40 HP Mariner Question

Hello newbie here. I purchased a boat with a 40hp oil injected Mariner. The serial states it's a 40EO. Not sure if it is a Mercury or Yamaha so this post may be in the wrong section. I believe the year of the motor is a 1986 since I have the original manual.
I have some questions. First off the lower cylinder seems to have low compression. I haven't had a compression test but you can feel it isn't as healthy as the one on the top. Are these motors worth rebuilding? It's missing the starter and the oil injection is out of it so it's being ran on a mixed fuel/oil. Any leads on parts?
Thanks ahead

It's up to you, what it's worth. I fixed one up. I still couldn't tell you if it was worth it, or not. I am happy with it. It's probably made by Yamaha. If so, the parts are expensive and hard to find. If it does have low compression (it needs to be checked), motors that age are prone to corrosion and pitting: making it a challenge to get gaskets to seal. The oil injection was probably disconnected in favor of, the more reliable, mixing. Who knows; it might be fun!

If it's a Yamaha, they run great and last a long time. Worth more investigation.

Got a serial number?

Jeff

If you are mechanically inclined, a total rebuild on a twin cylinder can run you maybe 800'ish bucks (if you can get parts) - that's pistons, rings, bearings, carb kit(s), gaskets, waterpump kit etc.

At the end you have a "like new" motor if done right and complete.

A new 40 run 7 to 8 X that cost.

Now, if this is a 1986 Yamaha built Mariner (there was no 1986 40 horse "Merc", so if the year is correct, it's a Yami/Mariner) then you would have a hard time finding parts if a rebuild is needed. Not even the gaskets are still stocked. And if that's the case you could at least double or triple the cost to rebuild if you could find parts at all.

In general, a 1986 model would be rebuild-able. The issue with the Yami Mariners is that they were "originally" built with parts that Yamaha had discontinued, sometimes many years earlier, in order to produce a lower cost "no frills" motor that Merc could use to compete with, primarily outside of North America. And while well built, they were "technology wise" upwards of 10 years old the day they came off the assembly line.

But hey, find a serial as Jeff suggests and actually do a compression check - it may be fine..

So it's a Japanese made 1986 Yami/Mariner. Can I have a mod move this to the appropriate section? Maybe PM me a link since I'm new here and I'm not sure where it's going to go? I will update on what I'm going to do

This is the right place. Although built by Yamaha, and an exact carbon copy of an earlier Yamaha model, it is "treated" as a Merc product since it was built under contract for Merc and marketed/supported by them...

galamb said:

This is the right place. Although built by Yamaha, and an exact carbon copy of an earlier Yamaha model, it is "treated" as a Merc product since it was built under contract for Merc and marketed/supported by them...

Click to expand...

Anyone here have a used block for one of these for sale? One of the pistons is imploded and there is a hole in the block

sounds to me like you are better off to find another motor. even if it is one that needs rebuilding. at least then you can find parts at a reasonable price.

I'm moving forward with this build but need a new starter. Anyone know a part # I can use? Engine serial # is: 6E9 S 105218

OEM part, 50-97693M is long discontinued and sold for over 400 bucks when you could still get it.

Mastertech Marine (maxrules.com) has a compatible - part number MOT 5000N but lists at $352

You can try www.partsnetworkco.com - they have starters listed under the Merc part number for about $117.

If they no longer carry it or it's unavailable I would consider taking your current starter into a rebuilder. There are a few around and may be your cheapest option (compared to the 3 1/2 bills maxrules wants..)

galamb said:

OEM part, 50-97693M is long discontinued and sold for over 400 bucks when you could still get it.

Mastertech Marine (maxrules.com) has a compatible - part number MOT 5000N but lists at $352

You can try www.partsnetworkco.com - they have starters listed under the Merc part number for about $117.

If they no longer carry it or it's unavailable I would consider taking your current starter into a rebuilder. There are a few around and may be your cheapest option (compared to the 3 1/2 bills maxrules wants..)

Click to expand...

Actually the part # I have is 90-814840. Not sure if the 50-97693M will work. The old starter is missing. The flywheel is there for it but starter motor is gone

The OEM number I posted is the last one listed with Merc, for your serial, when it went totally discontinued...

I'd keep mixing it the old fashioned way because you're looking at spending money in something that's not needed and that's subject to fail.

i think you got a yamaha made mariner, copy of the fm series. And yes, I personally feel its worth rebuilding, just keep periodical maintenance on it. And i'm also willing to bet the bummed cylinder may be carburetor related.

I hope this helps.

Robby

A local company I know of runs two pontoon boats (for fishing trips). Each has a 40 hp Yamaha twin and they have pushed those boats reliably for decades! That's a great motor for you.

Worth rebuilding IF you can find the parts.

Jeff