1997 Force 120 lost power - bad cylinder #1?

nnk_boater

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Compression performed by dealer as of April 2014 when I took ownership - 1) 150 2) 150 3) 155 4 ) 155
First 10 hours, no powerhead issues.
Now, it has no power and won’t go over 1500 rpm. Starts with no problem. Problem occurred on the water when attempting to get up on plane.

Troubleshooting:
Compression now using my gauge (different than gauge used in April)
Cold – 1) 135 2) 150 3) 150 4) 155 (one squirt of fogger in each cylinder)
Hot - 1) 120 2) 130 3) 130 4)135
Spark good on all four cylinders using a€“ 7/16 inch using spark gap tester
Timing at cranking speed: 32 degrees BTDC
Tested running from remote fuel tank and€“ no difference
Observe fuel to remain near full in fuel filter installed after fuel pump.

I think there is an issue with cylinder #1 but, current compression does not look that bad. Is there anything else I should look for before removing the head?
 
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brushhippie

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As long as they are within 20% you should be good. Force motors tend to have higher compression...but a buck twenty on the low side is not bad at all...and well within the 20%.
 
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pnwboat

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I would not remove the head just yet. Compression looks OK. Fuel filter should be installed between the fuel pump and carburetors. Does the primer bulb get good and firm after squeezing 5 or 6 times?

Does the engine run OK other than the fact that it won't go over 1500 RPM's? Does it idle fine?
 

jerryjerry05

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The later model Forces comp is not the same on all cyl.
There is a difference in #1 and 4 compared to #2/3
Someone posted the actual readings on here a while ago.
IF?? You have a different gauge then the readings might change with the gauge.
A 15# difference IS a problem in these motors.
If I had 10# difference in my motors I'd be looking for a problem.
Start with a different gauge, take out all plugs, no oil in the cylinders.
Makes no difference if it's hot or cold.
Let it spin until the gauge stops going up.
Then get a bore scope or internal camera.
Or pull the head.
The head gasket could be bad?
You run in salt water? Living in Va. you probably do.
No mater how good you flush you never get all the salt out.
 

nnk_boater

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First, many thanks to all the experts that have chimed in. At first I was alarmed as my compression numbers were low on all cylinders compared to the numbers taken in April by the dealer. Again, that was a different gauge. Then, I read the manual, page 1-18 states - "IMPORTANT: By design, the #1 cylinder on the 90 and 120 engine is generally 10 psi lower than the other cylinders. The #4 cylinder on the 120 is generally 5 psi lower than #2 and #3. I've spent some time trying to determine if my gauge is anywhere near accurate (Harbor Freight). I conclude that it is accurate based upon comparison to another new gauge from a big box store and the gauge on my compressor measured using my compressor. Regardless, we are really focusing on differences in cylinders and not the actual magnitude. That said, the numbers posted are as accurate as I can get. By the way, the HF gauge no longer holds the pressure reading (my bad) but still works and I will be swapping for another HF gauge soon. Let me know if posting a video of the running motor as I increase rpms would help. I did not mention that as I increase rpms, I hear a disturbing loose metal on metal sound. It is a nice day here and I am looking forward to pulling the head - $30 for a new head gasket and an unobstructed view of all cylinders verses "bore scope or internal camera", I choose remove head. I just want to be sure I am not missing something trivial that will provide a quick, painless repair before I start surgery. If a bad head gasket can be the cause, that would be like hitting the lottery at this point.
 

jerryjerry05

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NYBO might be on to something with the reeds.
The later models have some problems with them.
The reeds should have NO affect on the comp.
IF??? Your under 50 and don't plan on dying soon??
Then buy a good gauge. I paid $160 in 1986 for a tester kit(does diesels too).
Never had a problem since then.
 

Jiggz

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Instead of the head, start with the carburetor removal to inspect the reeds. Try saving the gaskets for you can re-use them if not order new ones. These "newer" 120's are well known for reed breaking problems. Another indication of reed problem is the large amount of fuel oil mixture blowback from the carbs. To test for this, remove carb air covers and hold a paper towel in front of the carb about 4~6 inches away, not too close it will get sucked in. And not too high it won't catch anything. Try running the motor and see if the paper towel will get wet in a matter of seconds. Test each carb, whichever wet the most start with that carb for reed inspection.
 

nnk_boater

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I removed the head. From the pictures, it looks like it was due, it has some holes. Is there a secret to removing the lime scale buildup from the head? Also, in the pics, you will see pitting in the head - this is at about 1 o'clock on each cylinder. Since my compression was good, I am thinking I clean it up the best I can and ignore the pitting.

