Vernier cam wheels...

I agree here Ken, hence the stepped key that took forever to get right by working backwards from the recommended Vv lift and Vv to Vv clearance at that lift. A lot of hand work although very worth it in the long run.
Regards Mike

I'm a bit sceptical. It might be critical to get a well-developed race cam spot-on the recommended timings, if the guy who developed it has a great reputation and is really willing to pass on his expertise to bring his competition up to his level and you intend to use exactly similar exhaust system as on his race bike.. However I believe that every road bike is a compromise to comply with noise laws and cater for the lowest common denominator amongst the customers. It would not matter what cam I used, I would try moving it backwards and forwards whenever I changed the exhaust system. What you lose in top end often reappears in the mid-range where it might be more useful. - Depends on the circuits too.
Back in the olden days, the Triumph race kit for the Tiger 100 worked very well, however it was completely specified right down to the exhaust system specification for two types of circuit - megaphones and straight pipe. A 2 into 1 is a different story.

lcrken said:

We might have to agree to disagree on this one. My mentor on the subject of cam timing, who had more hours of Norton dyno time developing cams than anyone else I know of, told me that for his race cams I needed to be within one degree of the specified timing or I would be losing power. For a street bike, not such a big deal, but for a race bike, the maximum horsepower is achieved by paying attention to all the small details, including precise cam timing.

Ken

Click to expand...

Would that mentor have been Mike Libby, C.R. Axtell's understudy? Or was it Axtell himself?

JimC said:

lcrken said:

We might have to agree to disagree on this one. My mentor on the subject of cam timing, who had more hours of Norton dyno time developing cams than anyone else I know of, told me that for his race cams I needed to be within one degree of the specified timing or I would be losing power. For a street bike, not such a big deal, but for a race bike, the maximum horsepower is achieved by paying attention to all the small details, including precise cam timing.

Ken

Click to expand...

Would that mentor have been Mike Libby, C.R. Axtell's understudy? Or was it Axtell himself?

Click to expand...

It was Axtell. I was using one of his #3 grinds, but with a very close lobe separation (102°), for the first time, and he was warning me about making sure I had enough valve-to-valve clearance. That was when I also asked him how critical the cam timing was, and he said to keep it within one degree. He's the one that told me about making offset keys to get it right. I'm sure it would have still worked quite well if it was off by more than that, but he was serious about getting everything right. Getting the really high horsepower numbers is all about getting all the details right. The difference in power might never have been noticed by a rider, but it would have shown up on the dyno. I'm pretty sure that for milder cams, like the stock Commando cam, the performance would not be nearly as sensitive to timing variations.

Ken

Hi Ken a rebuild on an 850 recently proves that theory. Mates bike had a rebuild, standard flat top pistons PW3 cam , ported head (same guy that does my head work) and once up and running it ran out of puff at the top end.
Owner thought carbs , so we tried 4 x different sets , premiers , Mikunis, Flat slides, all to no avail and I kept thinking it felt like cam timing.
Sure enough , guy who assembled it had a look under the timing cover and found he was one tooth out between the pinion and idler gears.
It was retarded so hence the no top end. Now sorted.
Regards Mike

Good to get some real experience with results. I'm not real surprised either. One tooth on the pinion gear is good for 15° timing change, and that's a lot of retard.

Ken

Do some people still actually build their motor and run it without first checking it with a degree disc and dial mike ? I have never believed in timing marks on cam wheels. And if I change the exhaust system lengths, I don't expect the cam timing to stay at the optimum setting to suit the exhaust. Especially a 2 into 1 pipe does a lot that is very different to separate pipes with megaphones. I suggest that if you buy a PW3 cam designed for separate pipes and fit a 2 into 1 exhaust without adjusting the prescribed timings to suit it, you might be doing yourself a disservice. What I try to do is progressively advance the cam in the Commando engine, then test it - however it would be better if the set-up was separate inlet and exhaust cams as in a Triumph engine. I believe the Nourish engine might be much better than the Commando engine because of this aspect.

I sometimes wonder about the large pipe diameter which some people use in their 2 into 1 exhaust systems. I use a smaller internal diameter pipe so that it matches the ID of the port stub all the way to the collector. I think that a smaller diameter pipe allows the standing wave to be more easily established, so the system probably works a bit better. Years ago I did a fair bit of work with a 2 into 1 pipe to get my Triton going. I progressively adjusted the exhaust cam timing and found if the opening was advanced beyond 80 degrees ATDC, the motor slowed. However up to that point it went progressively faster. The biggest thing which killed the top end was any slight restriction at the outlet of the collector. Overall the bike was much more competitive with the 2 into 1 exhaust. With megaphone exhausts, the bike was hopeless.