MCM 140 dwell

[mrsaundep]

MCM 140, Serial number, 5568367, with Delco Distributor

I rebuilt the engine last year after a core plug popped out. This included work on the ignition system such as new distributor cap, all leads, points & cond, rotor, plugs, and a full tune up as per manual #3 including setting the dwell and timing correctly. Since then she has been running great. Last time out she was good for an hour at about 2500rpm, then the revs started to hunt, up/down~2-300rpm for a few minutes, then she stalled. Would restart but would only run erratic and would stall at less than 1000rpm.

Have checked and renewed fuel filter/water seperator as there was some dirt in there. Also checked fine filter in the lift pump and the mesh at the carb inlet both clean.

Checked Cap, leads, plugs, points etc, all look good.

Re-checked points gap and then tried to check the dwell, but I cannot get it steady and the best I can get is it wandering between 30-34 deg. Same reading when cranking on the starter and when running and (trying to) hold revs steady ~1750rpm. Can't really check the timing as the revs hunt too much, have tried moving the distributor (advancing and retarding) from it's existing position and it does not improve, so I need to fix the problem before adjusitng timing.

I am presuming that this indicates a problem in the distributor (springs, weights?), and my next step would be to dismantle and inspect it. Anybody disagree and is there something else I have missed before I do that?

Many thanks, Paul

 

[Don S]

Re: MCM 140 dwell

The bushings and/or distributor shaft are worn and causing the problem.

 

[mrsaundep]

Re: MCM 140 dwell

Thanks Don. I have been toying with the idea of converting to electronic ignition (I have the cash ready to do this). Do I use this as the excuse to go for it, or should I simply try and repair of the Distributor?

 

[Don S]

Re: MCM 140 dwell

There are no parts for those distributors. Does that help narrow it down any?

 

[mrsaundep]

Re: MCM 140 dwell

Looks like a 'no brainer' then! I am searching for a thread with a full list of parts required for the electronic ignition conversion but so far cannot find one. Could you kindly help with this please?

 

[Don S]

Re: MCM 140 dwell

Many convert to the EST distributor. Mercruiser has been using them since 1990.

http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-120.html

 

[mrsaundep]

Re: MCM 140 dwell

Good day,

Further to the above, I strippd the old dissy and found the bushes were worn and the clearance was well over spec, and also the hole in the drive gear where the roll pin is fitted was worn and the pin was actually slack. So I purchased the 3.0L Delco EST distributor kit from Michigan Motorz as recommended above by Don S.

I have finally received the parts from the States and got round to start the installation today and have a couple of questions please; I have removed old coil and distr, installed the new coil and 'distributor' mechanically.

Electrically I found that the old coil had TWO wires connected together onto the coil ‘+’ terminal;
- 1 purple/yellow - connected to the starter motor solenoid,
- 1 brown colour (but when I dug further into the harness it was actually a pink/purple colour) – cant trace where it goes to as lost in the harness wiring.

I have checked the Battery voltage = it was 12.6VDC.
The Voltage on purple/yellow wire to the coil + (with Ignition key in the run position) = was 0.0 VDC!
The Voltage on brown (pink/purple under the harness) wire also connected to the coil + (with Ignition key in the run position) = was 11.4 VDC.

The Instructions from Michigan motorz only mention 1 wire purple/yellow. These instructions also state that the voltage to the EST coil “should be 12V - battery voltage”, but that it must be more than 10.9 volts. I am getting 11.4V, but as stated my battery voltage is 12.6. So I guess that a resistor must be fitted?

Now then, the Mercruiser manual#3 wiring diagram shows the purple/yellow wire between coil and starter motor, and a purple resistor wire. So I appear to have both these wires on the installation but I am confused as to why I have 0V on the purple/yellow wire and 11.4V on the purple resistor wire?

So, my questions are;

1). Which wire(s) of the existing purple/yellow @ 0.0V and purple wire @ 11.4V should I connect to the purple wire on the new EST pigtail plug to the coil?

2). Or, should I run a new cable direct to the coil to give full battery voltage @ 12.6V direct to the purple wire on the new EST pigtail plug to the coil? If I should run a new wire, where is the best source (location) to run the wire from?

3). Is the grey wire connected to the old distributor the tacho cable? (This is not shown on the engine wiring diagram I have from Manual #3).

I am quite tempted to experiment, but am a bit worried about blowing something up!! So I thought I would dig into the mass of experience on here yet again!

Many thanks in advance for your helpful replies...
Paul