Mercruiser Alpha one loud knocking

[oscardawgg]

Its been awhile since i posted, but have read and reread alot of posts trying to get help. You guys are great experts so i figured it was time to ask

I have a 87 marlin with a mercruiser alpha one 180. I was having problems with it and decided to take it to boat place to tune up and make ready for upcoming fishing season. Took it to the place, they said that the impeller water pump was fried, and had to install new one. Also distributer cap was broke and fixed that. they fired up the boat and immediatly called me saying there was a knock in the engine. They leaned towards bad rod, but didnt do any checks for it.

I looked up stuff on this site and got to checking the engine.

1. Started engine and one by one disconnected spark plug wires to see if knock went away. This did not stop the knock so i dont think its a rod problem.

2. noticed that the front part of the circulation pump was leaking.

3. put the motor into forward and reved it up and radiator cap started blowing fluid all over the engine. Its a brand new cap rated to 20lbs

With all this going on i am begining to believe that the circulation pump is screwed up. Would that cause the knocking??? The guys at the boat shop told me to get a different moter and switch it out. They told me to get a 170 for the 2 barrel carb.

I am tired of this thing being busted and am trying to get it up on the lakes again. What do you all think???

 

[JustJason]

Re: Mercruiser Alpha one loud knocking

the only thing you can do is get a mechanics stethoscope and pinpoint your knock.
What engine is this?

 

[Bondo]

Re: Mercruiser Alpha one loud knocking

What engine is this?

Ayuh,.. The Dreaded 470....

My Guess is,... You've got Several things going on....
Obviously the circulating waterpump is Bad....
The bubbling out the rad. cap says a Blown headgasket,..

A Compression,+ Leak-down tests will give you some insights to what's Wrong...

 

[JustJason]

Re: Mercruiser Alpha one loud knocking

Ayuh,.. The Dreaded 470

hummmm.... i didn't see that. the only thing i saw was

They told me to get a 170 for the 2 barrel carb.

i had no idea what the op was talking about.

But to the op.... if you do have a 470 cut your losses and toss the boat.

 

[Don S]

Re: Mercruiser Alpha one loud knocking

I have a 87 marlin with a mercruiser alpha one 180.

The 180 is the 1987 Version of the 470, but it has the 4bbl Qjet carb.

Took it to the place, they said that the impeller water pump was fried, and had to install new one.

I would guess you must have had an overheat, which the 470's don't handle very well. That would explain the head gasket problem.
Drain the cooling system, then start the engine for a few seconds and see if the knock is still there.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

ok thanks for the suggestions. I am going to go and drain the cooling and see if it still knocks. If it is a blown head gasket how much and how long? I am mechanically inclined but new to boats.

Is it worth it or should i just invest in the other engine???

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

ok so i started it up again. Started off running slow but got up to good idle. knocking sound is light but can still hear it. put into forward and knock gets louder. Got back next to engine and its coming from in around the coupler were the drive shaft goes in. No shaved metal in site just this loud knock that sounds like metal squeaking in metal. no noise from the top or sides. No knocking from front of engine.

Knocking or squeaking got louder and then engine just quite. Takes two or three tryes to get it to turn over again. Engine is acting like it wants to quit.

what do we think?

also had a thought that i could record the whole thing and put on youtube for you guys to see and hear.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

little more info: just replaced bellows and gimble bearing.

boat shop replaced all the stuff in lower unit.

sound is coming from motor side of boat, not the gimble side.

 

[Don S]

Re: Mercruiser Alpha one loud knocking

Remove the outdrive and see how it starts.

Have you checked the gear lube in the drive? Did the shop forget to put any in it? Wouldn't be the first time it happened.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

i put the new gear lube in there, but they may have drained it so i will check. to remove the outdrive i will have to drain it again right???

 

[Don S]

Re: Mercruiser Alpha one loud knocking

No, you don't have to drain the lube out to remove the drive from the boat.
Put control in forward gear, disconnect aft trim cylinder pin, remove 6 mounting nuts and pull the drive.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

thanks don. I got my buddy coming tomorrow to help me pull the drive and then i can fire it up again. Hopefully all is well.

What can it be besides the gimble or ujoints? Like i said i heard alot of noise coming from the motor side of the drive shaft. anything else i should start looking at? I am really not believing its a rod.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

took the outdrive off. started engine and knocking still there. couldnt keep engine running and then it just stopped trying to start. It would move alittle bit and then nothing. the starter was engaging over and over but no motor. It would be like that for about 10 to 15 starts and then try and kick over and then back to the no start.

Also i pulled outdrive and the bellows was full of gear oil. is that normal?

getting frustrated...starting to believe that different boat might be only answer.

 

[meesh]

Re: Mercruiser Alpha one loud knocking

No that is not normal. Input shaft seal is toast.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

thats the upper seal right???

 

[Don S]

Re: Mercruiser Alpha one loud knocking

Yes, but it probably has a bad yoke. They get grooves in them and the seal won't seal on it. You have to replace the yoke. But if the engine is junk why worry about a leaky drive.
You have a motor with either bad bearings or badly scored cylinders and pistons.
Time to pull it apart and look it over.

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

What should i be looking for? I finally got a cherry picker and a engine stand. But i have to pay daily for it so i am trying to make it fast. What signs for the bearings?? Or the bad cylinders and pistons??

 

[Bondo]

Re: Mercruiser Alpha one loud knocking

What signs for the bearings?? Or the bad cylinders and pistons??

Ayuh,... It should be painfully obvious when you find the Problem....

 

[oscardawgg]

Re: Mercruiser Alpha one loud knocking

opened up oil pan and there was some metal shavings in it. dumped everything out and there was a piece of a piston in there. I have to strip all the motor down now to get piston out. Do you think i need to get it machines? Is it time to switch for a differnet motor?

 

[Don S]

Re: Mercruiser Alpha one loud knocking

Do you think i need to get it machines? Is it time to switch for a differnet motor?

I think you need to get someone that knows about engines to look at it.
There isn't a mechanic here that can answer that question without knowing the condition of the block, crank, cam, etc.
If you can't tell by looking, then you would have to get another engine or long block. But you still need to find out why you have a broken piston if you can. There may be something else that caused the piston to break.