1990 Merc outboard 115 piston replacement

Hi everyone. I'm a new boater (more or less) and new to the forum. I just picked up a 1990 SeaRay BR160 with an outboard 115 2-stroke (oil injected). For now I'll save the whole story for another time but currently I have an unexpected problem that I'm determined to solve and get this boat on the water. I'll need some of your collective intelligence to make it happen!

The engine had a real hard time "turning over" past a particular spot when I got it. After some testing, I determined that the starter was probably weak and replaced it. With this I was able to get it fired up and running. But before long it was stuck at the spot again. Yanking on a rope around the flywheel will not budge it a bit, whereas the rest of the rotation is quite easy. So I pulled out my new plugs and noticed 1 was darker and had some metal particles stuck to it. This was the same cylinder that had a significantly lower compression reading then the rest when I tested (70, 62, 85, 80 top down). So I decided to pull off the side cover to get a look at the pistons. As I suspected, 2nd from the top is busted up on the side right at the exhaust port. Don't know if the ring failed first or if there was an oil problem in that cylinder first or what. But I know the piston needs replacing. The cylinder wall looks good but I supposed it would need honing? Hopefully the rod isn't damaged.

Now I'm wondering how screwed I got here but I'm not real interested in abandoning the boat and selling it. I'm brave (probably foolishly) and willing to work work for it. I've done engine work but not hardcore internal stuff like piston replacement.

I've seen the 1 or 2 threads discussing similar topics. I'm going to check with a local machine shop tomorrow to see if they would do the replacement if I disassemble and bring the necessary parts. Any advice/tips including but not limited to necessary parts list would be great. I ordered the Seloc manual today but it looks rather disappointing so I supposed I should get the factory manual.

Thanks for any help saving my rough introduction to the boating world!

Re: 1990 Merc outboard 115 piston replacement

You haven't provided your s/n but you can check your s/ns on the inside cover of this manual:

http://1manual.com/Mercury manuals/Service Manual PDFs/TwoStroke/13645_2/cover.pdf

You must have Adobe Acrobat reader installed to use this manual. If you scroll down to the lower part of the opening page, you will see the various engine components in red. Click on the one you want and when the first page opens, click on the "Save As" icon at the top LH corner of the page and you can save it to your computer.

Gerry

Re: 1990 Merc outboard 115 piston replacement

Pictures of the damage will help determine the CAUSE of the failure which MUST BE corrected or it will occur again.

Most common cause of piston failure is a fuel restriction in the carb leaning the mixture, overheating the piston until it either 'sticks' to the cyl or melts part of the piston.

Any rebuild ALWAY rebuild all carbs and the fuel pump, the kits are cheap, and also rebuild the water pump to ensure proper cooling.

Re: 1990 Merc outboard 115 piston replacement

Serial Number: C227590

I've got that manual/pdf but the 4 cylinder powerhead page is missing (of course).

Thanks for the tip, the carbs were rebuilt recently (I was told) but I will definately inspect them and have just rebuilt the fuel pump. I'll do things like the thermostat. The water pump consists of just an impeller in the lower unit correct?

Thanks for the replies. I'm about to call the machine shop to see if they can help me out but will need some tips if I end up having to do the actual piston job myself.

Re: 1990 Merc outboard 115 piston replacement

A lot has changed on this story. I can explain later but I have a quick question. Why is the "timing pointer" on the flywheel cover adjustable? How do I know if its in the right location?

Re: 1990 Merc outboard 115 piston replacement

Mickeyd, you set the pointer using a dial gauge. If you can get a hold of one of Jay Smiths gauges www.jaysmithracing.com your life will be greatly simplified. The procedure is in the Service Manual and if you call Jay he'll walk you through it.

Basically, you insert the dial gauge into the plug hole on #1 and find out where dwell is and then set the pointer. O on the pointer is not TDC on #1 which is why it's adjustable.

So did you wash the aluminum off the that bad cylinder with muriatic acid or did you find someone nearby that would bore a blind hole? Just curious.

Re: 1990 Merc outboard 115 piston replacement

I'll tell the whole story later... right this moment I'm trying to check timing. I got a dial indicator and did the pointer alignment. However, I'm not seeing any marks with my timing light. I don't know if there is something wrong with my eyes or timing is way off. I'm just doing idle timing at the moment. Not sure whats going on. HELP?!?!?

Anybody know approximately what the throttle/timing arms should look like at idle position? Right now they are pretty much in a straight line.

Re: 1990 Merc outboard 115 piston replacement

I've been assuming number 1 on this 4 cyl is the top, not the bottom. I'm not wrong on that am I?

Re: 1990 Merc outboard 115 piston replacement

The timing light seems to flash when the marks are about 1 quarter of a flywheel turn back from where they should be.

Re: 1990 Merc outboard 115 piston replacement

Timing light on cylinder 3 fires much closer to the mark. The switchbox and coil wiring does match the manual. This makes little sense. Could there be something wrong with my "trigger"? The firing should be pretty much evenly distributed across the rotation of the flywheel correct?

Re: 1990 Merc outboard 115 piston replacement

It appears nobody is listening but..

My latest observations are that 1 and 3 seem to fire/blink at the same time 45 degrees behind where 3 should be.

I had tested the resistance values on the trigger previously. Now I'm thinking the switchbox may be faulty. This is a disaster and I'm too disgusted to continue at the moment.

