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Mercury 9.8 diagnosing engine ticking

L

loopyboat

Member
I'm working on a Mercury 9.8 that has a distinctive ticking noise at all RPMs. It sounds and feels as if it might have a bad connecting rod bearing, because when I manually rotate the flywheel there is a good amount of play in it. Is this a sign of a bad bearing?

Good spark and compression is at 120 both cylinders. Lower unit is also good and I believe the noise to be coming from the powerhead and not the lower unit. This noise happens when the cover is off, so I don't think anything is rattling.

I also removed the spark plugs and pushed down on the pistons during the downstroke with a brass rod and it did NOT move, so I don't think it's a bad wrist pin bearing.
 
The pistons move almost immediately after I move the flywheel, but as I said when I rotate it back and forth there is about a 1/16" free play before it starts to move the pistons.

There doesn't seem to be any end play in the crank, I don't have an indicator to check but it doesn't feel as if the flywheel moves at all up or down.
 
I found the problem, one of the coils had a spark coming out the side of it, so I suspect the engine was only running on one cylinder, causing it to make the noise (I'm guessing because it was running at half the power). Does this make sense?

When I did a spark gap test, the coil showed good spark, not sure why it tested good but I'm almost positive I wasn't firing on that cylinder when the engine was running.
 
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