My first time with a timing light, can someone help me interpret?

  • Thread starter Thread starter Jamie
  • Start date Start date
J

Jamie

1987 740 GLE
B230F

I finally got my hands on a timing light to see if my timing was indeed
off and causing my lack of power.

I connected the light as per the instructions and let the motor reach
operating temperature. At normal idle the light hit about on the 10 --
off to the right of 0. I turned the throttle assembly slowly and the
light moved about 2 inches more to the right, then RPMs picked up and
the light then went off to the left as RPMs increased.

Did I do this right? At idle, where should the light be?

PS: I am not sure exactly what angle I need to be looking at the
hash-marks. I tried to look from different angles and I am convinced
the light is to the right of 0, nearest to the 10.


Thanks!
 
Jamie said:
1987 740 GLE
B230F

I finally got my hands on a timing light to see if my timing was indeed
off and causing my lack of power.

I connected the light as per the instructions and let the motor reach
operating temperature. At normal idle the light hit about on the 10 --
off to the right of 0. I turned the throttle assembly slowly and the
light moved about 2 inches more to the right, then RPMs picked up and
the light then went off to the left as RPMs increased.

Did I do this right? At idle, where should the light be?

PS: I am not sure exactly what angle I need to be looking at the
hash-marks. I tried to look from different angles and I am convinced
the light is to the right of 0, nearest to the 10.


Thanks!
Click to expand...

Looks about right. On my '93 240 the ignition timing spec in the
Bentley manual says 12 +/- 2 deg. BTC. When I checked my car it was at
about 10 at idle just like yours. You might be able to run a touch more
advance, but certainly your pictures don't show anything which would
explain poor running.

John
 
Here are the photos of the timing light. You can see the 10 mark
farthest on the right. Haynes says 12 degrees BTDC at 750rpm, which I
guess is Before Tap Dead Center. I am not sure what to make of this:

http://www.flickr.com/photo_zoom.gne?id=153341427&size=l

http://www.flickr.com/photo_zoom.gne?id=153341433&size=l

http://www.flickr.com/photo_zoom.gne?id=153341432&size=l

http://www.flickr.com/photo_zoom.gne?id=153341428&size=l
Click to expand...
At idle it should be about where you see it. When you accelerate the
motor from idle it should back up to about 5*BTDC then advance to about
30 something by 3000 RPM. If you remove the top cover section and shine
the light on the cam timing mark the dot on the cam should be a few
teeth to the left facing the motor.One tooth at idle, three plus teeth
at full advance.

If the motor really bogs when you put your foot in it off the line, and
takes throttle better when you let off or press the throttle gently to
accelerate, you've probably got a restricted catalytic converter or
something else restricting the exhaust. I forget why you had the motor
redone (and it looks like the guy did a very nice job) but if it was
spewing antifreeze, or oil, or raw fuel into the exhaust it doesn't take
long to trash an old converter.

Now as I said yesterday if you set the mark you're looking at in the
pictures to the zero mark on the outer timing cover and look down inside
the lower section at the crank pulley, the index marks inside there
should be aligned and the cam shaft pulley dot will either be aligned
with the top inner cover mark (#1 firing) or 180* away (#4 firing). If
it's on #4 then turn the motor through 360* one time and check the marks
again. If they don't align you've found the problem. Either the belt has
slipped, the roll pin in the cam has broken and the pulley has slipped
on the cam shaft, or the outer sheaves have turned on the crankshaft
hub.

Bob
 
Just curious, but is that 10 degrees advance, or 10 degrees retarded?

IOW, is there a 0 to the left of it, or a 20 (obscured, can't tell).
 
Thanks all!

The original mechanic insured me he carefully aligned all of the gears
and I guess after I pay a guy $130, he'll tell me if the marks are
still aligned.

BUT, the exhaust is in bad shape. The muffler broke off, so I taped it
back together at the pipe with aluminum tape. It shot black rusted
metal out when I patched it - but was quiet.

Yes, it used to spew oil splatters before I had the engine work done.

It still has an oil drip from the rear main seal after driving it, but
doesn't seem to do it in the driveway BEFORE driving.

Is there a way I can check to see if it's the catalytic converter? I
guess remove it? Will it have to be cut off?

Thanks!
 
What I may do is cut the exhaust just before the cat with my hacksaw,
run the engine and see what that does.

I can always use the same aluminum tape to put the pipe back together
until I get a new muffler.
 
Jamie said:
What I may do is cut the exhaust just before the cat with my hacksaw,
run the engine and see what that does.

I can always use the same aluminum tape to put the pipe back together
until I get a new muffler.
Click to expand...
A really quick and dirty (no fooling!) test is to loosen the collector
between the exhaust manifold and the exhaust pipe, then put your face to the
tail pipe and exhale hard. You should feel very little restriction. If you
feel back-pressure doing that your engine will certainly feel the same sort
of restrictions.

My limited experience with blocked exhaust is that the effect is more
obvious at full throttle; not much seems to happen between 1/2 throttle and
full throttle.

Mike
 
Jamie said:
Thanks all!

The original mechanic insured me he carefully aligned all of the gears
and I guess after I pay a guy $130, he'll tell me if the marks are
still aligned.

BUT, the exhaust is in bad shape. The muffler broke off, so I taped it
back together at the pipe with aluminum tape. It shot black rusted
metal out when I patched it - but was quiet.

Yes, it used to spew oil splatters before I had the engine work done.

It still has an oil drip from the rear main seal after driving it, but
doesn't seem to do it in the driveway BEFORE driving.

Is there a way I can check to see if it's the catalytic converter? I
guess remove it? Will it have to be cut off?

Thanks!
Click to expand...
Besides the quick and dirty test I mentioned before, the Haynes manual for
my daughter's Honda has a slick test using a manifold vacuum guage. Warm up
the engine and note the idle reading on the guage. Rev the engine to about
2000 rpm and let it stabilize, then watch the guage when you release the
throttle. If the guage drops quickly and returns to the idle reading within
2 seconds, the exhaust is clear. If the guage appears to hang for a moment
or very gradually returns to the idle reading it indicates blockage.

Mike
 
Ahhh -- I guess the logic in that is that by revving up the engine you
are creating a pressure against the exhaust restriction, and when you
let off, if there is an obstruction, the pressure will gradually
decrease as trapped air escapes.

If there is no blockage, there is no resistance and the air escapes
instantly.

hmmmm -- I have no gauge and not sure who in this little town would.
They might. I may have to opt for the exhaust disconnect test.

Thanks!
 
I went home at lunch and unbolted the catalytic converter and ran the
engine - it still hesitates and stalls when I pump the pedal.

I guess the catalytic converter can be ruled out.

I need to maybe revisit the AMM. I unplugged it and it started and then
stalled when I gave it gas. I really don't know how to test it besides
trying another AMM.

I guess I'll still have the full timing check performed next week.
 
I am rethinking the AMM and leaning away from it. When the car is
idling, I can easily rev the engine to high RPMS and hold it there.

The car starts fine
The car idles fine
Once I get into 3rd gear I can easily accelerate smoothly up to 75+ mph
and the car runs like a charm.

But, when I "bump" the accelerator at an idle, just a hair each time,
it stalls for a second or two in park or neutral. I can easily
accelerate "through" the stall and work the engine back up, but that
first 1/4 turn of the accelerator causes a dip, sometimes a sputter and
small backfire.

So, when I shift into drive, no power until around 3rd gear when I am
up to about 40 mph, then the engine starts to run just fine.
 
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