Low compression on all 4 cyliners on Force 120

[rigasr]

I have a 1999 Force 120 on a Bayliner 1800 (18 ft). Last week on the lake it struggled with power, was onlynable to get 22 mph. I ussually get about 30.
I thought the timing was out as i had just removed the flywheel to reattach the gear ring which was knocked off by a cheap/bad starter. I checked the timing but that is still perfect at 30 deg. Fuel pump and lines all checked good.
I rented a compression meter and tested each cylinder. Getting about 50, 50, 60 and 55 psi for cylinders 1, 2, 3, and 4. Reading this forum i belive i should be getting about 120 psi. I thought maybe the rented meter is faulty so i rented anothr on from a different parts store, same results.
I visually inspected the head gasket from outside but dont see anything so dont think its a blown head gasket.
The motor starts up fine though, it idles fine just doesnt have the power it used to have.
Is this a clear case of engine rebuild i.e. Bore, new pistons and rings? Or could it be something else?

 

[JB]

Re: Low compression on all 4 cyliners on Force 120

Howdy, rigasr.

I suspect that you did the test incorrectly. . .for 2 reasons:

1. All 4 cylinders are very close, only 10psi span. This does not happen if there is a damaged cylinder or two. The likelihood that all 4 would go bad by the same amount at the same time is so small that it is near impossible.

2. The engine runs and makes nearly as much power as when you are happy with it. That does not happen when the engine is mechanically broke.

Go to the Engine FAQs Forum and do a decarbon procedure, then do a new compression test using the instructions given there. Let us know the results.

I am quite sure you don't need to rebuild your engine. Good luck.

 

[roscoe]

Re: Low compression on all 4 cyliners on Force 120

Agree with JB.
With the posted compression numbers, the engine would not run and would certainly not get you to 22 mph.

More likely that you lost spark on one cylinder.

 

[jerryjerry05]

Re: Low compression on all 4 cyliners on Force 120

Remove all the plugs and redo the tests.Then spray some oil in the cylinders and see what #s you get then.Let it turn over a bunch of times.
Like Rosco said,possible lost spark on one cylinder.Do a spark test.outboardignition.com has test procedures for the electrical system.

Profile? You might be close to someone who can help.J

 

[rigasr]

Re: Low compression on all 4 cyliners on Force 120

Hi, i'm not sure how i could have done the compression test incorrectly. I screw in the one end of the meter and crank the motor a few times.
I did a basic spark test already and all plugs fire. Will do a decarb this weekend and recheck compression.
Thanks all.

 

[fucawi]

Re: Low compression on all 4 cyliners on Force 120

you need to have a well charged battery and take all the plugs out ..remember to fit and ground the plugs dont just leave the leads hanging ..can damage a CDI unit

 

[bentle]

Re: Low compression on all 4 cyliners on Force 120

I own a 125 force outboard and also had to do a compression test. when I first tested compression I was getting some lower numbers, not nearly as low as you had. I later noticed that my engine was turning over slower than normal. so I charged the battery back up and kept my portable power supply on hand to hook up if I needed to. I checked again and got 120 on 3 cylinders and about 115 on #2to cylinder
meaning a huge difference. also try and look for any hoses on the engine that may be leaking, disconnected, or even missing. One other place you may look into is your reed valves. They are located behind the carb. intake manifold. Make sure they
are flat and flush with the cages. I don't really think that is your problem but it,s a
place you can loose some compression. do the de carbon though cause it will help.

 

[roscoe]

Re: Low compression on all 4 cyliners on Force 120

you must remove a 4 plugs and open the throttle for the compression test.

Can't just take out one plug at a time.

 

[rigasr]

Re: Low compression on all 4 cyliners on Force 120

Per the compression test FAQ posted on this site, opening the throttle has no affect. I however did the compression test exactly per the instructions as posted on the FAQ section and also tried with the throttle open and the results are the same.

Compression test by JB: http://forums.iboats.com/showthread.php?t=391323

Motor turns over fast while cranking, battery is relatively new and was charged overnight as I knew I would be doing quite a bit of cranking. I suspect the low compression allows the motor to crank easy and turn fast.

Can the reed valves really affect compression?

I will do the de carbon this weekend.

Thanks again all.

