'86 evinrude 150 V6

[dudemaaan]

I just got an 86' skeeter, my first boat. The motor is an evinrude 150 identification plate : E150STLCDC

The compression on one of the cylinders is low. all are around 105-110 except one reads 55. I've never worked on marine engines but I'm experienced with rotaries and all kinds of automotive piston engines, so I'm sure I can figure it out.

The guy that owned the boat before me said sometimes the boat would run great like nothing was wrong, and other times it didn't have enough power to get on plane.

Does this sound like a broken piston ring or maybe just a carbon stuck ring that some sea foam could cure?

If it turns out to be the piston ring, is it worthwhile to just replace the rings on the one piston or should they all be done at once? I've never had one of these apart (yet) so I'm not entirely sure what all is involved. Any help is greatly appreciated.

[CDK]

Almost a quarter of a century old; the compression loss probably isn't the only issue.
Assume that one cylinder doesn't contribute any output power, the other five would still generate 125 hp and 83% of the torque. The boat would still get on plane, just a bit slower.

If you're experienced with automotive engines, let the engine idle without the cover and listen carefully. If the compression loss is caused by wear, all cylinders sound equal, if there is mechanical damage like broken rings, corrosion spots or a deformed piston, you can hear and feel that. With a piston having a lot of friction the engine may lose lots of power.

Are there butterfly valves in the intake that could be damaged?

Of course you can try to repair just the bad cylinder, but to get the piston out you need access to the crankshaft, which is a "major operation". Should you intend to keep the engine, it is probably wise to disassemble the rest also.

Does the ignition advance mechanism rotate freely? Most of these engines are controlled mainly by shifting the ignition timing.

[dudemaaan]

The condition of the motor externally looks really good for being this old. I still have to get a few things replaced to get the boat before starting it, but as soon as I do I'll see what I can hear.

If I tore into the engine for the one cylinder I would of course inspect the others. I just wasn't sure if common practice was to replace all the rings, or all the pistons and the rings, or just replace the bad one. Especially since the compression numbers seem really good.

I'm not sure what butterfly valves you're talking about? The only ones I know of are for the carbs.

I'll check the ignition advance too. Is there a good place for online manuals or anything? Thanks for the advice!

[CDK]

You'll find the parts to be very expensive, so if the other cylinders have a good compression it would mean wasting a lot of money replacing parts that still perform well.
But what if there is severe cylinder damage in one place?

I mentioned the butterfly valves in the air intakes because most outboards have these. If there is visible damage, one cylinder may have " inhaled" a shard of steel.

[dudemaaan]

If one cylinder is shot then i'll have to either find another motor, or is it possible to have them re-sleeved? I know I've seen overbore kits for them. So that would be an option too. I'll just have to see once I'm in there. I may have located another engine for it too, my brother in law is looking into it.

EDIT: Are the butterfly valves you're referring to called reed valves?

[powerabout]

you can rebore one cylinder and fit a new piston cheapest thing to do.
Re-sleeve is also do-able but that repair will cost more.

There are millions of these engines out there and I would say very cheap to repair.
Some stuff is NLA but with so many engines out there you can find the stuff.
A std size piston is still current from BRP and about USD100.00 ( and so it a current v6 Etec piston)

With such a difference in comps I wouldnt run it without finding out why.
Pull the bypass cover off ( outside of cylinder ) and have a look you should see the story when you wind the engine over by hand.
You would also want to renew the head gaskets so you may as well pull them off as you will need to anyway.

Yes as CDK says the reeds chip off and when you swallow steel ones it will damage something.
Unless it has been contunually over reved or someone has altered the reeds they are good for well over a 1000hrs in that motor.

[dudemaaan]

Thanks for the advice. That all makes good sense. I just picked up a book for this motor so after I study it and feel ambitious I'll check these things out. Thanks again

[CDK]

Originally Posted by dudemaaan

EDIT: Are the butterfly valves you're referring to called reed valves?

YES..!

