Distributer Trigger Causing No Spark (Sometimes)

[Aust1150]

Great Forum and I think I have learnt a few things - so here goes with first question... Mercury 1150 / straight 6 / Thunderbolt Ingn / Aust serial 8047344 (not sure that this will let you date the engine but i assume is late 70's ??)

Have rewired internally through new home-made connector (commercial waterproof auto connector flat plug type), to point in external harness; due to eroded insulation. Re-did all internal wiring including new connections from existing stator to rectifier. Could not replace ignition trigger wires (3) from distributor but thought would be okay. All went well and runs well. (Except...)

Occasionally (last week), get absolutely no spark to plugs or from coil. This seems to occur in the morning after leaving overnight. For whole week, was able to use each day, as spark seems to come good after engine warms in sunlight. Engine then runs flawlessly for whole day skiing (as presumably remains relatively hot). ps. I have disconnected the mercury switch.

My theory is (without knowing the mechanical structure of the distributor 'trigger'), that the trigger is 'sticky' in some way and 'frees up' as warms up. Is this possible?

Because everything runs flawlessly after obtaining a spark at plug, am not thinking ignition pack or coil problem.

I have fiddled with this problem for awhile, thinking that by pulling plugs / coil leads etc., I had stumbled blindly on a short term fix, as could eventually get the motor to spark. But recent experience seems to suggest problem has got worse and was not fixed by internal re-wire, (although have been able to run every day after letting engine block warm up - note, it is mid summer here so nights are not cold, very mild).

Questions...
1 Could someone tell me more about the trigger system in the distributor?
2 What do you think of my theory about temp and a 'sticky' trigger?
3 I assume I will need a replacement distributor - is this the right fix do you think?

May still get the shop to fix this (don't think I would replace distributor), but would like to be a bit more knowledgeable before asking for work to be done. Thanks for any advice.

 

[Chris1956]

Re: Distributer Trigger Causing No Spark (Sometimes)

I had a similar incident with an intermittent trigger. It died completely after a short time. Hopefully yours will die as well, or get completely heathy.

Since you are having some wiring trouble, make sure the red and white wires on the switchbox have a full +12VDC, when the ignition is on. Make sure the grounds are clean on the coil, dissy, starter, and lower cowling to block. Clean the distributor cap and rotor with some solvent and maybe some sandpaper. The rotor does not come off the shaft, so do not try to remove it. Check the spark plug wires for arcing to ground.

 

[Aust1150]

Re: Distributer Trigger Causing No Spark (Sometimes)

thanks for Reply Chris, after re-wiring i am fairly confident of good 12V supply and good connections (with exception of distributor trigger wires not replaced).

As far as the dist cap goes, since engines runs well (all day with dozens of successful restarts) once an initial spark is obtained, am not thinking cleaning of dist & rotor etc.

Am still interested in exactly how the trigger functions mechanically (has a 'disc chopper/rotor type thingy' ??)

Also, does anyone knowing the trigger system think that ambient temperature could help a dodgy unit fire up?

 

[Aust1150]

Re: Distributer Trigger Causing No Spark (Sometimes)

Just a little follow up on my original post and particularly question about how the trigger actually works. I may be looking a bit dumb with my questions about temperature and mechanical action.

Is the trigger switching mechanism some form of induction current being supplied to the switch box? (ie. there is a chopper/slotted plate and magnet involved??)

If this thing has no moving parts, my theory about it working better after warming up seems a bit dodgy - yet it does run perfectly for remainder of day after giving an initial spark? mmm.

 

[rodbolt]

Re: Distributer Trigger Causing No Spark (Sometimes)

the trigger on that motor is a Hall effect device.
google "Hall Effect"
basically it works by the changing magnetic field created by passing a metalic object through a magnetic field.
the collapsing magnetic field induces a small voltage in the trigger coil which is fed to the switchbox.
in the switch box this ac signal is rectified and fed to an SCR gate.
this gate allows the condenser in the switch box to turn the ign coil primary voltage on and off.
from there the secondary voltage is fed though the distributor cap,rotor and the plug wire.
biggest issue we had was cold solder joints in the trigger assy.
DO NOT attempt to remove the rotor from the distributer shaft. only cure for a defective trigger is to replace it.
last one I did was 320 for the trigger and about 6 hours to complete the job.

 

[Aust1150]

Re: Distributer Trigger Causing No Spark (Sometimes)

Thanks for the info on how the trigger sensor works RodBolt. (and also for advice on not trying to pull the rotor!)

Given the way this sensor/trigger works, I am surprised that it fails and behaves in the intermittent way i have described. Is it still reasonable to attribute my problem to the trigger?

Has anyone pulled a failed unit down and worked out what goes wrong - is it simply the wiring to the (coil/magnet/field??) sensor and could it be repaired (can you get into it)?

I wonder why when I get the unit to run in the morning, I am then able to use all day without repeat of the problem.

How difficult is it to pull the distributor and then to disassemble with a view to replacing the trigger?

I did see a reasonable price on a complete distributor on eBay that i might try and follow up.

Thanks again for any input.

 

[Aust1150]

Re: Distributer Trigger Causing No Spark (Sometimes)

Sorry RodBolt, I just re-read your comments and missed that you said the problem with the trigger tends to be cold solder joints (Is that what you are saying?). So presumable that could explain the temperature related behaviour I have commented on (ie. expansion renewing a contact etc.).

Are you saying that I cannot get into this thing to try and fix such a problem (cold solder joints)?

 

[Aust1150]

Re: Distributer Trigger Causing No Spark (Sometimes)

I guess there's not much more to be said at the moment - a new distributor for me I think.

Thanks to Chris and RodBolt for their comments; I have a much better understanding of the field triggers in the distributor. In some ways it still fits with my observed fault occurances if fault is due to cold solder joints.

Thanks again for a great forum and the professional comments.

 

[Chris1956]

Re: Distributer Trigger Causing No Spark (Sometimes)

You can buy rebuilt trigger assemblies off the web. They are in the low $200 I believe. I also have an '77150HP inline six distributor motor with a broken #1 conecting rod. The rest of the parts are good. You can PM me

 

[Aust1150]

Re: Distributer Trigger Causing No Spark (Sometimes)

Chris, I thought I'd post this last question here for anyone else who may end up reading this thread...

I just went and pulled the covers off my motor to have a look at how the distributor is mounted. I have previously pulled the top cowl support plate when I re-wired the stator leads but didn't take that much notice of the dist. - when I remove this again, does the dist. drive belt come off easily and the dist. body easily removed from the block?

Then, I see the rotor shaft has various bearings etc - is it relatively simble to extract and replace the trigger assembly?

(Thank goodness for exploded parts diagram on this website...
http://www.dougrussell.com/partscat...ction=getcomp&colid=01&coldesc=1150&index=463)

I will eventually need to give this over to a mechanic for timing, but have in mind that I could do the dist. rebuilt first??

Thanks for any further advice.

 

[Chris1956]

Re: Distributer Trigger Causing No Spark (Sometimes)

I replaced the trigger assembly in a few minutes, after the dissy was on the bench.

To remove the dissy, you remove the pulley cover bolt, pully cover, belt and then the pulley. Now loosen the three 5/16" bolts under the pully mounting area, and the dissy will pull down and out.

Leave the belt hang, remove the various grounds, the throtle linkage and the dist. cap