help on rattling noise from rear of engine
05-18-2020 | 11:29 AM
#11
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Joined: Jul 2007
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Have you pulled the drive off and checked to see if the phantom noise disappeared?
May be a "Way out there" item to check (and easier to check than pulling engine) as most times it sounds like a "grinding" or "howl" that is transmitted through the transom assembly.... but, if the big Tapered roller bearing on the top of the drive carrying the input shaft behind the yoke is on its way out/ or merely several rollers have flat spotted on the bearing, it will be hard to detect and doesn't transmit from outside the boat (unless really bad) - just behind the engine in the compartment.
.. and yes a bad bearing can/ does stop making noise at a certain rpm as the harmonics level out.
May be a "Way out there" item to check (and easier to check than pulling engine) as most times it sounds like a "grinding" or "howl" that is transmitted through the transom assembly.... but, if the big Tapered roller bearing on the top of the drive carrying the input shaft behind the yoke is on its way out/ or merely several rollers have flat spotted on the bearing, it will be hard to detect and doesn't transmit from outside the boat (unless really bad) - just behind the engine in the compartment.
.. and yes a bad bearing can/ does stop making noise at a certain rpm as the harmonics level out.
Last edited by speicher lane; 05-18-2020 at 11:33 AM.
05-19-2020 | 08:52 AM
#14
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Joined: Nov 2004
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From: On A Dirt Floor
Thanks guys,
there is no flywheel cover but there could be something in behind there, I fished a magnet down behind the flywheel and did not catch anything.
There is no Y pipe and I think the mufflers are HPI, I can stop the external rubber flappers with screwdrivers and still heve the rattling noise. there are no internal flappers in the cmi tails ahead of the mufflers. I may just need to pull the engine but would like to know if anyone has seen this, very strange.
there is no flywheel cover but there could be something in behind there, I fished a magnet down behind the flywheel and did not catch anything.
There is no Y pipe and I think the mufflers are HPI, I can stop the external rubber flappers with screwdrivers and still heve the rattling noise. there are no internal flappers in the cmi tails ahead of the mufflers. I may just need to pull the engine but would like to know if anyone has seen this, very strange.
I’ve seen multiple Corsa’s do this, thus why I asked. Doesn’t mean HPI’s are immune.
05-19-2020 | 08:32 PM
#15
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Joined: Jan 2001
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From: south east of dome island
both mufflers sound the same with the scope so I think I can rule them out. per above on fuel rail scope I have a holley carb so no fuel rail here.
I will try to see if the coupler is loose somehow before I bull the thing. thx
I will try to see if the coupler is loose somehow before I bull the thing. thx
05-19-2020 | 08:35 PM
#16
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Joined: Dec 2019
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From: Manistee
I have the same noise in my boat. Pulled the 330, put a 420 in it with new exhaust and tips, reused coupler and bellhousing, still the same noise. I would say it has to be one of those things. Nothing visually wrong with them upon reinstall 🤷♂️
05-24-2020 | 12:46 PM
#18
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From: south east of dome island
put on a new coupler and new coupler bolts, the ones with the shoulder for tight fit ent to the coupler holes. someone had just used regular grade 8 bolts. Noise fixed, all good now.
05-24-2020 | 06:36 PM
#20
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Joined: May 2009
Posts: 627
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From: Indiana
So what was the noise? Defect in coupler, wrong bolts so coupler wasn’t actually tight to flywheel, or wasn’t centered because shoulder bolts weren’t used? Weird that it made noise even with drive out and no spline shaft in coupler. Kudos to you for finding that.
