Check ignition point

[Jan S]

1977 M100 6.9 USA version

I'm about to check the ignition point. Is the "needle" in pic the measuring point? Or have I misunderstood?

[daantjie]

Indeed

[Jan S]

Thanks, daantjie!

[goldacre]

Get the timing instructions off the Library as it's checked at three positions, idle, 1500rpm and 3000rpm and each has its specific degrees. When I did mine at idle to '0' degrees it was then 4 degrees out at 1500 and 3000 rpm so my initial at '0' degrees idle was advanced to 4 degrees thus my 1500 and 3000 rpm was spot on which is where our engines run most of the time.

Pull rotor off shaft in distributor and there should be a felt pad in there, a few drops of sewing machine oil or as many mechanics did, used the trans dip stick to drop in the trans fluid off it :/ your call. Over time the throw weights can stick together and the springs wear.

The manual says to leave vacuum lines on from memory but the Haynes manual says to leave off, the tech manual in the Library has it all listed but you need to read the whole Doc to get head around it, also if you have AC...

JG

[Jan S]

Thanks for tips, goldacre!

I checked the timing tonight. At idle 900 rpm timing showed 5 degrees to the right of TDC. I assume the engine turns clockwise, hence this is 5 deg before TDC, i.e. advanced, right?

(Idle should be 600 rpm for a 1977 USA 100.985. When I replace the thermostat the cooling water will go from current 55 deg C to spec 87 deg C and the aux air valve will fully close and idle will hopefully get close to 600 rpm. A lot of ifs here  )

The only manual I found is this: https://handbook.w116.org/cd/Maintenance/My72/772.pdf

Idle says ignition TDC with vacuum. No information regarding 1500 and 3000 rpm? Am I overlooking something?

Do the spec depend on fuel? My engine run on unleaded 95 octane.

[UTn_boy]

There are four or five different sets of ignition timing specs for the 6.9.  We need to know if your 6.9 engine was originally out of a Euro car, Australian, Japanese, U.S, or Swedish car. 

[Jan S]

The car itself is a 1975 US-version 450 SE (116.032), originally with AC version 1 and engine 117.983
The current engine in the car is 1977 US-version 100.985 (engine upgrade done by one of the previous owners)

I would say the engine upgrade job is "halfway done", or let's say it could have been better .... e.g. AC is not reinstalled, windscreen washer system not installed ... and the list goes on I guess.

It's an fairly "stripped" engine and engine room compared to a standard 6.9 I would say.

[goldacre]

Hi Jan S, did not realise you had the 6.9, my bad :/

Will dig out the pdf for my 4.5 litre 450SEL spec but it's on my Uni computer I think my cousin borrowed:(

They have alot of 6.9 specific and combined docs so have to scour around to find info...



JG

[Jan S]

Thanks for helping out, goldacre!

[Jan S]

Got this information from a forum friend in Norway. Text is in Swedish.

Engine: 1977 USA 100.985 i.e. 6.9

My understanding of the procedure is:

- At idle 800 rpms with vacuum is TDC (this is referred to as "when adjusting")
- At idle 800 rpms without vacuum is 7 degrees before TDC (this is referred to as "when assembling")
- At 1500 rpms without vacuum is 9-16 degrees before TDC
- At 3500 rpms without vacuum is 27-33 degrees before TDC

So, procedure is to check timing in that sequence? Sounds ok?

I measured timing yesterday at 900 rpms ..... 5 degrees before TDC (5 degrees to the right of 0 degrees on the disc, I assume it's before)

[goldacre]

Wow, quite a range of degrees at 1500 and 3500rpm. But yes in that order.

When we did mine each time the timing was adjusted the idle would shift so its back and forth, use a precision guage for the rpms not the car tachometer, you can buy a really flash strobe light that can do all that and even show you the degrees digitally, my brother in law has one and its amazing.

