Camshaft 850 stock vs. PW3

justin scroope said:

Thought I should mention my PW3 experience. Chilled cast iron PW3 cam purchased 8/1/2015 from Mick Hemmings, set at 145 thou lift of inlet pushrod at TDC, snapped in half adjacent to and inboard of the rev counter scroll after 15,ooo miles in an 850 mk 2. I also fitted a standard chilled cast iron camshaft purchased from Andover Norton 6/11/2012 which has worked well for 80,000 miles in a 1970 Fastback. Hope all goes well for you.

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That's interesting. I snapped a chilled cast iron camshaft tightening the nut up to the book torque of I think 40 ft lb. So don't go more than 20 ft lb and use red locktight. But you snapped it internal of the rev counter scroll. That is not good at all and there is not much you could do about that.

acadian said:

Also note that the values provided by the cam manufacturer are likely based on a specific follower profile, so using radiused lifters with a cam designed for flats will make anything but the lobe center values redundant

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Yes I assumed the OP was using standard flat followers. I didn't see any mention of radius followers. Sorry if I missed it.

The numbers are definitely based on the standard Commando flat followers

Equal lift on intake and exhaust 4 degrees btdc on the exhaust stroke works well.
This is also called the crossover point.
It's a simple way to do timing, provided you have dial indicators set up to register lift.

Glen

I did as was mentioned earlier in this topic and enlarged the lift curve provided by Joachim, then estimated IN lobe center using lift at 6 mm and 8mm and came up with IN centerlines of 96.5 and 97.0 respectively. To my eye this range of centerline appears well centered on the nose of the lift curve. The larger IN centerline numbers of 100 and 102 reported by others appear to my eye to be shifted well to the right of the center of the IN nose. We are assuming the cam is symmetrical to make any of these estimations, thus measurements at 2, 4, 6, and 8 mm lift should all provide essentially the same centerline. I guess the final arbiter here will be the operator reading the degree wheel on this specific engine.

With respect to Worntorn’s comment about x-over timing, we could also get a good look at that too from enlarging Joachim’s plot, but there was evidently an issue with data acquisition on the EX lobe closing side that rules out making an accurate estimate of where the x-over timing occurs.

The fitting instructions supplied with the camshaft by Andover are quite comprehensive, mentioning:
- 15ft/lbs max torque for the sprocket nut as the shaft is made from chilled iron casting
- chain tension
- opening/ closing timing
- checking clearance at pushrod tunnels and piston to valve
- checking valve spring coil bind
- etc.

I just went into my shed to check everything. The inlet lobe center is fully up at exactly 100 degress. I checked the degrees at 1mm before and after full lift and took the middle between these two degree values.




Then I moved the timing chain sprocket and the gears to move the valve timing further retard. I checked the timing of the inlet again, same method. Now the lober center is fully up at 105 degrees. 106 degrees is the correct value as per spec sheet.

Opening and closing timing measured:
Inlet opening: 47.5 BTDC (Andover spec: 50 degree BTDC)
Inlet closing: 81 BTDC (Andover spec: 82 degrees ABDC)
Exhaust opening: 84.5 BBDC (Andover spec: 84 degree BBDC)
Exhaust closing: 45 ATDC (Andover spec: 48 degrees ATDC)

All degree values measured at 0.011inch pushrod lift as per Andover instructions.

Moving the camshaft retard by 5 degrees gives me more clearance between inlet valve and piston:



Withoug gaskets used for the mock-up, I measure about 1.5mm clearance. I think its looking good now.

Thanks a lot for your comments everyone!

Sounds like you’ve nailed it.

It’s another lesson that these things should be checked!

I just went through the same exercise with a Steve Maney race cam. Like yours, from a reputable source and it SHOULD have just gone in on the marks.

I’m not sure, but I suspect both yours and my cam may be produced by the same manufacturer. Which might go some way to understand where, if not why, this error originated.

Opening and closing timing measured:
Inlet opening: 47.5 BTDC (Andover spec: 50 degree BTDC)
Inlet closing: 81 BTDC (Andover spec: 82 degrees ABDC)
Exhaust opening: 84.5 BBDC (Andover spec: 84 degree BBDC)
Exhaust closing: 45 ATDC (Andover spec: 48 degrees ATDC)

Still a bit disappointing the cam isn't perfect. I'm sure it will make no real world difference but still.

Changing your mufflers might make a bigger difference than changing your cam timing. When I had the cam reground for my 850, I did not care what it became within reason, because I knew that whatever it was, I could get it to work. All you really need is a cam which is not destructive. If the lift or closing rates are too swift or if it has too much lift, it can do damage. If you end up with a motor which produces decent torque, the rest is gearing and handling. Top end power is largely irrelevant, because you should not use Commandos for all-out drags down very long straights..

If you are using a new or reground cam, it is always wise to put plasticine in the valve cut-aways and turn the motor over. Then use a razor blade to section the plasticine to see how much valve clearance you have. Even with a standard exhaust system, I would advance the timings you have specified by about 5 degrees.

johnm said:

That's interesting. I snapped a chilled cast iron camshaft tightening the nut up to the book torque of I think 40 ft lb. So don't go more than 20 ft lb and use red locktight. But you snapped it internal of the rev counter scroll. That is not good at all and there is not much you could do about that.

