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Old 02 January 2021, 03:21   #1
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compression and wires I.D. from magneto on mariner 15c 684 help please??

Hi and happy boating new year to all here.

i just picked up this mariner 15c 684 1981. yet to download a manual.
does anyone know what the pair of cables are for (sheathed in bright blue) are for that come out from under the magnito?
a similar pair also go off to the single ignition coil.

any help be great.
also,
this has not been used in many years and only in freshwater as a back up so im told.
after a compression test, both read at 70 -75.
what can (should i do) to check and improve this without braking the head down etc.
what is the proccedure of checks to help rectify for greater compression?
ive yet to start it as the fuel filter etc need a good scrub out.



any links of advice always apprieciated.
apoligies for spellings and grammar im truley dislexic.
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Old 02 January 2021, 04:37   #2
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Quote:
Originally Posted by daijinks View Post
Hi and happy boating new year to all here.

i just picked up this mariner 15c 684 1981. yet to download a manual.
does anyone know what the pair of cables are for (sheathed in bright blue) are for that come out from under the magnito?
a similar pair also go off to the single ignition coil.

any help be great.
also,
this has not been used in many years and only in freshwater as a back up so im told.
after a compression test, both read at 70 -75.
what can (should i do) to check and improve this without braking the head down etc.
what is the proccedure of checks to help rectify for greater compression?
ive yet to start it as the fuel filter etc need a good scrub out.



any links of advice always apprieciated.
apoligies for spellings and grammar im truley dislexic.
Spare wires are likely charge wires ready to plug into a rectifier for charging a battery. Compression is low you may find it comes up after a run if you can get it to start. Maybe try a few squirts of neat 2 stroke oil down the plug holes with the pistons facing upwards & turn it over a few times to get oil around the pistons & rings to help with initial start up once its running let it run till its hot & see how it runs. Dont get too hung up on the compression readings as they are notoriously misleading. If it starts & runs uk use it and see how it goes
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Old 02 January 2021, 06:51   #3
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I'd second the above in all respects. Get it running in a bin for ten minutes then by all means take a compression reading for interest but as long as it starts and runs OK don't worry about the exact figures as long as they remain fairly even as you have found already.
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Old 03 January 2021, 18:38   #4
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thanks there, that's reassuring, appreciated.

very soon I will fire it up and see how it goes after a carb clean up.

ive attached a concerning image of the head gasket showing a small area of yellow corrosion at the seal with a dry spray residue below. Its around the mid left section.
i have wider photo shots.

regardless of the engine working soon, I wanted to know if this is an obvious tell tale sign of gasket failure or just pure chance corrosion on and around the surface given the compression test was only 70 on both.

as there is no verbal history with this engine when i bought it, I am simply trying to intercept any up coming issues with such old but trusty rigs.
any pointers, as always welcome.
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Old 03 January 2021, 18:57   #5
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the wires are both green (with photo)

yes both the wires are green. I do not own a multi meter (yet) so just very curious as to their potential use and do they need to go into other electrical componants not on this exsiting engine to

photo attached.

BTW after lots of seaching I cannot find any images or diagrams of this Mariner 684c 15m 015284 circa 1977 -1980s. Ive looked at some Yamaha ones but they only seem to go back to 1984.

perhaps no to colour photos back then.
any pointers welcome.
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Old 04 January 2021, 03:10   #6
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Regardless of the engine working soon, I wanted to know if this is an obvious tell tale sign of gasket failure or just pure chance corrosion on and around the surface given the compression test was only 70 on both.
No idea, it looks minimal. Get it up and running before you start worrying about gasket failure. If you need to split this thing then you're into a potential wold of pain with bolts breaking. If that area remains dry, just leave it. If it starts weeping water and oil you can revisit.

A good site for parts diagrams is boats.net
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Old 04 January 2021, 06:23   #7
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A pic of the outboard would help here-if it's the Yamaha/Mariner 15hp from the 80s I may have a PDF manual for it.

<Edit> Found the manual but it's 218mb. Think I have the parts microfiche for it too. It's black and white and you may struggle with it but it's got wiring diagrammes.

I'll need somewhere to send a yousendit link to. Drop me a private message with an email addy.
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Old 04 January 2021, 06:43   #8
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Likewise I'd not worry about that sign of corrosion along joins in the engine sections. I've seen it loads in older outboards where they are running fine with no gasket leaks. It's been my theory that it's just where the paint is most likely to fail at the very edge of a casting/component and then corrosion starts unrelated to leakage.
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Old 08 January 2021, 05:34   #9
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Hey thanks everyone. Reassured there. I'm cracking on as my manual for a 15c pre 80s is now in the post. The engine is three stories up in a room so until all checks are done I'm not taking outside you'll understand.
I've been checking for spark - the HT leads look good, the plugs are old but work in the bottom one but trouble is the main top ignition coil does not produce a spark where as the bottom one does on both plugs. These is pre-cdi I understand.
I have no multi-meter or such and would need to learn how to use it.

