Motor needs help.

[Cmal08]

I have an 86 mercury 35 hp motor and it runs real rough. Just for some back story to maybe help diagnose. I had it on the river at the end of the season, was running fine then on the way back to the launch it started knocking and died. Figured swap the plugs because finger crossed it was just running of one cylinder, not the case. I compression tested it and both heads tested at 145 psi and held for 10 mins. Iv got it to start and the flywheel is wobbly as a son of a gun and still knocking. I think it's crank related but figured I'd ask for others opinion before I bring it somewhere and she'll out money to get the same answer. Video link posted below Thanks in advance!

 

[racerone]

Just a wild guess on my part, but I think the crankshaft is broken.

 

[racerone]

I think this is an expensive repair.----Your location ?

 

[Cmal08]

Haha that's what I was thinking but I was hoping someone would hopefully have some secret news for me to a simple fix. I'm in nh.

 

[racerone]

If you can do the repairs yourself it is possible.------If you have to hire a shop you are better off finding another motor.--

 

[Cmal08]

Unfortunately it would prob be a hired job simply because I don't have the time. It sucks to because I have an identical motor for parts but it's a mechanical trim instead of power trim and from what I read I can't just put the power trim on the spare motor. I also tried taking just the power head off and all the studs are frozen so it's sounding like the simplest way to go is buy a new motor (ouch).

 

[QBhoy]

Both heads ?? Be a fine thing…Oh man…wish it might be better news…but perhaps even just looking at that flywheel, might not be a good sign.

 

[jimmbo]

It is amazing how these things can run with a Broken Crank. Even if you replace the Crank, the rest of the Rotating Assembly, Pistons and Rings will need a thorough Inspection. Cheaper to replace it with another used/abused engine

 

[Chris1956]

Gee, swap the powerheads.

 

[racerone]

Post #6 clearly states that studs appear to be frozen or jammed with corrosion.----A common issue with salt water motors.----A new motor is likely a good option.

 

[Cmal08]

Both cylinders* my mistake. Yea I'm thinking that's the most popular opinion is ditch that grenade and go with a different motor. I appreciate all the confirmation to what I suspected before spending stupid money to hear what I already knew.

 

[BWR1953]

Well, at least you might be able to sell it to someone for parts and recoup some of your money. Post that video of it running on Facebook Marketplace or craigslist and see if you get a bite.

 

[Chris1956]

Gee, it takes a lot to make the powerhead bolts non removeable. Put a good box or open end wrench on 'em and try it. If the studs come out, OK. If they break, that's OK too.

If you need to split the nuts, that works as well.

 

[racerone]

These are studs that are quite long.-----Often jammed in the exhaust housing with corrosion products.----A challenge for most folks to get the power head off.

 

[Chris1956]

Gee easy stuff. Break 'em, twist 'em out if necessary, split the nuts, or turn them with a chistle. A box wrench makes it work.. Once you have the nuts off, lift the powerhead with a lift of some kind. Push it to break it loose. Corrosion will give it up on mounting bolts.

The studs are course thread, standard steel. shafts. The powerhead nuts are fine thread 3/8 nylon lock nuts. Easily replaceable