Mercury Mark 6A

[Aidan Smith]

Also working on a Super Silent 6 from 1959. It DID have spark for a brief second on the upper plug, then nothing after I cleaned and regapped the points.

Are the condensers known to fail on these motors? I think that the coils are OK, but I will not be able to test them until Friday.

Thanks

"Shells sink, dreams float. Life's good on our boat."
1921 Elto Light Twin F
1950 Mercury KF-7
1951 Mercury KG-7
1959 Mercury Mark 6A

[JACQUES]

most condensers fail eventually   can you do basic test…(short – open – capacity kick or measurements )   some mercs have tricky “insulating blocks” in the ignition system so check for airline cracks which could allow shorting out sparks

check spark wire continuity from plug boot back to ignition coil (s)  see chatgpt info

Step-by-step servicing procedure

1. Access the magneto / points

   • Remove cowl and any retaining hardware, then pull the flywheel (use a flywheel puller). The breaker points and condenser are usually mounted under/around the flywheel on these 1950s Mercury units. aomci.org

2. Visual inspection

   • Look for oil/water contamination on the points or condenser, cracked insulation on HT wires, corroded connections, or arcing marks. If the points heel (the fiber pad) is badly worn or the faces are pitted/blue, replace the points. maxrules.com

3. Clean or replace points

   • If only lightly dirty, clean the contact faces with a points file or fine emery, then wipe with contact cleaner. If pitted or rough, fit a new points set. Setting the gap is critical (see step 5). MarineEngine

4. Replace condenser (capacitor)

   • Condensers commonly fail after decades; replace with a modern equivalent sized/voltage-rated for magneto use. Replacements are readily available from vintage parts suppliers — don’t risk a weak condenser (causes weak or no spark). Smokstak+1

5. Set the points gap (pre-timing)

   • Typical magneto/points guidance for vintage outboards: about 0.012″–0.018″ (0.30–0.45 mm) is commonly used. Many restorers set ~0.015″ (≈0.38 mm) as a safe target, then fine-tune timing. Small changes in gap change ignition timing — set the gap first, then time the magneto. Use a feeler gauge at the maximum cam lift (follow the manufacturer method if you have the manual). themagnetoguys.co.uk+1

6. Lubricate the cam / pivot

   • A tiny smear of distributor/cam grease on the rubbing block/cam contact prevents rapid wear. Don’t over-grease where it can fling onto electrical contacts. oldcroak.com

7. Check coils and wiring

   • Use a multimeter to check primary/secondary resistance of coils (if you have coil specs from a manual). Inspect HT leads and caps for cracks; replace if brittle. If coils are open or shorting, they’ll need rebuilding/replacing or a professional magneto service. aomci.org+1

8. Timing

   • With the points gap set, reinstall flywheel enough to rotate by hand and observe when the points open (or use a strobe/timing light on running motor if possible). Many vintage Mercury setups require firing roughly at a point before TDC — manuals/forum threads explain the exact advance angle for each model. If you don’t have a timing mark, set the gap with the cam high-point method then fine-tune on the test tank. aomci.org+1

9. Test firing

   • Reconnect HT leads (or reinstall plugs), turn the engine over by hand to confirm sparks at each plug (use a plug removed and grounded safely to check spark visually), then run on a test tank with proper choke/throttle adjustments to check idle and advance behavior.

10. If things still misbehave

• Common causes after a points/condenser service: wrong gap, weak condenser, cracked coil insulation, magneto assembly seating (flywheel key/fit), or advance mechanism mis-set. Forum rebuild threads and magneto-specialist videos walk through diagnostics—mail-in magneto rebuilders exist if internal coil or cam ring work is needed. aomci.org+1

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Replacement parts & repair services

• Where to buy parts: OldMercs, MarineEngine parts listings, eBay listings for vintage points/condensers. Match by model/serial if possible. oldmercs.com+2MarineEngine+2

• Magneto rebuild shops / specialists: Many restorers refer to small specialists (mail-in) or local antique outboard shops — forum threads list names and experiences. If coils are bad, specialist rewind/repair is usually required. aomci.org+1

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Quick troubleshooting checklist

• No spark at all: check condenser first, then coil continuity, then points opening.

• Weak, intermittent spark: dirty points, leaky condenser, cracked HT lead.

• Timing oddities after changing points: re-check gap and re-set magneto position; small gap changes = a few degrees of timing shift. Smokstak+1

 

 

Joining AOMCI has priviledges 🙂

[JACQUES]

check for cracked insulator blocks    do basic testing on condensers or simply replace  60 year old parts   ask chat gpt for detail test procedure.  check coil  electrical cotinuity to boots.

Joining AOMCI has priviledges 🙂

[RICHARD A. WHITE]

With your wonderful exuberance towards these old motors… You would do well to find a Mercotronic or Stevens ignition tester. If you are feeling REALLY ambitious, there are instructions to make your own out there…really helpful with these old girls..

http://www.richardsoutboardtools.com
classicomctools@gmail.com

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Aidan Smith

[Aidan Smith]

I haven’t actually used one before, but I will learn. Do you know what the condensers are that go in there? I thought you could get them at NAPA.

"Shells sink, dreams float. Life's good on our boat."
1921 Elto Light Twin F
1950 Mercury KF-7
1951 Mercury KG-7
1959 Mercury Mark 6A

[JACQUES]

just go on chat gpt and ask  here is one answer

For these vintage magneto condensers (like the 398-693 / 18-5206 replacements):

• The capacitance is generally around ~0.15 μF to 0.20 μF (sometimes quoted as ~0.18 μF) with appropriate voltage rating (typically 400–600 V or higher) for ignition use.

that said   the common .22uf OMC condensers should do and available if not you can go  ceramic  just for trial

if you have the condenser casings you can just refill them with .22uf  if fitting in modern ones  is complicated fit wise.

see articles  parts 1-4

Magazine Articles | Western Reserve Chapter

 

 

 

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