PW3 cam for 850

I don't think that it is too out of line to consider a JS1 and a BSA lifter setup. Although this system also likes a bit more compression and tighter ports, I find the range is really broad and quite toasty up top.

I also find the lumpy idle damned attractive. It gets well deserved attention at stop lights, yet takes off butter smooth with a distinctive "RAP" that cannot be dismissed nor denied. It's awesome!

Recent changes show the this cam is available for stock lifters that you send in to be ground for 1 1/8" radius. Quite a savings, but the BSA shit is awfully nice.

FWIW, here's my experiences.
Standard 850, no known changes to the head or barrels. The standard cam was badly work on one set of lobes, so had to be replaced, and the cam followers were refaced. The DS cam bush was totally shot, so they were replaced by Steve Maney. who also did the cam followers.

I bought a PW3 cam since I was planning on doing some further changes with compression etc. The short story is that I could not find suitable pistons at the time, so ended up reusing the ones in the bike. I wanted to use the JS 0.003" gasket, but after measuring the valve - piston clearance, I went back to a standard gasket.

I had no problems with the cam tunnel nor any other part of the valve gear. With the standard gasket, there was ample clearance for the valves, so it was basically install, measure & check, button up.

Difficult to say how much change there was before and after the cam change though, since obviously with a very badly worn cam, performance was way down, but my point is that sometimes, you can be lucky and find that fitting a PW3 cam is very simple. No guarantee though, so expect the worst.

Since then, I've replaced the rods & pistons with the JS 10.5:1 ones, the head has been swapped for a ported, converted 750 one and a couple of other changes as well, so I'm hoping for good results this year. It does all get a bit expensive though, so it all depends on what you want to achieve. For a daily rider, I would be inclined to go for a good standard cam I must admit.

/Steve in Denmark.

Robert_Norton said:

Peter R said:

Hello, can any of you tell what will be the effect (positive and/or negative) of fitting a PW3 camshaft to an otherwise stock 850 ?

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There are a number of videos, posted by Jim Comstock on youtube, who is the member here known as "comnoz," that demonstrate the valve action(s) with various cams at different RPM'S. Draw your own conclusions by watching these two videos:

https://www.youtube.com/watch?v=L0_pud6vcuw

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Robert

The video link you show above does not make the PW3 cam look very good. It says "significant valve bounce" at 6500RPM and "Severe valve bounce" at 7000 RPM The test was made with "the best valve spring ... so far... for the PW3 cam" ... "a Honda valve spring ... with titanium retainer".

Maybe it was not your intention to spread bad news about the PW3 cam but thats how the video comes off when it says the valves are "beating up the seats" and that its "just a cam with very severe ramps" etc.

The PW3 cam is quite popular and for good reason but the closing ramps are abrupt and that's what causes the valve bounce shown in the video.

I had a cam which was very close to the PW3 profile but I changed the ramps so they lower the valves gently down onto the seats to eliminate the valve bounce. It was a very time consuming and expensive project requiring a custom cam master but I felt it important to cure the abrupt ramp and valve bounce problem shown in the PW3 video. Its up to the buyer to choose what cam they want. This is a race cam. A hotter cam always raises your powerband higher into the RPM range.

jseng1 said:

Robert

Maybe it was not your intention to spread bad news about the PW3 cam ...

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Jim (jseng1),

Not trying to spread bad news about anything, just trying to make sure Peter R doesn't make a decision without having all the information available to make the best one for him. The videos are informative and straight to the point. However, for all I know -- which isn't much! -- you can tinker with other variables (springs, rocker arms, and who knows what else?), to reduce the bouncing.

If Jim Comstock is going to go to the trouble of helping the collective by posting online videos showing the results of his testing, the least the rest of us can do is share it with others who may benefit from our doing so.

Jim also posted some JS2 cam results, which I have not watched, but I saw the titles listed while viewing the titles of the uploads in his youtube channel.

What I'd really like to know is how much a stock cam bounces when wound up to 7000 RPM -- when set up optimally.

There are a couple of Webcam grinds, 12 and 12A, that Jim Comstock discussed here, in this thread: cams-t12813.html . If those cams performed well in the Spintron testing, they would be what I'd be looking at, and probably the plain 12 and not the 12A.


How much does lightening the rocker arms help to prevent bouncing? If at all?

I had a D+ Norris cam in a bike years ago, and could never get the thing to run right. Wouldn't pull past about 6000 RPM's. I'd probably be dead now if it had, but it was a very disappointing and frustrating experience. One lobe was completely gone at 5000 miles after the rebuild. At the time, when I was trying to get it to run correctly, I considered lack of fuel, air, wrong mixture, and maybe considered the timing. Never thought about the compression, or that it might have been a head flow problem.