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Old Britts list the camshaft nut at 80 ft/lbs!

• Camshaft sprocket nut (06-7774) 60 to 80 ft lb depending on cam metal.

http://www.oldbritts.com/n_torq.html

This version of the manual doesn't seem to list it. https://nortonownersvic.org/wp-cont...-norton-commando-service-manual-from-1970.pdf

I'm pretty sure that the one I have at home said 25 ft/lbs because I'm about to do and theses stories of broken cams is not reassuring.

Not that I trust the manuals, I mean they do say the MkIII cams are made out of cheese. But they don't say what kind of cheese.

I think @comnoz said something about parmesan.

swooshdave said:

Old Britts list the camshaft nut at 80 ft/lbs!

• Camshaft sprocket nut (06-7774) 60 to 80 ft lb depending on cam metal.

http://www.oldbritts.com/n_torq.html

This version of the manual doesn't seem to list it. https://nortonownersvic.org/wp-cont...-norton-commando-service-manual-from-1970.pdf

I'm pretty sure that the one I have at home said 25 ft/lbs because I'm about to do and theses stories of broken cams is not reassuring.

Not that I trust the manuals, I mean they do say the MkIII cams are made out of cheese. But they don't say what kind of cheese.

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None of the factory service manuals I looked at, from 1969 to 1975, give a torque spec for the camshaft nut. They just say to tighten it securely.

Also, they all, including the MK3 manual, list the camshaft material as EN32B, a common case hardening carbon steel. If the PW3 is a chilled cast iron cam instead, it might require a different torque value, but I don't know what it would be. I've always just used red Loctite on the nut and tightened it "securely".

Ken

Andover fitting instructions which came with the PW3 camshaft specify 15ft/lbs with Loctite for the sprocket nut and 4 ft/lbs for the contact breaker bolt.

lcrken said:

None of the factory service manuals I looked at, from 1969 to 1975, give a torque spec for the camshaft nut. They just say to tighten it securely.

Also, they all, including the MK3 manual, list the camshaft material as EN32B, a common case hardening carbon steel. If the PW3 is a chilled cast iron cam instead, it might require a different torque value, but I don't know what it would be. I've always just used red Loctite on the nut and tightened it "securely".

Ken

Click to expand...

All the PW 3 camshafts I have seen are chilled cast iron. - not carbon steel.

Do not tighten above 20 ft/lb and Andover say 15 ft/b. They will snap. I have personally done it. Use red loctite.

acotrel said:

Changing your mufflers might make a bigger difference than changing your cam timing. When I had the cam reground for my 850, I did not care what it became within reason, because I knew that whatever it was, I could get it to work. All you really need is a cam which is not destructive. If the lift or closing rates are too swift or if it has too much lift, it can do damage. If you end up with a motor which produces decent torque, the rest is gearing and handling. Top end power is largely irrelevant, because you should not use Commandos for all-out drags down very long straights..

If you are using a new or reground cam, it is always wise to put plasticine in the valve cut-aways and turn the motor over. Then use a razor blade to section the plasticine to see how much valve clearance you have. Even with a standard exhaust system, I would advance the timings you have specified by about 5 degrees.

Click to expand...

I agree on the exhaust and checking the valve clearance. I would add valve spring coil bind check as well

The thing is that any bike has to be tuned as a package. With the particular purpose in mind.

Nice easy tourer, open country bike, city bike, windy hilly road street bike, show pony, short track road racer, endurance racer etc etc etc. Plus you need to stay within the rules, street noise, race rules. Who is it for ? A young kid out to prove himself or an old bloke going for a quiet road. There is no one answer. Even on something as basic as gearing.

Advancing 5 deg over standard is an old racing rule. But I would personally hate it on a street bike.

I have talked to Peter Williams (PW) about this cam and why he designed it. He used a mainframe computer at Warwick university to do the cam dynamic calculations. Velocity, acceleration,jerk etc. Using computer modelling for cam design was pretty advanced for those days. His aim was to design a performance cam with good dynamics minimizing wear and valve instability. He discussed at lenght the experiments his dad Jack Williams did with the 7 R engine using strobe lights and film cameras to investigate the valve spring breakages on the 7 R. Cam design is much much more than opening and closing points. It all about stability of the full valve train. Read Gordon Blair - a friend of Jack Williams.

There are some people on this site that know an awful lot about this stuff ;-)

When I built my Seeley 850, I did not believe in it. But having raced it a few times in recent years, I am amazed at how good the 850 motor actually is, even when close to standard. Mine gets a gutful of methanol, but even so it is surprisingly good. My cam is close to standard 850, but the bike is quick enough to win against a lot of larger and carefully hopped-up race bikes. 'Torque wins races'. I just wish I had raced it when I first built it. In those days, it would have been outstanding, but we did not know. To me, it looked like it would blow up in it's first race. The only reason I raced my short stroke Triton for so long, was it had a billet crank and the motor was almost indestructible. Compared with the Seeley 850, it was a nightmare to ride.

Just a short update. I decided that the clearance between inlet valve and piston was not enough. As mentioned earlier I want to go up to about 9:1 compression which I want to achieve by not using a base gasket, 0.5mm copper head gasket and machining about 1mm off the head. So I decided to machine pockets into the pistons....now I have about 3mm clearance so heaps of space. Piston crown is still thick enough (hopefully).