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Low Compression Outboard

zhandfull

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Bought an old 2 stroke outboard and it has low compression. Looks like may need a rebuild. Not above doing the grunt work myself. Any good machine shops for outboards in Havasu or IE area of CA? Not super familiar with 2 strokes. Can I leek down cylinder to locate low compression reason. Has to be rings, or head gasket issue I would think. The color on plug has me thinking possible head gasket or cracked cylinder.
1996 Force 120
Compression below:
#1 =135
#2 = 65 plug has a different look, rusty brown look instead of oily black like others.
#3 = 165
#4 = 170
 

Crazyhippy

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Pull the head, the motors are unbelievably simple.

Essentially a car motor stood on end. Intake comes thru the oil pan, so you can access rod bolts fairly quickly if needed. Head is literally just a chunk of aluminum bolted on to hold the spark plug...

There is magic and skill in designing and getting every last HP out, but basic tear down and rebuild are SIMPLE!
 

Markus

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A 1996 Force 120 hp 4 cylinder (I thought they were 5 cylinder, but maybe those were the bigger engines) engine is most likely not worth rebuilding.

Not that the Force 4-cyl is a very bad engine, but it is pretty much worthless even in good shape.

170 lbs compression is very high for a 2-stroke outboard.

With some luck, it is all caused by carbon deposits, and the piston rings on #2 are stuck.

Start by running a strong dose of PEA-based cleaner through the engine, and let it soak for a few days. Mercury Ring Free and Chevron Techron Marine are some options for mixing with fuel. Yamaha and others used to have products that you spray through the spark plug hole. If still available, use one of those, as only God knows what rubber components were used on that engine.

If that doesn’t do it, take off the cylinder head and pray that head gaskets are still available in case the engine still has life in it (you can Google to find out). Depending on what you find, options include:
1. Pick up another 120 hp Force for free or thereabout
2. Pick up a 115 hp 2-stroke Yamaha, which was the best engine in that size bracket
3. Pick up a 120 hp 2-stroke Nissan/Tohatsu if you don’t like V4 look of the Yamaha
 

zhandfull

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Looks like a head gasket. Some rust on cylinder. Going to see if I can clean it up with new gasket and make it run a couple more years. Any tips on what to use to clean up cylinder. Hoping the rust has not started pitting cylinder. One of those green scrub pads work with some light oil work?

Anyone know of a shop/store that may have a head gasket in Havasu today or Monday?
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zhandfull

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On the positive side. I wanted a boat with an outboard because I’m to Fing old to be bent over a transom working in some distorted position on the motor.

It’s nice to be able to stand up and work on this thing.
 

zhandfull

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Taking a closer look and #2 has a bad score. Think this outboard is done.

What are my options for repowering? There is a power head close to me with 147# compression for a 1k. Might be a bandaid fix to get back on water quickly. Little skeptical about buying without pulling head and taking a look at this point.

How about a newer four stroke engine. Any of the Honda, Yamaha, Mercs plug and play where a DIYer can install and hit the water.
 

Bugginout

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From the looks of the car in your sig you are a little more handy than most. I'm not a whacker guy but can't you bore it and put new pistons in it?
 

lbhsbz

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Taking a closer look and #2 has a bad score. Think this outboard is done.

What are my options for repowering? There is a power head close to me with 147# compression for a 1k. Might be a bandaid fix to get back on water quickly. Little skeptical about buying without pulling head and taking a look at this point.

How about a newer four stroke engine. Any of the Honda, Yamaha, Mercs plug and play where a DIYer can install and hit the water.
Put a head gasket on it…it’ll probably run another 30 years being down 3hp from new. If it was something desirable where it would be sorta devastating should it blow up properly…like a 2.5 L merc, then I’d take steps to lessen the chances of that happening…but a Farce 4 cylinder?…run it.

In my experience…the only thing compression seems to help with is starting…after they’re running, as long as the piston doesn’t have a hole in it…they run fine. I replaced a clapped out merc V6 with chrome peeling off the cylinders and scoring and broken rings that were bonded to the pistons with aluminum smears and the boat didn’t run a single MPH faster with a fresh powerhead (120 on all holes) on it…was just easier to start cold.

