Discussion in 'Norton Commando Classic Motorcycles' started by Fullauto, Apr 20, 2018.
So what was the outcome of Ken's cam - thought it was going for test.
Actually, I think it's the other way around. Adding radius to the follower increases the angle where the lifter and cam come together so more speed is required to float the lifter on the oil film.
I like using a little radius on the lifter as a way of modifying the ramp and seating rates to help with valve train stability or shorten the effective duration to move the powerband down a little or just to avoid valve to valve contact on some cams.
I have seen on the spintron that just adding a 6 inch radius with some cams that were designed for flat tappets, will let them run an extra 1000 rpm before valve bounce becomes a problem, without changing the timing enough to affect the operation.
The Norris D+ comes to mind as well as the flat tappet version of the N480. These both become much more stable with a 6 inch rad on the lifter.
Maybe, but when you machine flat or radiused tappets to a smaller radius than the cam was designed for then you shorten the duration of the cam while the lift remains unchanged, you increase the lift acceleration and you increase the stress/load on the cam surface and that effects the wear rate. You increase the low end performance but you lose some top end. There is always a choice of trade offs.
Comstock - when you radius a flat lifter to 6" you are also lightening it and that is one reason that valve bounce is reduced.
Ken of Full Auto - please post a photo of your worn cam lobes so we can actually see what's going on. A measurement of wear on the nose would also be helpful.
Jim, I wonder if the PW3 Valve bounce evidenced in the Spintron would also occur when compression and combustion are added to the picture?
The way the inlet valve bounces from 6k on makes you wonder how the cam could add power at top, and yet we know from racing results that it did just that.
Still seems a poor choice for a low rpm single carb touring bike, but it's surprising to see that valve bounce right where the cam is supposed to be most effective.
My thoughts as well.
There is little cylinder pressure to affect the valve bounce at the time of closing. I doubt there would be much change.
Lot's of seat pressure can help with the valve bounce when racing. Of course lot's of seat pressure will affect the cam life. Jim
Fast Eddie said:
That makes sense Jim. When trying to imagine this, it seems to me that mildly radiused tappers would aid the process a little too.
A radius on the follower, if small, worse'ns the situation. Even a radius of 6 inches makes such a small difference, you have to go to four places of decimals to see it.
Point taken Snotzo and Jim.
In my minds eye, two radiused surfaces acting together should create a better oil ‘wedge’ and help force more oil between the two.
nothing is forcing the oil in - the contact pressure between two surfaces is forcing oil out.
The slower the turning speed of the cam, the thinner the oil film that manages to survive, and the position where the oil film is thinnest is when the peak of the cam is positioned in contact with the follower, and valve spring pressure is at it's maximum.
As Comnoz has explained, a very different situation exists within a running engine.
All talk about lubrication may or may not have any bearing on PW3 camshaft failures, but hopefully if FullAuto is able to obtain a competent metallurgical analysis of his camshaft's failure, we may all learn something useful that will remove a great deal of speculation, myself included.
Semantics perhaps Snotzo, but the oil that is adhered to each surface is surely ‘forced’ into the gap as the cam rotates towards the follower and the two surfaces come together?
Lifter weight has little to do with valve bounce.
It can affect valve loft over the peak. Jim
I note that Comnoz has an oilfeed direct to the cam on his street bike -maybe if lubrication is an issue this is the way to go - Dunstall offered something similar many years ago or perhaps Jims arrangement is different
My system is similar to Dunstall's. I installed that system in the early 80's after having two cam failures in a row. In hindsight it seems the cam failures were a result of a poor choice of lubricant -not a lack of lubricant. I still use it because its there and maybe it helps some. It did require an oil pump with a little more volume to keep the oil pressure above zero. Jim
Its one of those things that I think about and have never done . So you have drilled the cam ? My current thinking is that with my 71 cases i could install a feed which would exit through the old breather holes and then turn it off by a manual tap its basically to give the lobes a good oiling by filling the trough the cam runs in.. Naturally it will need a breather else where such as one of your sump type.
Yes, The cam is drilled with a delivery hole on the leading side of each lobe. The fitting in the case has a long tube that starts out as a close fit in the cam drilling. Then it gets smaller and ends about the center of the cam in an attempt to deliver oil evenly to all 4 lobes. There is also a carb idle jet in the fitting to limit the amount of oil. I think it was about .017 diameter or maybe .012 -I don't recall for sure.
The valve bounce problem with the PW3 was solved over a year ago by creating more gradual ramps to replace the abrupt ramps of the original PW3. A lot of help and data was contributed to create this new Norton cam.
The image below compares the difference of a gradual ramp cam to an abrupt ramp when the profile is moved on the graph so that both ramps can be viewed as if they start at the same place.
Cams designed for radiused lifters show less wear than cams designed for flat lifters - when both cams/lifters produce the same lift/duration. The cams designed for radiused lifters have more surface area and a rounder nose to help spread out the stress as shown in the image below.
The original Norton lifters can be converted to a 1-1/8" radius to take advantage of this situation as below. The contact area doesn't go beyond the ends of the stellite pad.
Or you can spend more money for lighter BSA lifters with tappet blocks and get higher RPM.
Some will still buy the cheapest cam they can get and replace it more often. Some will radius the lifters and use them with pointy cams that were designed for flat lifters - a higher stress situation creating more acceleration approaching full lift and reducing the contact patch area over the nose.
Others want their parts to last and will take the plunge.
Either way - the PW3 cam and its performance characteristics has become very popular since its creation by the great racer and innovator Peter Williams and its here to stay.
I have been sitting on the report for a week. I will not be releasing the results until cam and followers have gone back to be tested by the suppliers. Let me dispel a few myths first. 4,000, 1200, 1500 , 26,000 miles before failure. They are the ones I know about. Why the disparity? Because I had the NASA coatings applied to both the cam and followers when the engine was rebuilt. The only reason my cam lasted so long was because of the coating. This was confirmed by the metallurgist. I am an absolute believer in the use of appropriate coatings on our old clunkers. Living, confirmed proof. During the rebuild, the cam and followers were liberally coated with the appropriate lubricant. To suggest that the damage occurred early due to incorrect lubrication is plain silly in my case as the motor would not have lasted as long as it did if it was damaged early. The engine builder is very experienced with Nortons. I was speaking to the boys at CIC Coatings yesterday, but Paul was quite coy about the actual coating applied. Trade secret apparently, but I will try to weasel it out of him for the edification of all.
I run Penrite 20/50 motorcycle oil with the correct zinc additive. The metallurgist agreed that the oil choice was appropriate. Oil changes were at 1000 miles, except on my big trip where the mileage doubled without a change. The engine was very clean inside on disassembly. The crank had to be reground and main bearings replaced.
All in all, a very disturbing report with ramifications for all. My reference to Andover Norton as the supplier of the cam was incorrect. The PW3 was supplied by Mick Hemmings about two and a half years ago.
Forgive me, I don't quite follow. You had 3 failures in 6700 miles with AN PW3's, then used a coating and next failure (Hemmings) took 26,000 to happen?
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