1988 Mariner 5 HP - Fresh rebuild w/ Yamaha OEM parts but no Start

gk-da-man

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Joined
Aug 7, 2010
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About 3 weeks ago I bought a seized 88 Mariner 5hp outboard. The block is yamaha stamped and I had rebuilt another 84 mariner/yamaha 5hp that came with a donor motor and had a bunch of donor parts laying around and figured I would give it a go at trying to get the seized motor running since cosmetically in great shape. I pulled and opened the powerhead to find both the top and bottom bearings seized and the piston frozen in the cylinder. With some light coaxing from my 2lb deadblow hammer I was able to get the piston out. The rings were frozen and shot completely, the top ring came off with little complaint in one piece but the bottom broke about every half inch as I prized it out of its groove. I took my 2" fine wire cup on my drill to the cylinder and cleaned it up - same procedure I did when rebuilding my other motor.

Since there isn't a good local merc/mariner parts house locally I visited my friendly local powersports shop in Thousand Oaks, CA which carries yamaha and ordered the 2 bearings (part 93306-204U0-00) and a new set of rings (part 6G1-11610-00-00). I installed the parts and bolted everything back up - went together easy enough. The bearings were identical and perfect, the rings seemed a bit smaller than the previous set but given that i believe the yamaha and mariner motors are the same specs I just rolled with it.

Side topic: I soon learned why it had seized, I opened the carb to clean it out and found it completely disintegrated internally from corrosion and the throttle cable was so stiff it wouldn't return. This thing had been either sunk or had a ton of saltwater in the fuel. Thankfully I had a complete spare carb from my donor motor, but it needed a carb kit and I needed a new throttle cable. Back to the yamaha shop, I picked up the parts tonight, did the carb rebuild and reassembled the motor completely.

I probably gave it 30 pulls tonight without so much as a good kick. I pulled the plug and can see that I do have a nice strong blue spark. The plug also appears to be getting fuel. I hooked up my compression tester and I am only seeing 50-55 lbs of compression. I dont know what it is supposed to be but that seems low. I know it may also be that the rings have not had a chance to seat. So - a couple questions 1) do I have a parts interchange problem on the piston rings? 2) What is the appropriate install order on the rings, I installed the silver ring on top and the dark ring on the bottom. 3) Any other thoughts on what I might try to get this motor to fire?
 

Faztbullet

Supreme Mariner
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Mar 2, 2008
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15,589
Re: 1988 Mariner 5 HP - Fresh rebuild w/ Yamaha OEM parts but no Start

Compression to low to support combustion and if piston was stuck that bad cylinder wall likely pitted and has excess blowby from pitts or incorrect rings
 

gk-da-man

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Joined
Aug 7, 2010
Messages
8
Re: 1988 Mariner 5 HP - Fresh rebuild w/ Yamaha OEM parts but no Start

Compression to low to support combustion and if piston was stuck that bad cylinder wall likely pitted and has excess blowby from pitts or incorrect rings

Thanks for the response. I dug some more and found Marineengine had a Yamaha part number cross ref and the rings are wrong. Supposed to be 6J1 not 6G1. Ordered the NLA old stock quicksilver ones just to be 100% sure I have it perfect this time.
 
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