Is this Rod Knock on my Yamaha F100?

[Barnacle Bill]

Get yourself a mechanics stethoscope (they are cheap) and you can determine exactly where that noise is coming from.

[Slab]

Listen to this 90 hp yami, sounds alot like my F100. Hmmm, what do you think?

[keeferfish]

I thought Cool Slab Likes Kid Rock, then I reread the title.

["D"]

As you know, I know absolutely nothing about working on any engine. However , how would it sound with the cover on it? Maybe some of the noise is just because the cover is not muffling it.

[Slab]

As you know, I know absolutely nothing about working on any engine. However , how would it sound with the cover on it? Maybe some of the noise is just because the cover is not muffling it.

Yes, it will be muffled, but a guy gotta know if'n it's gonna blow up or not prior to adding the muffler! And what's cool is, that other video sounds a lot like my motor, at least to me. So maybe it is normal, and maybe a guy could put on that muffler and not worry. That's what I'ma hoping.

My motor still shakes more than what would be normal. I just ordered a vacuum guage kit to tune the carbs up real gooder, hoperfully.

[gunwhatgun]

I don't want to seem or sound like a know it all lol, because I most certainly don't know more than I do know. That being said, first and foremost on my mind would be checking valve lash. Unless I missed it or perhaps you don't know, the cause of the initial rebuild was not disclosed, only that the guy you got it from gave up on it after an overheat and a seemingly temporary seize. If this is the same engine that you posted with the impeller that was rubbish a bit back, that explains the overheat. It also comfirms the owner that sold it to you may have not been Johny on the spot about maintenance, if the first rebuild was caused by poor ownership, then those pistons the "look ok" and rings that seem "ok" coupled to valves not set correctly and you have all the ingredients for a headache. Heat does wicked, evil things to metal and chasing small things can make you crazy. On that note, Yammies need a special adapter for a compression tester (I think) which is weird because Mercs don't, and again, all my knowledge of O/B's is 2 stroke. I don't know how hard it would be to remove the rocker cover and adjust the rocker/valve lash would be, but I would want to before a loaded test. I have had engines that ran flawlessly on the hose in the driveway and fell flat on the water. Good compression unloaded is a good indicator at best, speaking strictly of an engine that has had known issues. Again I don't mean to sound like an azz or a armchair mechanic, I have just taken this path to Wonderland many times.

[Kevin22]

Those older yamis are always noisy and clanky sounding, but yours does sound a little rough. I think it just needs a tune up, clearly its had a rough lift. Lash the valves, hook it up to a remote tank and add a tiny splash of 10w oil in the gas along with some seafoam and let it eat on the lake. Again, i dont hear a knock per say more so just top end clanking and chattering

Often you hear the motor clanking before you hear the motor running when a boat comes idling by



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[Slab]

I don't want to seem or sound like a know it all lol, because I most certainly don't know more than I do know. That being said, first and foremost on my mind would be checking valve lash. Unless I missed it or perhaps you don't know, the cause of the initial rebuild was not disclosed, only that the guy you got it from gave up on it after an overheat and a seemingly temporary seize. If this is the same engine that you posted with the impeller that was rubbish a bit back, that explains the overheat. It also comfirms the owner that sold it to you may have not been Johny on the spot about maintenance, if the first rebuild was caused by poor ownership, then those pistons the "look ok" and rings that seem "ok" coupled to valves not set correctly and you have all the ingredients for a headache. Heat does wicked, evil things to metal and chasing small things can make you crazy. On that note, Yammies need a special adapter for a compression tester (I think) which is weird because Mercs don't, and again, all my knowledge of O/B's is 2 stroke. I don't know how hard it would be to remove the rocker cover and adjust the rocker/valve lash would be, but I would want to before a loaded test. I have had engines that ran flawlessly on the hose in the driveway and fell flat on the water. Good compression unloaded is a good indicator at best, speaking strictly of an engine that has had known issues. Again I don't mean to sound like an azz or a armchair mechanic, I have just taken this path to Wonderland many times.

Any and all advice welcome. Thank you. Good to know about the adapters for compression testing. Already eyeballing a few on the jungle site. And the impellor was my doing. When I first got it running, I did not run it with water. My fault 100%, cause I inspected it prior and it was fine. And the problem with the valve adjustment is, it uses shims, not a rocker with an adjuster (cams on top the valves). I'll find a pic

[skeetbum]

I know the process of setting the valves but not the specifics. A feeler guage checking the gap between the shim and the valve stem(lash?) is what I remember of those, and that’s from motorsicle days. I do t think it has a deep knock like a rod would have but the top end noise is what I agree with. One step at a time you’re headed in the right direction.

[gunwhatgun]

Yeeeesh, that looks like a lot of work. It is commendable to own up to the impeller, a lesser man would have let the other guy take the fall lol. I don't know, nor do I need to know what your investment is in this engine but at some point the time comes to just see what happens if the juice isn't worth the squeeze on having the valves done. If you had a boat rigged for a Yamaha and could hang it easily, I say give it a shot. Something is not sounding right, but that does not mean its catastrophic, I drove an '84 mustang 6 cyl with a rod knocking for 2 years and sold it running . Best case scenario, it runs but not at 100%, worst case, you find out why it was having problems to begin with.