Orientation of the advance unit

[narrow_monza]

Hello,

I'm about to start working on the ignition timing. My first basic question is about the orientation of the advance unit.
When installed, does the cam lobe supposed to be at the 2 o'clock position or the 8 o'clock position? (see attached photo).

Thanks

-Adrian

photo 2(5).JPG

photo 1(3).JPG

[DewCatTea-Bob]

[quote= narrow_monza ...
" I'm about to start working on the ignition timing. "

____ This reminds me of what the additional details were (which you may yet need to know about) concerning the use of the bridge-block circuit we were discussing within your other related thread...
I'll try to soon post the added info in THAT thread, later.



" about the orientation of the advance unit.
When installed, does the cam lobe supposed to be at the 2 o'clock position or the 8 o'clock position? "

____ When the piston is at power-stroke*TDC, then the points should be held as if just opened,, so that's nearest the 2-o'clock position !
(* You can determine ps.TDC by checking that the camshaft/bevel-gear timing-dots are aligned when you install the AAU with it's lift-ramp [of the points-cam] set near 3-o'clock.)



" (see attached photo). "

____ Which "photo" ? _ You haven't placed any file-comments below any of your three posted-pix.
Anyhow,, NONE of those three pix show the points-cam located in the correct TDC.position,,
so I must assume that your pic.shots were taken when the engine wasn't set right-at either TDC.position, and/or your camera's axis-shot was off-level to some degree, (which then pretty-much renders the pic.shots useless for O'CLOCK-readings) !


Hopeful-Cheers,
-Bob

[narrow_monza]

[quote= narrow_monza ...
" I'm about to start working on the ignition timing. "

____ This reminds me of what the additional details were (which you may yet need to know about) concerning the use of the bridge-block circuit we were discussing within your other related thread...
I'll try to soon post the added info in THAT thread, later.

" about the orientation of the advance unit.
When installed, does the cam lobe supposed to be at the 2 o'clock position or the 8 o'clock position? "

____ When the piston is at power-stroke*TDC, then the points should be held as if just opened,, so that's nearest the 2-o'clock position !
(* You can determine ps.TDC by checking that the camshaft/bevel-gear timing-dots are aligned when you install the AAU with it's lift-ramp [of the points-cam] set near 3-o'clock.)



" (see attached photo). "

____ Which "photo" ? _ You haven't placed any file-comments below any of your three posted-pix.
Anyhow,, NONE of those three pix show the points-cam located in the correct TDC.position,,
so I must assume that your pic.shots were taken when the engine wasn't set right-at either TDC.position, and/or your camera's axis-shot was off-level to some degree, (which then pretty-much renders the pic.shots useless for O'CLOCK-readings) !


Hopeful-Cheers,
-Bob

Hi Bob,

I went back and made sure the piston was at TDC and the points cam was about 2'oclock as you mentioned.
Also, at TDC, I set the points gap to .35mm.
For static timing, I checked that the points open up at an angle before TDC which falls in the range stated in the workshop manual (Advance with Engine Still = 21 to 23 degrees before TDC).
Do I also need to check the timing with the mechanism fully advanced as suggested in an article I read in the Tech section?

Thanks

-Adrian

[Nick]

Ultimately, the timing is correct when the bike runs best. If you don't have a degree wheel setup and strobe to check it when running, just advance it incrementally until you get kick-back when starting or until you notice detonation, then back it off a bit. Once you get to that point you know you're pretty close. From then on you can play with it until you find the sweet spot, or just leave it alone and ride the bike. Just keep an eye on the spark plug and make sure it looks okay (not grey!).

[DewCatTea-Bob]

[quote= narrow_monza ...
" I set the points gap to .35mm. "

____ Instead of setting the gap within the minimum-range of 12 to 14-thousandths, it's rather beneficial to set it nearer to the max.range of .018" to 20-thou). _ That way, when the gap has become worn-away & lost the 6-thou difference,, then only engine-performance will suffer, (without points-arcing taking any undue toll on point-contacts).
This thoughtful concern helps deal-with a wear-issue* which affects how much mileage can go between tune-ups, and most owners prefer to get the extra-mileage which the 6-thousandths (of extra cam-follower wear) will additionally provide.
(* The same wear-issue which the oiled felt attempts to reduce.)



" I checked that the points open up at an angle before TDC which falls in the range
21 to 23 degrees before TDC). "

____ That's indeed proper static-advance for the stock n-c.250-engines which don't employ a battery-powered ign.system, (Mr. "narrow_monza").
____ BTW, if you choose to include a diode within the ign.power-circuit, then you could rather make use of a 28-degree AAU, (without overheating the ign.coil).



" Do I also need to check the timing with the mechanism fully advanced as suggested in an article I read in the Tech section? "

____ If you've found the condition of your AAU to be unfrozen & freely/fully workable, then there's really no need to do-so, except just to confirm that you've correctly set the ign.timing properly.


Hopeful-Cheers,
-Bob

[narrow_monza]

[quote= narrow_monza ...
" I'm about to start working on the ignition timing. "

____ This reminds me of what the additional details were (which you may yet need to know about) concerning the use of the bridge-block circuit we were discussing within your other related thread...
I'll try to soon post the added info in THAT thread, later.

Hi Bob,
I just picked up a bridge-block to include in your suggested wiring scheme (my other thread).
You had some additional info you wanted to add?

Thanks

Adrian

[DewCatTea-Bob]

[quote= narrow_monza ...
" I just picked up a bridge-block to include in your suggested wiring scheme (my other thread).
You had some additional info you wanted to add? "

____ Yes, it has to do with 'ign.timing' (most related to the mag.rotor's phase-mounting position onto the crankshaft).
And I've wanted to include the extra info but, it seems I've needed just a little more motivation to excite me into actually getting-around to posting it. _ So I've been waiting to learn whether you actually intend to go-with the electrical-scheme that requires a pair of diodes (which are neatly contained within the rather easy to mount bridge-block).
__ I'll now soon post most of that info within your other thread, (since that's where it's already been established to be most related to).


Hopeful-Cheers,
-Bob