Side Mount Advanced Timing

[TSnyder]

So as some of you know i have been working to get my freshly rebuild 8n up to par for a few weeks now on and off. It runs but hasn't run quiet right and lacks power. Also she can be corrected and runs smoother with the choke slightly pulled out. Regardless i don't have a timing light so my cousin headed on over this weekend to help me set the advanced timing on my sidemount 52 8n. I fired up the old girl (already had set the basic timing) and we had the light hooked up. We marked the flywheel on 0 degrees and proceeded to set the advanced timing (his light has degree ofset knob on the back of it). We started by setting the 400 RPM idle at 4 degrees (wasn't much off). Then we headed to the 1200 RPM speed and the timing advance was off... we set it there and moved to i believe 2000 or 2100 RPM and it again was off. There is a each time we moved to a different RPM the timing was off. I'm assuming this is due to bad cam weights or similar in the distributor. By the time we set the 2100 RPM timing and moved back down to 400 RPM to recheck it and see how much it was off it was 34 degrees! I seems bassackwards from what it should be... (advancing as the engine slows)... this is a bit screwy. I'm guessing i'm in for a distributor rebuild.

Any ideas? What all needs replaced?

Thanks, Tyler

 

[Bob]

1. With the initial timing set to 4º, WHAT was the total timing advance @ 2100 RPM's?

2. That being said, we had an incident a couple of years ago where someone had put a later (NAA) distributor cam and advance in an 8N distributor making it RETARD @ speed rather than advance. HOWEVER, that engine ran REALLY badly and I'm not yet convinced that has happened to your's.

 

[Dell (WA)]

Tyler........waddda ya know, yer timing changes everytime you change yer engine rpms. (shock!) Unfortunately it is NOT a linear relationship, that is what the automatic timing advance does. Set yer timing a 4*BTDC and don't mess with distributor again. Max advance is 17* at 1500rpms (I think); or a total of 13* from idle. (4 + 13 = 17) It should stay at 17* all the way to 2200rpms. .......Dell, yer self-appointed sparkie-meister

 

[TSnyder]

Dell, If you check your your manual there is a chart for the timing advance. I know and understand that the timing advances when the RPM speeds up... this is caused from the cam and weights in the distributor. I also know it isn't a linear relationship. The problem is, going by the chart in the manual it doesn't even come close to matching what is happening in my N. As i speed up, the spark doesn't advance correctly. I don't remember the exact amounts it did advance or retard so i'll have to write them down and get back to you.

 

[R Geiger]

Did you move the distributor to get the 4 degrees at 400 RPM? Don't quite understand the light you are using.
If you have 4 degrees at 400 RPM and the higher rpms do not fall in the specs, I would clean the flyweights and make sure they are moving. You should not have to reset the timing at the higer rpms, you're just checking to see if it is within the range on the chart. If not the mechanical advance is not working right.

 

[Anonymous-0]

Sounds to me like somebody needs to read timing light instructions!

 

[Jerry/MT]

You do know that the distributor has a advance weights and springs that advance the timing as the rpm increases don"t you? So when you set the timing at a speed somewhere slightly above idle, then you change the speed, the timing will change. that"s the way the centrifugal advance works. You set an initial point( 400 rpm) and the spring tension will determine the the timing at any other rpm.
You can change the advance curve (degrees of advance vs rpm)by changing the tension on the springs.

 

[Hobo,NC]

set the base somewhere around 4,5,6 degrees,,, go to WOT and check total,,, if around 17,18,19,20 lock'er down.... if you still need choke timing is not yer problem... i never worry much about the base i shot for the total...

BTW yer inductive light don't work well with copper core plug wires and non resistor plugs... It will jump all over the place,,, you gotta be good to time a N with one...

 

[Jerry/MT]

The advance system only increses and decreases timing from some fixed reference point based on the position of the distributor. It makes an incremental changes relative to the baseline reference point, nominally 400 rpm and 4°BTDC( example only). So if the advance at 1500 rpm is 15°, the the total advance is 15° + 4°= 19. When you now set the total advance to 19°@1500 rpm by rotating the distributor, you cranked an additional number of degrees of advance into the distributor, presumabley 15°. So the baseline timing changed. So your total advance is 34°. Now when you slow back down to 400 rpm idle, your timing will be at 19°BTDC. (I made up these numbers just to illustrate the point. I don"t want all the N gurus jumping up and down about what the real advance and intitial timing are.)
Some of these distributors have an advace curve that goes "flat) (becomes constant) after so many degrees of advance. In this case you can be even further off.

For the mathematically inclined, the total timing =(the initial timing) + d(advance)/d(rpm) X change in rpm from the reference.

d(advance)/d(rpm) is controlled by the springs and weights and the mechanism. The intial timing at the initial rpm are controlled by the mechanic setting the timing.

I hope you find this helpfull in understanding what you were trying to do and why it wasn"t working.

 

[TSnyder]

Jerry,

This makes perfect sense now. I did tear apart the distributor and am currently rebuilding it (the bushing in the bottom was shot and this wasn't helping the points gap or how it ran). When i go to retime it i will make sure i do the math. Thanks for the heads up!

Tyler

 

[Hobo,NC]

What you see is what you get you don't add nuttin to it... its stamped rite thar on the flywheel for all to see no math needed... plain and simple read the number that flashes before your eyes that align with the indicator...

Its a straight up mechanical advance nuttin you can split like a when a vacuum control is added to the mechanical advance even then total is total when all the stars in the universe align up just right what you see is what you get no math needed...

Maybe I don't understand your/his post but will take a shot at it,,, when you use a lite with a degree wheel you turn the wheel to find zero (no matter what RPM),,, you read the the degree wheel while keep'n the zero (TDC mark) aligned with the pointer (index mark)

 

[JMOR]

(quoted from post at 14:14:56 06/21/11)
What you see is what you get you don't add nuttin to it... its stamped rite thar on the flywheel for all to see no math needed... plain and simple read the number that flashes before your eyes that align with the indicator...

Its a straight up mechanical advance nuttin you can split like a when a vacuum control is added to the mechanical advance even then total is total when all the stars in the universe align up just right what you see is what you get no math needed...

Maybe I don't understand your/his post but will take a shot at it,,, when you use a lite with a degree wheel you turn the wheel to find zero (no matter what RPM),,, you read the the degree wheel while keep'n the zero (TDC mark) aligned with the pointer (index mark)

ep! probably like Josephpk said up above! :roll: