Opinions on 1964 Merc 500?

[kmead]

Good morning all. My wife and I are going to look at a 1966 Thompson Sea Coaster that comes with a 1964 Mercury 500 50 HP. The Cheap Outboards book by Max Wawrzyniak seems to advise against owning Mercury outboards as they are overly complicated to work on and require special tools. This motor hasn’t been run in 10 years, so I’m wondering what all might need to be done to it, and is it really much more difficult to work on than a similar size OMC engine. We might have the option of buying the boat without the motor. If so, how much might that reduce the price? Looking forward to hearing your thoughts.
Thanks.

[JACQUES]

Best engine I ever had till my ETEC 75  had 2  of them one was a Classic 50. (see pic)

As always the critical part is testing compression, look for near equal+/-10%   evaluating overall  level of TLC received since 1964, (picture shows a really nice  well kept engine )    salty or fresh water engine ?. …actual test run result if possble by seller .  if auto oiler (added on  a 1964)    I would get rid of it and go premix 50/1  check wiring for  crumbling  wiring (possible easy fix  if handy  and good barganing chip to lower price.)

they do love fuel being carbed but smooth idling all day on 5 gal.

if you buy….do usual stuff like, change impeller  check GC oil for leaks   try a pressure-vacum test, refill  , clean the carbs , check ignition etc…

and a Mercury Black spray can will make it like new  but your’s probably just needs a touch up on the GC !!

Hard to service  compared to OMCs      Yes to some extent  but experts here will help,  visit John’s old Mercury site and get a service manual

 

see cheap and good source to download books

Mercury Outboard Manuals and Models Directory

note: on my first 50  that  fat side plug needed  surgery due to a broken wire inside  due to flexing  .. but it was an easy fix ! engine would die when turned to one side.  to port if I remember….

 

 

 

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[kmead]

Thank you, Jacques. I appreciate all the time you take in writing your reply.
What do you mean by pressure-vacuum test, refill?

[JACQUES]

To properly test a GC  it must meet two measurements  one involves pressurizing the GC  with an air pump. ( this confirms oil will not leak out during operation .. egress)    The drained of oil  GC should retain about 10-12  PSI for a few minutes.  IF the pressure drops spray soapy water on the drive, shift and prop  seal areas to identify the culprit.   Prop shaft seal are the usual bad ones  due to monofilament spooling in the GC and destroying  the seal.   Pull the propr and check!!

The  second test is a vacum test to measure the GC capacity NOT TO LET IN any water when   the GC cools off after long runs. Cooling  reduces  the inside  pressure and tends to suck in water  (ingress)

Here is a good  video explaining  it.    But don’t let that discourage you.. That Ob looks pristine.   JUst check out the wiring in case it is brittle and  crumbling… it may not be of course

worst case scenario some folks just dump the  GC oil  mid season  and refill with fresh. ….saving the cost of a reseal job.. Oil is cheap!

I purchased that pump in the video on Amazon ..wors fine… the real thing is $100+  the pumps checks pressure and vavum

Bing Videos

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[kmead]

Thanks so much for the explanation!

[Pondrocket]

Great engine there. Don’t pass it up if you have the chance to pick it up for a fair price.

I’ll have to take a look at the book you’re referring to before I can give you a qualified opinion on what it says.

As for the Mercury 500 in question, I’d suggest changing the water pump impeller first, then firing it up and giving it a good test run. After that, I would plan on going through the following:

• Carburetors
• Magneto/ignition system
• Fuel lines and fuel pump
• Electric starter and recoil starter

As long as the wiring hasn’t been chewed up, cracked, or badly deteriorated, it should be fine for the time being.

Keep in mind, this is a 60-plus-year-old motor, so it’s going to need some TLC. Once you work through these items and get everything updated and properly adjusted, you should have a fine-running engine that will give you years of enjoyment.

Don’t let one book change your mind about these old Mercurys. They can be a little tricky to work on, and you definitely need some patience, but all in all, the Mercury 500 is a great motor to own and run.

Travis

[kmead]

Well, it did follow us home so we are the proud new owners of the boat and the motor. All I’ve done so far is to take the cowling off and discover that there’s no spark to the plugs. Previous owner suggested the points might need to be sanded, so after I get a service manual, I’ll try to do that.

[JACQUES]

sure looks like a fine engine….loved and cared for    no sparks may not be a big headache after you read up on it or ask chat gpt

slow and easy does it  keep us post on progress!

 

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kmead

[kmead]

Finally unearthed the points and they were stuck fast with corrosion.

Cleaned them with sandpaper, but one half of the points has got a little crater in it. I would like to replace them if I can find a source, but so far I haven’t been able to. Can anyone direct me to a source?
Or is it OK to file the points down until the crater is gone?

[JACQUES]

no choice if NLA… but they should be available..

for now  just polish them up  and see if you have sparks.   check condensers !! or simply replace them…they are there  to stop this pitting.

Testing them with a VOM  or capacitance tester is not sufficient

IF bad   (open or shorted)  they are bad

IF tested OK… you still never know how they will perform under load and heat  so best to replace them otherwise to be 100% certain you can always build yourself ta condenser tester.. I did  worked great

 

see parts 1-4 oncondensers… part 2  covers the test box design by mr. Mohat… write to him for plans

Magazine Articles | Western Reserve Chapter

Drill down this site in the  OUTBOARD      Merc  500 2 stroke ARCHIVE sub sections for breaker part#s…for your  serial number  on theengine .. look in EBAY

EzPartsWeb

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