F150 knocking on start up

[Kwilson6488]

Hello to all. I'm new to the forum. I have a 2005 Yamaha f150 that I recently purchased. I was told when I purchased the motor that the lower unit was bad and that the lower was making a knocking noise. I checked compression on the motor before I bought it myself. 185 psi on every cylinder. So as soon as I got it home I fired it up on the stand with the lower unit dropped hoping to confirm the bad lower unit. However the knocking sound was still present. Motor fires right up and only knocks a few seconds then goes away. Motor runs good once cranked. If anyone can explain what's causing the motor to knock for a few seconds on start up would be great

[99yam40]

just a wild guess on my part would be a shredded balancer with debris plugging up the oil pick up screen

[TownsendsFJR1300]

Plus 1 ^^^...

Here's a pic of the balancer removed as Yamaha updated it with the latest being a type 4.

Your year engine likely has a type 1 or type 2. My 06 had a type 2 balancer. Both should be replaced with a type 4

This is a type 3 I replaced with a type 4 as it starting making noise:






Pulling the balancer doesn't take long but will let you know if the composite teeth failed and got sucked into the internals of the engine.

[pstephens46]

Updates from OP?