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Author Topic:   Unusual Sound During Decelleration
Captain Jack posted 11-06-2003 07:37 AM ET (US)   Profile for Captain Jack   Send Email to Captain Jack  
I am interested in buying this very nice used 1999 MONTAUK 17 with a 90-HP Johnson outboard. I noticed when the boat is running on plane and we throttle back to idle, an unusual and very noticeable sound occurs. I think it is the propeller, shaft, and gear case still rotating from the remaining forward movement of the boat, as though it were wind milling (water milling?). The sound goes away when at rest or power is added prior to coming to rest. I have owned many outboards before; except Johnson, and never noticed this. Any ideas?
jimh posted 11-06-2003 08:38 AM ET (US)     Profile for jimh  Send Email to jimh     
I think I can coax a strange sound from my engine, too, if I get it into the same situation you describe. When the boat is slowing, if the engine throttle is rapidly cut back the propeller will turn faster by the flow of water past it than it would from the revolution of the engine shaft. This produces are gear-gnashing sound.

I think this sound is produced by the clutch mechanism ("dog"). I try to operate the throttle so as to avoid that situation.

[Changed TOPIC; was "1999 BW Montauk & 90 HP Johnson."]

Bigshot posted 11-06-2003 12:07 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
That occurs especially if you just yank it back to idle. Basically the water is still spinning the prop and engine like a Jake Brake on a truck.
dgp posted 11-06-2003 08:32 PM ET (US)     Profile for dgp  Send Email to dgp     
The Jake Brake permits large trucks to descend long, steep grades at a controlled speed. It was the first practical mechanism for altering on demand the valve timing on a truck diesel engine, thereby converting the engine to a power absorbing machine.
The principle behind the Jacobs Engine Brake engine retarder is simple. It's a hydraulically operated device that converts a power-producing diesel engine into a power-absorbing retarding mechanism by opening the engine's exhaust valves near the top dead center (TDC) of the compression stroke.
whalerron posted 11-06-2003 10:01 PM ET (US)     Profile for whalerron  Send Email to whalerron     
C.J., all of the newer Johnson 90 hp motors make that sound. When the motor is running at high RPMs and you quickly cut the throttle back, the motor makes that noise. The best way I can describe it is that it almost sounds like somebody shaking a coffee can full of marbles. Somebody else said it sounds like a Jake brake and in a way, it does sound like a mini Jake. The sound is normal.

- ron

Bigshot posted 11-07-2003 11:14 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My 225 will do it but I don't recommend doing it all the time. If the engine is spinning 5500 and you pull off the throttle and engine rpms are gradually coming down until you come off plane, how are the cyls getting oil? Might not be an issue and probably is not, but don't make a habit out of it is what I am saying.
Tom2697 posted 11-07-2003 11:23 AM ET (US)     Profile for Tom2697  Send Email to Tom2697     
Cars make similar sounds if you slam an automatic transmission into Park while the car is still moving. Outboards make a similar noise if you accidently disconnect the safety kill lanyard while at speed.

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