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I know the flak I'm going to get for this but I gotta do my due diligence.

Yesterday when starting up my Honda BF50 out on the lake, it started making a different noise. In addition to the normal low rumbling, it started to make a higher-pitched metal rubbing noise, not quite a click, but it does sound like metal rubbing on metal with a rhythm tied to the engine revs.

It happens in forward gear, exactly tied to the engine revs, it happens in neutral, and it happens in reverse, always tied to revs.

This tells me it's not coming from the prop or anything in the lower housing (otherwise it would be a different sound in different gears). I popped off the cowling and it does sort of sound like it's coming from the top somewhere i .e. on/in the block. eg. the valves.

Since I was already under way, all I could do was check the dipstick. (The engine was warm). Oil came gushing out of the dipstick. So at least I know there is some oil in there. I dumped a litre of oil in whiIe I was at it.

Full disclosure: I am not good at oil checking ands maintenance.

The wind died so I had no choice but to motor 5nm home. The litre of oil did nothing to mitigate the rubbing noise. It did seem as if the noise was worse at low speed and seemed to get quieter up beyond four knots, but that is easily attributable to simply being drowned out by the normal sound of the motor.

Made it all the way home, praise Poseidon.

Wondered if anyone has any suspicions, or suggestions. Otherwise, I guess I'm headed for the repair shop. Or the repair guy is headed for my slip...

I would check the timing belt tensioner. The bearings can seize up. Best to not run it like that at all or you will be replacing the heads when the belt breaks. This happened to my brother's Yamaha. Simple fix but the belt, pullies must stay exactly where they are or the valve timing will be off. Use nail polish if you need to to mark position.
KB

Here is a video of it, for all the good it'll do.

It doesn't sound bad in real life as it seems to in this video. My crewman had difficulty picking out the sound. although he is not as familiar with my motor as I am, and his hearing is not optimal.

Tsatzsue wrote: ↑Mon Jul 07, 2025 9:19 am I would check the timing belt tensioner. The bearings can seize up. Best to not run it like that at all or you will be replacing the heads when the belt breaks. This happened to my brother's Yamaha. Simple fix but the belt, pullies must stay exactly where they are or the valve timing will be off. Use nail polish if you need to to mark position.
KB

I'll check that out. On a scale of 1 to 10 experience level, how difficult is that? I know how to operate a ratchet driver, and I've replace my throttle cable and water pump impellor, but much deeper into the guts than that might well be outside my wheelhouse. Torque wrenches are a little outside my wheelhouse.

I would check if anything is touching the flywheel. I see posts about "magnets" that can come loose and touch it.

The part that jumps out at me is "oil came gushing out".

That's not supposed to happen. It sounds like there was too much liquid in the crankcase and it came out when you pulled the dipstick.

A stuck float in one of your carbs and a gas tank tank under pressure from a hot day sailing could allow fuel to enter a cylinder, leak past your rings, and contaminate your oil. The things to look for are: too much oil, oil that is too thin, and oil that smells like gasoline.

A leak between your water jacket and an oil passage would also allow your engine to "make oil". The things to look for here are: too much oil and milky colored oil.

If, by some lucky chance, you just put too much oil in the engine the symptoms would be: too much oil, a frothy "whipped oil" on the dipstick.

The sound I think I hear in your video sounds to me like it is coming from your valve train.

Hot day --> gas tank expands --> tank vent does not (vent) --> float valve in one or more carbs allows fuel to pass --> gas pushed into one or more cylinders --> leaks past rings into crankcase --> gas in the oil --> oil too thin --> improper lubrication --> noisy lifters. That's my guess and I'm sticking to it.

Sounds like a problem for a professional.

If his nose confirms my suspicions, the fix is well within the skills he's already demonstrated.

If it turns out to be water in the oil then the fix is changing a gasket that is just a little past where he's already been OR the block is cracked and it is probably unfixable.

I'm pulling for the easy fix.

Be Free wrote: ↑Mon Jul 07, 2025 5:29 pm If his nose confirms my suspicions, the fix is well within the skills he's already demonstrated.

If it turns out to be water in the oil then the fix is changing a gasket that is just a little past where he's already been OR the block is cracked and it is probably unfixable.

I'm pulling for the easy fix.

Yes, oil change would be easy.

The oil gushing out also caught my eye. More clarification would help. Especially if he added a liter of oil on top.

