Ignition woes

[oscar]

I'm after a bit of advice and have a few Q's.  '73 350se d-jetronic.

Firstly, where do you aim a timing light. I can see markings on the crankshaft but I can't see the plate or pointer on the block for referencing timing?

Secondly, aiming at a spot on the left where I could see the shaft I noticed that the shaft appeared in roughly the same spot but was erratic, ie went backwards and forwards.  What does this mean?  BTW, this is with all 8 cylinders firing.

Thirdly, a few days ago, the car was running on 7 then 6 cylinders.  Battery, injectors, plugs, leads Ok. Problem cylinders 1&7

My next discovery had me baffled.  With the motor running I discovered that when I slowly put the lead back on the #7 spark plug it would fire then die when the lead was pushed fully onto the spark plug.  About 1/2" off pushing the lead all the way onto the spark plug would see the cylinder coming back to life.   Now these leads seem in good nick but I replaced it with a silicone lead and converted a new plug and the distributor terminal to a push-on type nipple. 

Problem solved,,,, sort of.  Before I did the #1 cylinder a workshop mechanic came by and said about the leads are like old Honda leads but the problem was with the spark plug.  Sure enough, changed, #1 spark plug, used the old lead and I'm back with 8 cylinders thumping away with that nice tone eminating fom the exhaust 

So is it plugs or leads?  What have you got?
Old plugs, Bosch W8DC, German, good nick, 6months old 2-3000km at most, look undamaged.  Only 2 have been replaced
New plugs, NGK BP6ES, Japanese.

Leads are all Bosch threaded type with 1kohm resistors apart from#6 which has a 5kohm resistor.

[oscar]

Hi styria,

The problem leads were mainly the four on the R side that deteriorated after being covered in brake fluid when the master cylinder failed.  The four replacements were from a donor car that my mechanic had laying around.  I'm not ruling out new leads just yet, I just can't believe that all 8 are now firing with the same leads but new plugs of a different type are in #'s 1 & 7.

Any idea on the erratic timing and where to point the timing light?  The back and forth appearance of the crankshaft differs by around one cm.  Another look today and I still can't find the reference pointer on the block.

[s class]

Oscar,

On my M117 which I presume will be the same as the M116, I point the timing light down at the right hand side of the front of the motor (as I stand in front of the car looking at the engine).  There is a metal "peg" sticking out just above the vibration damper which I align the timing marks to.

In terms of the timing oscillating around, this is actually quite normal on older engines, and is due to wear in the distributor, erratic operation with the crank position sensor, and uneven firing strength between the various cylinders.  In fact, getting a stable idle timing on an older engine is nearly impossible. 

I would say that in your case, with your odd mixture of ignition leads and spark plugs, you are almost certainly not getting even spark performance across all cylinders, even if they are all running.  I think that once you get your firing issues sorted, the timing stability will improve.

Ryan

[oscar]

Your both right I feel.  Don't know about the baseplate yet, something else I'll have to investigate.
I have a thing for Bosch.  I have Bosch power tools and my leads are bosch and I'm disappointed to have put 2 NGK plugs in. The engine's running qutie well at the moment, starting well even in the sub zero temps we're experiencing at the moment. But it's not quite right IMO. 

There's improvements to the igniton system to be made which is routine maintenance really.  Now I believe it is leads and the distributor needs seeing to.  I can't measure dwell angle (yet) without a meter.  I'll be busy at work with a lot of study to be done in the next 3-4 weeks.  A little while after that I have two weeks holidays with which I'll tackle this issue with a bit more gusto.  New points, leads and pull the distributor and give it a good clean.  There's a lot of junk on the baseplate.  I'm guessing the slide tray for the FI points are a bit scrappy too.

Keep any suggestions coming, I have a bit more reading to do before I check all this.  I'll have another look for the timing pointer on the block ryan.  Thanks for the tip.  I hope it hasn't broken off.  I found a line drawing of it in my Haynes manual, so I think I know what I'm looking for.  We'll see.