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low compression on #2 cylinder after fresh rebuild. 1986 120 hp

B

bayliner trophy

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Hi folks. I was recently blessed with a remarkable used 1986 Bayliner Trophy bass boat. The Force 125hp outboard on it had recently been rebuilt and the former owner was very good about keeping the boat up. It has 35hrs. on it since the rebuild and for some reason, it has little to no compression on the #2 cylinder. I plan on taking the power head apart to see if it's a ring issue however, I am not real familiar with out board engines and before I take this thing apart, I wanted to ask if anybody knew another reason for this activity. I have checked the cylinder and the piston with my inspection camera and all appears to be fine inside. I am at a loss so if you know some thing I don't, I could truly use the info. Thanks.
 
Re: low compression on #2 cylinder after fresh rebuild.

If the camera doesn't show anything then the head gasket could be bad.Spray some oil in the cylinder.Do a comp test and see if the results go up.
If they go up then the rings could be bad.No change could be the gasket.
Post your results.
Fill out the profile,you might be close to someone who can help.J
 
justintime said:
those motors are junk
they always run lean
i have seen over 10 of these motors with bad #2 or #3 cylinders!!
Click to expand...

I don't think they made a 120HP in 1986. You must mean 1996. Not nearly as good of an engine. The worst built 1972-1991 is a much more durable product than the best built 1992-1999. Specifically, Mercury puts out crap and Force was no exception. If you are lucky then it is a 1986 and you have a much better engine than anything Mercury has ever produced. It will run forver on about $50 maintenance per year including a new battery every 5-6 years. I include the battery because actual Force engines use a $3 rectifier instead of a $90 regulator. The rectifier never breaks and it never strands you in middle of lake with dead battery, but it does shortens battery life by a year or two.

At any rate - I think that you can retrofit Chrysler-Force reeds (1972-1991) into a lot of Mercury Force engines and eliminate the lean-running self-destruct feature. If not, then you can put in a set of Boyensen reeds for $100-$150 and improve the situation. Boyensen are still composite and will eventually crack like a mercury so they should be put on a maintenance rotation for replacement every few years. The chrysler reeds give you less pep and power but your engine will last forever with minimal maintenance. The Mercury built engines will self-destruct no matter what you do if you run lean on a cracked reed.
 
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Hey Thanks again for the info. I did the compression test without injecting oil and then injecting the oil. I got no change. I have a cylinder leak down tester that I am going to use however, I discovered that the cylinder in question has ZERO compression. I repeated the tests over and over to confirm the the compression tester was not giving a false reading. By the advise and direction You gave me, I think I am going to pull the head and look at the head gasket. I will wait until i get a reply to confirm that you all agree. any advice helps and I can't thank you all enough.
 
Hey Jerry, Do you know anybody selling a used 125 power head? It appears to me that the out board mechanic that the previous owner hired was a bit under qualified. The pistons are standard bore and the cylinder's are aprox. 20 thousands over bored. I'm just a dumb cop but wow!!! I still can't understand how the other 3 cylinder's could have a solid 120 lbs. of compression and the #2 have zero. I did the leak down test and all 4 were leaking down under pressure and the #2 cylinder has visible damage to the piston as well as serious damage to the cylinder wall. I am going to have a different tech look at it and give me an estimate but I think the power head is shot. suggestions??
 
I didn't see any markings on the top of the pistons and again i am no expert but i had the guy that tools all my custom bike parts come down and even he said that the pistons had way to much slop in them. I did however speak to a force outboard technician who said that the skirt is the the closest area to the cylinder wall and it will allow the piston head to float a little. He looked at the pictures i took and said that the damage was due to water. I talked to the guy who rebuilt the motor and he is acting as though he doesn't remember the job. I am going to bring the boat to him thursday and see if that rattles his memory a bit. Thank you all very much for the info and when i get this thing water worthy again, we will have to get together and go fishin one weekend. I will let you know how the recheck goes on thursday and i will check out the motor on craigslist you recommended. Talk to you all soon i hope. Take care.
 
I sent you a PM about a motor here in Sebastian.Look for it at the top of the page next to your name at notifacations.The guy's real interested in selling.Jerry
 
New pistons have up to 0.020" clearance at the top and only 0.004" at the skirt ( bottom of piston )-------------So they do feel very loose when you wiggle them.
 
U should start your own thread.
Whats very loose.You need measuring tools.To make sure the cylinder isn't out of round,the piston is good.
I take mine to a machine shop and give them the specs that are supposed to fit.They measure for me and tell me what I need to do.
Go to iboats and post there.J
 
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