Simple question about setting timing

JFENG

JFENG

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On all my British cars you set timing at a specific idle rpm. Then you check advance at one or more higher RPM.

What’s the advantage of setting timing at higher engine speeds (1700, 1800 RPM)?
 
That’s when the mechanical advance is at its max.
you are checking your distributor for advance

o teeth is TDC
3-4 teeth Is idle
7 teeth is full mechanical advance

116 teeth on a flywheel
360~116 = 3.10* per tooth
In California We see flywheels often have 3 marks- TDC, idle and 1800 rpm (22*)
 
Also, there is a steel ball on my flywheel that aligned with the bell housing arrow at 1700rpm, with my timingnlight set to 0degrees.

Just for fun I advanced the timing light setting, and much to my surprise I saw a second steel timing ball appear at exactly 22 degrees (advanced). This is the mark SFDon just mentioned.

the BMW guys were nice enough to install markers for those with non adjustable timing strobes and another for those with an ‘advance style timing light. How considerate!
 
And so, you can set advance at idle or at the book speed of 1700. When I set it at 22 def advanced at 1700rpm (22deg ball), the 0 degree mark is aligned with the bellhousing market at 710 rpm.

Why doesn’t the book just say “set to 0 advance at 700rpm.” And make the 1700 a check of distributor advance mechanism?
 
I paint every single flywheel with 2 colors
first I set crank to TDC
There is a mark there and it’s get painted one color
i move the engine 7 teeth, I paint that marker the other color
i don’t paint idle marks
 
The "O" ball is the TDC ball, it comes into the window when the crank pulley lines up to the mark on the lower timing chain cover and rotor is over plug #1 (TDC). This I painted blue. The "Z" ball is the 22 degree advance ball and is used to set timing per the book. This I painted red. So if you set your timing to 22 @ 1700 with the timing light so that the Z ball shows, then set the advance function on light to 22, the O ball will show in the window. You can then see what your timing is at idle by the timing light advance function. Set the light back to zero then advance the light until the O ball is visible, this will be your idle timing. I am running 25 degrees advance at idle and 36 degrees all in with the triple Webers.

DIY - 123 Distributor Ignition Timing with Carburetors

I'm embarking into new territory regarding the potential of the 123 distributor that I think is being overlooked. I am no engine expert but from my research on the web (dangerous I know), that old school tuners used to set initial timing with a vacuum gauge and/or a "highest idle" procedure...
e9coupe.com e9coupe.com
 
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I put a timing mark on my balancer and a tab to match so I can see it readily. Watching thru a small hole in the bellhousing behind the carburetor for a BB to fly by at 90 mph seemed a little strange.

ih2XIOx.jpg
 
Stevehose said:
. I am running 25 degrees advance at idle and 36 degrees all in with the triple Webers.
Click to expand...

Steve,
I think you’ve done more creative stuff with timing than anyone outside of a race shop.
You are our resident timing guru.

After reading your posts on the subject I tried a bit more advance with the stock distributor. What is working well is 6degrees more advance than the book says (28 rather than 22 at 1700rpm). I just finished a 35 mile drive with long uphill highway sections where pinging is likely to happen. So far all seems well, and the car has noticeable more pep under both light and heavy throttle. I attribute this partly to the need for more advance since my carb setup is still a tad richer than desired at greater large throttle openings.

What is clear to me is the std timing is not optimal for my state of carb tuning and quality of gas (93 octane but with 10% ethanol) .

I stopped by the shop that does major race prep for me, and the mechanics all agreed that with modern gas older cars seem to be fine with significantly more advance, up to the low 30’s on some. But I didn’t have time to bump it up another 3-4 degrees. If I had a 123-tune it would be so much easier to optimize.

I’m deviating from the factory spec, which some might find distressing, but if it works better I don’t care

John

PS:
 
I'm just a blind squirrel on a quest for more nuts! If you're using the stock distibutor and you advance it 6 more degrees, then your all in timing will also be 6 more degrees which in theory could be a problem if you push it hard. The beauty of the 123 is that you can advance the timing at idle and mid rpm's which the M30 seems to love but still cap it at 36 or so to prevent blowing the engine up at high rpm under heavy load. Back in the day the idle timing was retarded to pass emissions, not for best performance, that efficiency can be recaptured by more advance early on. Increased idle rpm from adding advance proves this (until the engine says no). The 123 allows you to do all this without physically recurving the standard distributor with weights etc. to keep the all in advance out of the danger zone. All engines are different, each will tell you what it likes based on its internals and condition.
 
