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OHV Norton Cams

Post 1948 OHV Norton valve timing is very ‘soft’. If you are trying to get the best out of your engine it is one area that significant gains can be found. You can get a bike to go well with standard cams but it is important that the timing is spot on - don’t rely on the dots! You can check your valve timing against the figures shown on this page. If you would like a little more performance from your bike - read on to see what your options are.

Irving’s Recommendation

This diagram is a copy of the one found in Phil Irving’s ‘Tuning for Speed’. He recommends that if a set of cams give timing figures similar to these they are suitable for fast road work and can be retained. If the durations or overlap are shorter then it is time for a new set of cams.

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Available Options

Now that we know what to aim for, we can look at what we have. This table compares the standard ES2 cam data to Irving’s recommendations and a couple of other cam profiles.

Notation:

  • BT = Before Top Dead Centre

  • AB = After Bottom Dead Centre

  • LC = Lobe Centre (The position in the middle of the opening point and closing point)

  • AT = After Top Dead Centre

  • BB = Before Bottom Dead Centre

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A few observations from this table:
  • Standard ES2 valve timing is softer than Phil Irving’s recommendation so there are definite gains to be made by changing.

  • The Norton International cam is a lot better. Not surprising as the Inter is a very sporty bike.

  • The 500 Inter is the same bore and stroke as an ES2 so would be a good setup to aim for.

  • Unfortunately it isn’t as simple as fitting an Inter cam. They are a different design so don’t fit. They would also give too much lift due to the extra rocker ratio on the OHV Norton.

  • The ES2 race cam included is readily available. I suspect these were designed for a short stroke engine though. In my opinion the durations are too long for an otherwise standard ES2.

  • The ES2 race cams were fitted to my Norton ES2 for a while but eventually I removed them as the bike lacked torque and wasn’t nice to ride at low revs.

  • A 16H cam gives timing figures very similar to the Inter. They also give similar lift once they’ve gone through the 1.26:1 ratio on the rockers.

  • If you can get hold of a set they are a straight swap for the ES2 cams. You might need to experiment to get the timing as close as possible though. DON’T RELY ON THE DOTS!

  • Norton redesigned the timing chest on the OHV models in 1948. Pre ‘48 cams don’t fit later engines, and vice versa. If you find a set make sure they are the correct ones.

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