Help needed, random clunk from back of engine/boat

[par1969]

I went WOT for about ? mile in my 1978 Sea Ray with a 350 and an Alpha 1 drive. As I was idling to shore I both hear and felt a clunk, almost like I hit a rock or something. It happened a few more time as I idled to shore at totally random intervals. I opened the cover idling in neutral and it was happening again randomly, sometimes twice in 15 seconds and sometimes not for a couple of minutes. It sounds like it is coming from the back of the motor/boat. It almost sounded like a bolt or something metal in the bell housing getting caught on the flywheel gears once and a while with a slight metallic ping and hard enough to be lightly felt throughout the boat. I removed the lower bell housing cover and verified this was not the problem. if I increase the revs it doesn't appear to happen, although I have am very reluctant to test this theory much. Any other ideas on what it could be? All help would be greatly appreciated.

 

[Bondo]

Re: Help needed, random clunk from back of engine/boat

I went WOT for about ? mile in my 1978 Sea Ray with a 350 and an Alpha 1 drive. As I was idling to shore I both hear and felt a clunk, almost like I hit a rock or something. It happened a few more time as I idled to shore at totally random intervals. I opened the cover idling in neutral and it was happening again randomly, sometimes twice in 15 seconds and sometimes not for a couple of minutes. It sounds like it is coming from the back of the motor/boat. It almost sounded like a bolt or something metal in the bell housing getting caught on the flywheel gears once and a while with a slight metallic ping and hard enough to be lightly felt throughout the boat. I removed the lower bell housing cover and verified this was not the problem. if I increase the revs it doesn't appear to happen, although I have am very reluctant to test this theory much. Any other ideas on what it could be? All help would be greatly appreciated.

Ayuh,... Drain the drive oil, 'n look for Metal....

 

[par1969]

Re: Help needed, random clunk from back of engine/boat

Ayuh,... Drain the drive oil, 'n look for Metal....

I will have to do that. I just assumed that if it was the lower unit it would have been a more frequent and consistant clunking noise as well as only happening in or out of gear not both.

 

[Don S]

Re: Help needed, random clunk from back of engine/boat

The shift dogs in the lower unit are probably starting to round over from years of use and the drive is actually jumping out of gear and back into gear every now and then, or It may be that your shift cable is worn and not pushing it all the way into gear anymore and allowing it to jump out of gear. If it does it to often, it will will damage the gear and shift dog beyond use.

 

[edamarino]

Re: Help needed, random clunk from back of engine/boat

there are flappers (to prevent water backflow) in the exhaust Y usually they have a little rubber seal around them but it does wear off. but that is most likely what you are hearing. i have a brand new motor in my boat and can still hear mine doing the exact same thing

 

[cr2k]

Re: Help needed, random clunk from back of engine/boat

You must have some helacious flappers to be able to feel the flap.

 

[Doernuth]

Re: Help needed, random clunk from back of engine/boat

Or the starter could be bad. If the spring retaining the drive gear fails the gear can vibrate out and hit the flywheel causing a clunk. Had this happen on a car once.

Just a thought....

 

[par1969]

Re: Help needed, random clunk from back of engine/boat

Thanks everyone for the replies, I now have some ideas to look into. Owning a boat sure is fun but the maintenance/repair never seems to end.