve but not the other, the valve head.

A (collective noun in here) of valves.

A: As a general rule, exhaust valves suitable for modern fuels are non-magnetic (i.e. austenitic) whereas inlet valves are magnetic (i.e. martensitic). However, your valves are probably not designed for modern fuels, so that is probably of no help. I was reminded by this letter that some older Triumphs did have inlet and exhaust valves of the same size, so that would make life more difficult as far as identifying which is which is concerned. You could try scratching the valve faces with a scriber or similar to test the room temperature hardness — which might give you an idea, but otherwise it could be time for new valves and sets anyway as this will prevent any worries about unleaded fuel. I shall be looking at this topic in the future.

About the Author

Bertie Simmonds

As a child Bertie (well, Robert back then… blame his sister for the nickname) was exposed to motorcycles thanks to his uncles. They would show up at his house with a lovely lady as pillion throughout the 1970s and 1980s. After a naughty time on field bikes (it’s what we did back then) Bertie passed his test in the early 1990s and became a reporter for MCN in 1995, moving to the sports desk and covering World Superbikes in 1996. With a change to Bike Magazine in 1997, he stayed until 2000 as news, features and road test editor. Moving into PR with Cosworth, Bert was bored with cars and returned to bikes in 2001 with Two Wheels Only, becoming editor in 2002 and leaving to be freelance at the end of 2004. With almost a decade freelancing, Bertie joined Mortons in 2013 and became editor of Classic Motorcycle Mechanics, a post he’s desperately clung to, to this day. And no, he’s never had a pretty girl on the back of his bike.

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