Twisted Prop Shaft

[wmk0002]

My wifes uncle recently bought a 2003 Mercury 25hp. It supposedly hit something with the prop and resulted in this twisted prop shaft. This isn't something Iv'e ever came across but told him I'd help him out. Seller already had it pulled so I was able to look at the drive and pinion gears and all looked good. I pulled the lower unit and the driveshaft was straight an seemingly undamaged as well.

I checked spark and it was very good. Then checked compression and was only seeing 70 psi on top cylinder and about 105 on the bottom.I decided to see if it would briefly fire up with some SeaFoam sprayed into the carb throat but it never even tried to fire. My assumption is that the flywheel key is probably sheared and it is way out of time but I haven't gotten to pull the flywheel yet. What are some other things I need to check that an impact that did this to the prop shaft may have caused? The compression numbers are concerning but hopefully it is a just a head gasket. I wish he would have checked those before buying...I would not have even purchased or would have negotiated the price down much further to offset the risk. Not my money though

 

[nccatfisher]

For one I have never seen an engine fire on straight Sea Foam.

 

[wmk0002]

For one I have never seen an engine fire on straight Sea Foam.

I'm fairly certain I have used it in place of carb cleaner in this situation in the past since Seafoam contains lubricants.....but I may be misremembering.

 

[dearl]

Flywheel key for starters, the compression is concerning...I mean it will run like that but not like it should.

Im with nccatfisher, the Aerosol sea foam is pretty oily stuff. I de-carb engines with it, but they are running, and will usually bog it down if you hit it too hard. Try pumping the bulb and use the red manual primer to see if it will crank. Do the flywheel key first though.

 

[wmk0002]

Flywheel key for starters, the compression is concerning...I mean it will run like that but not like it should.

Im with nccatfisher, the Aerosol sea foam is pretty oily stuff. I de-carb engines with it, but they are running, and will usually bog it down if you hit it too hard. Try pumping the bulb and use the red manual primer to see if it will crank. Do the flywheel key first though.

I decarb with it too and get the same bogging as I bogg it down at about 1/3 throttle until it kills the engine. I think if it doesnt work as a starter fluid its more due to the fact that it comes out in more of a liquid form rather than an aeresol spray and may not suck up through the crankcase like it should. I may have to test it on a good motor just to see now.

I don't have a mercury fuel fitting or else I would try. Guy is supposed to be getting one today to bring over.

Head gasket is really the only hope on the compression. I have freed up rings in the past but never had one cylinder be that far off from the other from just stuck rings.

 

[turbotodd]

Usually on a mercury 25 (2 stroke) if the cylinder compression is that much difference from one to the other and the gauge is accurate and the hose is screwed tight to the head, the engine itself is likely to have issues. That could be a crank seal, piston, rings, a ton of things. I am hoping it's not a mercosil block. If it is, it's junk. They have a tendency to delaminate the cylinder lining material, a lot of times due to a failed (stuck open) or missing thermostat.

 

[wmk0002]

Usually on a mercury 25 (2 stroke) if the cylinder compression is that much difference from one to the other and the gauge is accurate and the hose is screwed tight to the head, the engine itself is likely to have issues. That could be a crank seal, piston, rings, a ton of things. I am hoping it's not a mercosil block. If it is, it's junk. They have a tendency to delaminate the cylinder lining material, a lot of times due to a failed (stuck open) or missing thermostat.

I think it is the mercosil block. I pulled the head to look at the gasket but it is really just a cover for the water jacket and there is not a true removable head. I also couldn't pull off the exhaust cover as it is a 2 piece cover and the outer one has two extra long screws that don't seem like they can be removed without pulling the powerhead. I did use a snake type camera (not a true borescope) to look in the cylinders and I really didn't see anything that looked like scoring or would seem to be a cause of low compression. Haven't pulled the flywheel yet to check the key but when I do I will see if it looks like the crankcase seal is leaking.

Also did get it to fire on premix fuel squirted into the throat so pulled the carb and it was nasty. I'm going to clean it but not rebuild as is as to not waste any money on it and see if I can get it running. If it will run I'll try to do a decarb and see what the compression looks like after that. I'd say it is highly likely it's toast. Hopefully the used parts demand for these is high and my wife's uncle can recoup his money. Myself, I have appreciated the chance to work on a model I'm not familiar with. May help me down the road if I decide to buy one of these myself.

 

[jethro]

I priced out a new prop shaft on my '95 Merc 25... almost $800. For a motor worth $700.

 

[wmk0002]

I priced out a new prop shaft on my '95 Merc 25... almost $800. For a motor worth $700.

 

[muddywaders]

"mercosil" will be printed on the starboard cylinder if not chrome bore both very hard material and may not show damage even if piston is toast.Best to remove exhaust cover by partially disassembling lower cowl as well remove inspection covers on transfer ports to see if piston is scored.Parts in demand for this motor are cowls(mint),carbs,elec.start,ptt and of course good prop shafts lower units and powerheads! m.w.

 

[wmk0002]

"mercosil" will be printed on the starboard cylinder if not chrome bore both very hard material and may not show damage even if piston is toast.Best to remove exhaust cover by partially disassembling lower cowl as well remove inspection covers on transfer ports to see if piston is scored.Parts in demand for this motor are cowls(mint),carbs,elec.start,ptt and of course good prop shafts lower units and powerheads! m.w.

Appreciate the info! This one doesnt have a lot going for it then. Good parts include Ignition components, recoil starter, carb, cowl, new aluminum prop, tiller, and lower unit components (aside from prop shaft obviously). Electric start components may be good but its missing the brushes on the motor so not sure about the rest.

 

[crazymanme2]

I use to race those motors.
They have a chrome bore & are usually not rebuildable
A good motor will have 130 # + compression