Is my motor toast?

[Big Chief]

Looking for insights before I tear this apart...

I have a 1981 470 Mercruiser motor. It’s been running great for the last 6-9 months. I bought the boat after sitting for 1+ years.

I crank the motor once a week if I'm not using the boat... the other day I cranked it just fine, ran it 5 minutes and shut it down. As I shut it down, I noticed a small "click, clunk" as it powered down. I didn't think too much of it at the time...

So I go to crank it up today before a trip... and the first crank I get... "clack, click, clunk"... It tried to fire like normal... So I change battery over (crossing my fingers) and crank again... it goes about 1-2 revolutions... and SIEZES!

I say a few cuss words, hold my breath... and try one last crank hoping my starter just quit... the starter engages just fine, but the motor is seized.

I've done some minor work on motors when I was younger, my nothing major. I pulled the valve cover off... no cracks, nothing loose, nothing seemed lodged... all seemed okay.

What’s the best way to attach this? Its obvious, this is inside the motor at this point.

 

[freddy063]

I was in the same type of trouble a few weeks ago, my outboard runs great most of the time, on occasional it wouldn’t turn over. Acted like it seized . well long story short, it ended up being a bushing in the lower unit seized on the shift, the motor was fine, 43 bucks later alls well. So don’t thinks the worst, test other things, like remove everything you can from the motor to see if the motor spins free. Not sure how your lower unit connects but try to isolate the trouble by eliminating parts, Good Luck Is the boat in the water? might want to get it out and work on it with some muffs on it.

 

[lodgecreekgrady]

It could be a bad riser and you got water in the cylinders. Take the spark plugs out and look for water in the cylinders. If you find water in the cylinders then it will also be in the crankcase so be sure to drain the oil and refill that too. It could also be like freddy said and not in the engine. You will have to pull the lower unit from the boat and check the gimble bearing and lower unit to see if they are seized.

 

[richie rich]

If the piston seized in the cylinder, you will be hard pressed to crank it over by hand using a wrench on the crank bolt....try that after the plugs are removed and the drive unit disconnected or in nuetral.....dropping the oil can tell you a lot as well

 

[Big Chief]

A little more information.

The boat is out of the water. I last ran it in the water about 3 weeks ago... just fine.

I cranked the motor last week... it ran fine, except on the power down... motor made a funny noise.

Plugs are 9 months old. I pulled them, 2 were dry... 2 seems to have a slight bit of moisture (water). The actual plugs, were in decent condition.

I pulled the alternator belt, so there was no load on the crank.

So far, I have only tried to crank the motor about 6-7 times since these issues... trying to limit the amount of times I try to turn it over.

Interestingly, after I pulled the plugs, I tried to crank it again... IT TURNED NOW... made some clunking noises though. I tried again, and it would not turn. So I changed the battery thinking I needed more power. It turned again, but I noticed a slight "smoking" from the crankshaft balancer... I also noticed some small "chips" fly off. There is no load on the crank though. I noticed the balancer had about an 1/8 inch clearance from the C-ARM motor mount. I dont recall what the clearance used to be though.

I think I'll post pictures next?

Not sure if that has anything to do with this... If not, my next step would be to pull the outdrive...

 

[Big Chief]

I just replaced the oil about 1 month ago... It still has a light color to it. Can't tell if its still new... or if its water. Its looks fine though, doubt its water. The old oil was dark black... didnt seem like any water was in it.

NOTE: For the past few months I have been going through oil more than usual. At first, I thought it was burning quick... but then I think I found it was a bad valve cover gasket. I noticed a slight drip near the rear of the motor... I never got a chance to replace it though. Although, now that I just pulled the valve cover... I have a new gasket.

 

[no problem]

Assuming your starter is functioning properly my guess is that the motor jumped time. Meaning your timing set is damaged. Good luck!

 

[JeffN]

Chief - I read your post with some interest because I lived with a pair of these motors for over twenty years in my boat before replacement. I am not a mechanic by any means but these motors do have some interesting habits. That is not a balancer or just a balancer anyway on the front of the motor. 470 motors have a magneto on the front of the motor, unless yours has been converted to an alternator. As these motors get old the magnets inside the magneto become unglued from the housing and fall away. This WILL lock up the motor when youy try to start it, I had one do this. The noise you descibe sounds very familiar. If you have pieces coming out there it may well be magnet pieces. You may be able to put a socket on the nut at the front of the mag and just try to rotate the motor back and forth with any luck you may here a grinding noise coming from the magneto. You MAY even dislodge the pieces and and the motor may rotate freely. At that point your motor is not fixed but you have narrowed down problem perhaps. Then if you have a manual check on how to pull the magento and see if the motor rotates after. If the magneto is toast at one point there was an alternator kit available to do away with the magneto as a repair option. If you don't feel comfortable with the job find a tech in your area that is familiar with this motor, that should save you some money. Most guys will be just throwing darts if they don't know the motor. The problem could certainly be any of the issues described in above posts but I would add the magnet issue to your list near the top. If I were in your shoes I would check for water in the motor first and then if thats OK go to the magneto.

I am no wrench wizzard but I would check this out before I began tearing too much apart or removing the drive. From what you describe it appears that the mag may indeed be the issue.

 

[VeroWing]

I absolutely agree with JeffN on his assessment. Reading your symptoms, this is your most likely problem. I've also had more than a few of the 470 & 485 engines, and this is one of their inherent issues. Repair can be as easy as getting a puller and pulling the magneto (pully) and epoxy gluing magnet(s) back into place. Better fix is to update to the alternator and do away with the magneto system. I would not try to start engine until you have checked this out.

By the way those engines were some of the most fuel efficient engines ever built. They were actually 1/2 of a Ford 460 auto engine, and used the Ford 460 head. One other inherent problem with these engines was that the water pump was mounted on the end of the camshalf, and after a while the seal separating coolant from entering block would wear a groove around camshaft making a coolant leaking situation. A sleeve kit is available to place over camshaft wear area, that will resolve this problem. Other than these two easy to deal with problems, these motors were very durable and long lasting. IIRC, you are supposed to use only straight sae30-40 motor oil, and not a blend type such as 10w30, etc. Good luck with your repair.

 

[JeffN]

So what did you find?