Another cam question 4s (2013)

lcrken said:

Jerry Doe said:

1) Wondering why my bike had a 4s cam? Did the factory use these? Something tells me they did not.

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Not unless someone really screwed up on the production line. Only production Commando engine with 4S was the short stroke 750. On the other hand, there are plenty of examples of Commandos with "wrong" parts coming out of the factory.

Ken

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Jerry,
You better get the micrometers out and see what it really measures up to be. It may not be a 4s anymore.

piting our scouring is the issue , it just looks the fairly normal ' not right across ' mateing .
The cylinder must be croked ( Just KIDDING ) .

WHAT ' one ' should LOOK at ( also ) is the Cam Follower mateing face . If these are pretty well fine , its pretty well fine .

A carefull light stoneing , without rocking , going down to 1200 wt. paper , on glass .So your actually POLISHING them , isnt a bad idea .
Same trick on the cam too , paper on a straight flat thing , kept dead square / flat . rolling cam as you go .

The 4S with decent valve springs , shimmed to +40 thou on lift . 34 mm carbs , and knocking the baffles out should see it chewing on H2s .
My humble opinion is the $s is the big base ( +20 thou heel ) 2S cam . Minus 20 thou on the heel . As in 2S lift profile +20 on the lift curve .
so with the overlap set about 3 - 4 deg btdc , and a kiwi Ign. that holds the advance down , you get a two stage cam .
You can be coarse 7 careless with the throttle below 3.000 rpm's .
above 3.500 you cant. above 4.000 its ' warp factor 6 scotty , if the throttle is on the stop . WFO is seldom required or used .
as ' count to ten ' & your doing 100 , if you dont forget to shift gear .

Can be a bit crankey & quick for in the city , but if youre touring / recreational rideing , and youd prefer a Spitfire to a Tiger Moth , go for it .

Std will pull better under 3000 , 4S cams up stonger past 4000 .Clutch gets vicious at 2000 , not quite sure what happens letting it in at 3000
but hang on tight if you try it . At about 40 with the 23 T. sprocket had to go for second to get sudden and serious acceleration .
Ran 32 Mk IIs , BSA Adv , 8.7 comp , 2S & W&S springs on the 750 . Told a XS 11 does 11s by a XSer , Told it wasnt as slow as the 11 others
( Commandos ) by the bloke that took it for a ' 20 minute ' :? . Not quite sure how far a experianced nortoneer
manadged , think it was 45 miles .

Jerry, RGM can repair or reprofile a cam and also nitride. this is considerably cheaper than buying a new unit. I have had them do a few for me now (standard core to 4S spec) and i am happy with the results.

Says it a new cam so no regrind needed but then why bother asking for opinions from revealing photo's.

General random online samples of cam lobe photo finishes







And one that's got a familiar looking lobe with one that's done for.


Thanx for altering me RGM is able to restore cams cost effectively.

Just to add my two cents .....
I had some stock cams made for me at Johnson cams and they advised the stock Norton cam profile was machined to spec,
however, the keyway was not located to spec. I put the degree wheel on three stock cams and all of them were out by four or five degrees confirming what Johnson cams had advised. The new stock profile cam was set with a vernier cam sprocket (from RPM Motors) to the factory specs and the subsequent improvement in performance was substantial. The Megacycle 560 NR was measured and was found to be dead nuts on.
Learn how to degree a cam and use the vernier sprocket in your assembly.

hobot said:

... one that's got a familiar looking lobe with one that's done for.

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That's the one.

There has also been a photo of one with multiple trashed lobes...

norsa1 said:

Just to add my two cents .....
I had some stock cams made for me at Johnson cams and they advised the stock Norton cam profile was machined to spec,
however, the keyway was not located to spec. I put the degree wheel on three stock cams and all of them were out by four or five degrees confirming what Johnson cams had advised. The new stock profile cam was set with a vernier cam sprocket (from RPM Motors) to the factory specs and the subsequent improvement in performance was substantial. The Megacycle 560 NR was measured and was found to be dead nuts on.
Learn how to degree a cam and use the vernier sprocket in your assembly.

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As if it isn't bad enough that I lie awake at night wondering if my cam is hard enough, now I have to worry about whether the keyway was cut accurately too? "Oh spirits! Why do you torment me so?"

Here is an impromptu poll: How many of you have put a degree wheel on your stock cam and found it to be out of spec? How many have found it to be in spec? How many have never done it at all and are driving around wondering why it is so hard to get the timing set? Just curious.

Russ

Good question. I time all my race cams with a degree wheel on the crankshaft and dial indicator on a lifter, but have never checked a stock Commando cam. I have checked both a 2S and a 4S factory camshaft, and both were within 0.5 degrees of the specified timing when installed with stock timing gears and keys. For the race cams, I normally have to use either vernier sprockets, stock sprockets with additional keyways cut, or custom made offset camshaft keys to get the timing where I want it.