The fastest two Nortons I've ever ridden both had stock cams. Bike #1 was a 1970 Roadster, with a 19 tooth countershaft sprocket, and a single Mikuni. Don't know what intake manifold it had, although I don't think it was anything special. That bike had no problem pulling redline in 4th gear, which was an indicated 105mph. Very quick, too. The only area where a 19 tooth sprocket falls short is the increased revs at freeway cruising speeds. I think that bike had a Boyer in it. It belonged to a friend of mine. My brother had a MKIII with a single Mikuni, and that bike wouldn't go much faster than about 90. Was fine up to that speed, though.

Bike #2 was a low mileage 74 850, with a fresh valve job on a stock RH10 head (maybe milled 10 thousandths), sleeved Amal carburetors, Boyer ignition, 20 tooth countershaft sprocket, and 27 inch Dunstalls that had had all the internals removed. I wound that bike up to 7000 RPM in 4th gear just once, which it did surprisingly easy, resulting in 110 MPH being indicated on the speedo. The bike felt dangerously light at that speed, so I never attempted to ride it that fast again. There was no fairing on the bike, and it had euro style handlebars.



Here's a couple of links to a youtube video showing the bike with the D+ Norris cam in action vs. the 1970 Roadster mentioned above:

https://www.youtube.com/watch?v=Hr4rMneeR1Q

https://www.youtube.com/watch?v=lFTgeRNzUdc





.

The stock Norton cam or the Combat com do not have bounce problems with a stock valvetrain and fresh springs.

The Combat cam needs about .070 more preload on the stock springs or better springs. The stock springs sack out pretty quickly with the combat cam.

I have spun both to 7500 rpm. Jim

I think we should remember that Jim Comstock's work with the spintron was intended to inform choices for a motor running way beyond 7500rpm.

if you are building a road motor this isn't a real concern, PW3 designs will survive 7000rpm and be fun to ride if you have everything else set within useful parameters.

I am also of the opinion that the OP may well find that a stock cam in a well built motor can be a lot of fun too. Way way back I started racing with a stock cam in a 750. I had a lot of fun and achieved a National licence in my first season.

Thanks for your thoughts/opinions guys, much appreciated.
Al in all I am gravitating towards keeping the stock cam when rebuilding the engine.

Somebody on this forum verified my experience when I advanced my near-standard 850 cam by 12 degrees and got a major increase in torque.

acotrel said:

Somebody on this forum verified my experience when I advanced my near-standard 850 cam by 12 degrees and got a major increase in torque.

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I am sure I am not the one you speak of, but I advanced the JS1 10^ to attain awesome all around performance. This could have been a fluke or maybe a poorly cut keyway, but maybe not.

pete.v said:

acotrel said:

Somebody on this forum verified my experience when I advanced my near-standard 850 cam by 12 degrees and got a major increase in torque.

Click to expand...

I am sure I am not the one you speak of, but I advanced the JS1 10^ to attain awesome all around performance. This could have been a fluke or maybe a poorly cut keyway, but maybe not.

Click to expand...

Pete,

We decoded your cam timing previously at the link below, and you did in fact have one of the cams with the mis-located keyway, so that when you advanced it 10 degrees, the actual result was that you advanced the IN centerline from 105 to 103 deg, so 2 deg actual advance, which would make a great running machine.

http://www.accessnorton.com/radiused-cam-raced-years-bean-oil-t21574.html?hilit=pete.v js2#p282166

WZ507 said:

pete.v said:

acotrel said:

Somebody on this forum verified my experience when I advanced my near-standard 850 cam by 12 degrees and got a major increase in torque.

Click to expand...

I am sure I am not the one you speak of, but I advanced the JS1 10^ to attain awesome all around performance. This could have been a fluke or maybe a poorly cut keyway, but maybe not.

Click to expand...

Pete,

We decoded your cam timing previously at the link below, and you did in fact have one of the cams with the mis-located keyway, so that when you advanced it 10 degrees, the actual result was that you advanced the IN centerline from 105 to 103 deg, so 2 deg actual advance, which would make a great running machine.

http://www.accessnorton.com/radiused-cam-raced-years-bean-oil-t21574.html?hilit=pete.v js2#p282166

Click to expand...

2 degrees advance (instead of straight up timing which is equal lift of both symmetrical lobes at TDC) is the best way to go. Yes - some early cams had the keyway a little off as machined new by Megacycle so I sent out instructions with every cam describing a simple way to check the timing. I hassled and paid Megacycle extra to get them to correct the keyway location. I started checking every cam to verify that the keyway was correct. They are all correct now and I am getting cams from other cam grinders as well as Megacycle. Megacycle is the only US cam grinder that makes brand new Norton cams. Web cam requires cam cores. I found someone else to make new cams from billet as well but it takes longer to get them and you have to order large quantities.