 

[bentle]

Re: Low compression on all 4 cyliners on Force 120

Yes if the reed pedals are not seating or sealing all the way against their cages then yes you will
loose compression there. Reeds are made to last for a very long time so it may not even be your problem. Try the other things first and then look into that last. Once we start pulling carbs off it
Can be a headache to sink them back in correctly.if you can try and look for any broken, cracked or even missing hoses that work with crank case compression. Good luck and keep on it
and you will figure it out. Oh and if you don,t already have a manual then may I suggest on getting one.kinda like swimming with your hands tied without it. Again good luck.

 

[bentle]

Re: Low compression on all 4 cyliners on Force 120

Deleted this cause it was the same as my last post. Hate it when that happens.

 

[Frank Acampora]

Re: Low compression on all 4 cyliners on Force 120

Here is a case of trying "snake oil." (Seafoam) You may simply have stuck rings and the cleaner MAY free them. On the other hand--it is rare and i would not expect this on all four cylinders---you may have broken some rings. If your engine has semi-keystone top rings, they are more prone to breaking than the square type.

So, first try cleaning the engine and see if compression comes up. If it does not, remove the head and exhaust cover and visually inspect the cylinder bores and rings.

At 60 PSI, I strongly doubt that there is enough or any damage requiring rebuilding. I just finished fixing an engine with 60 PSI on one cylinder. Turned out that both rings were stuck. On this one, I had pulled the piston, so judicious application of heat released them, I was able to clean them and the grooves, and reinstall. Compression came up to 130

 

[rigasr]

Re: Low compression on all 4 cyliners on Force 120

Thanks Frank for your input. First thing, I will be decarb'ing it this weekend. Now, after decarb, if I dont see any improvement its possible I could have stuck rings due to bad oil or gas or something. BTW: The plugs were quite dirty/carbonated when I took them out for the compression test. I did replace them though.
I am hoping though that the decarb will help with the compression.

The question I have is, how can I tell if the rings are stuck if it ever gets to the point that I need to remove the head and exhaust plate? Do I need to pull the piston to tell?

 

[JB]

Re: Low compression on all 4 cyliners on Force 120

Yes if the reed pedals are not seating or sealing all the way against their cages then yes you will
loose compression there.

Disagree. Throttle position has no effect and even the presence or absence of reeds has no effect. Measuring compression in a 2 stroke is all about cylinder walls, rings and gaskets; complicated by equipment, conditions and technique.

 

[jerryjerry05]

Re: Low compression on all 4 cyliners on Force 120

Never seen a motor loose comp on all 4.
JB's right about the reeds.No affect on the comp unless they were all siezed and not letting in any air.
It's possible the head gasket has blown and it's blown between 1@2 and then 3@4 NOT likley!!
Do like I said and squirt some oil in the cylinder and see if it brings up the comp.
Post the new #s Remove the head and look for a bad gasket and then damaged pistons.rings and cylinders.

 

[RZR2007]

Re: Low compression on all 4 cyliners on Force 120

Have you got another compression tester around? As JB said, motor runs to good to be that bad on compression...

 

[rigasr]

Re: Low compression on all 4 cyliners on Force 120

I've used 2 testers already. I couldnt believe the results either with the 1st tester so I rented another one and have same results.

 

[Frank Acampora]

Re: Low compression on all 4 cyliners on Force 120

Yep, JB. Right as rain. Since the bypass and exhaust ports on a 2 cycle outboard are open at the same time,--during a compression check,--the cylinders go to atmospheric pressure. Presence or absence of reeds, carb position, or presence of carb does not affect compression results UNLESS the battery is low and reeds and closed carb cause crankcase vacuum to slow the cranking speed considerably. Then, leakage past rings becomes a bigger factor.

Note that during running, cylinders may or may not go to atmospheric and may even have some positive pressure due to exhaust blow-back. (This is actually the principal upon which tuned exhaust and tuned pipes work.)


And I still think it could be stuck rings.

 

[JB]

Re: Low compression on all 4 cyliners on Force 120

Do the decarbon treatment, rigasr. Then worry about repeat tests, tearing stuff apart, etc.

There are a lot of things you can do to fix problems, and you can get tons of good advice here on how to do them provided that you have that problem.

We are trying to get you to eliminate and/or identify problems with the aim of not fixing anything that ain't broke

 

[jason32038]

Re: Low compression on all 4 cyliners on Force 120

The only reason all cylinders would go bad that quick is if you forgot to mix oil in with the gas...or if your ran it hot without knowing it. I've learned to hope for the best..but expect the worst with these engines when compression starts getting low.