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Worn PW3 cam

Discussion in 'Norton Commando Motorcycles (Classic)' started by Fullauto, Apr 20, 2018.

  1. worntorn


    Dec 22, 2006
    Phil Irving for starters.
    Beyond that, I won't put words in anyone's mouth, ask the experts here. We all know them and they are pretty generous with advice.
  2. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    As far as the PW3, it has a lot of lift but relatively short duration for that much lift. So it can and obviously does make a decent amount of midrange torque in Ken's bike. Sometimes things just may work together that would not be expected. I am sure the high velocity port of the Fullauto head helps overcome the problems associated with the big cam.

    However, that does not make up for the fact that the PW3 is going to put the valvetrain to the fire -including the cam. Durability will not be its strong point no matter what it is made of. On a bike that is going to see a lot of miles, there is probably better choices for a cam. Jim
  3. jseng1


    Nov 26, 2009
    I think you missed the valve seat pressures - see them in the 2nd line for each spring.

    Comstock conical 240 lbs at .4" valve lift.
    recommended install 1.4" (seat pressure 103)

    Stock Norton dual springs 224 lbs at .4" valve lift.
    recommended install 1.250" (seat pressure 85)

    RD racing springs 218 lbs at .4" valve lift.
    recommended install 1.350" (seat pressure 97)

    JS conical beehive 225 lbs at .4" valve lift.
    recommended install 1.450" (seat pressure 93)

    Note that Comstock actually recommends installation height between 1.370" and 1.4"
    so if 1.370" installation height is used then the conical springs have a seat pressure of 113 lbs and 250+ lbs at .4" lift.

    Full Auto's cam was likely soft and the biggest reason for the premature wear but increased spring pressure throughout the lift starting at low RPM through mid range RPM can only cause even more wear for an already bad situation.
    Last edited: Apr 23, 2018
  4. bill


    Jun 1, 2003
    i like how you like to play with numbers. you state his install is .370-.400 where you want .450 so there is the difference in seat pressure. you want an exact number but he gives .030 leeway. at the same install height where are your springs at v his??? you are not comparing apples to apples. another thing that has been shown, the more rapid the opening ramp and closing ramp the harder it is to maintain valve train control. i think i will follow comstocks recommendation as he has done the testing on an actual norton not some generic engine with all kinds of differences in the valve train from an automotive application.

    PS not a fan of the PW3

  5. Snotzo


    Mar 12, 2013

    I certainly did not miss the installed data in your post, but have to say you are clearly attempting to make a case in favor of your beehive spring against the conical spring as supplied by Comstock.

    In my view this is not a spring issue at all, but one of unsuitable camshaft material.
    Mr. Rick and madass140 like this.
  6. Fullauto

    Fullauto VIP MEMBER

    Apr 13, 2009
    Finally. The words of wisdom from the man. This is the first time I've heard this. So, how do you account for the people who have had PW3 cams fitted for years with no issues? I am anxious to put this motor back together with all the right bits because of the mileage I do. However, my PW3 has given me the performance that has been particularly satisfying and I do not want to give this up for something more top endy. What, in your opinion, is the best cam for my needs, being strong from off idle all the way through? Bearing in mind that the standard Commando cam is outclassed everywhere in the rev range by the PW3 in MY engine.
  7. baz

    baz VIP MEMBER

    May 26, 2010
    What was the main difference you noticed between the stock cam and the pw3?
    I only ask as I am slowly gathering parts to build another commando 920
    I have a stock cam and a 4s but was considering the pw3 but I'm a little put off now!! Cheers
  8. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Maybe many of those PW3 cams have been in for years... but how many miles? Not many clock up your kind of mileage on classics Ken!

    Also... you do often state how you like to use low revs (ie below 3k) and I wonder if this is bad for the cam due to reduced oil fling / splash to lubricate the cam and the increased stresses as explained by Snotzo?

    Web Cam 312a with radiused lifters is used and favoured by many as a strong ‘street cam’ ie most improved mid range and slightly improved top end. Megacyle do a similar grind but I forget the number.

    JS #1 cam is very effective IMHO, but possibly a little too ‘top endy’ for your needs IF I understand your definition of mid range & top end correctly.

    All of the above are hard welded steel cams. Definitely the hardest wearing option, as I understand it at least.
  9. jseng1


    Nov 26, 2009
    Snotzo - As I said in my last post "Full Auto's cam was likely soft and the biggest reason for the premature wear". Note that there are 4 brands of springs in the comparison.

    bill - The spring pressure numbers change according to installed spring height. The Comstock conical spring pressures are higher and there is not enough room to reduce it by increasing the spring height with a stock head. Comstock has already designed his spring retainers so the collets are deeper than others to try to reduce that pressure and he is running out of available spring height and the bottom washers are already thin.

    With the stock Norton and the RD springs you can increase the installed height and reduce the pressures even lower than they recommend. But I am only showing the recommended heights/pressures. The JS beesprings come in 2 options - street installed height and race track installed height (different bottom washers). This post is about Full Auto's street bike so we're talking about street spring pressures.

    There are several factors that determine cam longevity - material, oil, spring pressure and lobe design - including cams designed for flat lifters and longer lasting cams designed for radiused lifters. Hard welded cams are available from Webcam, Megacycle and Johnson cams. ENB40 plasma nitrided cams are available from Newman on special order. This discussion group is about making comparisons and honest technical imput is appreciated.
  10. worntorn


    Dec 22, 2006
    The information has been here all along, but you weren't seeing it as you were very happy with your choices.
    The wear factor is a big one for your bike.
    There are probably only a handful of Norton owners logging the miles that you are.

