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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10964
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1986 mercruiser 3.0 that has a rattle behind the

Customer Question

I have a 1986 mercruiser 3.0 that has a rattle behind the timing cover. The engine runs great. Has 40 psi oil pressure, and a full dips tick. Could the problem be timing gears?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

Yes it has to be the gears. Due to the age of the engine they are worn pretty good. Does the rattle lessen when rpms are increased?

Customer: replied 1 year ago.
almost goes away when put in gear at idle
Expert:  Tan replied 1 year ago.

Are you sure the noise is behind the timing cover? Could the noise be the water pump?

Customer: replied 1 year ago.
I used a stethiscope and it is definitely louder at the timing cover
Customer: replied 1 year ago.
What would a marine dealer charge to replace the gears?
Expert:  Tan replied 1 year ago.

Ok what you are hearing is gear lash this is the space between the gear teeth rattling. Once you apply a load the gears stop rattling. The gears are worn time to replace them.

The gears will run about $150.00 and about 3 hours labor at the rate in your area.

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