50hp mercury outboard knocking after timing belt replacement

[dub1620]

Hello and thanks for viewing my post.

Engine:
1975 mercury 500
2stroke
50 h.p.

This engine ran great for over a year. I replaced the timing belt, after it broke, and somewhere along the way I screwed something else up. At first I attemted removing the flywheel with a puller from an auto store( the typical 3 jaw with a bolt in the middle). After a few attemps I realized I needed the special mercury puller. so I got it and the flywheel came off pretty easy.
Unfortunately I didnt mark the flywheel prior to removal, I put it back together.
After re aligning the flywheel and pulley to specs i found online, (using the engraved marks on the flywheel and arrow on the pulley).

I put the prop in a trashcan of water and it ran great for a few minutes.

Then I took it out on the water and it ran great for ten-fifteen minutes. all of the sudden at full throttle the engine began making a very loud knocking noise. I removed the top cover of the engine and could see that the flywheel was wobbling. I tried to tighten it, and it wasnt loose.

I am not sure what I did, or how to fix this.

thanks for any info related to this

 

[1946Zephyr]

Re: 50hp mercury outboard knocking after timing belt replacement

Oh crap. It sounds to me like you have a 2 piece crank shaft now. I would pull the flywheel back off to make sure, but if it ran great and didn't have a wobble before, then it sounds like the crank is broke.

 

[Faztbullet]

Re: 50hp mercury outboard knocking after timing belt replacement

Crank, upper bearing failure or broken flex plate on flywheel. Also motor is a 1975 or prior as 1976 was a CD ignition......

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

Crank, upper bearing failure or broken flex plate on flywheel. Also motor is a 1975 or prior as 1976 was a CD ignition......

Im trying to figure out what is going on, but i cant get any further than just below the flywheel.

I have removed the flywheel, flywheel pulley, stator, timing belt, but cant get any further.

There is a housing(possibly plastic) on top of the engine right where the crankshaft is exposed that i cant seem to remove. I believe this is where i need to begin assessing my problem.

If not, how else would i check the shape of the upper bearing or crank, I looked at the plates on the flywheel and all seem to be in good shape.

Is it possible that my flywheel is shaking due to timing.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

Oh crap. It sounds to me like you have a 2 piece crank shaft now. I would pull the flywheel back off to make sure, but if it ran great and didn't have a wobble before, then it sounds like the crank is broke.

How would i know if the crank is in two pieces? it does have a little play i it, but not very much maybe a 1/16 of an inch???????

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

If I were to reassemble it so i could crank the engine, and take a video, could i post it on here or maybe a link to youtube. I can get it to run, but the flywheel wobbles while it spins.

 

[bktheking]

Re: 50hp mercury outboard knocking after timing belt replacement

Upper crank bearing by the sound of what you're describing.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

can that be verified by removing the flywheel and going in that way, or do i need to strip the front of the engine(carbs,distributor,etc) to properly inspect the engine.

 

[bktheking]

Re: 50hp mercury outboard knocking after timing belt replacement

Looking back, did you torque the flywheel to spec. You may have not and the flywheel let loose, if you are lucky that all it is and pray you didn`t damage the crank. Pull the flywheel and go from there.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

I put it all back together, put the flywheel back on to proper torque specs, and it still wobbles. It didnt fully start up and idle, but it did kick over for a second or two, and made a pretty loud knocking while it was running as well.

I video taped it on m phone, but cant seem to upload it. I will tr a dif camera tomorrow.


Would my engine crank over, and fire up for a second if the crank was broke?

Could this be related to timing?

thanks for any info, it is much appreciated.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

Here it is running

 

[bktheking]

Re: 50hp mercury outboard knocking after timing belt replacement

You need to figure out why the flywheel is wobbling before anything else. Pull the flywheel and plugs and shift into gear. Have someone rotate the prop and watch the crank to see if it's bent.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

it doesnt seem to wobble when it is turned by the propeller,with the fly wheel off, but it may not be moving fast enough..................

 

[bktheking]

Re: 50hp mercury outboard knocking after timing belt replacement

Then it's possible the flywheel taper is damaged, this is all guesswork as it's not in front of me.

 

[Laddies]

Re: 50hp mercury outboard knocking after timing belt replacement

You either damaged the hub or the flywheel flex plate when you put the 3 jawed puller on it.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

You either damaged the hub or the flywheel flex plate when you put the 3 jawed puller on it.

If it is the hub or the flex plate, are these fixable problems or should i get a neew engine?


BTW: I do have a seperate bare powerhead that is the same year and model........

 

[bktheking]

Re: 50hp mercury outboard knocking after timing belt replacement

Grab a used flywheel, I missed the 3 jaw puller part, you probably bent the center of the flywheel.

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

I already tried replacing the flywheel and it didnt change anything.

Could it still be the flexplate, or the hub?

 

[bktheking]

Re: 50hp mercury outboard knocking after timing belt replacement

Is it the flywheel that has 8 bolts holding it onto the hub with the large center nut that holds it to the crank?

 

[dub1620]

Re: 50hp mercury outboard knocking after timing belt replacement

yes.