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Discussion Starter · #1 ·
I need to start a thread just for this. I got this back from my dad a couple weeks ago and when you throttle it up it has this horrible screeching sound. I can't seem to pinpoint it, even with a mechanic's stethoscope. My first thought is that it's some kind of metal on metal contact inside the engine but I would think something like that would shatter my eardrums with the stethoscope. It almost sounds like a high pitched whistle, like perhaps an exhaust leak or vacuum leak. Anyone have any idea what's going on here?




As of now I'm planning on rigging it up so that I can start it off the tractor so that I can rule out the trans. Then idk, hope to God that spraying braklean around the intake area reveals a vac leak, and worst case start tearing it down to look for some kind of obvious damage.

Oh also you can hear it just starting during this test mow about 15 seconds into the video when the engine encounters some load from the tall grass:

 

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Discussion Starter · #3 ·
Hmmm. Not sure what the equivalent would be on this thing. I still don't get why when placed on various spots on the block I don't hear anything screeching like that if it's internal to the engine. Very strange.
 

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That's a wierd sound. My best guess: Something's intermittently chafing/binding.

I like your idea of pulling the engine and running it disconnected from the trans. But that's a bit of work. Have you tried removing the clutches, especially the rear one, to see if it still makes the noise? When everything's in neutral, the forward clutch is not spinning, but the rear one is.

If none of that yields any clues: Try removing all the tins. It's safe to run the engine for a few minutes without the ducting in place. If that changes the noise, you probably have something on the flywheel chafing on something on the tins.

If all that fails, try running it through the gears. When you select "forward", does that change the noise? Reverse? Perhaps by changing the load on various parts of the system you can alter the noise, and thus get a hint about what's causing it.
 

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'81 Gravely tractor, 50's 60's 70's 80's 90's Gravely tractors Various Honda Power equipment
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Maybe a baffle breaking lose inside the muffler or exhaust pipe causing the noise?
Check all the mower deck pulley bearings and belt tensioner pulley bearing? Drive shaft bearing?
Notice how the engine didn't lug or slow down when mowing the slightly long grass? Typical Gravely tractor for you. Built like a 'Timex' Watch.
Check all the sheat metal mounting everywhere, engine tin, hood and rear fender mounts, shift lever consol plate mounting screws.
It may be a muffler noise that it is starting to rot out and go bad, like a baffle inside it loosening up and rattling? Good question.
When the engine is under a load the exhaust note will change and work harder as the engine is under the load causing it?
 

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Discussion Starter · #6 ·
That's a wierd sound. My best guess: Something's intermittently chafing/binding.

I like your idea of pulling the engine and running it disconnected from the trans. But that's a bit of work.
Actually the engine is off currently because I wanted to go ahead and get more rtv on the bearing plate bolts, and while I was at it I had a look at the rear bearing and it looked the same as when I had it off to replace the gasket months ago.

Have you tried removing the clutches, especially the rear one, to see if it still makes the noise? When everything's in neutral, the forward clutch is not spinning, but the rear one is.
That's a good idea. The stethoscope thing didn't seem to make any noises when touched to the cup there but that's a pretty easy thing to remove.

If none of that yields any clues: Try removing all the tins. It's safe to run the engine for a few minutes without the ducting in place. If that changes the noise, you probably have something on the flywheel chafing on something on the tins.

If all that fails, try running it through the gears. When you select "forward", does that change the noise? Reverse? Perhaps by changing the load on various parts of the system you can alter the noise, and thus get a hint about what's causing it.
Well in the first video all the tins but the one on the right are removed, and it's only on because it's pinned in by the muffler. I later removed the muffler hoping it was just a whistling exhaust leak and the noise remained. More leads on stuff to try though
 

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Discussion Starter · #7 ·
Maybe a baffle breaking lose inside the muffler or exhaust pipe causing the noise?
Check all the mower deck pulley bearings and belt tensioner pulley bearing? Drive shaft bearing?
Notice how the engine didn't lug or slow down when mowing the slightly long grass? Typical Gravely tractor for you. Built like a 'Timex' Watch.
Check all the sheat metal mounting everywhere, engine tin, hood and rear fender mounts, shift lever consol plate mounting screws.
It may be a muffler noise that it is starting to rot out and go bad, like a baffle inside it loosening up and rattling? Good question.
When the engine is under a load the exhaust note will change and work harder as the engine is under the load causing it?
I began to suspect the muffler too because I'm actually not fully convinced that it's a metal on metal noise. But it was still making the noise with the muffler removed. Also in the first video most of the tins are removed, and strangely it's only when throttling up. I'll rig up a way to start it off the tractor to rule out anything on the actual tractor. (it's already been removed so this won't be that much more work)
 

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strangely it's only when throttling up.
Wierd. But it's a clue. If you run it off the tractor (please put it on something solid, and clamp it down if you can) and it still makes the noise, I'd start thinking about stuff under the flywheel (icky) and maybe even the governor (double icky).
 

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Discussion Starter · #9 ·
maybe even the governor (double icky).
Ah ok, I'm pretty sure I installed the rear cover correctly and the governor seems to operate properly but it was really iffy installing it, this little pin has to somehow go right in this one hole perfectly as you're lining up the cover onto the crank. That wouldn't be so bad to check real quick to see if there's some weird stuff going on. It's when throttling up and when under load so it certainly makes sense.
 
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