3.7 Engine noise at rear of motor near transom

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ElectraGlide H2O

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Jun 15, 2012
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I have a 1989 boat with a Mercruiser 3.7 motor that I just purchased a couple of months ago. I have had the boat out on the lake about 7 or 8 times and it runs great. However, at a RPM just above idle (maybe 1500 to 2000) I have this ringy or tingy kind of noise towards the rear of the motor. I describe the noise this way because it has a higher pitch than some kind of motor knock which I have heard before. This occurs in or out of gear. It seems to disappear at higher RPM's or at least I no longer hear it. This noise does not have a rotational rhythm and is sporadic (tone remains the same but sequence varies... ting... ting, ting, ting... ting, ting). Any ideas???
 
ktbarrentine

ktbarrentine

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Re: 3.7 Engine noise at rear of motor near transom

Sounds like possible gimbal bearing and/or u-joint noise. Does it change at differing outdrive trim settings? Have you had the outdrive off for routine maintenance? Might be worth a pull-off look see. Then you can check the u-joints face to face, and lube the zerks. Have you greased the gimbal bearing since you got it? (although u-joints and gimbal would be rotational noise...so I would lean more towards the shudders discussed further on here.. not too difficult to check those, either)
 
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southwest395

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Re: 3.7 Engine noise at rear of motor near transom

Does it sound like a rattle noise. Mine did it in the lower rpm and as it got higher couldnt here no more. My problem was there a exhaust flap in the lower elbow. Its has a metal bar and flaps are metal but covered in rubber. But the purpose of it so water does come back into the block. Easy fix and cheap.807166A-1_med.jpg
 
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ElectraGlide H2O

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Re: 3.7 Engine noise at rear of motor near transom

ktbarrentine said:
Sounds like possible gimbal bearing and/or u-joint noise. Does it change at differing outdrive trim settings? Have you had the outdrive off for routine maintenance? Might be worth a pull-off look see. Then you can check the u-joints face to face, and lube the zerks. Have you greased the gimbal bearing since you got it?
Click to expand...

I have greased the the gimble bearing and the zerks since I got it. I purchased it from a much more organized person than myself. He has all the service records for the past several years and the upper and lower units were resealed by a marina last July. So i would cautiously asume that ujoints would have been in good shape at that time.
 
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ElectraGlide H2O

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Re: 3.7 Engine noise at rear of motor near transom

So far I am inclined to agree. I had totaly forgotten about the flappers. It does sound just like a rattle that flutters. Gosh how the old mind forgets things. Did I fail to mention that I am just returning back to boating and Mercruisers after about a 15 year sabbatical. This is a wonderful site and its members and help are awsome. The help even comes with pictures....now that I can understand ha! Thanks for the info Southwest395.
Would anyone else care to weigh in. Maybe there is a better suggestion/answer. Hey lets hear your thoughts!!!!! Thanks again guys
 
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stonyloam

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Re: 3.7 Engine noise at rear of motor near transom

You asked for it;). Your 470 engine needs a little more TLC than some others. Main thing, NEVER let it overheat. Keep an eye on the temperature gauge and when you are at operating temp. under load note where it stabilizes, and mark it on the gauge face so if it ever starts to creep up over that mark find out why and fix it. Learn how to change the impeller and replace it at least every other year. Ask the previous owner if he ever had the waterpump cam seals replaced, and when. Open up the engine compartment and locate the weep hole on the lower starboard side of the engine waterpump and make sure it is open (a toothpick will do) and every now an then when the engine is up to operating temperature and running take a look to make sure it is not leaking. Buy yourself a inexpensive little antifreeze tester and check the coolant, should be about 50/50 good automotive antifreeze. When you take the boat out for the fall, just remove the boat transom drain plug and then remove the AFT plug on the heat exchanger and drain it right on the ramp, and your freeze protection is done, never have to worry about a cracked block in the spring. If it has not had an alternator conversion, keep an eye on the voltage, if it starts to jump up to above 15 volts, or stops charging it will be time to get it done (Breezeworks.net) That is about all I can think of for now. Have fun and welcome to the "470 club" :facepalm::D
 
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southwest395

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Re: 3.7 Engine noise at rear of motor near transom

Most of the time if a gimbal bearing or a u-joint you will fell some shakeing in the steering when you drive. You can also look down at the shaft coming in to the block. if there alot of shake or play then go with the gimbal or u-joints.
 
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ElectraGlide H2O

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Re: 3.7 Engine noise at rear of motor near transom

Stonyloam,
thanks for all the great info and tips. Funny that you should mention the water pump seals, I just read about that problem area on another site. Thanks for the winterizing tips. I hope with proper maintenance that I will get several years of service out of this boat and motor. I love the 470 for all around power and gas consumption. I know that the 470 has had it problematic areas throughout the years with the voltage reg. being one of them. I did the breezeworks conversion a couple of weeks ago and all is great there. Over all it makes you wonder why a company would stop production on what seems to be a real winner. Different strokes for different folks!!
 
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southwest395

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Re: 3.7 Engine noise at rear of motor near transom

The Mercruiser 470 is a great motor. But you have to keep on maintance. When you got one problem expect more.This is my first year with a mercruiser 470. The previous owner did winterise it properly. Ive had to change plugs wires, sperator plate, voltage regulator, had the heat exchanger repaired cause they had water in the tubes crack two copper tubes, had to change impeller, u-joint bellow, raw water hose, shifter bellow, ehaust bellow, exhaust flapper, and the exhuast boot.
 
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southwest395

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Re: 3.7 Engine noise at rear of motor near transom

And another tip make sure that impeller is good. It supplies the raw water to the voltage regulator. If its not cooled it will over heat and go bad. Then its time to buy another voltage regulator $500.00 plus or the altenator conversion kit for $395.00
 
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a1nowell

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May 12, 2009
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Re: 3.7 Engine noise at rear of motor near transom

Electraglide,

Your statement, "Over all it makes you wonder why a company would stop production on what seems to be a real winner," is funny!

I can't wait til Bond-o reads it.

Larry,
another 470 owner
 
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