Yanmar 3gm 30 engine seized

Jun 12, 2013
203
Hunter 31.5 Cedar Creek
Hi, I'm trying to un seize a yanmar 3gm 30. I have a loaded the engine with marvel Mystery oil, squirted PB blaster into the injector holes and after three weeks I was able to move the fly wheel counter clockwise 30° but it won't move clockwise any more than 5° either way with the breaker bar and socket .i'm starting to round the corners on the nut that holds the pully on to the crankshaft so I need to buy another nut but I'm not sure of the thread size and thoughts on the seized engine next step?anyone out there help me with that? thank you very much for all your help christian
 
Jun 1, 2016
101
Hunter 28.5 Lake City, MN
How long has it been since the engine was run?
The first thing that I would consider is that it could be loaded with water or fuel. Did you release the pressure valves on the top of the engine?

Mike
 
Nov 6, 2006
8,425
Hunter 34 Mandeville Louisiana
Pull the head. The seizing you are talking about will have toasted the rings and probably the cylinder liners as well..
 
Oct 25, 2011
572
Island Packet IP31 Lake St. Louis, Montreal
Not sure the 3GM30 has cylinder liners. I agree with kloudie. Pull the head and you;ee be able to see what's going on
 
Jun 12, 2013
203
Hunter 31.5 Cedar Creek
I've been trying to avoid pulling the head! Under the valve cover the rocker assuming looks perfect no signs of water! One of the decompression levers was frozen I'll fix that and see if it makes a difference! If I go the route of pulling the head I'm afraid of snapping an exhaust manifold bolt or the intake bolts? Any special instructions on removal sequence of the head removal available
 
Oct 25, 2011
572
Island Packet IP31 Lake St. Louis, Montreal
I have a soft copy of the shop manual. You're welcome to a copy

Matt
 
Dec 31, 2016
262
Beneteau Oceanis 351 Charlottetown
The question is, why did it seize. It could have a bent rod, broken valve (or spring), a broken piston, that would allow it to turn a few degrees and no further.
 
Jun 12, 2013
203
Hunter 31.5 Cedar Creek
The motor turned over easily four years ago when I bought it but at that time there was some water in the intake manifold no water underneath The valve cover with the injectors removed and the decompression levers and place it turned over
 
Jun 12, 2013
203
Hunter 31.5 Cedar Creek
I remove the valve cover and then remove the rocker assembly and pushrods but I'm thinking could it be that the decompression levers have to be pushed down in order for the Engine to turn over
 
Dec 31, 2016
262
Beneteau Oceanis 351 Charlottetown
If you removed the valve train ,it's going to be very difficult to turn the engine over ,as the valves now won't open it all to decompress.
 
Nov 6, 2006
8,425
Hunter 34 Mandeville Louisiana
If the injectors are out, there can be no compression lock. As I noted in a previous post, the head needs to come off . Then you can bump the pistons with a hammer and a wood block. bumping should be on port/starboard sides of the individual pistons to gently rock them in the bores and loosen the rusted rings.. A broken stud is not a problem in an engine that is frozen already.
 
Jun 12, 2013
203
Hunter 31.5 Cedar Creek
Ok I guess it's time to remove the head! Question can it be removed with the intake and exhaust manifolds attached?

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