Re: 1990 Merc outboard 115 piston replacement

Verify trigger wire colors and position on the switchbox, this is critical to firing order.

Is your flywheel one piece? Some older models have a bolted on outer to a center hub, it is quite common for somoeone to have it apart and not reassemble it 'clocked' correctly which easily makes it appear that timing is way off.

Remove all spark plugs and turn the motor by hand til the top piston is at TDC, mark the flywheel with chark or dot of paint, repeat for each cyl.

Now start the motor or crank with timing light and see where each mark is, all should show very close to the same place. Any that appear in any other 'clock' position is cause for suspicion.

Coils # from top to bottom to match cyls. verify green wires from switchbox to coils are correct and not switched around.

Re: 1990 Merc outboard 115 piston replacement

The easy way to figure out if the switchbox is wired up wrong is move the timing light from #1 to #2, then #3 and finally #4. If you do that and still don't hit the mark then you either have a bad trigger, switchbox or your flywheel may have been assembled incorrectly. I think the firing order is 1,3,4,2, can't remember off the top of my head. Too many years of using color codes I guess.. LOL.

Re: 1990 Merc outboard 115 piston replacement

Thanks for the reply. I think its 1,3,2,4. I've been flashing this timing light so much I may go blind but I've got some definitive observations and some theories. I should post a diagram to explain this. What I'm seeing is a 90degree shift in timing. However on top of that spark 2 fires in 2 consecutive locations (where 1 should be assuming 90deg shift, and where 4 would be at 90deg). 3 also has a similar situation. The shift could indicate trigger, switchbox/cdi or inner magnet on flywheel. The magnets all appear fine and don't seem to have moved. The tigger ohms tests check out. So between that and the extra dual firing going on my current hypothesis is the switchbox (perhaps the internal bias circuitry) being screwy. I shall post my story leading up to this in a few. Any advice before I drop more money on a new switchbox is much appreciated.

Re: 1990 Merc outboard 115 piston replacement

Dual firing is a switchbox. Dual firing is best verified with an inductive tach, the culprit cyls will read twice the other cyls.

The old Force switchboxes would develope this problem which would cause that cyl to run lean and toast a piston.

Not a real common problem on Merc boxes but it has been know to happen.

Replace the switchbox.

Re: 1990 Merc outboard 115 piston replacement

Ordered one last night from **********. Not the cheapest part so thanks for the additional piece of mind. My nerves are running thin with this project so hopefully this will set all straight.

CharlieB said:

Dual firing is a switchbox. Dual firing is best verified with an inductive tach, the culprit cyls will read twice the other cyls.

The old Force switchboxes would develope this problem which would cause that cyl to run lean and toast a piston.

Not a real common problem on Merc boxes but it has been know to happen.

Replace the switchbox.

Click to expand...

Re: 1990 Merc outboard 115 piston replacement

If anyone is interested in how I got here from my initial post...

I did bring the powerhead into a local boat/machine shop. Unfortunately the piston in question was quite busted up and the cylinder dome was beat up and particles had gotten down and affected the crank journal. He claimed it wasn't worth fixing. Frustrated I decided the same day to order a remanufactured powerhead from crowleymarine. 2300 + 200 2day shipping + 100 core = $2600. Painful but I decided it was the best path overall. So I cleaned up the carbs and rest of the parts and installed my new powerhead last weekend. I have check/adjusted things as best I could. I drained and filled fuel tank with non-ethenol gas and 50:1 oil mix as perscribed in crowleymarines break-in.

Last but certainly not least was timing. Got a dial gauge and timing light. But of course all was not well. I ran in to the problems I described above and after much further frustration I decided to throw down more cash for a switchbox. Waiting for that to ship and I reeeeeaally hope it sets everything straight. I think the SELOC manual mentions that bad coils can sometimes damage a switchbox so I'm a bit worried about that.

Here is a question. With the plugs pulled (doing cranking tests for timing) do the plugs need to be grounded to prevent damage to coils or switchbox? SELOC says to ground them all but unless I only ground the 1 I'm testing, I get nothing with the timing light.

Good times.

Re: 1990 Merc outboard 115 piston replacement

Don't buy from "**********"... worst experience I've had with a business in a long time! They SUCK!

Re: 1990 Merc outboard 115 piston replacement

The electrical energy HAS TO go somewhere, therefor the plug wires MUST BE GROUNDED, or you risk damage to the switchbox. Period.

The timing light is triggered by the current passing thru the plug wire, no current, the light will not flash.

So either leave the plugs IN and the wires on the plugs, OR, to ease the strain on the starter and battery, remove the plugs and GROUND ALL THE WIRES.

It COULD be possible that a direct grouond allows the voltage to remain loow where a plug gap causes additional resistance, forcing the voltage to rise higher and the inductive pick-up on the timing light senses the higher voltage. So instead of gounding the #1 wire, rig it to your adjustable gap spark tester, this way you have both the gap causing the higher voltage to arc AND a safe path to ground for the current so you won't possibly damage the switchbox.

Re: 1990 Merc outboard 115 piston replacement

That all makes sense to me. Thanks. Perhaps I did damage to the switchbox by not grounding them. I have an inline spark test light I can use. Hopefully that's enough draw to trigger my timing light pickup. But I've only got one of those.. Maybe I'll just connect the plugs and ground them without screwing them into the block.