1975 650 knocking sound

[clancy1010]

I have bought a 75 650 that had not been run in years. The carbs proved it. I have them clean and back on. I fired up the engine and it sounds like I have a tinny knock just below the flywheel. I have not ran the engine above idle so I do not know if it will go away at a high RPM. The motor has 150 LBS compression on all 3 cylinders. Does any one have any ideas as to what the noise is? I have a big fear that I have bought a motor with a bad rod. The knock is a higher pitch than what a rod my sound like. Thanks for the help

 

[arsenalpsu]

Re: 1975 650 knocking sound

sounds like piston slap to me but I haven't worked on this motor

 

[outboardnut]

Re: 1975 650 knocking sound

It's hard to answer this one without hearing it, but those old merc do naturally have some noise to them while running.

If its' a motor that old I would assume you didn't pay a fortune for it. I
would run the motor and not worry about it. If it gets louder you'll know yes, I have a rod about ready to do. If it goes no big deal just buy another one.


The key word you said up there is tiny. If tiny gets louder you'll know you have a problem.