I have the same motor. Perhaps it is the flywheel touching the coil assembly as mentioned above. If you take the flywheel cover off and rotate the engine by pullrope or by starter you can see if that is the case. Take the spark plus out to make the rotation easier.

See this thread

https://forums.iboats.com/threads/honda ... nd.181933/

let me know if you need the manual for this motor.

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm The part that jumps out at me is "oil came gushing out".

I should have checked when the motor was cold but I was underway by then. Had been motoring for a half hour.

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm That's not supposed to happen. It sounds like there was too much liquid in the crankcase and it came out when you pulled the dipstick.

By "gushing" I just mean coming out. It didn't spray or anything. It only formed an arc of maybe an inch i.e. as if under nothing but gravity pressure.

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm A stuck float in one of your carbs and a gas tank tank under pressure from a hot day sailing could allow fuel to enter a cylinder, leak past your rings, and contaminate your oil. The things to look for are: too much oil, oil that is too thin, and oil that smells like gasoline.

The oil seemed normal to me. Dark brown, consistent, not too thick, not too thin, no bubbles. I didn't notice a smell but I didn't think to check.

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm A leak between your water jacket and an oil passage would also allow your engine to "make oil". The things to look for here are: too much oil and milky colored oil.

Def not milky.

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm If, by some lucky chance, you just put too much oil in the engine the symptoms would be: too much oil, a frothy "whipped oil" on the dipstick.

This occurred before I put any oil in.

If anything, I am sinfully negligent at checking and topping up oil. My first assumption upon hearing funny noises was, of course, that my oil has run dry.

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm The sound I think I hear in your video sounds to me like it is coming from your valve train.

Could be. It sounds a lot more brutal in the video than to my ear. That's why I said "for all the good it'll do".

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm
Hot day --> gas tank expands --> tank vent does not (vent) --> float valve in one or more carbs allows fuel to pass --> gas pushed into one or more cylinders --> leaks past rings into crankcase --> gas in the oil --> oil too thin --> improper lubrication --> noisy lifters. That's my guess and I'm sticking to it.

Again, the oil did seem fine.

Russ wrote: ↑Mon Jul 07, 2025 12:29 pm I would check if anything is touching the flywheel. I see posts about "magnets" that can come loose and touch it.

Y'know, this would do it. Sound is about right. Other than the noise, there were no deleterious effects on my motor running, even after motoring home for an hour at five knots.

I tried to convince myself that the sound was loudest at 1-2 knots and got much better above four knots, but I felt that maybe it was just drowned out and I was wishful thinking. But something rubbing the flywheel would do that.

Especially since I haven't taken her out for several weeks. Some poor spider in there, just living its best life, and then "AGH! WTH is this???"

If you are comfortable with the condition of the oil then perhaps it is something under the flywheel.

I had a problem with mine where the covering on the exciter coil started coming apart. It was my own fault caused by severely overheating the engine. The heat melted the wiring inside the coil in addition to causing the covering to unravel. Without the exciter there was no spark so I don't know if it would have caused a similar sound but I'm sure something would have been touching under the flywheel.

Has the engine overheated? Did you move either of the coils when you had the flywheel off?

Be Free wrote: ↑Mon Jul 07, 2025 4:04 pm The part that jumps out at me is "oil came gushing out".

That's not supposed to happen. It sounds like there was too much liquid in the crankcase and it came out when you pulled the dipstick.

A stuck float in one of your carbs and a gas tank tank under pressure from a hot day sailing could allow fuel to enter a cylinder, leak past your rings, and contaminate your oil. The things to look for are: too much oil, oil that is too thin, and oil that smells like gasoline.

A leak between your water jacket and an oil passage would also allow your engine to "make oil". The things to look for here are: too much oil and milky colored oil.

If, by some lucky chance, you just put too much oil in the engine the symptoms would be: too much oil, a frothy "whipped oil" on the dipstick.

The sound I think I hear in your video sounds to me like it is coming from your valve train.

Hot day --> gas tank expands --> tank vent does not (vent) --> float valve in one or more carbs allows fuel to pass --> gas pushed into one or more cylinders --> leaks past rings into crankcase --> gas in the oil --> oil too thin --> improper lubrication --> noisy lifters. That's my guess and I'm sticking to it.

Ditto!
I think Be Free is on to something with the gush and valve train…

How old & estimated hours on your engine?

Best Regards,
Over Easy

Did you ever figure out what it was?