Crank rotor scribed lines - are they TDC?

[Flatspot]

While my 74 850 is apart I’m doing several things at the same time, Electronic Ignition, Electric start, Cleaned carbs

my question is to do with the 2 scribed lines on the rotor, are they at TDC? Rotating the crankshaft with a spanner on the nut seems to show they are.

if so then it seems possible to use a protractor and then scribe a line on the stator at 31degrees for Pazon Surefire. Then rotate the crank back to the line so I can guesstimate the setting for the timing sensor. Too simple and I’ve got it wrong?

I think I’m giving myself a couple of headaches and a bit of Catch22 included, I need to setup the starter with the engine running, I need the ignition near enough so I can strobe it, and then I need those 2 done to set up the carbs so it will run - what can I get done first?

 

[maylar]

my question is to do with the 2 scribed lines on the rotor, are they at TDC?

Nope. Only when you set them to be with a degree wheel or dial gauge.

 

[L.A.B.]

my question is to do with the 2 scribed lines on the rotor, are they at TDC?

There is no corresponding fixed TDC mark to line either rotor mark up with (so any fixed TDC mark will be your own).

The (correct) rotor mark lines up with 28/31 (points/electronic ignition) degrees on the timing scale at full advance so a degree disc etc. is used to check the accuracy of the timing scale.

 

[Flatspot]

I’m struggling to do any joined up thinking today. I am failing to understand how to use a degree disc ( I do have one ) to determine either TDC or how to then determine of the timing scale is correct.
I’ll have a bite to eat, then interrogate YouTube to see if I can find someone to help me. My brain hurts

 

[joe czech]

if i'm understanding this post.... in theory and from what i remember -- i'm thinking they are supposed to be, but with tolerances and tolerance stack-up, who knows. seems to me, when the rotor's keyway slot on the end of the crank is at the 12 o'clk position, the pistons are also at TDC. the rotor's scribe marks should be at 12 and 6. no expert and somewhat of a norton novice, but the way i did it -- IMO, only true way is old school - with a degree wheel and piston stop. two direction measurement, and center the readings. doesn't hurt to repeat the procedure. once true TDC is established, easy enough using the degree wheel to find timing's BTDC mark, set the timing, and verify the scribe marks and the factory timing scale accuracy. finalize with a strobe.

 

[Mart UK]

Just for my understanding: Isn't the crank fixed in relation to TDC and the rotor is fixed by virtue of the Woodruff key? So, is the purpose of the timing disc to check the accuracy of the timing scale inside the outer case?

 

[L.A.B.]

when the rotor's keyway slot on the end of the crank is at the 12 o'clk position, the pistons are also at TDC. the rotor's scribe marks should be at 12 and 6.

When the Commando crank is at TDC, the rotor keyway is at approximately the 6.30 clock position.

ignition timing

Taking a second look at commando cranks.:(

www.accessnorton.com

If the same rotor mark is used as for normal ignition timing then it's the one opposite the rotor keyway slot.

 

[htown16]

I had a rotor where the outer part was loose on the inner. Not super loose but you could turn it at least a few degrees. It was on a Triumph. Later model Triumphs and BSA's have a notch on the flywheel that you can check with a special tool to verify crank position. On a Norton you are stuck with using a degree wheel. Best method is to use a piston stop and split the difference to get an acccurate tdc.

 

[Schwany]

Do what you are thinking of doing, it will be close enough to start the motor. Then finish the final fully advanced timing with it back together and fine tune the carburetion. Being a Mensa member is not required to get it done, and you can do it with that protractor, but you might not get very many Likes. he he

 

[marshg246]

While my 74 850 is apart I’m doing several things at the same time, Electronic Ignition, Electric start, Cleaned carbs

my question is to do with the 2 scribed lines on the rotor, are they at TDC? Rotating the crankshaft with a spanner on the nut seems to show they are.

if so then it seems possible to use a protractor and then scribe a line on the stator at 31degrees for Pazon Surefire. Then rotate the crank back to the line so I can guesstimate the setting for the timing sensor. Too simple and I’ve got it wrong?

I think I’m giving myself a couple of headaches and a bit of Catch22 included, I need to setup the starter with the engine running, I need the ignition near enough so I can strobe it, and then I need those 2 done to set up the carbs so it will run - what can I get done first?

Keep in mind that the rotor turns with the crank. One mark is the timing mark and the other is 180 degrees out. The rotors are not Norton-specific. The same rotors were used by other manufacturers.