The fresh powerhead has been on the boat for 7 years or so, and I’m not nice to it…runs like new. I did a compression test for a perspective buyer and one side was down quite a bit…had a broken ring in one hole and scored cylinder/scuffed piston in another and pitting on one of the crank journals……you’d never know it behind the wheel. I put a fresh one on for whoever buys it, but I’m gonna put the old back back on something…maybe throw some rings in it (and a crank)...only because I've got 'em on the shelf. If I didn't, I'd just mill another .060" off the heads and call it a day lol.
 
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Flying_Lavey

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I would suggest throwing a straight edge and a feeler gauge on the block and head to make sure they aren't too warped also. Engine could have had a cooling issue causing the failure by warping the head or block. You replace the head gasket and that is the case, you could end up with the same situation very quickly.
 

HST4ME

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Scrap it, it's a late model with the 8 pin Merc harness, find a used Merc something to plug in. I wouldn't spend a penny on it.

Someone in this thread I wouldn't listen too, they don't know what a good motor runs like. It all boils down to do you want to go on the water with your family and friends and enjoy yourself, or deal with a clapped out pile of shit.
 
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zhandfull

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Scrap it, it's a late model with the 8 pin Merc harness, find a used Merc something to plug in. I wouldn't spend a penny on it.

Someone in this thread I wouldn't listen too, they don't know what a good motor runs like. It all boils down to do you want to go on the water with your family and friends and enjoy yourself, or deal with a clapped out pile of shit.
Lol. The plan when I bought the pontoon a few months ago was to try and get a couple years out of it before upgrading the engine Didn’t think that was unrealistic being a patio boat. Might have to patch it up and keep the Force going for a while longer.

The bad thing is I don’t know shit about outboards regarding compatibility or much else. Learning quickly though. I had bought a repair manual for the Force and it looks pretty damn simple.

That’s interesting about the 8 pin connector. So I can find a later model 200 merc and bolt one in with minimal effort? What about EFI engines. Do I need different fuel system or controls or is it all under the engine cover?
 

HST4ME

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All an old school pontoon needs is 115 hp. Merc has a 8 pin to newer motor adapter for $65. Shop for a newer 4 stroke and enjoy the boat.
 

Markus

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If you want to minimise your outlays, buy a head gasket and hope that it runs for a couple of years. (I wouldn't, but I am not a Force kind of guy)

If you want something economical and reliable, get a Yamaha or Tohatsu 2-stroke. Need to re-rig wire harness and gauges, but it is not a lot of work.

If you have some money to spend, get a newer 4-stroke Merc and use that 8-pin to 14-pin(?) adapter.

Whatever you do, don't spend more money than the price of a new headgasket on that Force engine. The cost of the head gasket is higher than the value of the motor with a new head gasket.
 

zhandfull

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How about a 2002 Merc Optimax those any good?

Upgrading to a four stroke probably not in the budget. Might be able to pickup a older 2 stroke from someone upgrading though.
 

lbhsbz

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Scrap it, it's a late model with the 8 pin Merc harness, find a used Merc something to plug in. I wouldn't spend a penny on it.

Someone in this thread I wouldn't listen too, they don't know what a good motor runs like. It all boils down to do you want to go on the water with your family and friends and enjoy yourself, or deal with a clapped out pile of shit.
Obviously not ideal for a performance application...but if the motor is not worth anything and still runs and it's going in the trash anyway when it comes off the boat...nobody gives a shit if the pontoon boat does 27mph or 24mph...why not run it till it's scrap before you scrap it...was my point here.
 
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Markus

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How about a 2002 Merc Optimax those any good?

Upgrading to a four stroke probably not in the budget. Might be able to pickup a older 2 stroke from someone upgrading though.
If i remember correctly, 2002 was the first year when the optimax had the bugs worked out.
 

zhandfull

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got a head gasket for the Force 120. Will put that on next weekend. Piston has excess play in the bore so not sure it will last long. If it runs, thinking it will be like a ticking time bomb.

