PW3 Cam Timing

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Jun 7, 2009
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I fitted a PW3 cam some time ago. It went straight in on the standard timing chain set up and sprockets as per instructions.
I've spent a lot of time sorting other issues and am now getting back round to the cam.

What sort of timing error could I expect from the standard set up. Is it worth my while opening things up and checking or should leave well alone?

There's no problem with the way the engine runs just not sure I'm getting the best out of it.


Plus or minis 10 degrees is what Les Emory told me. I have found them 5 degrees out on the stock settings. Checking it is not that bad but you will need a one inch travel dial indicator, a way to hold it on the moving valve stem collar. Also a dead stop and a degree wheel.
Not heard about issues with vernier sprockets before, what's the problem?
I have a good vernier that I use on one of my motors. It depends on where you get it from. I foolishly bought one from Norvil years was on the piss, so went staright in the skip!

If you have the head off, check that you have 145thou lift at TDC...I can't remember the timing figures offhand, but with my PW3 it was spot on with standard timing gears
Hi there, so who is selling good vernier, cause apart norvil, Rgm, who is making them???
I was lucky to get a Rob North framed commando racer. Mick Hemmings built the bike to race in the 80s but it was banned by the classic racing people because it wasn't a triumph or BSA tripple. I am rebuilding the engine at the moment and bought Mick Hemmings engine rebuild DVD. He fits a PW3 to the engine he is rebuilding in the video and uses the standard timing. He even checks the valve timing to show it is correct. Even as a trained mechanic I think Mick's DVD is a must if you haven't rebuilt a Commando engine before. I am still learning about Commandos but from my investigations, the only cams that seem to be machined accurately are the PW3s. I am replacing the 7S in my engine with one even though it looks to be hardly used. I am photographing the rebuild as it goes and will try and post the photos once it is complete.
I don't know who sells a good vernier nowadays, but my cam grinder is really good,. and of the 4 different cams he's made for me, all were spot on, so no need for a vernier anyway!!

mrbodgit, I remember that Rob North commando, if I remember rightly Mick won at Suzuka on it! In fact, the first time he used a PW3 cam in anger, he won the F750 race of the Year at Snetterton on his proddy bike....beating all the Rob North triples too, and set the fastest lap of the you probably know, top end power is more important than anything else at Snetterton with those long straights, so th PW3 obviously works!!
Generally, two problems with the Norvil verniers. First, they're not very concentric, with a lot of runout, but so are a lot of factory original sprockets, so you can live with it, if you choose to. The real issue is that the small diameter pin that locates the sprocket tends to beat the holes for it into an oval, and the timing starts to retard. Les made some in the beginning with an aluminum sprocket, and they beat the holes out almost immediately. I tried one of those, and it wore so badly I had to replace it after one race. I think he quit supplying those pretty quickly. I've used his steel ones, and they worked OK for a while, but I usually had to replace them on the race engines each time I tore them down. I eventually junked them, and went back to making offset keys to get the timing right. Might not be such an issue on a street bike, but I've not tried that, so don't really know. They're not a complicated design, and it should be possible to do a better job, but then they'd probably have to cost more, and the whole project might never get profitable. Much easier to keep selling the current design.


Rich_j said:
Not heard about issues with vernier sprockets before, what's the problem?
Hi many thanks for your replies, so now I think that the guy who could make "offset" keys for camshaft , with different shape could have a big market :D
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