Is this Rod Knock on my Yamaha F100?

[Slab]

I found another video, these f100's just sound like that I think.



Dang are they noisy.

[Ketchn]

Sounds high side to me , but I don’t work on motors anymore, no clue on that one , some motors run with upper side noise and never have serious issues

[BabyFinster]

With it running rough, could the timing be off by one tooth. Heat from overheating could have stressed the camshafts and changed the timing slightly. Did you set it with a timing light or just line up the marks? I agree with the valves could need to be adjusted as
well. This could be a combination of several very small things creating one problem. If the timing was off slightly, you could be getting a pre-detonation or if it’s off the other way a retardation of firing and that would give you a rough running and possibly a clunky sound motor. What does your exhaust smell like?


Sent from my iPhone using Crappie.com

[Slab]

I only lined up the marks. Never thought to use a timing light, I'll have to do so. And really no smell of fuel when running. Thank you for your feedback. Any and all feedback is very welcome. Thanks

[Atimm693]

I'd say the cadence is about right to be related to the pistons and rods, too fast for valvetrain. It sounds more like a top end noise to me, like piston slap or a wrist pin. How'd the pistons fit in the bores?

That style of valvetrain is not usually prone to noise. If it was overheated, I could see the valves tuliping and sinking into the head, but that would cause a lack of clearance and a loss of compression, not a noise. It would be wise to check them regardless.

I would try installing the airbox or just covering the carbs one a time with your hand. Sometimes the induction noise can sound like a "thunk" at idle.

You can also unplug the coils one a time to try and narrow it down to one cylinder. Often a rod bearing will quiet down when that cylinder is unloaded (not firing).

[Rojo]

What I think I'm hearing too. Piston slap will go away as the engine warms up. If it don't go away its most likely not Slappin'. Never heard of Yamaha's having short skirts.

[Rojo]

The big V-6 engines I work on have Variable Valve Timing, if that engine has the VVT units on the Camshafts may have a control solenoid issue with them stuck advanced.

[Slab]

The big V-6 engines I work on have Variable Valve Timing, if that engine has the VVT units on the Camshafts may have a control solenoid issue with them stuck advanced.

Nope, no vvt, unless you can count on some belt stretch! I’m getting timing light, 4 vacuum gauges. Will tune up and add intake pipe, and do comprehensive compression test. Once it all comes in. I had a timing light, have not seen it in years! Doh


Sent from my iPhone using Crappie.com Fishing mobile app

[BabyFinster]

When checking the timing, see what the service manual says for the timing indicator to be on that engine when using a light (example: Light connected to cylinder #1 and proper timing is 4 degrees or whatever number before TDC at recommended idle speed.) I would set timing with the air box on it and everything else that sets the motor up to run normally. Check gap on plugs. If old or unsure of age, replace and gap to Yamaha spec. You can also check the coil packs for voltage and resistance. Broken or worn high tension leads to a spark plug could also cause of firing issues as well. Also a sidenote. If you have older rubber vacuum lines on this motor, make sure none of them have pinhole leaks in them. Old rubber tends to crack and wear, especially at bar fittings with hose clamps or metal ties. Loss of vacuum could cause fueling or carb issue.


Sent from my iPhone using Crappie.com