Manuals

croz

Cadet
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Feb 28, 2019
Messages
21
Just bought a boat with old 70hp 3cyl. Mercury. Want to buy Owner/operators manual. Also repair manual #90-96135 1980.

Anybody know if its worth bringing back? Where these motors known for problems?

Key was not with boat. How to jump ignition and start wires to see if starter engages? Motor turns by hand, shifts and engages prop. Has good compression.

Thanks for response
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
You can buy either the key or a brand new ignition switch most any place that has boat supplies. As for whether the engine is worth bringing back to service, only you can make that decision. If it seem to look good and once you get it running, sounds good, then I don't see any problem. Yes do buy the factory model specific shop manual for that engine and not an after market version. You won't regret buying the factory manual. JMHO
 

croz

Cadet
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Feb 28, 2019
Messages
21
3cyl 70hp 1980 Merc Whats the best way to find a manual (original)? How many years did Merc make a 3 cylinder 70hp? Thanks!
 

gm280

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Jun 26, 2011
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14,585
3cyl 70hp 1980 Merc Whats the best way to find a manual (original)? How many years did Merc make a 3 cylinder 70hp? Thanks!

I can't say if this is the best way to buy any manual, but I have a 1976 Johnson 40 HP engine and I searched for it on line. The model number will really help get the proper manual. I found my factory shop engine specific manual on EBay. JMHO
 

racerone

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Dec 28, 2013
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They started with a 3 cylinder 65 HP in 72 that became a 70 in 77 model year.-----There were issues with #1 cylinder dome cracking on them.----Make sure you look at the impeller / poppit valve on the cooling system..
 

The Force power

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Feb 3, 2019
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To get a key for it, open the control-box to where you can see the back of the ignition-switch; if you're lucky....the little sticker with the key# is still there with that search on ebay they are usually around $3.00 + the shipping :(

if not...and for now to check the motor over before dropping coin on it;

use a jumper-wire from the Pos. therminal to the pos. therminal on the starter-solenoid to get the starter going, to stop the engine you will need to shorten the wire from the ignition to ground.

I'm at work right now (lol) but I can elaborate/give better directions later(still have 70hp 3 cyl. 1981 on a stand sitting here)


But as Racerone already stated (& I worked on 3 of them) these motors were notorious for blowing the #1 Piston
 
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croz

Cadet
Joined
Feb 28, 2019
Messages
21
motor turns and driveline turns when I jump starter. Haven't used compression gauge but seems ok. Thanks for info. Any idea what the reason for #1 piston burnout? Love this site for info from people that have been there!
 

The Force power

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Feb 3, 2019
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2,241
Welcome, I have been visiting this site for years, before I became a member; I thought it was time for me to join & share my knowledge that I picked up over the years.

You should really check the compression on all cylinders! I had two of them with the #1 blown & had to do a piston-ring swap on them.

To answer your question on why "the #1 piston goes" ; don't have an answer but I'm sure Mercury has figured it out. lol

I only have a theory and suspect it has to do with the oil return-line
 
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