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Old 09-29-2009, 02:16 AM   #1
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Default Hmm...engine knocking or something else?

Did a quick 35 minute run at 3000 rpm (30mph with some tab down due to chop) and back the same this past weekend. As we were idling down the canal my wife who was sitting aft mentioned that the engine note was slightly 'off'. It felt 'ok' to me underway although I did think it felt like it was dragging at speed, although I attributed that to my still getting accustomed to the trim tabs.
Temp gauge was spot on (175), oil pressure was 45psi (at idle, which is good) so I didn't really think much of it. We pull it out of the water, get her home and as I'm flushing the engine I crawl under the cowl and notice an inconsistent knock coming from the back of the engine. It sounds low in the back and hard to place. I revved the engine up to 1500rpm, engine sounded silky smooth, knock became more faint. Got out of the boat to turn on my Salt Away intake and noticed that there was quite a bit of white exhaust coming from the water outlet NOT the prop exhaust. I've never seen that before on my boat. I turned off the engine, checked the oil...perfect level and very clear, out drive gear oil was at the 'full' mark.

Do you guys think this is something worth taking it in for or am I just being a bit paranoid?
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Old 09-29-2009, 02:56 AM   #2
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Default Re: Hmm...engine knocking or something else?

well...I'd get a pipe of about 2 ft...place it down in the back of the engine while it's running (trying to not get it on the shaft)...then put your ear to it....

if you still hear of a knock that sounds metalic...I'd take it in to a mechanic to have him look closer....you could also pull a compression check....might be a main bearing or rod bearing...might also be a coupler or u-joint...
.not going to know from how you described it...

might probably be best to let a mechanic look at it now that I think of it..
SP :|
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Old 10-05-2009, 02:58 PM   #3
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Default Re: Hmm...engine knocking or something else?

Well, she's at the mechanic...dropped her off Sat. Based on my description he said it could be as simple as an adjustment to the throttle cable (maybe the clutch is just slightly trying to engage) or gimble bearing or U-joint (he doubted this as the boat is only 3 years old and that typically the 'knocking sound' would be consistent, not inconsistent). Since I did wreck a prop and slightly bent my skeg a few months ago he said worst case could be that I fractured a gear tooth and that it took time for it to break off and that is what the inconsistent knock is. I'll know for sure this week.
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Old 10-05-2009, 07:28 PM   #4
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Default Re: Hmm...engine knocking or something else?

heck..if I'da known you had hit something ...the drive top bull gear would be my first idea to check....they aren't that strong and sometimes will break a tooth after an impact....don't ask how I found out...but it cost me 2500 bucks to find out...


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Old 10-05-2009, 07:44 PM   #5
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Default Re: Hmm...engine knocking or something else?

Quote:
Originally Posted by seapuppy
heck..if I'da known you had hit something ...the drive top bull gear would be my first idea to check....they aren't that strong and sometimes will break a tooth after an impact....don't ask how I found out...but it cost me 2500 bucks to find out...


SP :|
I spun the hub and bent the prop. Didn't think it was that big of a hit. It was low speed. I know guys who go through props with every full tank of gas (not really), and they don't break gears (unless they are just ignoring the noise!) :0
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Old 10-07-2009, 03:00 PM   #6
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Default Re: Hmm...engine knocking or something else?

Mechanic gave it a clean bill of health, actually commended me on such a clean boat. He went over it with a stethoscope and said he couldn't hear anything out of the ordinary. He said that I may be hearing the exhaust flaps that have become louder due to the factory rubber coating wearing off. So he greased the gimble bearing while he was in there and told me to come get it.

Chalk one up to an over sensitive ear. ops:
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