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rattle sound in power head

S

Solar Ice

New member
Looking for some help identifying a rattling sound in our power head. We have a 1979 70HP Mercury 2stroke 3cyl. A rattling sound is coming from the power head when at idle, as the rpms increase the sound seams to dissipate but not sure due to the increased noise. The rattle is also there at low rpms in gear but becomes quite when you place it in reverse. It sounds as if it is coming from the top of the head. A new impeller was installed with no effect on decreasing the rattle. The fly wheel is solid and turns with some difficulty, as it should. Any advise would be helpful.
 
There are a number of different approaches to this.----Some will argue.----But I would do a compression test first.---Post your numbers.------How long have you owned this motor ?----There is always the possibility that motor was submerged and not recovered properly.----That would result in damaged / corroded bearings.----Or pull the bypass covers and see if pistons / rods have too much play in them.
 
We have owned it for 3 years previously it sat at our friends house for 11 years. It has never been submerge. I did a compression test 124 top piston 125 the other 2. It has run great and quite for the previous 2 years 4th time out this year the rattle started.
 
Since the sound goes away in reverse maybe the problem is in the LU and the sound is being conducted thru the driveshaft, you can remove the LU and put a garden hose on the water tube - run the motor at the rpm where the rattle occurred. A loose prop or a bad bearing in the LU can cause noise too.
 
Flywheel flexplate flywheel-flexplate.jpg
 
Check this out before doing anything: Remove the flywheel nut and the flat washer below it. That flat washer MUST be the correct one or you'll get that rattle (don't ask!)

Jeff
 
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