Steve,
I checked my +6 degrees by doing repeated long WOT’s in 5th gear up a hill (starting at 2500rpm). No pinging. I also did multiple hard accels they gears 1-2-3, and no pinging. So, I think it’s fine for now.

Of course when it’s mid summer and 95 degrees it could be different story.
 
@Stevehose What is the max total of mechanical plus initial advance on a stock distributor and at what RPM does it occur? How much advance does the vacuum advance add at light throttle cruise?

Thanks.
 
As a baseline perhaps also check your timing at 3500 rpm.

bfeng said:
Steve,
I checked my +6 degrees by doing repeated long WOT’s in 5th gear up a hill (starting at 2500rpm). No pinging. I also did multiple hard accels they gears 1-2-3, and no pinging. So, I think it’s fine for now.

Of course when it’s mid summer and 95 degrees it could be different story.
Click to expand...
 
Here's the data from the manual. I add 8 degrees vacuum advance for cruising.

Screen Shot 2020-10-14 at 7.08.53 PM.png



Dick Steinkamp said:
@Stevehose What is the max total of mechanical plus initial advance on a stock distributor and at what RPM does it occur? How much advance does the vacuum advance add at light throttle cruise?

Thanks.
Click to expand...
 
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31-35 total, which agrees with the race mechanic’s observations.

I will measure my total advance w/o vacuum advance at 3000 rpm when I have a chance. But for now I’m leaving it at +6.

Jaguar was nice enough to provide a vernier timing adjustment that facilitated easily repeatable offsets to timing without having to rotating the whole distributor. The original purpose was to adjust for variation in gasoline quality. I use it to dial in more advance for cold weather touring
 
Thanks, Steve. Makes perfect sense. With a stock engine and dizzy, 31-35 total initial plus mechanical, all in by 3,500, and another 12-16 vacuum advance at light throttle cruise.

These numbers are what I am used to seeing with most 60's/70's street engines. The only exception might be that total initial and mechanical is usually all in by 3,000 or earlier...but most older street engines don't spin like an M30 :)

I would guess you are only adding 8 vacuum because your mixture is a little richer at cruise than stock and you don't want to "light the fire" as early as you would with a stock engine and stock carbs?
 
I'm all in at 3k rpm. Yes I'm being conservative on the 8 degrees vac advance, I could go more but I am dubious if any cruise vac advance actually does anything for fuel economy when running 3 thirsty Webers.

Dick Steinkamp said:
Thanks, Steve. Makes perfect sense. With a stock engine and dizzy, 31-35 total initial plus mechanical, all in by 3,500, and another 12-16 vacuum advance at light throttle cruise.

These numbers are what I am used to seeing with most 60's/70's street engines. The only exception might be that total initial and mechanical is usually all in by 3,000 or earlier...but most older street engines don't spin like an M30 :)

I would guess you are only adding 8 vacuum because your mixture is a little richer at cruise than stock and you don't want to "light the fire" as early as you would with a stock engine and stock carbs?
Click to expand...
 
Stevehose said:
Here's the data from the manual. I add 8 degrees vacuum advance for cruising.

View attachment 103879
Click to expand...

my question:

so using an strobo lamp, two ways:


1- set the lamp at 0º. set 1700 rpms. = you see the ball in the window = 22º BTDC

2- set the lamp at 22º. set 1700 rpms = you see the O I T mark = 22º BTDC


if this is correct, then:

3- set the lamp at 32º (30 to 34º). set 3000 rpms = you see the O I T mark = 32 BTDC

is this correct ?
is there any other mark before the ball in the damper that shows 30 or 32 or 34 º , i dont think so

regards
 
Correct for the factory CS specs, if you don’t see the ball(s) then the distributor needs adjusting. #1 you would see the “Z” ball. CSi has a different spec.
 
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