mercury 7.5 seized

[shetland536]

serial number 9427136
working fine last year but not flushed out after use,has been sat in the garage since,now it will not move.
i can go in and out of gear ok and the prop is free in neutral.
i dont want to throw a lot of money at it so if i cant fix it cheaply i may sell it as spares or repair instead.
is there a common part that seizes in engines?
should i take the leg off and see if the engine will turn then?
i dont want to buy a manual just to find out i need to spend £200 on bits.
any advice?
i`ve had the plugs off and soaked the bores with wd 40 and left them for the last 2 weeks.
i only ran it for 5 minutes last year so could it be seized from not being used?

 

[BarryH]

hmm, a difficult one this, could be a few things but most commonly it is normally the pistons/rings that sieze. Pointless taking the "leg" or gearcase off as you have proved that all is fine there.

For a really good penetrating oil go for diesel. It'll unsieze most parts overnight or in a day or so. It'll then need easing round by hand. Obviously take the plugs out to do this. If it is siezed solid then depending on the age of the engine it may well be an uneconomical repair, tho not impossible. I would say it would cost more than your £200 estimate tho.

On the other hand, if you take 3 parts soft sand, 2 parts sharp sand and 1 part OPC and mix together in a large bowl/barrel while adding water until you get a sort of think creamy texture then add the engine with part of it protruding and leave over night, you'll have a very fine homemade anchor for a DIY mooring!

 

[shetland536]

interesting about the deisel,i shall try it.

 

[Alrob]

i would whip the head of for a look & a push !! (after lots of lubrication of course)

 

[Kawasaki]

The rings seize to the piston, the piston siezes to the cylinder , in most cases.
"A 2 week soaking in WD 40" and still no movement sounds a bit dire.
As Barry says it,s the "top end "that normally suffers from standing.
Yes they can seize from lack of use!
If you can,t get it to rotate,take the heads off and poke about inside.
The descision can be made then as to its future as a power source or a mooring accessory!

 

[alb40]

The mercury doesnt have a cylinder head - its a jam jar cylinder and head in one job.

As said, chuck some diesel down the hole, and it will come unstuck fairly swiftly. WD40 doesnt work for unseizing engines, as its more of a water repellant than an oil.

For the fastests results tho, oil heated so its smoking hot and chucked down the bore always worked for old steam engines!

 

[Kawasaki]

Know what your saying ref wd, it,s the "hot oil treatement" or take the jamjar apart.
Never actually messed with one of those. How old do We reckon the lump is?

 

[BarryH]

Last time I saw a 7.5 Merc it was a blue band one. Fairly old I'd say as most of the Merc/Mariner outboards in the low hp bracket are rebadged yams/Tohatsu's.
A good little engine in its day. Lots are now mooring anchor fodder.

 

[Kawasaki]

Sounds like had it then, if the bits cost more than 50 drinking coupons!

 

[shetland536]

not giving up yet. deisel has been installed,i shall give pistons a tap and a whack tomorrow.
if no joy then its hot oil.
if no joy then its cold water!

 

[BarryH]

Don't hit pistons too hard. The crown of a piston isn't that strong and more than likely made of an alloy of some sorts so will fracture/crack/break fairly easily. Leave the diesel in and give the flywheel a rock every now and then.
A year is not a long time to have an engine stood idle so I reckon you've a good chance the beastie will breathe again.

 

[Kawasaki]

alb40 reckons you,ve got a jamjar cylinder, if so you,ll have to remove it prior to piston bashing!
If so, no bashing will be required.
Good luck on your release--- hopefully!

 

[shetland536]

quote-- give the flywheel a rock every now and then.

am i ok to keep going into forward and reverse and just keep rocking the prop?
the way i`ve got it on the bench it would be easier.

also, i was going to give it a bash through the plug holes rather than take the "jam jar" apart.

if this goes again i`m going into the marine motor repair business!!

 

[BarryH]

ah well if its on the bench the even easier. Use as socket on the flywheel nut with a large'ish crack bar. Obviously you can only go in the clockwise direction but gentle easing should do it.

I'd not use the prop myself as you'll find theres probably a bit of a reduction there so the prop isn't spinning at silly speeds in the water plus you could be placing undue stress on the gearcase componemts and you've probably got some sort of protection for the gearcase be it a shear pin or some sort of cush drive in the prop hub.

Get stuck and I'm down in wareham at the w/e with a van load full of tools working on my boat!

 

[shetland536]

new post on the 21st