Ken

I've rarely masured a cam, auto or motorcycle that was at factory specs. I once measured the cam on a 4 cyl Kawasaki that did'nt run quite right, it was 10 deg off and had never been apart.

I rebuilt a BSA 441 Victor engine awhile back, it's cam was on the money. You have to check them.

If you run it at 5000 rpm half throttle in second , and snap the throttle shut then full ,it lifts , and the front stays up on the shift to third ,
IT's ON SPEC . !

...."If you run it at 5000 rpm half throttle in second , and snap the throttle shut then full ,it lifts , and the front stays up on the shift to third ,
IT's ON SPEC ."........sounds like fun Matt.........Jerry just bite the bullet and shop for radius cam and followers from JSmotorsports and get the push rods to go with them, oh and get the lightweight pistons and longer rods too......go on you know you want to,,,,,I love spending other peoples money

The PW3 cam from Mick Hemmings is meant to be excellent, but you will need to relieve the engine cases to allow enough clearance. I have just fitted one to an engine but I haven't finished the bike to try it yet. But if you're going back to a standard cam, why not get the genuine item from Andover Norton, then you know it's right. The new cams have wider lobes than they used to be.

I am going to put a standard cam in. I always use a degree wheel and dial gauge. On my MK2 valve timing was right on the money. I agree that you have to check it. I hope this bike will be ok as I heard bad things about vernier cam sprockets. I think they are the ones that auto adjust the chain right?

Anyone need a 4s cam?

cheers- Jerry

Jerry Doe said:

as I heard bad things about vernier cam sprockets. I think they are the ones that auto adjust the chain right?

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OK, I'll bite. Anyone care to expound a little more about the vernier cam sprockets. Herb Becker discouraged their use but I thought for other reasons.

And cjandme is probably right, at least about the light weight pistons, longer rods and loving to spend other peoples money. I have no horse in this race but since you have the cases open, pefect time to reduce reciprocating mass.

I would love to get those engine parts. The thing is $. I have already spent thousands on MK3 rebuild. At this time based upon past experience I am very happy with standard performance and minor motor modifications. I think a well built commando motor will do me. I have some mods I am doing for sure; that need doing:

1) head 40 thou skim, black valves etc..
2) Tri spark
3) hydraulic clutch
4) Quaiffe GB shell
5) Better starter motor and wires
6) Premier carbs
7) head steady

I already have my new pistons and already have new super blends on crank. There are more mods I am doing, but nothing that major. Now a days I just plod about at 70 or 80 MPH everywhere. I had my MK2 tuned before last rebuild and it ran really well. De-tuning it was best thing I did. I know they are more reliable with JS parts, but I simply cannot afford it. I am probably going to sell my MK2 soon to help pay for some parts anyway and get another bike with ES (Triumph) as my back is bad and I cannot start my MK2 easily these days. Mk2 is one sorted commando - going to teach girl friend how to start it is the other option

Ms Peel ran a vernier cam sprocket to find after her stuck open throttle wipe out the peg in the adjuster had beaten its self a bit silly and had almost backed out of its hole which would or destroyed engine head to cases - with valve and piston clash, instead of just bending crank some and messing up the stuff on either end of the crank, but not so bad as I got another 2000 miles out of her before deciding a whole new once in a life time [for me] money and mind sucker. I may re-use the vernier for a while to dial in cam degree, then remove and do the key way+ cog teeth alignment method for long term safety and bit lighter spinning element. I like its holey appearance that matches rest of Peel's style but unless I can figure out a way to fix the pin in place for all the heat and cyclic jerking vibration, I can see why Herb Becker is down on them.

If was my cam in this instant case I'd have it cryogenic tempered, nitrided then micro-polished, which would cost more in time delay than money out lay. I could of had Peel going years ago with her very potent accidental Combat engine set up - but decided she was my last opportunity for a dream machine so spending and processing her as I can - with constant set backs d/t life's surprises - but committed not to compromise spending on anything till she's done or I am.

Ya know, what is now concidered the standard profile used to be the race cam.

I think I read that some where.

That's the beauty of a Norton twin. The cylinder head flows so well it does not usually take much to get good reliable performance out of the motor.

Thin head gasket and open pipes, otherwise standard mk3 850, works for me. My son-in-law has had some sport bikes and dirt bikes but still raves about the Norton.
First time on it, he pinned the throttle with the engine not fully warmed. It gave a cough, then caught. I watched as the bike nearly shot out from under him. Guess he wasn't expecting that from an old bike!
I'm with Jerry, the stock or near stock Commando was already a great performer. The best part of the 850 engine is the great linear torque band which starts down very low. I would never trade that for a bit more top end,not on a road bike.

Glen

pvisseriii said:

Ya know, what is now concidered the standard profile used to be the race cam.

I think I read that some where.

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The standard Commando cam is the same profile that was used in the Dominator SS, and was considered a pretty sporty cam at the time.

Ken