Motor won't CRANK over! Pictures of bad pistons...

randomact · Sep 20, 2007

Hello all,
I recently purchased this boat 3 months ago in which the motor seemed to be working ok, when I say ok I mean that it would still take 3-6 times to start it and eventually it would go. Up until recently we were out at sea and the motor didn't want to turn over at all, after 90 cranks we got it started and we managed to get back to the DOCK, when we tryed to give it full throttle the boat would go knowhere and sounded like it was spooling upthe prop and I was moving knowhere. When I kept the throttle in very low speed the prop would turn just enough to get us in. Since then we figured we had a blown head gasket so we pulled the head off. I was curious what is going on here since I know nothing about boats regarding the damage that has been done. Am I better off buying a new motor, vs the cost trying to repair this 70 HP motor? I posted pics of the damage as well as a video of the motor trying to start. Thanks in advanced to all who help

bertthedefender · Sep 20, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

Other than a spun prop, how did the motor run when it actually started?

My 70hp motor never started very well when we first bought it years ago. After being stood a few years with occasional turning over and oiling, it didn't want to start at all. It turned out to be the stator. It was one of the original faulty black plastic covered ones. The resistance test suggested it was faulty and after taking off the flywheel it was obvious it was shot. After replacing it, it fires up first turn of the starter.

baxtr · Sep 20, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

new pistons 100 bucks each, Wrist pin bearings 12 bucks ea, cylinder boring and honing 75 bucks a hole (last yrs price (wisconsin)) Full gasket kit 80 bucks. SERVICE MANUAL 30 bucks. Your time and patience, that's about it.

Doing that math and comparing it to the price of a new motor is what sold me on rebuilding my 125 last winter.

Kajun37 · Sep 20, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

looks like you broke some rings..........if you dont want to rebuild this yourself.. its not worth it to bring to a mechanic and pay his prices....ya better off parting it out on ebay then buying another motor.

baxtr · Sep 20, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

Kajun37 said:
looks like you broke some rings..........if you dont want to rebuild this yourself.. its not worth it to bring to a mechanic and pay his prices....ya better off parting it out on ebay then buying another motor.

Yep, should have mentioned that about not worth paying a mechanic.

Still love that merc pic of yours Kajun

randomact · Sep 20, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

how does one go about getting the holes rebored? Do I have to remove the whole block? once I remove it then all I do is add a few parts put it all backtogether and I am back in business for under 1000?

baxtr · Sep 20, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

to bore it out you need to completely strip it....completely. Pistons,crankshaft everything out, then you take it to a machine shop that does outboard motors, not just an auto shop.

did mine for around 500, but I only did 2 of my 4 cyl, so you would prolly be bout 200 more for the extra piston and extra cyl boring. It's not that difficult to do yourself, just take lots and lots of pics so you know how it goes back together, and be sure to get a manual, tells you specs, what needs loctite, what torque for bolts, etc....

Daphne444 · Sep 24, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

I'm also very interested in any comments that can be made regarding the pictures of the pistons. I will have to pull the head of my 1990 90hp to see why I only have 80 psi compression on my #2 piston (the other two are closer to 120), and if it looks like this I may then have a better idea of what I am looking at.

Anyone else have any comments as to what they see and what it means?

Thanks

rudedude · Sep 24, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

Well I agree with the others that the rings look to be munched. It also looked like # 1 was a little lean and #3 looked to be running a little rich, might have been only due to #3 holding a little more oil at shut down.

But it did look like the rings wanted to come out and see daylight.

I would do a rebuild myself, there not that hard to do.

If you dont have deep gouges or scoreing in the cylender walls you could hone then your self , just make sure you MIC them as you go.

Get a manual first thing, your gonna need it.

baxtr · Sep 24, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

Daphne444 said:
I'm also very interested in any comments that can be made regarding the pictures of the pistons. I will have to pull the head of my 1990 90hp to see why I only have 80 psi compression on my #2 piston (the other two are closer to 120), and if it looks like this I may then have a better idea of what I am looking at.

Anyone else have any comments as to what they see and what it means?

Thanks

Daphne,

When you pull the head, check for breaks in your head gasket, also try decarbing the engine, may just have a bad head gasket or stuck rings, 80 is low, but I would think you would see lower if your pistons looked like the pics above.

Mark42 · Sep 24, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

You should look at the price of rebuilt short blocks here at iboats and see if they are in your price range. If the rest of the motor is good, and you can do the work, swapping in a short block is a good way to get a new powerhead on your outboard.

EDIT -
Scratch that. Part it out and buy a good used outboard.

baxtr · Sep 24, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

prolly 2 grand for a rebuilt powerhead, better off DIY

Nate3172 · Sep 24, 2007

Re: Motor won't CRANK over! Pictures of bad pistons...

What were you running for oil and at what mixture? Number three looks wet only because it wasn't firing. It appears to me this engine has been overheated or was not run with the correct oil or oil mixture. My advice-- rebuild it. The whole thing. Disassemble it completely and take the block into a machine shop and have them bore it and hot tank it. Verify first that it doesn't already have oversized pistons and that it is a standard bore so the machine shop can determine if it can be bored oversized. If those gouges in the cylinder walls are too deep you will need to have the cylinder liner replaced. An automotive machine shop can do this for you if they are a good one. Had mine done at a local auto machine shop for $80 a hole and they did a great job.

Motor won't CRANK over! Pictures of bad pistons...

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