A question of timing.

I want to be sure I'm looking at this correctly. The Workshop manual states that there should be 10 rollers between the mark on the intermediate gear and the mark on the cam gear when the timing marks painted on the intermediate gear line up with the punch mark on the oil pump gear. The punch marks on the intermediate and cam gear are lined up with a tooth and not the valley. So, is the first roller to be counted to the right of the intermediate gear mark and the last roller to be counted to the left of the cam gear mark?

Secondly, if the above is correct, why would someone advance the cam by one tooth, assuming it was done on purpose.

6 links, 10 pins, count 'em.



Some people like to change the timing, but you better make sure what you're doing there, I chose not to do it.

Dave
69S

DogT said:

6 links, 10 pins, count 'em.

Some people like to change the timing, but you better make sure what you're doing there, I chose not to do it.

Dave
69S

Click to expand...

Thanks, that illustrates it much better than the Workshop manual. It appears mine is one tooth advanced and has been since before I got it. No wonder I've been fighting carb issues.

That is from the workshop manual, just an early one.

Dave
69S

DogT said:

That is from the workshop manual, just an early one.

Dave
69S

Click to expand...

Oh, I've never seen any other than the 73 version I guess. Any tips on getting the cam gear nut off? I was thinking of cutting a piece of mild steel and making a jam bar to bolt to the tensioner bolts. I understand that I shouldn't put too much pressure on the intermediate gear unless I find a way to support the outboard end of the gear shaft, and I don't have a cutaway cover.

Item 30 here? http://www.oldbritts.com/1971_g1.html

I don't remember having any problem removing that nut, but it may depend on what state your engine is in. Still got the primary drive on, just put a block of wood in the primary drive chain to keep it from turning. Or put it in gear if all is together, if not, I'm sure there are people here on the forum that will send you a 'holy' timing cover, I have one to loan if you'll pay postage. Best bet is a impact wrench, or just put a good 6 point socket on it and give it a whack with the rubber or hide mallet.

Dave
69S

Just a follow up, thanks for all the help. I got the valve timing reset to factory specs and the engine now revs like it should. I'm still at a loss to determine what the PO hoped to accomplish by advancing the cam, if it was on purpose.

It's nice to see a follow-up report with a positive result.

Fine tuning of the camshaft timing is an accepted tuning option. However it is best to stay with standard in my opinion unless you really understand what you are doing and complete a few checks.

Jumping one tooth on the cam sprocket make a difference of 40 deg in camshaft timing. Read the section half way down the page of this article to get a description of your options.

http://victorylibrary.com/brit/norton-c.htm

If the previous owner knew what he was doing he would not have just advanced the sprocket one tooth but will have also re indexed the intermdiate gear as described in this article.

On the other hand he may just have made a mistake ) The way you describe the performance improvement this may indeed be what he did.

For my race bike I always dial in the cam. That is when I buy a new cam I carefully measure the cam liming for all four lobes with a degree wheel and dial guage. This is a good way to check cam manufacturing quality and also what the quietening ramps are like to check the recomended tappet valve clearances.

What you may find is that if you install the cam just using the standard settings it may be 2 or 3 degrees advanced or delayed compared to the desiged specification.

2 or 3 degrees advanced is OK but delayed is not so great.

If you read the article you will see how to adjust the timing by reindexing the sprocket and intermediate gear. But I would not recomend this unless you have a good idea of what you are doing. I always go back to basics and work it out for myself because I have actually read another article where the description was exactly the wrong way round.

These little changes and many others added together are what make the differnce between a 45 bhp Commando and a 55 bhp Commando. Cam changes are usually best made together with exhaust and inlet tract tuning. Get it all right and you will have another 10 bhp.

Please note if you try this the CHECK the VALVE PISTON CLEARANCES.

john

Thanks, I see what can be accomplished with proper timing changes. All the PO did was rotate the cam sprocket one tooth counter clockwise, which if I read this correctly, advances the cam 20 degrees in relation to the crankshaft. Now that I've got it set back to factory specs I can go back to dialing in the carburetion.

cyclegeezer said:

Thanks, I see what can be accomplished with proper timing changes. All the PO did was rotate the cam sprocket one tooth counter clockwise, which if I read this correctly, advances the cam 20 degrees in relation to the crankshaft. Now that I've got it set back to factory specs I can go back to dialing in the carburetion.

Click to expand...

Wrong, one tooth on the cam=40 degrees.
As in,
-40(one cam tooth) +45(3 crank teeth)=5degrees advanced

Yes, go back to carbs now.I

Ludwig or anyone, have you advanced a 2S cam Combat for any improvement?
I tried to fiddle Ms Peels vernier cam adjuster but got confused and only got valve and piston clash on test turn so put it back straight up till more knowledge gained. In general advancing cam widens the power band while retarding tend to more max peak powerband.

ludwig recommended that I change the sprocket timing when I was rebuilding mine, but being old and stupid, I chose the path of least resistance and went with the factory setting. It's way past me.

Dave
69S

NOW , for the FIVE THOUSANTH TIME , this iconic device ran a 2S advanced aledgedly Five Degrees .



The Devious plot being I had been sold the Camshaft as a " 3S " ( oh Fudge ) .
After years of reasearch I had ascertained the " 3S " camshaft timing figures and proceedures .
With great skill , dexterity & patiance , it was set , and checked , and reset & checked . Then
the checking was checked. After that it was resett and fiqures checked . Then I checked the overlap.

Setting the thing wih the overlap about right , & early rather than late , I think I got it 3 Degrees advanced on the " 3S " INTAKE settings . Maybe .
anyway. iT WAS ONE LINK AND TWO TEETH OR WHATEVER , 15 DEGREES MINUS ten , TO GET FIVE , which was three , allowing for the two variation
and the fact that it wasnt actually the right timing specifications for that camshaft in the first place . :shock: :? :lol: Such are the vissisatudes of life.

So , the bars ard went like stink , dakka dakka dakka , Varrooom , Warp Factor NINE. Scotty . This was ascertained 10.000 later when I fittedA a STANDARD CAM

the little writeing , according to Sherlock Holmes , could not be ascertained AS OTHER THAN " s s " UNDER THE MICROSCOPE .Not the previous ' 3S ' as the dept. of wishfull thinking had implied .
Nevertheless , with the fancy carburators , at 4.000 rpms , warp drive was entered.ALSO the tendancy to ignor redline was more predominant with the std cam & clearances.Rather than the .016 3S clearances
I had used on the 2S / ' S S ' Combat ( black ) cam .So there we are . Now you know .Theres a thing . By Golly .More of a wind out powerband than a rally responce type , though I didnt make a habit of holding high rpms ordinarilly .Though theres the time . . . one being 11 miles in six minutes and not getting out of third ( 23 T gearing ) really , as it was ' a bit damp ' . so it was responceive at 4.000 +, just illegal in 3 gears .

Just to rub it in , heres another representing impecable taste . :lol: 8)

Oh, my, what a group of Nortons and old farts. Is that in NZ? It sort of looks like Austin.

Dave
69S

Yep , the ' West Island ' .


Bottom pic is Fredful's work .
post148958.html?hilit=long range fastback#p148958
I kinda thought it was Aus. what with all the Wine & getup .