I am quite frankly amazed by the thesis PW3 cams are destined to have a short life. In the family we currently have 3 Commandos running on the PW3 with no incidents so far:
- the oldest in our "family racer". The cam has been in it for over twenty racing seasons, together with the tappets. Other things went wrong on the engine during this time- crank broke twice, one on my son, one on me; valve seat fell out after 40 years but Andover Norton declined my warranty claim form for that.(Shame on our company! Supposedly because racing use is excluded in warranty terms, not to mention there was no 40-year-warranty in 1972).
The engine has as many horses as the best works race engine ever on the test bed if I can believe Peter Williams, but more torque. During the many seasons it was raced by more than half a dozen riders, some gentle though pretty fast (my daughters), some less gentle but faster (a couple of friends who are real racers), some in between (my son Tim and myself).
As for mileage the Scitsu does not record mileage, unfortunately, but at one three-day meeting I was the record holder in timed laps out of more than 150 competitors and frankly the bike has probably seen more miles around race courses than most.
- Tim's Roadster Commando. Not sure about the total mileage but the beast has been on the road for about a decade.
- My short stroke Signal Orange Roadster. Forgot to write down the mileage after completing the restoration but I reckon it has done between 17k and 18k miles since I restored it. Last rode it tonight, home from work. Nothing wrong with the PW3 cam it seems! Got home all right, no suspect noises from the valve gear.
Our technical buyer Ashley, Commando rider (with a Fullauto head on his) comments:
1. Valve stem collet location height, if this dimension from the valve rose to the lip where the collet seats is less than a standard valve, you will have problems. This increases valve seat pressure, not ideal. It also allows the spring less distance to travel before coming coil bound.
2. Fitting a new head or having valve seats replaced. This can induce major problems, even with standard parts, the standard valve springs are close to coil bound in normal use, this came about due to the spring staying the same and heat insulators being used under the spring cups, on the MK3 where the manual shows to fit them on the inlets – the springs are shockingly close to coil bound. Now if you have fitted new seats the position where the valve sits on the seat may not be in the place it was before, if it is 1mm nearer to the piston crown, this will increase the height to the collet position and thus the spring will be under more compression when fitted – as per 1. More seat pressure, not ideal, and less distance for the spring to travel and thus 1mm (0.040’’) of your envelope towards coil bound eroded.
Now you can see even with what seem like insignificant changes using even a standard cam there is not much wiggle room. When changes have taken place it is wise to check the valve to piston clearance, coil bound, rockers engaging with underside of the head, cam tunnel clearance, etc. Even though many have fitted PW3’s and had no issues, it does not mean they that don’t or can’t exist.
Then there is spring type and rating, this is another subject on its own, nested springs do a good job, still used on the Eurofighter as it was the only solution. One piece, beehive, barrel springs can be superior, but are these days designed for a specific fitment, just because the work on a Triumph, does not mean they will work in a Norton. No spring designer or manufacturer would design a spring to have a wide range of uses or fitments.
Mick Hemmings- probably the guy who built most engines using the PW3 cam- builds all the engines and fits the PW3 and has no comeback re. wear - but always uses new followers.
My engine man Rudi also builds practically every other engine using the PW3 and has done it for many years. He built the family racer engine over 20 years ago and repaired it since if/when something went wrong. No comebacks on PW3s from that quarter, either. But he, like Mick Hemmings, checks valve spring pressures and makes sure the springs can't get coilbound, checks if there is enough space around the cam in the pushrod tunnels, and checks clearance to the "snouts" of the cylinder barrel guiding the tappets, as well as valve clearances to the piston crowns.
We had a case only recently where another friend put a PW3 cam in his engine, did NOT check clearance to the tappet tunnels, and the cam touched the "snouts" and sort of "smeared" a ridge on them. Result: a pushrod jumped out, and traces of the cam on the tunnel snouts but NO DAMAGE ON THE CAMSHAFT. This was only last year, I watched him taking the barrel off and saw the PW3 cam still in mint condition.
I love the characteristics of that cam. It gives more oooomph all round and makes every Commando even more of a joy to ride. My youngest daughter first rode the PW3 equipped "family racer" when she was an unexperienced 14-year old girl and loved it instantly. It rides like a road bike, only a lot faster- fine even for a novice and amazingly quick with the right rider at the helm!
Joe Seifert/Andover Norton