    A good resource book is Phil Irving's " Motorcycle Engineering"
    It covers just about anything one needs to know about road going motorcycles.
    Durability was very important to him as was appropriate tuning for end usage.

    If you plan to go racing, then his " Tuning for Speed" is a great companion book.

  11. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    I can do a custom Stelite buildup Webcam similar to a PW3. Slightly less lift which you will not miss. It would be a little easier on the valvetrain. It would be a special order.

    Or my most successful cam has been the 312A. It's easy on the valvetrain. I try to keep them in stock. Jim
    Last edited: Apr 24, 2018
  12. Fullauto

    Fullauto VIP MEMBER

    Apr 13, 2009
    SOLD! I'll send you an e-mail.
  13. Fullauto

    Fullauto VIP MEMBER

    Apr 13, 2009
    The PW3 is stronger everywhere. Very linear delivery, but remember that I'm using one of my heads which has superior port velocities. It made as much difference as putting on the Fullauto Tech head. I was amazed from the word go and still love the thing. It is an extremely tractable motor. I had an 850 with a Combat cam which really took off at 4500 and revved very hard. I believe the 4S is even more like that but I have no experience of them. Looks like Jim fas offered me a solution. See his post on this thread.
  14. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    PS, If you like the way your engine ran before then find out what your lobe center angles are set at.
    Then set the new cam at the same angles.
    Fullauto and madass140 like this.
  15. Fullauto

    Fullauto VIP MEMBER

    Apr 13, 2009
    Well,this is interesting. Normally, I would have thought so. So I had the cam and lifters coated with some fancy NASA developed coating and while the cam is toast, the lifters are almost perfect. This has made me a big fan. I don't even know what it is. I shall attempt to find out. With the good torque and the higher gearing, you just don't need to rev it to stay in front of the traffic. It's quite subtle but I definitely use less revs than before I had the cam fitted. It is also very rapid in getting from 50 to 70 MPH in 4th gear. A big difference.

    If you look at my videos, you will see how I ride and while it looks quite sedate, I'm travelling at the speed limit in KPH, but using MPH on the speedo, if you get my drift. Moving along without all the fuss and bother.
  16. johntickle


    Dec 3, 2009
    When using high lift cams like the PW3 a number of "situations" causing abnormal wear can occur:
    - The cam lobes can touch the crankcases
    - The cam lobes can touch the cam follower tunnels
    - The cam followers can touch the "roof" of their tunnels
    - The rockers can touch the "roof" of the cylinder head
    - The coils can "bind"
    - The valve collars can touch the top of the valve guides
    - ...
  17. ZFD


    Jan 23, 2010
    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
    chaztuna likes this.
  18. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    I have to say I am surprised at your results.

    Last time I installed a PW3 in an otherwise standard 850 engine and did back to back dyno tests I got results that were similar to dobba.

    Quote " PW3 Performance wise, no real benefit (3 hp from the bottom end to put 2-3 hp at the top end) apart from a bit more of a 'crack' to the exhaust."

    And I might add a little rush feeling in the midrange as it begins to work.

    By the way, I would say this is about average for any race cam installation without comprehensive engine building. PE3 or Webcam.

    I'm not concerned about coil bind or cap to guide bind with the conical springs but there is one thing you might want to look at and that is possible interference between the top of the rocker arm [right over the pushrod] and the top of the head. I have had to remove a bit of material there before with big cams. Jim
    Last edited: Apr 24, 2018
  19. oldmikew


    Jul 25, 2015
    Joe and John Tickle both point to mechanical fitment issues - certainly Norman White supplies his with full fitment instructions and it may be there are clumsy souls who get this wrong but surely that would only suggest isolated failures.
    And then there is the issue of valve springs and seat pressure.. If an engine is reved then Comnoz is surely right re valve spring pressure on thr nose of the cam.. The cam knocks the valve open and thereafter it is controlled by the spring the cam lobe and follower are only really in ' floating contact ' not the same as valve float . If the spring pressure is too light then the cam lobe will re establish contact with the follower late at an unfavourable aspect . On these failed cams is it on the trailing or facing edge of the lobe that the hardening has worn and paved the way for more serious erosion

    But supposing the wear is not happening high upthe rev band but on modest revs say below 3-4000. Then there will be heavy contact between th cam lobe and the follower and this I take to be the JS point about spring pressures..

    Piper cams used to do some very trick Norton stuff and I raised this issue of cam wear with them . They said that usually it was because engines had been allowed to idle before the two surfaces (the cam and the follower)had work hardened. So if you have a new build engine with PW3 and run it in for 500-1000 miles then this is not good. If you put a PW3 in a well run in engine and can rev it the outcome might be more favourable.

    Finally there is the point about lubrication... The Dunstall so called pressure feed.. Has any one tried this..

    I appreciate that many here have forgotten more about Norton engines than I am likely to ever know
  20. worntorn


    Dec 22, 2006
    The " in use for many years" type references don't mean a lot, unfortunately.
    I have a trials bike that I've been using for many years but it still shows only 497 miles covered since new on its tiny but functional speedo.
    There are plenty of old bikes in GB that get used every year but still fail to do ever much mileage . Maybe a bit more than my trials bike, but still not a lot.