1989 Yamaha 50hp, engine noise

tal

Petty Officer 1st Class
Joined
Nov 21, 2003
Messages
214
A few months ago I had the boat out on a fishing trip and everything appeared in normal working order and good running condition. The following weekend I took my folks out on a fishing trip and things started to go wrong. <br /><br />At first it would bog and die out at WOT like it was starving for gas or something. When I tried to start the boat after drifting to a stop, it wouldn't crank over immediately, like it was seized up (battery cables felt hot too, but I assume this was from the starter struggling to turn the motor). After sitting there about 8 minutes scratching my head wondering what to do, I decided to try another crank, this time it started up fine. Got up on plane and started running about 3/4 throttle and it died out again. Once we got on plane again I was able to keep the boat at about 1/2 throttle without it dieing. We finally made it back to the doc.<br /><br />My fuel lines, bubble, and gas tank are in good condition, in fact, I had my dad pump the bubble when it was bogging out but it didn't seem to change anything. I rebuilt the carbs a while back and it had been running fine ever since. I even run the gas out after every use and put stabil in the tanks. I gave a trusty mechanic a call hoping for some help.<br /><br />The mechanic told me it sounded like the engine was "seizing up". He said the only way you could be certain was to pull the head and check for cylinder wall scarring and damage. I did this and found no deep scratches or anything else that looked out of shape per his description. I put the head back on and installed all new oil lines and check valves (oil injected) sine the originals were becoming decayed. <br /><br />Hoping that one of the oil lines was the problem for the engine seizing up, I decided to take it to the lake and give it a try. Got up on plane and still dies after a brief running period, just like before. In addition, I have this tapping or knocking sound that gets louder with engine rpm's. I can't figure out what it is, but the engine still runs strong until it dies out. I have the fly wheel off looking around because that is almost where the noise appears to be coming from. Oh, I told the mechanic what happened and he said he'd have to look at it in person, but I don't have much time to drag my boat an hour away just for a "look"<br /><br />Any help would be appreciated, I tryed to be as thorough and possible, and questions plz ask.
 

Ray Neudecker

Lieutenant Commander
Joined
May 25, 2004
Messages
1,656
Re: 1989 Yamaha 50hp, engine noise

If you have a chirping noise, the crank seal on the top side of the enine is bad and needs replacing.
 

tal

Petty Officer 1st Class
Joined
Nov 21, 2003
Messages
214
Re: 1989 Yamaha 50hp, engine noise

It sounds more like a loud clicking or knocking noise. I'm going to take it out today being very careful with it and listen again. Maybe I can find out a little more about it.
 

myriopod

Cadet
Joined
Sep 5, 2004
Messages
7
Re: 1989 Yamaha 50hp, engine noise

Originally posted by tal:<br /> A few months ago I had the boat out on a fishing trip and everything appeared in normal working order and good running condition. The following weekend I took my folks out on a fishing trip and things started to go wrong. <br /><br />At first it would bog and die out at WOT like it was starving for gas or something. When I tried to start the boat after drifting to a stop, it wouldn't crank over immediately, like it was seized up (battery cables felt hot too, but I assume this was from the starter struggling to turn the motor). After sitting there about 8 minutes scratching my head wondering what to do, I decided to try another crank, this time it started up fine. Got up on plane and started running about 3/4 throttle and it died out again. Once we got on plane again I was able to keep the boat at about 1/2 throttle without it dieing. We finally made it back to the doc.<br /><br />My fuel lines, bubble, and gas tank are in good condition, in fact, I had my dad pump the bubble when it was bogging out but it didn't seem to change anything. I rebuilt the carbs a while back and it had been running fine ever since. I even run the gas out after every use and put stabil in the tanks. I gave a trusty mechanic a call hoping for some help.<br /><br />The mechanic told me it sounded like the engine was "seizing up". He said the only way you could be certain was to pull the head and check for cylinder wall scarring and damage. I did this and found no deep scratches or anything else that looked out of shape per his description. I put the head back on and installed all new oil lines and check valves (oil injected) sine the originals were becoming decayed. <br /><br />Hoping that one of the oil lines was the problem for the engine seizing up, I decided to take it to the lake and give it a try. Got up on plane and still dies after a brief running period, just like before. In addition, I have this tapping or knocking sound that gets louder with engine rpm's. I can't figure out what it is, but the engine still runs strong until it dies out. I have the fly wheel off looking around because that is almost where the noise appears to be coming from. Oh, I told the mechanic what happened and he said he'd have to look at it in person, but I don't have much time to drag my boat an hour away just for a "look"<br /><br />Any help would be appreciated, I tryed to be as thorough and possible, and questions plz ask.
 

myriopod

Cadet
Joined
Sep 5, 2004
Messages
7
Re: 1989 Yamaha 50hp, engine noise

Hi, I seem to be having the same problem with a 30hp Yamaha. Perhaps we can compare notes.<br />dcdcu@yahoo.com for contact thanks!
 

tal

Petty Officer 1st Class
Joined
Nov 21, 2003
Messages
214
Re: 1989 Yamaha 50hp, engine noise

I have narrowed down the problem for those interested. It seems I have a burned piston. More specifically, the lowest piston from the top. I suppose it might be referred to as the number 3 piston. You might be wondering how I came about this conclusion, so here it goes. <br /><br />I continued running the boat and diagonosing every which way I could. From soaking carbs for 48 hours to splicing barb ends in place of the fuel bubble, nothing worked. I did a compression test on the engine about a month ago and that #3 was 10-15 psi lower than the other. I talked to a mechanic and he said that wasn't really much to worry about. When I took the boat to him today after running it one last time to find it only die out on me, we did another compression test. From the top down, it went like this : 115, 117, 0. I just frowned when I saw the gauge read 0psi. <br /><br />Apparently my last 3-4 runs of the boat have completly finished off that cylinder, dropping the pressure to a now "0" reading. The mechanic told me the reason the engine would run for a while then stop is because the cylinder would finally heat up and seize the motor. Strangely enough, the motor would kick over and continuing running after this happens, but would be rather weak and putter along when I attempted to give it throttle. <br /><br />I'm now looking at a rebore/rebuild and will most likely do the work myself. I would really enjoy an 80-85 hp on the boat, but that route seems too costly. <br /><br />My suggestion to you myriopod, is to get a compression testing gauge and see what your cylinders read. If you have a low cylinder watch it closely. If you have the same "clack" in the motor that I did, then you probably don't have much life left on it.
 
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