 

[joe czech]

When the Commando crank is at TDC, the rotor keyway is at approximately the 6.30 clock position.

ignition timing

Taking a second look at commando cranks.:(

www.accessnorton.com

If the same rotor mark is used as for normal ignition timing then it's the one opposite the rotor keyway slot.

might be getting things mixed up a bit with the alton rotor - ???????

don't do this enough to remember from one day to another.

 

[Flatspot]

Right, it’s getting late and I’ve a belly full of BLT, and so I’m getting a bit tired.

Firstly, I’ve created a piston stop device from an emptied old spark plug and a rod I can’t lose when off TDC.

Then I’ve created a miniature degree disc that is slightly smaller diameter to the stator. I’ve backed a downloaded print onto a CD disc (Steppenwolf, Born To be Wild (get your motor running )

Now I can degree my rotor, and then scribe the stator at 31° I need to fit my new timing scale as the old one is nfg. Then I can check how accurate it is.

Now I can’t go any further as I can’t turn the crank without a clutch fitted.

a late edit - my initial quick look shows my upper and lower rotor lines at 12 and 6 almost exactly.

 

[Fast Eddie]

Cool, sounds like you’re getting there. Remember only one of the rotor marks will correspond with TDC, t’other is BDC. Good tip is to clearly paint the TDC one. You wouldn’t be the first person to time your motor cock on... but 180 degrees out...!

 

[L.A.B.]

might be getting things mixed up a bit with the alton rotor - ???????

Timing with the Alton rotor uses the normal timing scale as far as I'm aware, therefore, the rotor timing mark and the keyway must be in the same position as the Lucas rotor.

a late edit - my initial quick look shows my upper and lower rotor lines at 12 and 6 almost exactly.

Although of course, the Commando cylinders aren't vertical so the crank keyway isn't in line with either TDC or BDC.

 

[Flatspot]

Cool, sounds like you’re getting there. Remember only one of the rotor marks will correspond with TDC, t’other is BDC. Good tip is to clearly paint the TDC one. You wouldn’t be the first person to time your motor cock on... but 180 degrees out...!

OK.

 

[Flatspot]

Although of course, the Commando cylinders aren't vertical so the crank keyway isn't in line with either TDC or BDC.

I thought that a while after posting it. OK it’s perpendicular to the base of my lift when there’s 32psi in front tyre on a centrestand

 

[Time Warp]

My question is to do with the 2 scribed lines on the rotor, are they at TDC? Rotating the crankshaft with a spanner on the nut seems to show they are.

if so then it seems possible to use a protractor and then scribe a line on the stator at 31degrees for Pazon Surefire. Then rotate the crank back to the line so I can guesstimate the setting for the timing sensor. Too simple and I’ve got it wrong?

I found the stock degree plate (on the outer covers I have which might not account for much) to be fairly accurate (within 1.5°) but did not know that for a fact until I checked it.
I was only interested in a TDC while I was there and an actual 30° mark for the Pazon setting (over the recommended 31° give or take 1.5° based on the OEM scale)

I elected to use the positive stop marking the stator BTDC and ATDC then using those to mark the TDC in the mill with rotary table, then 5° graduations to 30° then a 32 °.

Drum brakes are Death man on that same day had mentioned using a dial gauge to set TDC so I wasted some time and set TDC with a micron dial gauge which was this inaccurate due to rock over TDC. (FWIW which would be nothing unless demented)

 

[Fast Eddie]

Its worth remembering that different people do recommend tweaking the ign figure a bit one way or t’other for better performance or to cope with modern fuels.

Moreover, every type of ign system on the market today has a different advance curve and many different points at which full advance is achieved, some not reaching full advance until 5,000rpm, some early Boyers allegedly just kept advancing!

So, basically, unless you fully study your advance curve, you’ve got no idea what you timing is below full advance at all, however accurate it’s set!

All I’m getting at here Landspeedracer is that whilst you should of course set things up as a accurately as you can, do not lose sleep over trying to get to within a few minutes of a degree. Frankly, these old motors don’t really care that much. Ensuring good, fat, powerful spark yields more dividends than chasing the last degree of accuracy in my experience.

 

[Time Warp]

The flip side might be plenty of folk have probably spent a small fortune on an engine then blindly hope (or more likely not even give it a thought) the stock degree plate is accurate when it might not be, I would hazard a guess many who go to the trouble of using a positive stop and degree wheel still do not check the ignition plate.

With a scale from TDC it would be very easy for me to plot at RPM the full curve to compare to what Pazon have on their website or at least what it is doing in the idle, off idle range for both cylinders (and up)

 

[B+Bogus]

I've found that the timing marks on the chaincase are quite often up to 5 degrees out, so checking manually is essential, IMHO