Once you have idle and rpm sorted check 1500 and then 3500rpm degrees and if they are out of spec go back to idle degrees and adjust to compensate. If 1500 and 3500 are all over the place the innards of the distributor like springs are faulty and/or the weights could be gummed up if not lubed often enough 

JG

PS: the manual will give you specifics but timing is a true art and you will feel and hear the car settle when you get close to but with some needed compensation for an old car, a Swiss Mechanic in Perth told me this and he is brilliant, knows all the European cars, very intuitive to which is a blessing in a mechanic, by the time you drive Into his workshop he already has a good idea where to look and what's wrong 

[raueda1]

Wow, quite a range of degrees at 1500 and 3500rpm. But yes in that order.

When we did mine each time the timing was adjusted the idle would shift so its back and forth, use a precision guage for the rpms not the car tachometer, you can buy a really flash strobe light that can do all that and even show you the degrees digitally, my brother in law has one and its amazing.

Once you have idle and rpm sorted check 1500 and then 3500rpm degrees and if they are out of spec go back to idle degrees and adjust to compensate. If 1500 and 3500 are all over the place the innards of the distributor like springs are faulty and/or the weights could be gummed up if not lubed ofter enough 

JG

PS: the manual will give you specifics but timing is a true art and you will feel and hear the car settle when you get close to but with some needed compensation for an old car, a Swiss Mechanic in Perth told me this and he is brilliant, knows all the European cars, very intuitive to which is a blessing in a mechanic, by the time you drive I to his workshop he already has a good idea where to look and what's wrong 

I suspect that this is a common situation.  If it seems hard to get consistent readings try rebuilding the distributor.  "Rebuilding" in this case is really just a total teardown and cleaning of the distributor innards.  Eventually the lubrication hardens into glue and gums it all up.  Do a search, there's a detailed thread on the topic.  I did it and it made a world of difference.  Cheers,

[goldacre]

Indeed  the next step in progressive diagnostics. My brother in law came across a rare distributor for a sports Holden (186S) people said had failed, he took it out the bin and went home with it and pulled it apart and as raueda1 says the weights, I this case, were lightly  rusted together! So polished them up and lubed it and this is where I learnt the purpose of the felt pad inside the top of the distributor shaft under the rotor and the ATF trick, I prefer sewing machine oil myself, you don't need much but it's a serviceable item so I do when doing oil changes.

Another test is get a length of vacuum line and place onto vacuum advance and retard devices and give a gentle suck and hold it at vacuum with your tongue, if it holds good, if not the diaphragm has failed.

A good example of this fault is when starting off from a stop and the engine hesitates slightly, more so in basic everyday cars with carbies not sure if this occurs in our high tech Mercs 

JG

[Jan S]

Thanks to both of you!

before I start messing with the ignition timing, I will clean the cooling system with citric acid, replace the thermostat, replace all hoses (I'm still working on the hoses), fill new coolant and adjust idle to 600 1/min (currently my AAV is not closing due to low temperature, hence idle is 900 1/min) and adjust CO. Maybe I have to chase vacuum leaks as well.

Winter is coming to Norway. Temperatures are below zero at night. Hence I consider doing the ignition job in April (no garage with heat  ). No need to rush, the car is getting close to winter storage.

I opened the distributor the other night and it looks quite ok, hence I'm not considering a rebuild at this stage, maybe later. I want to see the timing adjustments first.

I will keep you posted on the development .... it might take a few months 

[raueda1]

Thanks to both of you!

before I start messing with the ignition timing, I will clean the cooling system with citric acid, replace the thermostat, replace all hoses (I'm still working on the hoses), fill new coolant and adjust idle to 600 1/min (currently my AAV is not closing due to low temperature, hence idle is 900 1/min) and adjust CO. Maybe I have to chase vacuum leaks as well.

Winter is coming to Norway. Temperatures are below zero at night. Hence I consider doing the ignition job in April (no garage with heat  ). No need to rush, the car is getting close to winter storage.

I opened the distributor the other night and it looks quite ok, hence I'm not considering a rebuild at this stage, maybe later. I want to see the timing adjustments first.

I will keep you posted on the development .... it might take a few months 

When you say "opened" do you mean you looked under the cap?  If so, you can't really tell anything.  There's another chamber underneath and another shaft and a plate if I remember right.  They all need to move freely but get so gummed up that you'd think they were just one piece.  Erratic timing is a symptom.  So is drop in rpm when AC is switched on etc.  You'll have a fun little job in April!  Cheers,