Got some engine

[Seattle Scott]

that is somewhat intermitant but is constant when thottling up and running at high RMP in gear. Doesn't happen in neutral and doesn't happen when running at low RPM. First I thought it was mechanical, that something was banging around involving the shaft or the folding prop because the sound seemed to be coming from somewhere lower and aft of the engine. Had the prop checked when I had the hull scrubbed and I examined the shaft/coupling under power and see no misalignment or anything loose. Now I think the sound appears to be coming from the exhaust discharge. Yanmar 4JHE. No other symptoms. Engine moves the boat great and runs well and smooth. Could this be caused by some problem in the exhaust system something related to the muffler? I ran the engine about 50 hours before the symptom developed. I am not yet educated on exhaust systems, mixing elbows etc., so I am just guessing on the muffler issue.Scott

 

[Pat McCartin]

Scott...

I'd have the yard check your alignment. Tolerence is .003" that's hard to see. Because the sound doesn't hapen in neutral the driveline is the obvious place to look first.Pat McCartinInland Marine DieselAtlanta, GA

 

[Ed A]

Scott my boat and yours must be sisters

I would pull the exaust elbow down and be sure there is no build up there. its not to hard to do and probably should be checked anyway. the muffler has glass baffels, if one came loose and was rattling arround it could cause a restriction or a lot of noise? dont know. did anyone check the strutt and the cutlass bearing. if the cutlass bearing were bad you would really hear it. you should have no movement in the shaft at the strutt. get down there and pull push and shake and see if you can get movement. if so you may need a new bearing. Or the strutt itself could be loose.Let me know what you find. btw what is your hull number?Ed A

 

[Seattle Scott]

Hey Ed, I had the hull scrubbed this month

in the water and had the strut and prop checked at that time. I will remove/inspect the elbow. I have hull 485ish.Thanks for imput.Scott

 

[Pat McCartin]

Scott....

Take a flash light and look all over your exhaust system. Your looking for carbon trails, usualy found a junctions and flowing against the exhaust flow. I doubt there is an exhaust leak with out these trails. I had a similar issue come up on another board. My first few guesses would be, soft motor mounts allowing the engine to bottom out during hard loading. Yanmar recomends a 5 year replacement cycle in a salt enviroment. The other thing that comes to mind is a shaft that's out of round. A shaft with a slight bend will exagerate it's out of round at higher speeds.Pat McCartinInland Marine DieselAtlanta, GA

 

[Seattle Scott]

Thanks Pat

The shaft under power "appears" fine to the eye. I don't see any out of round type movement. I will check the mounts since the boat is a year and a half new to me so don't know the age of the mounts. I will go over the exhaust stystem and look for leaks. Wish I could discern better whether the sound is a "pop" or a "clunk".Scott