All cylinders look good with the exception of #3, it has some very light scoring - see pics. Again, compression was good so, I'm inclined to ignore it (and don't want to remove a piston to hone it). I can just barely catch a finger nail in the lower score marks.

I had planned a rebuild of the carbs this winter anyway so, I will check the reeds when I remove the carbs. I'm hoping that is my problem. To answer pnwboat's question, it did start right up fine every time and idled well. When the problem happened, I ran the boat for thirty minutes after that to our destination (5 mph) and after eight hours, returned on a thirty minute trip at 5 mph. The entire time, it ran relatively smooth at about 1400 rpm.
 

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pnwboat

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From the amount of corrosion, it looks like maybe the motor was run in salt water? Regardless, the cylinders look OK, so that's good news. No real secret to removing the scale. Just some elbow grease and patience.


Like you plan, check the reeds and carburetors and see if you can find any problems there.
 

nnk_boater

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The reeds can be eliminated. Except for the reed gasket, they all look good. Lacking a smoking gun, that leaves me with the carburetors. I also have fuel pump rebuild on my maintenance list. The connecting rods have a little play (.035 in.) along the direction of the camshaft. All four have the same play so I suspect that is normal (or at least normal at this age).
 

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Jiggz

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Can you post close up pics of the piston tops especially those with scored cylinders and most especially #1. From the pics earlier posted, it looks like you have a broken ring on #1 piston as indicated by little dents at the 9-10 o'clock position. Unaware this may look like a little dent but behind it is really broken rings that got caught on the ports. Probably a better explanation for lower compression compare to the rest of the cylinders.
 

nnk_boater

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Here is the full size image of all four pistons. I see no dents, chips or imperfections of any kind in the cylinder tops. I will post close-ups of each tomorrow. The cylinder with the light scoring (#3) was one with the better compression compared to the others. #1 is the only one that might be suspect, but the #1 cylinder looks to be in good shape.
 
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Jiggz

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I guess what I was seeing is the stamping on the piston and not really a dent. However, after reviewing the rest of the pics, there seems to be a big difference in color on #3 cylinder head and obviously looks cleaner than the rest of the cylinders. The scoring is something to be concerned about as what causes it, i.e. lack of lube due to water intrusion (steam cleaning) or not firing at all?
 

jerryjerry05

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The gasket looks pretty rough but the sealing ring on each doesn't look like it's broken through anywhere.
The scoring on the one cylinder could be a broken ring.It looks like you might have caught it before it really did some serious damage.
You could run it like that. Might last a long time maybe not??Bought a 125 for resale and it ran great, great compression. Pulled the head to check to sell, and found a lot of scoring????
Since you have the reeds out, take the piston out and check.
 

nnk_boater

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Jiggz

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Thanks for the pics. The pistons and all the cylinders seems to be fine. One thing I noted is on piston #3. Note the deflector top which is cleaner compare than the other pistons. Additionally, the cylinder head (from previous pics) is also cleaner and lighter in color. I would surmised there was some sort of water intrusion just shortly before you decided to take it apart, or it could have stopped firing. Since the fuel pump is mounted on #3 cylinder, have you checked the fuel pump diaphragm?
 

nnk_boater

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I've got the fuel pump rebuild kit and might get to that this weekend. I'll take that opportunity to view the rings visible near the transfer ports.

Jumping ahead to the head reinstallation. What do you recommend for thread dressing on the head bolts, just some light oil on the threads and under the head of bolt? no Loctite?
 

Jiggz

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No loctite. These bolts are subject to different temps and are of different material than the head metals. I recommend using anti-seize instead preferably the copper based instead of the AL. I'll say inspect the #3 rings first before re-installing the head at least both on the transfer and exhaust sides. Cylinder scoring is not something that normally happens unless the rings have problems.
 
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