PLS. HELP, Merc. 125 lost power, unable to check compression.

[aquanuts]

Hello to all,

I purchased a Hewes 18 with a Merc. 125 classic. The engine would not get
the recommended WOT RPM's of 5250, only 4000 RPM's trimmed. I did a little
trouble shooting and found that the power pack and the #3 coil was bad. I also cleaned the carb.'s, checked the timing and all linkages. The boat ran great for about 10 minutes, running at about 4800 RPM's it suddenly lost power and made a very strange noise, now the engine would not idle and would stall out of gear, I finally made it back to the dock 1 hr later.

I took it home and checked for spark on all 4 cyl., all fired. I then proceeded to check the compression, now this is very strange. Pulled all plugs out and installed the compression gauge to one cylinder, the flywheel would make to turns and the bendix on the starter would kick back down, no matter what I did the flywheel would not spin more than twice and I was unable to get a max reading on any cylinder. I installed all plugs except one which I installed to comp. gauge and the engine would spin as long as I held the key on. Checked batt. voltage, good.

"WHAT THE HECK IS GOING ON"

So I checked the compression leaving all the plugs in except the cyl. I was testing. Read 135-140 on all 4 cylinders. The engine would not idle running it at home with the muffs on, very rough. It feels like the engine was dragging and some vibration was felt. Almost feels like the engine is out of balance or something. Never seen anything like this before. Suspected maybe the lower unit blew a bearing, removed lower unit, spins good.

Hope I didn't blow the power head!!!!!!!!!

Please help

Aquanuts is going nuts.

 

[cell]

Re: PLS. HELP, Merc. 125 lost power, unable to check compression.

If you fixed the ignition,and have compression.Then the only other thing to go through is the fuel system...

 

[aquanuts]

Re: PLS. HELP, Merc. 125 lost power, unable to check compression.

Thanks for the reply.

I cleaned the carb's and the previous owner rebuilt the fuel pump. I have also used a 6 gallon remote fuel tank with fresh fuel.

What puzzles me is the fact that I have done compression checks on a number of outboard engines including this one before I purchased it and never had one that I was unable to check the compression with all the spark plugs out. The flywheel appears to kicks back which drops the bendix on the starter.

I can turn the flywheel by hand with no plugs very easily to and it appears
to rotate good with no noise other than the air sucking thru the carbs and the compression escaping thru each cylinder.

??????????

 

[aquanuts]

Re: PLS. HELP, Merc. 125 lost power, unable to check compression.

Reason found;;;;;;;;
Just so you know, the reason I was unable to get compression with all
plugs out was because the top crank bearing and seal were damaged.
Just something to thing about if you have the same problem.

 

[j_martin]

Re: PLS. HELP, Merc. 125 lost power, unable to check compression.

Reason found;;;;;;;;
Just so you know, the reason I was unable to get compression with all
plugs out was because the top crank bearing and seal were damaged.
Just something to thing about if you have the same problem.

Thanks for the comeback. That's the way the whole community learns from your travels.

So, to analyze a bit, the flywheel was moving sideways, probably lightly kissing the stator, which would explain the rough running because of misfiring. Dead giveaway was starter dropping out.

Could you feel the runout (sideways play) of the flywheel with your hands?

 

[aquanuts]

Re: PLS. HELP, Merc. 125 lost power, unable to check compression.

J_Martin,

Thanks for the reply.
I really never checked to see if the flywheel had any axial movement.
I found the problem when I removed the flywheel and found that the upper crank bearing rollers had come up thru the seal and damaged the seal and stator. I rebuilt the motor, only real damage was at the top piston and the crank bearing journal cleaned up pretty good.
I did have to replace one piston and hone out that cylinder, replaced stator, crank bearings, stator, seals and gaskets.