[tunnels]

Put simply if you going to tear the motor apart do the best job possible and replace the rings , hone the bore , do all the seals and Gaskets . clean and check all the water galleries and do a number one job on it !! One exspence and no more worries even a head shave and a port clean and dont forget all the bits below where the motor attaches to the bottom part of the legs , also check the water pump and put a new impellor in and the seal where the pipe connects to the motor .
Run it in nicely before wanting to tear its pants off and give it a thrashing on the water .

[dudemaaan]

Alright the book I have is a Seloc repair manual for 73-91 evinrude/johnson outboards. I've read quite a bit in it already and been trying to search the forums for more information. The book is a bit vague in some areas and doesn't have a good exploded view of the engine.

What plate do I remove to gain visual access to the cylinder and pistons? I found the bypass covers in my book (3-10) but there is only one picture and I can't quite tell what I'm looking at. I took some pics of my engine and marked some areas, also marked the low compression cylinder in red. If someone could give me a visual idea of which plate should come off that would be great.

[tunnels]

Head off !Plate in the middle off !that plate covers the exhaust ports !and then you will be able to see the bore and the rings on the piston as it slides past the port as you turn the fly wheel and the piston goes up and down . Id be looking for marks in the bore as well . Remember the rings are pegged so they dont rotate on the piston and rings face only one way as well !!.and make sure the piston goes back the right way up !!
To get at the conrod bolts you gotta take the motor off and put in on the bench and the carbs and manifolds gota come off as well .
Remember you are dealing with a 2 STROKE !! SEALS AND GASKETS ARE CRITICAL . Simular to automotive engine but comletely differant .
Like i said because you will have the motor comletely disassembled make a good job do all 6 cylinders and rering them all , plus clean all the water ways every where . Check also your reeds when you get the manifold off .
If its all a bit daunting for you take it to a marine mechanic and let him do it.
Read the manual from end to end and then a second time . 2 stroke outboard motors are a complicated piece of machinery !! I have a v4 yamaha i i wont touch it , have been into mechanical stuff all my life . Will do minor stuff but not take it apart completely !

[dudemaaan]

Well it's a little daunting just because I've never worked on one before. But I figure if someone else can do it, then I can do it too. Marine mechanics are too expensive. I got the boat for free so I won't lose anything by playin with it.

[tunnels]

Ok i understand your concern , As i said you need to get the power head off the leg and work it on a bench will be the best way to start ! Need a big clear clean place to work so you can lay everyting out in the sequance that you dismantle the motor in and not just a big jumbled up mess scattered everywhere ,Keeping the bolts and nuts and washers in the right place with the bits you take apart . You will need a torq wrench when you start to re assemble the motor . The threads in the old casting pull out very easly and with great regularity on older motors as the castings get corroded between dissimular metals ( aluminium and steel ) and brittle with age !! Grease every nuts and bolts when you get to putting it back together again !! and wire brush all the threads on the bolts as you take it apart . Take extreme care cleaning the old gaskets off the casings as you disassemble the motor , Scratchs can and do cause air to leak in or out !!!!!!
Cant say it often enough!!! ITS A 2 STROKE AND NEEDS 110% GOOD SEALING EVERY WHERE !!!
And read the manual till you know every word off by heart !!Its what you got it for !!

[El Sea]

"Marine mechanics are too expensive" There is a reason for that.... if you snap off a head bolt then try to drill it out, then mess up a block! That's why marine mechanics are expensive.

Good Luck, keep us posted.

Absolute

Suckin Sludge & Havin a Gas

[dudemaaan]

Well breaking a bolt off can happen in any kind of mechanics. I'm not knocking what they charge, that's good for them. But I can't afford it. I'm sure there is a certain amount to learn just like with anything. Rotaries have their own unique characteristics, and are very similar in design to a 2 stroke engine. They have a power cycle every crank revolution, burn oil like a 2 stroke, and have no valves or camshafts like a 2 stroke. I've always had trust issues with sending things off to someone else to work on them, that and i'm poor haha. I'll keep everyone posted. I have a lot of projects going on and just started a performance store too so time is scarce, but I'll be working on the boat every chance I get.