Found and picked up a 150 Merc XR2 complete for $350. The guy I bought it from seem to think it had good compression and would run. I’m skeptical of course but the price was right even if it ends up being parts. Going to start messing with the XR2 to replace the force.
 
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zhandfull

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Funny how when looking for an old outboard they are all advertising that they run good. Then when you start pressing them on seeing it and doing a compression check. Usually the truth comes out. It’s got low compression on one or all the cylinders.

Here’s the project I picked up. Yeah it looks a little rough.
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IMG_1641.png

This is right up my alley to pick something up out of the dirt and try to bring is back to life.
On the positive side it ran 120 compression +\- a few psi on all cylinders. Yeah it’s dirty and maybe a little abused but for the most part 100% factory stock as far as I can tell. So no one has really screwed with it.

Compression check, remove oil injection, go through carbs, new impeller. And going to try and see if she will run.
 
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Markus

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Removing the oil injection is a good idea, but wait until you know that the engine is running well.

Before you do anything, run it on the hose. That gives you a baseline.

Then do carbs and impeller.

Run it on the hose again to get a new baseline.

Then mount it on the boat and run it.

Then consider removing the oil injection.
 

zhandfull

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Was it stored in a hole in the ground?
Almost looks like it. Carbs too dirty to try running. Intake was clean though when removing carbs.
 

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Ragged Edge

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Definitely replace the water pump. Those short vane impellers do not like to sit and you have no idea how old it was when the motor was removed.
 

zhandfull

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Removing the oil injection is a good idea, but wait until you know that the engine is running well.

Before you do anything, run it on the hose. That gives you a baseline.

Then do carbs and impeller.

Run it on the hose again to get a new baseline.

Then mount it on the boat and run it.

Then consider removing the oil injection.

Cleaned up the carbs on outside with carb cleaner and reinstalled with new fuel line to test run on stand. Waiting on carb kits anyways.

Was able to start engine on stand but it was not running great. Started checking each spark plug wire with timing light and it seems that I have no spark coming from cylinder 2 or 4.

Guess maybe I’ll swap some coil packs and plug wires around first before moving on to checking switch packs.
 

zhandfull

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Does Mercury still make switch packs for a 1987?

What’s the next best option if oem is not available, is CDI electronics any good?
 

stoker2001

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Does Mercury still make switch packs for a 1987?

What’s the next best option if oem is not available, is CDI electronics any good?
go with Sierra brand.available on Amazon.be careful tho,the good ones will say made in Germany right on them
 

HST4ME

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Just about everything is available aftermarket. The 2 liters were excellent motors, except for the oil injection, and worth throwing some money at.
 

zhandfull

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Changed out the trigger, stator, and switch packs. Wire was getting bad on trigger and stator. Think I fried the original switch packs when running compression test without plugs grounded.

Removed oil injection and two modules. One for oil injection and other for idle stabilizer.

Fired up on stand and ran it for a minute or so. No water pumping. Changed out the impeller. Old one was disintegrating. Was a bitch getting all the pieces out of pickup. Was using small screwdriver and air nozzle with some success. Then put the muffs on to try and flush them out. Finally just flipped it upside down and used air and screwdriver to get it clean.
IMG_1774.jpeg


Getting the lower back on is a real bitch working alone with outboard on a stand. Finally gave up till I can get some help.

Next up pop it valve, thermostats, and fresh gear oil.

Trim motor doesn’t seem to be working either so that needs looking at.

Lot of work but getting familiar with how this thing works.

Hoping to get some more years out of this 36 year old Merc 150.
 

zhandfull

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Oh yeah, had the prop fixed up. Wife wanted it for a candle holder. I will be reinstalling it shortly. 😁
IMG_1776.jpeg
 

zhandfull

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ground the ignition with the lanyard switch
I don’t need to ground plugs as long as switch ground is connected? In my case no switch connected yet. I can connect 8 pin black to black/yellow to ground ignition system.

Laid engine back horizontal to install lower unit today. So much easier than trying to lift lower unit in place with engine near vertical.

Fired it up this evening in tub of water. Love the sound of 2 strokes!

