1987 Yamaha Pro 50 Rattle When Rev'd

[sg_apollo]

Hey all,

I just picked up a '87 Yamaha pro 50. It was recently rebuilt. All new crank bearings, pistons, and seals. 150lbs compression on each cylinder. I ran the motor on the boat before I bought it and it ran awesome.

I got the motor home and replaced all the fuel lines. I also pulled the flywheel and cleaned the timer base as I wasn't happy with the stiff movement from the lubricant that was on there. Re-torqued to spec. I didn't run the motor on a hose when I bought it. Only ran it with the cowl on, on his boat.

I started the motor up to check for fuel leaks, let it idle for a bit to build some heat, gave her a light rev, and I hear a rattle sound when the engine rpms are slowing down after being rev'd.

Is this possibly piston slap from the aftermarket pistons? Possible clearance stacking? The builder used WSM pistons. When I rock the flywheel back and forth the only noise I hear is coming from the lower.

Listen carefully in the video and you can hear it, especially the second time.


https://youtu.be/6xfbsp7pYdo


Any suggestions?

 

[robert graham]

Sounds just like my C90 2 stroke triple Yamaha......I couldn't hear anything out of the ordinary....these old 2 strokes can make a racket.....maybe there's no problem with your motor....just a bit of paranoia maybe???

 

[sg_apollo]

Paranoia is definitely a possibility. I got burned on two pre-owned purchases before I knew what to look for. I learned from each experience, but there is always more to learn. I've been wanting one of these outboards for YEARS and have been working my butt off promoting up the corporate chain to be able to finally afford my dream set up. I checked for piston play with the wooden dowel trick. All good. Pulled the reed plate and looked inside and everything looked just fine. Guess we're just gonna send it and see.

 

[robert graham]

Poke around under the cowling while motor is running.....may be something loose under there. My throttle and shift control cable ends ( black plastic deals) were rattling a bit at certain RPM's.......a rubber band around them and no more rattle!....

 

[sg_apollo]

I found a couple videos on youtube of the old style 40/50's making the same noise on youtube. I already tried poking around. Listened to the bearings with using a screwdriver and everything seemed in order.

 

[99yam40]

make sure you have fresh gas, as it ages it looses octane and can cause preignition

 

[robert graham]

Years ago the wife and I were launching the boat and. I heard some rattling noise, I said "holy crap" something is bad wrong...better pull the boat back out and check it out....Wife said, "you're paranoid, there's nothing wrong, let's go fishing".....and she was dead right!....I've never forgotten that!!!