TB110 - Strange noise while running

[l008com]

This is a machine I've had lots of previous posts about and done lots of repairs to. It has a very subtle misfire that I just can't fix. Possibly low compression from slightly scraped up cylinder wall?

Either way, its plenty good enough. I mowed my large yard with it today and it works fine. It starts right up, it runs well, its as good as its going to get.

But heres the thing, it has one very strange problem left. Imagine your lawnmower is running on the driveway and it sucks up a leaf. The sound of the leaf kind of whipping around under the housing, until its gone. My engine is making a sound like that. It has been for a while now. Even when the machine is running, but not moving, so its definitely not sucking up any debris that is making the sounds.
So I think the sound is coming from inside the crankcase - something I did not open up when I was working on this machine. I took the head off and the valves, but I never removed the motor and looked inside . . . and I don't really want to now either since I finally got it running again.

Has anyone ever had a problem like this? What could it be? I can't imagine theres anything big and important broken off in there, or the sound would be much worse and the machine wouldn't be running. Like if a timing gear tooth broke off, or some other random metal? I did change the oil twice now, once after running the machine a bunch last year. I would think if it was something paper-like in there, it would eventually get stuck somewhere and have stopped, or burned up and gotten flushed out with the oil change.

I know in the end, the answer is going to be to open it up and see what, if anything, is going on in there. But its 10pm on a saturday night and I'm definitely not doing that now, and I'm not sure when I'm going to have time to do that either. Its loaded with fresh gas and oil right now :/ maybe next week I'll mow till its out of gas, then finish mowing with my other machine. Shame to waste another 16 oz of oil.
Oh and speaking of oil, could overfilling cause a sound like this? If it is overfilled, it would be by at most an ounce or two. I don't think its overfilled at all but dipsticks aren't all that precise.

I don't know, any thoughts or ideas before I try digging in to this again in a week or two?
I really want to sell this machine on craigslist but if it has some major internal damage and is going to self destruct the day after I sell it, I don't want to do that.

If you youre curious, this is a Troy-Bilt TB110 model with a B&S 550EX 140cc motor.
Body model: 11A-A2BM711
Engine model: 09P7020144F1
Engine serial/date: 18 0301 54 27126

 

[sgkent]

run it until it dies. In the meantime keep your eyes open for a good core engine. The noise could be rust on the flywheel, a loose piece of tin, grass and debris packed around the engine or a vacuum leak. The list is endless. You are not going to hear a piston scratch, nor is it going to misfire from that. If the compression drops from 110 PSI to 70 PSI every once in awhile it will still fire. You might hear a broken piston ring as a light knock. A misfire is likely to be electrical, or a vacuum leak, which you might hear as a wispy sound.

 

[Auto Doc's]

Possibly the pull start engage levers are not fully releasing or there is debris under the fan shroud. If it were serious the engine would not run correctly.

 

[l008com]

Ok so last night i went to 'prove' the sound wasn't coming from the plastic cover and it turns out, its coming from the plastic cover! HAHA. Thats good because now I don't have to remove and open the crankcase. But its bad because I still can't figure out where the sound is coming from.

The only think under the cover that looks like it could be making this sound was the end of the starter rope, past the knot. So I snipped that off and hot glued the knot so it would stay tied. I tested it again and no change at all.
The pawls look like they are retracting fine so I'm not sure where the sound is coming from, any ideas? I really want to fix that one last sound before I offload this mower.

Heres a video. The sound is hard to hear at first, but later in the video it gets super easy to hear. Also pics of the underside of the plastic cover are at the end:

 

[Auto Doc's]

In the video it is hard to distinguish the exact noise. Audio is tricky at times.

I will say that the top cover can magnify noise when it is in place. Any signs of rub marks on any of the pull start components? You may have to disassembly the center pull rope area and see it the starter dog retract springs are bad or in any trapped debris is in there.

These "worldwide" B&S throw together engines were not designed or constructed very well.

 

[slomo]

Fluttering sound starts at 1:12 into the video. I also hear a slight miss.

You said if you remove the top plastic cover it doesn't do it. Wonder if the black plastic grill is doing it?

 

[sgkent]

it is a groundhog hiding in the mower who giggles each time his feet get tickled by the shot of voltage of the ignition jumping to them. Also causes the misfire............

 

[l008com]

Yeah there is a misfire but thats not what we're trying to fix here right now. Towards the middle of the video, when i've taken teh cover off and i put it back on, the sound gets very loud.
It is definitely coming form the cover but I can't see anywhere it would be coming from, nothing looks worn or like its rubbing. Unless the vibration from the engine alone is causing the starter pawls to poke out ever so slightly. But even that doesn't seem right. Also I checked the black cover and all the different parts in the cover, everything feels tight. Very strange.

 

[sgkent]

Harbor Freight or Amazon stethoscope. Even a long piece of 5/16" hose moving around may help you isolate where it is loudest. Don't forget that muffler and exhaust leaks can make strange sounds sometimes. You didn't laugh at my groundhog joke. Shame.

 

[slomo]

It is definitely coming form the cover but I can't see anywhere it would be coming from, nothing looks worn or like its rubbing.

That is a 2 piece cover is it not? The red cover and the black ventilated grill

Oh and speaking of oil, could overfilling cause a sound like this?

? Nothing there is a precision fit. You answered your own question. If you remove the cover it's quiet.

Oh and speaking of oil, could overfilling cause a sound like this?

No.

If it is overfilled, it would be by at most an ounce or two.

Over filled is over filled. Keep it ON the full mark, not below and not above.

I don't think its overfilled at all but dipsticks aren't all that precise.

Precise enough for a mower engine. From all I've read, zero oil related failures so far keeping it ON the full mark.