Is there a difference between the two coils ? Apart from thier function for each plug. Can I just swap them over to see if that shows if it's a faulty primary coil?
Etc
I've seen the yamaha 15 equivalent has just one ignition coil ( possibly cdi).
Can this mariner be retro fitted with one of these to eliminate further electrical wobbles.
As always, Thanks for any pointers here.
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Old 08 January 2021, 05:40   #10
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Quote:
Originally Posted by daijinks View Post
Hey thanks everyone. Reassured there. I'm cracking on as my manual for a 15c pre 80s is now in the post. The engine is three stories up in a room so until all checks are done I'm not taking outside you'll understand.
I've been checking for spark - the HT leads look good, the plugs are old but work in the bottom one but trouble is the main top ignition coil does not produce a spark where as the bottom one does on both plugs. These is pre-cdi I understand.
I have no multi-meter or such and would need to learn how to use it.

Is there a difference between the two coils ? Apart from thier function for each plug. Can I just swap them over to see if that shows if it's a faulty primary coil?
Etc
I've seen the yamaha 15 equivalent has just one ignition coil ( possibly cdi).
Can this mariner be retro fitted with one of these to eliminate further electrical wobbles.
As always, Thanks for any pointers here.
Will post pics later of the coils.
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Old 08 January 2021, 06:25   #11
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Just swap the coil over or even just swap the low tension cable to see if it swaps the fault. Or the fault stays with the same coil
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Old 08 January 2021, 16:52   #12
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Just swap the coil over or even just swap the low tension cable to see if it swaps the fault. Or the fault stays with the same coil


Leaving the coils where they exactly where they are, Iíve swapped over the LT leads coming from under the magneto (orange normally feeds bottom secondary coil and grey feeds the top primary).
Turns out both coils will work if the orange lead is used on them but neither will work from the grey cable feed.

I donít no if this is a help but the spark is good and constant in the normal configuration of orange to orange on the secondary coil but when this working orange feed is used on the top primary coil, the spark happens for the first few pulls but then not again for a bit.

I totally disconnected the stop button during this as the feeds come from the orange and grey cables. ( I read this might short them if faulty itself).

Anyway, whatís my route now? Track the grey cable back to under the magneto ? Take it apart, strip the sheathing?

Are the coils identical and their primary or secondary use is irrelevant?
Do they receive different amounts of charge being primary and secondary?

Lord deliver me ignition this year.


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Old 08 January 2021, 16:53   #13
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Quote:
Originally Posted by daijinks View Post
Leaving the coils where they exactly where they are, Iíve swapped over the LT leads coming from under the magneto (orange normally feeds bottom secondary coil and grey feeds the top primary).
Turns out both coils will work if the orange lead is used on them but neither will work from the grey cable feed.

I donít no if this is a help but the spark is good and constant in the normal configuration of orange to orange on the secondary coil but when this working orange feed is used on the top primary coil, the spark happens for the first few pulls but then not again for a bit.

I totally disconnected the stop button during this as the feeds come from the orange and grey cables. ( I read this might short them if faulty itself).

Anyway, whatís my route now? Track the grey cable back to under the magneto ? Take it apart, strip the sheathing?

Are the coils identical and their primary or secondary use is irrelevant?
Do they receive different amounts of charge being primary and secondary?

Lord deliver me ignition this year.


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Hereís the coils
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Old 08 January 2021, 17:48   #14
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Coils are identical, are you sure thats not a cdi engine? Cdi bolts on just beside the flywheel? Wires go to triggers under the flywheel to cdi then to coils?
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Old 08 January 2021, 18:58   #15
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I canít see any other components around the flywheel or engine bay that might be electrical. Iím sure this is just a pre - 80s without cdi unit. Here attached is a diagram from marine engine for the 9.9c version which has the same setup. Same metal-type spark plug holders etc.

My manual arrives soon so I can compare the set ups.

Mariner 9.9C HP Flywheel Magneto Parts
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Old 09 January 2021, 03:49   #16
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If its none cdi then it must have points under the flywheel is there an inspection hole in the flywheel?
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Old 10 January 2021, 18:32   #17
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Hi Beamishken

Looks like thereís no way of seeing under the flywheel. ( see pics ) Iím gonna have to take it off. ( never ever done this before but hey in for a penny....)

Strap it fast then undo the nut ( looks reversed) then buy a puller I guess is the way to go.
I figure I have to align the TDC mark with the thin vertical prong on the side first and return it there too? mm perfect.

I should leave the 3 screws hold on something underneath?

Need to buy a torque wrench and get the setting from the manual thatís on it way from the USA !
Does it need to be in gear ?

And then check for dirt and erosion or damage on the 2 points underneath. It should be obvious if thereís bad contact on the primary one I hope.

I read to clean them just use a business card to rub between the contacts so it does not scratch them just polish.

I should be doing multi meter tests at this time too perhaps ? (I can borrow one).
before putting the whole back together.

As always cheers for guidance and encouragement.
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Old 11 January 2021, 03:31   #18
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If it were me attempting to check inside that flywheel I would undo the 3 phillips headed domed screws. That I believe will release the tin inspection cover and allow you access to whatever is inside. Once its off take more pics for further advice.
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Old 11 January 2021, 03:41   #19
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If I have the correct one you should see long slots under the plate like this pic so you can inspect and adjust the points.
fly inside.jpg
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Old 11 January 2021, 05:47   #20
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I reckon this is the setup you have if you read the text description for the 15C. It seems to fit with your description and images.
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