Bottom cylinder locked up flywheel wont turn????

[fluidjuice]

Hi all,
I didnt think i would be back so soon after all you guys help last year ,anyway i have a Mercury 1991 4 cylinder 40hp classic that has been converted to manuel oil in fuel.
Boat has been running great regualry , starts first time and been very reliable,pumping water fine.
I took it out yesterday and took 3 members of my family for a half hour trip.
Dropped them off at the harbour then went back out with my brother in law for a spot of fishing, once out of the harbour i opened her up and after about 1 minute at nearly full rpm,s she just locked up, stopped dead, upon trying to start her up again i noticed the starter would not turn the flywheel fully.
I took the plugs out and still could not turn the wheel by hand, It looks like the bottom cylinder is not moving so i have emptied half a can of wd-40 into bot cylinder and left.
If this cylinder has siezed , can it be unsiezed and if so how,also do you think this would be due to the impellor going ,or overheating.
Thanks for your response!!!!!

 

[Chris1956]

Re: Bottom cylinder locked up flywheel wont turn????

More than overheating can cause a seize. Lean running or overadvanced timing can cause it also. Now that you have soaked it for a while in penetrating oil, stick a brass rod down the plug hole and give it a rap with a hammer. it may loosen up. If so, take a compression check. There is a slight chance that the motor may be undamaged If the comprssion is 100PSI+ and even on all cylinders, you will not need a rebuild. You should pull and clean the carbs, replace the impeller and do a link and sync, before you use the boat.

 

[chris.olson]

Re: Bottom cylinder locked up flywheel wont turn????

If this cylinder has siezed , can it be unsiezed and if so how,also do you think this would be due to the impellor going ,or overheating.​

Thanks for your response!!!!!

I can tell you right off that it's not due to overheating because the top cylinder runs the hottest and is the first to suffer if the cooling system fails.

I don't know how you ascertained that it's the bottom cylinder that siezed (aluminum deposits on the plug maybe?) but before attempting anything else I'd pull the exhaust cover and baffle off the left side of the engine block and take a look thru the exhaust ports to see how bad it is.​

Pistons sieze to cylinder walls for one reason only - lack of lubrication. That can be caused by overheating - the temperature exceeding the lubricating capability of the oil, using the wrong type of oil, or lack of oil caused by either improper pre-mixing or a lean condition.​

If you see visible scoring on either the piston skirt/ring lands, or the cylinder wall, no amount of WD-40 is going to fix it.
--
Chris​

 

[MERCrazy]

Re: Bottom cylinder locked up flywheel wont turn????

Mercury 1991 4 cylinder 40hp


R.I.P. 2009