1977 Merc 500 Thunderbolt cranking issue

[Yurri]

Hi guys, need some help please.

I have a 77' Merc 500 Thunderbolt that I've owned for 1 year now. I ran it all of last summer and it cranked, started, and ran fine all season. I took it out of the garage, where it has been sitting for 4 months, this morning to test crank before heading to the river. I reconnected all power cables, primed, choked, and turned the key only to have it barely turn over. The battery is brand new and charged and the starter engages fine. I tried to manually turn the flywheel it will is extremely tough to turn. I have already pulled the lower unit to clear it from the equation, still hard to turn. could someone give me few places to look before I have to tear into the powerhead?

thank you

 

[racerone]

Re: 1977 Merc 500 Thunderbolt cranking issue

Will the motor turn easily with the sparkplugs out ?--Then try cranking with sparkplugs out.

 

[Yurri]

Re: 1977 Merc 500 Thunderbolt cranking issue

Just took all plugs out and it turns by hand with ease now. It turns over by key now too. Do you think a ring problem or exhaust maybe?

 

[Chris1956]

Re: 1977 Merc 500 Thunderbolt cranking issue

I think you have bad battery cables or maybe a bad starter. Those battery cables can rot out under the insulation.

 

[Yurri]

Re: 1977 Merc 500 Thunderbolt cranking issue

That is possible. They seem to be in good condition though. I checked all wiring as I have just finished rewiring the rest of the boat. It first thought it was the starter, so I tried pull starting it and it would barely turn over (plugs in). I know there should be a difference with them out but I should also be able to pull start also with relative ease right?

Thank you gents for your help
I'm new to the boating scene, but fairly mechanically inclined.

 

[Yurri]

Re: 1977 Merc 500 Thunderbolt cranking issue

Should I try fogging or spraying seafoam deep creep into the cylinders?

 

[Chris1956]

Re: 1977 Merc 500 Thunderbolt cranking issue

If she turns over smooth with the spark plugs out, it doesn't sound like a mechanical issue. I would think you should be able to pull start that motor, after a fashion. Check the flywheel for play in the bearing. Maybe the top main is bad and the flywheel had enough play to hang up? Something like the stator is hitting the flywheel?

 

[racerone]

Re: 1977 Merc 500 Thunderbolt cranking issue

What happens to outboard motors from sitting ?---Well if water is somehow ingested into the motor and sits on bearings over the winter.---Bearing will jam up.---Then come spring an owner will find motor stiff / hard to turn.---- Gets it freed up and is happy again.----But I say you need to look into this if you want the motor to last many more years.---Perhaps look at bottom crankshaft seals and bearing there.

 

[Yurri]

Re: 1977 Merc 500 Thunderbolt cranking issue

Well I took my starter apart this morning and two two of my brushes were stuck one of them crack. Ive cleaned my starter and found some replacement brushes. I'll put those in this afternoon and let you guys know the outcome. I only thought my starter was good.

 

[Yurri]

Re: 1977 Merc 500 Thunderbolt cranking issue

There really isnt any play in the flywheel at all. It's pretty solid. I feel confident the block being mechanically sound now anyway.

 

[Yurri]

Re: 1977 Merc 500 Thunderbolt cranking issue

Ok after cleaning and replacing with new brushes, back in operation. She cranks like a dream. Now to fix a fuel leak I found hiding behind the starter. Thank you guys for the help!