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90hp Mariner will not turn over a full revolution

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arnben

New member
90hp Mariner stopped on the lake. Starter would not turn it over. I can turn the flywheel approx 7/8 of a revolution, but it meets a hard stop turning from both directions. Pulled the plugs and the pistons move normally, except top one does not reach top dead center. I don't see anything wrong when peering in the spark plug hole.

Need some advice. Should I continue to look at the powerhead, or pull the flywheel and look for something broke there? Or could it be in the lower unit? Thanks in advance for a reply.
 
If you can't crank the engine over w/the spark plugs out then there is something mechanically wrong. Drop the LU and see if it will allow it to turn the crankshaft.
 
Aahhhhrgg! Sounds like you got something inside the motor that's jamming the pistons. Very rarely do these things come out right. Sorry.

Jeff

PS: It's not LU related if the flywheel turns like that.
 
Weird thing is that it's not seized, and I don't see any obstruction when looking through the spark plug hole. And there seems to be compression in all cylinders (just putting my finger over the spark plug hole when turning the flywheel). What could break to cause this effect? Should I remove the head? Or remove the plate on the side (I assume this is where the valves are)?

You're sure it can't be in the lower unit? I just want to start in the place most likely to be broken.

fastjeff said:
Aahhhhrgg! Sounds like you got something inside the motor that's jamming the pistons. Very rarely do these things come out right. Sorry.

Jeff

PS: It's not LU related if the flywheel turns like that.
Click to expand...
 
Possibly the cylinder sleeve moved.There are no valves on the side of the motor.----Removing the big exhaust cover will allow you to see and inspect thru the ports.---That will likely tell the story.
 
There's 'something' in a cylinder that's squished against the end of the cylinder by the piston. Let's hope it's not a reed valve part or a loose needle bearing.

Jeff
 
You were right--it's not the Lower Unit. Same problem with LU removed. I inspected the cylinders using a lighted borescope, and could not see anything stuck in there. But it could easily have been missed....

So, should I remove the side exhaust plate, or the head? Anyone heard of a failure like this caused by something broke under the flywheel?
Thanks for your advice. I will let you all know what I find.

fastjeff said:
There's 'something' in a cylinder that's squished against the end of the cylinder by the piston. Let's hope it's not a reed valve part or a loose needle bearing.

Jeff
Click to expand...
 
Pulling the "head" won't help--it's merely a water jacket cover. Pull the right side intake plate(s) off and take a look. Pulling the left side exhaust plate should be the last thing before a total rip down since the bolts like to snap off.

Jeff
 
Thanks for sticking with me on this one, everyone. As I see it, on this motor, the intake plates are not on the right side, but in the front, right behind the carbs. So, I'm assuming you mean that I should remove the carbs, and the intake plate is behind this. Would I be looking at the crankshaft then? And if so, I'm hoping that I can see the ports??

I heard your warning about breaking the bolts on the left side exhaust plate. I loosened 21 out of 24, but 3 are stuck tight. I did not break them off.

Thinking more about this.... could there simply be something stuck in one of the ports, hitting the piston skirt? So in other words, the obstruction prevents the piston from moving down, rather than an obstruction on the top face of the piston.

Thanks for any comments.



fastjeff said:
Pulling the "head" won't help--it's merely a water jacket cover. Pull the right side intake plate(s) off and take a look. Pulling the left side exhaust plate should be the last thing before a total rip down since the bolts like to snap off.

Jeff
Click to expand...
 
You are correct--no intake side covers on those. Sorry.

That leaves pulling that exhaust plate cover off. If you got that many loose without...you know...then it's worth trying to get the other few bolts out. If you have access to an air impact wrench, put it on the lowest setting and rat-a-tat away for a while until the bolts start to turn. Tale you time and let the vibration do the job.

That cover has to come off--period. When it's off, you should be able to see what's jamming up the works.

Jeff
 
Motor " stopped on the lake "----Most lakes that I know of are freshwater and the 20 or so exhaust cover bolts should come out with little or no effort.
 
I was being kinda wimpy with the bolts. A couple of them galled up a bit, but I got them out, and removed the exhaust plate.

The sleeve in cylinder #1 has shifted down by approx 3/8 inches, and the top edge apparently stops the piston (I can't see the top thru the ports). Racerone, how did you know? A guess, or have you seen this before? What would make this happen? The piston is not seized to the sleeve....

So, i'm assuming that replacing the sleeve should be left to the professionals. Or could I do it myself? How would I get the old one out? How would I get the new one in?

Thanks for all the help guys, and kudos to Racerone for guessing the slipped sleeve!

racerone said:
Motor " stopped on the lake "----Most lakes that I know of are freshwater and the 20 or so exhaust cover bolts should come out with little or no effort.
Click to expand...
 
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