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Lightning Cams


Website User
Non-VOC Member
Hi do lightning cams work well in a Rapide or are other changes needed? this is for a road bike not for racing....Thanks


Well Known and Active Website User
VOC Member
To gain much benefit from lightning cams you need the lightning pipes.
For road use I found little difference .
You need to shorten the lower valve guides to accommodate the extra lift. Regards John.


Well Known and Active Website User
VOC Member
Did I read long ago in "tuning for speed" that perfomance needs as much fuel as possible, burnt efficientley as fast as possible. (Big Cam, Big Carb, Big Exhaust?) Surely you need all three to go faster,not one or two on their own?

I had a MK2 cam in my Comet and it went like you know what (please remind me why I sold it) and I put MK2 cams in my D and that would pull 110MPH on the GPS no problem. "No good for road use", I think not.

Tom Gaynor

Well Known and Active Website User
VOC Member

In my experience, race cams and a low compression ratio make for an engine that pulls like a train: an excellent low speed performance and adequate high speed performance. I've done it several times, as have others. The fundamental recipe is the most radical cam obtainable, and a relatively low cr.
Unfortunately Vincent cams are "all pointy", instead of having a proper rectangular Manx Norton profile (like a house-brick: slam the valves open, keep them open as long as possible, slam them shut).
In the list of "things a boy can make or do" is to get Gary Robinson to grind me a set of cams with Rudge Replica profiles on Vincent wheels. Given that a 500 cc Ulster (6.9:1) so equipped will do 100 mph, "obviously" a Vincent twin would do 200 mph, which might, just, ease me ahead of Russell...... Bonneville beckons.......


Well Known and Active Website User
VOC Member

I agree with Tom in so much as the extra lift and duration seems to give more bottom end punch to a relatively standard engine. If however you complete the set, so as to speak, and add extra compression, open pipes of any configuration ( I run 2" two into one real short) and large carbs and matching ports then the engine becomes almost peaky, feeling flat below 4,000 as there's a big rush beyond that point (both financially in engine repairs and also speed).
Watch for clearance in you lower valve guide (as mentioned previously) as well as correct function of valve lifter and rest of valve train and you'll find Mk2 cams are fine for a standard engine. - David

Tom Gaynor

Well Known and Active Website User
VOC Member

For the record, I changed the original Shadow cams (1951 - Mark II?) for Gary Robinson 105's. I think these are the same profile as Mark II, with slightly different overlap timing. CR is 7.3. (Interestingly, so long as valves don't clout pistons, Manx Norton valve timing isn't apparently particularly critical. Within about 5 degrees is OK. But ignition timing HAS to be 34 degrees with a mag, or the ****** won't go.)
The Vin tends to "lie down" a bit over 90 (which I think means it needs more ignition advance than 34 degrees), but I rarely go above 90 anyway, and up to that it is "adequately fast". It won't match 'iggins 1200 Shabby Shadow though: he went away from me up the hill at Ballacraine like I was going backwards. However I saw him turn into Parliament Square, so there isn't that much in it.
What I love about the Vin is that if I pop it in to top at about 40 mph, I can cover an entire journey without changing gear again until it's time to stop, without feeling I'm "holding everyone up". Oh joy : a bike with four gears that could probably manage with two, first and top......
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