Jump to content

- - - - -

another?! timing and dwell questions

  • Please log in to reply
12 replies to this topic

#1 AlaskaMike


Posted 06 December 2008 - 01:37 AM

The dwell tester I have has two jumpers, a black wire and a green wire. I do not have instructions. As I understand the black goes to the chassis and the green goes to the negative side of the coil. Sound correct?

To measure dwell, do you run the car warmed up and with the vacuum advance hooked up on the distributor to observe the dwell measurement? - OR -
It doesn't matter because its measuring the percentage of time the points are closed - and that doesnt change based on engine temperature or vacuum advance?


The often posted graphics say to run the engine at 1400 rpms with vacuum advance disconnected. How do I dial in 1400 rpms? Do I do this on the SOLEX DIDTA?

Replaced all the ignition stuff and my brother picked his favorite timing by ear. The car easily dies below 1200 rpm, diesels when shut off, but is a lot of fun above 2000 RPM.


#2 fwardell


Posted 06 December 2008 - 05:06 AM

Hey there, I see you're having fun with that new '02! I wouldn't fool around with the dwell measurement myself - just set the points properly. Of course, it would be nice to KNOW the dwell is correct. I'm thinking the green is ground and the black should go to #1 spark plug wire similar to setting the timing, but don't do that without some further verification.For timing, warm up the engine to operating temp, remove and plug the distributor advance hose, run the rpm to 1400 like you said. One good way is to simply turn the idle speed screw (not mixture!) on the Solex until you get 1400 on the tach - my preference. Or have someone in the car do it with the gas pedal.

Valve adjustments are probably next on your list. Go to FAQ - Engine & Drivetrain - Valve Adjustment for BMW M10 Engine by Sam shultz.

Be sure and put that Haynes manual on your Christmas list!

1976 2002 Inka

2008 M5 Sapphire Black Metallic, 6-speed

#3 jimk


Posted 06 December 2008 - 06:47 AM

You are on the right track. Just try the meter leads as you say, if it doesn't read, swap them. It doesn't hurt anything if they are incorrect. DO NOT CONNECT TO A SPARK PLUG or it will blow your meter. You are measuring the degree turn of the distr cam when the points are closed. It is much more accurate than the feeler gauge method. The feeler gauge method gap is just a result of the correct dwell. Dwell is really the result of the minimum coll charge time at the highest rpm + some margin of time. Usually this is around 2.5-2.5 milliseconds. So just for fun, calculate the time it takes at 6500 rpm for the distr cam to turn for the dwell degrees and it will fall in that time frame. Different coils require different time.

The reason your engine runs-on after key off is that the timing is probably late and so the carb idle speed setting has been open a more to keep the idle speed up (or the idle speed is too fast right now). This gives too much air flow and when you key off, it trys to run without spartk. Set the timing right and reset the idle speed and the run-on should go away.

#4 c.d.iesel


Posted 06 December 2008 - 07:30 AM

DWELL does matter .

a noticable crispness to the performance when points
set by this method vs 0.016: feeler gauge method.

Performance is optimized because of optimum coil saturation between
spark firings - Doesn't matter which coil you use .
Go with a DWELL reading of 60 degrees, THEN set the
ignition timing.
Changing dwell/point gap will change yout timing.
Dwell must be correct before timing check

Special 'point cam grease' also prevents point cam lobe wear,
and point rubbing block wear. Point Cam grease from DELCO,
or BOSCH - many on-line sources. And a few drops of your
motor oil under the tiny felt pad in the center of the distributor shaft,
under the rotor. wiggle and rotate the shaft to work the oil down
into the mechanical advance (this is just as important if you have
points OR Pertronix electronics) the mechanical advance still
needs lubrication to advance/retard smoothly.

also find point cam grease at NAPA - or other parts stores

Mallory Point Grease
Posted Image

and BOSCH - 1 tube will last you a life-time
Posted Image

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

#5 tjones02

tjones02 Garage View Garage

Posted 06 December 2008 - 07:54 AM

What C.D. said... I second that.

Here's the Bosch Distributor Lube. Bosch part number 5 700 002 005
Posted Image

And a place that sells it... E-German Parts... http://www.egermanparts.com/

I'm still using the same tube that I bought over 15 years ago as an apprentice mechanic; they last a lifetime. :)

Key words: grease, points, dwell, timing, tube, cam

Tom Jones

Wrenches for Casey MotorSports in Petaluma CA
66 BMW16oo stored, 67 1600-2 lifelong project, 2 more 67-8 1600s, 86 528e 5sp 495k, 86 528eA Rosee's
Mom&Dad's, 65 1800TiSA, 70 2800, 72 2002Tii 2760007 orig owners, 03 325iT, 12 328iT

#6 quinnfiske


Posted 06 December 2008 - 11:21 AM

Just to chime in with some other points... The timing and dwell are not temperature dependent. Unlike modern cars, these old machines do not have a temperature feedback function.

The points gap is simply a different way of expressing dwell. They are the same thing. With a deft touch you can set the points gap and check it with a dwell meter.

The timing will affect idle speed. I turn up the idle speed screw to get to 1400 RPM, then set the timing. Then reset the idle speed to 1400 again. Then check the timing again. Finally rest the idle speed to what you want it to be.
I first owned a 2002 in 1975.

#7 ThatGuy


Posted 06 December 2008 - 12:51 PM

Just point out something interesting I found out, when the engine runs on after shutting it off, it's turning backwards.

Don't know why.
71, flat black
Beat to fit, paint to match.

Do what you love and you'll never work a day in your life.

"Some people spend a lifetime wondering if they made a difference, Marines don't have that problem" - Ronald Reagan

#8 c.d.iesel


Posted 06 December 2008 - 01:28 PM

.... " Just point out something interesting I found
out, when the engine runs on after shutting it
off, it's turning backwards.
Don't know why. ""

yes - and dat's not good for timing chains and
weak timing chain tensioners - that negative behavior
could be very BAD!! Fix cause A.S.A.P.

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

#9 AlaskaMike


Posted 06 December 2008 - 04:10 PM

I understand that I dont have an idle speed screw on the Solex DIDTA ... just a throttle, and an idle mixture. So I should use the throttle to bring it up to 1400 I assume.

Thanks for the tips!

#10 c.d.iesel


Posted 06 December 2008 - 07:01 PM

you do have an IDLE SPEED SCREW :

Posted Image

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

#11 AlaskaMike


Posted 07 December 2008 - 02:38 AM

Thank you that is the best diagram I have found for it now.

#12 Guest_Anonymous_*


Posted 07 December 2008 - 08:31 AM

I don't believe its always true that engine run on means the engine runs backward, but does it really matter? "Run on" can cause the engine to rotate clockwise or counterclockwise.

It does not take a genius to conclude the presence of residual fuel and a source of ignition (aberrant spark, glowing carbon particle, super high compression e.g. diesel effect) may cause the engine may continue to run. This is rarely a good thing, but particularly bad if it upsets wear patterns. Mechanical damage can occur when the engine turns without oil pressure since the oil pump function is now reversed.

Idle cut off solenoids found in most carburettors used on the M10 are designed specifically to eliminate the source of fuel and to prevent the run on you described.

#13 c.d.iesel


Posted 07 December 2008 - 10:10 AM

....." Thank you that is the best diagram
I have found for it now " .

Welcome - just turn to PAGE 70 in your BMW Owner's handbook

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"