Not sure if I have water circulating. Not getting water coming out tell tale. Probably going to replace thermostats and hoses when I do poppet valve. Removed the old thermostats this evening. Hard to tell if they were working. My wife is pretty understanding but I will have to wait till she’s gone to throw them in one of her pans on the stove to find out for sure. 😁 Heads were pretty clean when I ran my finger around inside where each thermostat goes. Haven’t broken off any bolts yet either. Definitely a fresh water only motor I’m thinking.
 
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HST4ME

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Not having the plugs grounded won't do anything to the boxes. What kills them is any sort of voltage to the black and yellow kill circuit or over voltage from the stator.
 

Markus

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I don’t need to ground plugs as long as switch ground is connected? In my case no switch connected yet. I can connect 8 pin black to black/yellow to ground ignition system.

The lanyard switch grounds the ignition. That way you don't need to worry about sparks trying to find their way to ground when doing a compression test.
 

zhandfull

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Lake tested the Merc 150 three or four months ago and it ran hot. Buzzer sounded. Let it cool off and idled it back in. Pulled the lower again and replaced the pickup tube. The old one had some damage on one end. It was probably affecting the flow a little. Had my manual this time and realized I had forgot a rubber bushing on the pickup where it slips in the guide tube on lower. Trip back to ramp proved that cooling system was now working correctly.

Pulled the carb to check them out and everything has been sitting now for a while. Carbs actually look good. Amazing how simple they are. Other than floats and jets I’m not sure if there are any other adjustments to be done.

Its been sitting for a few months now. Time to get back on it. Scoped the cylinders this weekend. Crosshatching looks decent and it has standard pistons. Had to look at reeds while I had it apart. They look good as well. Think I’m going to order some Carlson Reeds to replace what looks like originals.
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For picking this thing up off the dirt I’m still surprised about condition when working on it.

Planning on being back in a few weeks to put back together and lake test again.
 

zhandfull

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Going through fuel pump and didn’t see where this plastic button came from before it fell out.
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Saw a video that showed it install like this.
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Doesn’t seem or feel right.
Some fuel pump videos on YouTube show no button being used. 🤷‍♂️
 
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zhandfull

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Ran the pontoon through a couple test runs this weekend. So far so good with the Merc 150xr2 that I picked up out of the dirt for $350.

Changed out a bunch of stuff including:
*Water pump
*pop it valve
*fuel pump kit
*stator and pickup (wires were jacked)
*New CCM reeds for peace of mind.
*Thermostats
* fuel and water lines.

Trims not working. Think it’s the same on Force, going to swap them out.

Has a new top speed of about 29mph on the gps so that is nice. The Force only ran in the mid teens (with one bad cylinder).

Is it bad I’m looking for a 200HP now?
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zhandfull

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Ran the 150XR2 last weekend again. Have been getting the overheat alarm when running over 3,000 rpm. I back it down to idle and it goes off quickly. Cruising at 3,000 all day no issues.

Pontoon didn’t come with water temp or pressure gauge. I ordered pressure gauge and installed it last weekend. Merc manual I have says 15-25 psi. This outboard is running near 25 at idle and almost pegs the gauge at 40-50psi at cruise. High gauge reading is 30 but needle will continue going higher till it stops at the zero rest bar on the gauge.

I replace poppet valve and pulled it again last weekend to inspect. Now 250 miles away from boat. I’m wondering if I originally installed correctly. No signs on pressure gauge of it working. Nice smooth pressure increase on the gauge through entire RPM range. Second guessing & wondering if I sandwich the diagram between the correct parts of housing. Don’t think it would go back on if not in correct order.

Been watching this guy on YouTube with the same issue, high pressure and high temps. He has went through everything on his $500 Cee Bee boat (same engine). Hasn’t found the issue yet.
 
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HST4ME

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The thermostats basically only control low speed temps, the poppet controls the water pressure for higher rpm, if the water can't leave the block you get the over heat.
 

ChrisV

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The thermostats basically only control low speed temps, the poppet controls the water pressure for higher rpm, if the water can't leave the block you get the over heat.
So low pressure is better than high? Ideally what do you want for an 2.5?
 
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