Chrysler 120 HD spark question/problem

[chrome dome]

G'day,
as the title says,
Chrysler 120 spark problem
has fuel,
compression of 1. 145lbs good spark
2. 150 had no spark at time, dodgy plug threads,
3. 125 lbs had spark ' ' good thread
4. 145 has spark dodgy ' ' ' '

thinking No. 2 had a dodgy coil, swapped it with the one from No.1, now 1 & 2 have spark...but No. 3 doesn't,

scratching head now, numbers seems too good to be true but it does push out a lot of air from plug holes,
but the main question is about the wandering spark,
any thoughts?
cheers

 

[Nordin]

Re: Chrysler 120 HD spark question/problem

What ign.system do you have? Magnapower with dirtributer and drivbelt, Magnapower II or Prestolite? Come back with information about that, then it is easier to help you.

 

[chrome dome]

Re: Chrysler 120 HD spark question/problem

Magnapower II,
thanks

 

[Frank Acampora]

Re: Chrysler 120 HD spark question/problem

Magna-Power II was a "dodgy" ignition system when newly designed. It was a good concept but poorly executed and these systems regularly failed. Many were retro-fit to Magna-Power Motorola systems under warranty. As far as I know, parts are not available. (Chrysler used the term "Magna-Power very loosely to describe a number of ignition systems. MagII was the only system to have the electronics under the flywheel. It was the only Chrysler ignition system to use both negative voltage for one set of coils and positive voltage for the other.).

If you are having problems of any sort, my advice --if you wish to keep the engine-- is to scrap the Magna-Power II and retrofit with either a Prestolite non-distributor system (preferable) or a Motorola distributor system. Find a junker with either system and salvage the ignition.

Now, don't quote me because I haven't done this --yet-- but since you already have the top of the block set up for newer ignition systems, you very likely can use an early Force ignition system and with very little work. a late Force (Mercury) ignition. BUT: You need the complete system including flywheel.

 

[chrome dome]

Re: Chrysler 120 HD spark question/problem

thank you both for the info, advice and suggestions,
we'll have to see if we can find a 'good' dead one and swap bits,
there was one not far away a few weeks ago but it's gone now,

not having a good day with outboards, blew a spark plug out of a 65hp merc earlier today, cracked the cover plate, gotta weigh up the options on that one as well now
such is life,
thanks again for the help, much appreciated

 

[chrome dome]

Re: Chrysler 120 HD spark question/problem

ok..update,
after a period of sulking in the corner..and waiting for a day when it wasn't freezing out in the shed l decided to have another go at the horrible beast..
after doing a bit of more reading l decided l had nothin' to lose so changed the gapless plugs for conventional gap plugs from one of the other outboards...
now this time l have spark on all four, a little weak on no.3 but there none the less,
starting to feel like things may be happening, l had a good look at the lead ends and found one that wasn't sitting quite square in the rubber boot so played with that and whacked it back on,
hooked up the fuel line, primed it WELL and tipped a little bit of fuel in 3 plug holes, crossed my fingers and turned the key...and it didn't start LOL,

after 10 mins of waiting for the excessive amount of fuel in it to drain away LOL.. it is now running..a little bit rough but a bit of tweaking or maybe a kit or two should sort that out hopefully,

l'm still scratchin' me head a bit with this one, but my son will be happy when he gets home from work that his donk is finally running,

any problems likely to arise from using those plugs in this motor?
any other thoughts?

thanks again for the help,
cheers

 

[Frank Acampora]

Re: Chrysler 120 HD spark question/problem

Well, some guys swear by bent electrode plugs but I have seen engines with a hole melted in each piston at the plug. Bent electrode plugs are hotter than the surface gap plugs so use the coolest ones you can find. However, if you stay away from full throttle, she may run OK.

Surface gap plugs take more voltage to fire than bent electrode so your ignition system is talking to you. Most likely eventually you will need to replace it.

 

[chrome dome]

Re: Chrysler 120 HD spark question/problem

Thanks for your help Frank, it is much appreciated,
after reading your post l went and pulled the bent plugs and tried to start it with the gapless...no go..put the bents back in and she started first turn of the key again,
l know you are 100% right about the ignition/heat problem and there will be problems down the road with it as is, in the meantime we'll keep looking for a dead 'un to swap the ignition around, but he does have a couple of other outboards to go back to if/when it dos cark it,
thanks again,

 

[fucawi]

Re: Chrysler 120 HD spark question/problem

The holes in the pistons are caused by pre igniton ( thats NOT what the yanks call pinging which is caused by over advanced timing ) its caused by glowing deposits in the cylinder in your case the over heated plug electrode...the piston is the worst cooled component and its ali so it heats up and the pressure puts a hole in it when it melts.....it takes 11 seconds of pre ignition to hole the piston and its silent ...get the coldest plugs you can find and check the colour after a short run..if they are at all white you need to go colder

 

[chrome dome]

Re: Chrysler 120 HD spark question/problem

thanks for that info Alf..
11 seconds ain't a lot of time for nasty things to happen,
the "good" thing is that the motor is on a stand and so won't be run hard or even a lot now that it is running,
will look for the best cold plugs,
both hull and trailer need a bit more work before they can be used or registered
it's also the first days of winter here and no-one is real keen on going out in a "ski" boat..or any other boat.. atm LOL,
which gives him a bit of time to find another donor ignition..or even another donk..as this one IS a tad over the hull rating...and put this one on a bigger hull down the track,

thanks again,
cheers

 

[chrome dome]

Re: Chrysler 120 HD spark question/problem

continuing on with this motor on this thread, thought it was better to ask the question here than start a new one
will the stator/trigger on a 105 hp fit on this 120?
same size etc?
l don't know yet what ignition system it is, waiting on a reply,
thinking to swap those bits at the very least, the rest if suitable,
reason being spark on 3 & 4 isn't as good as 1 & 2, coils are wired as per manual
thanks