Engine Cranks but wont turn...Starter? <Checkout Video inside>

Mercruiser_120HP · Mar 5, 2010

Hi,
I've been reading this forum for a while and I think it has the best information regarding boats. I've been trying to diagnose this problem for a couple of weeks now and I'm out of ideas as to what's going on. I thought it was the starter but it does crank. I bypassed the solenoid and it still just cranks the same. The engine is a 1967 Mercruiser 120 hp 4 cylinder

The problem: Everytime I try to crank the engine, the engine turns slightly but it stops and seems like it is jammed. The problem occured when I took it to the lake. We had just launched from the docks and accelerating about half throttle out when the engine stops. Ever since then, it has been acting like this. Please check out the video, it'll give you a better idea as to what I'm talking about.

Video Link: http://www.youtube.com/watch?v=Ekf5y0I6AdA

captmello · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Looks/sounds like hydrolock. Pull the plugs and try the starter.

Mercruiser_120HP · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

captmello said:
Looks/sounds like hydrolock. Pull the plugs and try the starter.

Just pulled the plugs and tried cranking. Still same results. Any other ideas?

JustJason · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

if it still doesn't crank with the spark plugs out, time to pull the drive and seperate what's sticking from what's not sticking.

Bt Doctur · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Remove the drive and retest, if still jamming you most likely have :
jammed coupler/broken flywheel studs,
internal engine damage
broken piston/connecting rod or crankshaft
Removing the head would be the next option

a70eliminator · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

So even with the plugs out you have the same problem, see if you can turn the engine over by hand, bypassing the solenoid does not prove the starter is good, if you can turn the engine over by hand then the starter is bad or you have a loose connection somewhere. If you can't turn it by hand with plugs out then something more serious is wrong.

Bt Doctur · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Have you checked the prop?

Bondo · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Ayuh,.... I was wonderin' where that dockline went.....

Mercruiser_120HP · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Bt Doctur said:
Have you checked the prop?

lol...My prop is free to rotate. I'd like to crank it by hand but where can I do it. There seems to be a mounting bracket blocking the crank bolt. Would I have to remove the plate first before I can crank it?

Don S · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

That's a drive locked up. The only movement is the flex in the rubber coupler.

JustJason · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Betcha if you pull the 4 bolts that hold down the top cap on the drive and have a looksee you'll see you have no oil + tons of rust + a busted gear. It will take you all of 2 minutes to look.

Mercruiser_120HP · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Sorry guys this is the first time fixing a boat. I'm more comfortable with cars but what do you guys mean by pulling out/checking the "drive"? Can someone clarify where this is on the motor. I have a Seloc Repair manual I just bought so if someone can pinpoint where it is I might be able to use the manual to repair it. Sorry if I sound like such a newb.

ziggy · Mar 5, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

what do you guys mean by pulling out/checking the "drive"?

you need a service manual. go here. http://forums.iboats.com/showthread.php?t=288430 and look at #9. get #1. it's the real service manual for a '67 120.

what they guys are saying is it could be the drive that's locked up and not allowing the engine to turn over because of possible internal damage to the drive. if you remove the drive and the engine turns over. you can assume the problem is in the drive. if it don't turn over, back to the engine as having the issue.

this is the drive.

though you can only see the upper part. the lower part has the propeller on it.

the cap jj is talking about is the top part of the drive with the eye in it. held on by 4 bolts, 3 you can see in this pic.

get the book above and read through it. much info in it. with pics and instructions....

pulling the drive is not real hard to do. the book will have the exact instructions for you to remove it in pretty short order..

littlebookworm · Mar 6, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

To pull an Alpha drive: put the engine in forward; remove the two lock nuts holding the lifting pistons and disconnect the pistons; remove the six bolts holding the drive to the transom plate/bell housing; pull the drive towards you. Careful, it's heavy and awkward; best if yoy have a helper or a rolling stand. It may be stuck. If so, CAREFULLY use two large screwdrivers to pry it loose. As was said, you may have a stuck drive or a stuck engine. The only way to tell is to separate the two and try to turn the engine. Good luck and let us know what you find. Hy

Mercruiser_120HP · Mar 7, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

Wow good info guys. I just finished downloading the manual so I'll go ahead and pull the drive. I'll keep you guys updated.

achris · Mar 7, 2010

Re: Engine Cranks but wont turn...Starter? <Checkout Video inside>

ziggy said:
.....
pulling the drive is not real hard to do. the book will have the exact instructions for you to remove it in pretty short order..

Best I've done is 6 minutes....

Chris....

Engine Cranks but wont turn...Starter? <Checkout Video inside>

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