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I've purchased a Scag Tiger Cub with 1200+ hours with a blown engine. I decided to take on the project of a complete engine rebuild. I cleaned up the block that had 2 broke piston rods and galled crank shaft journal. I took the housing to a local machinist who measured the cylinder diameter and assured me it was within specs for standard piston/rings. He said the crankshaft was toast. He didn't take any crankshaft bearing/bushing measurements in the housing. I ordered rebuild kit with new rods. Bought a used crankshaft on ebay with warranty. I reused ignition coils and valves. After lots of stressful work to get everything back together by the book, I started the engine and was pleased that all seemed fine except it has a whistling/squealing sound coming from the engine. I pulled the muffler, hoping ...then pulled the cover off the flywheel and saw nothing out of sorts. I'm thinking about the crankshaft bearing/bushing that's built into the housing must has been out of spec. ?? Before I tear into the engine again, does anyone have a clue what kind of mess I may find ? The engine seems to run fine otherwise, 100 PSI compression. I've pulled the flywheel looking, pulled the heads off to check gaskets for leak. Is it possible the valves could cause the whistling ? I'm stumped ! I made a video with my phone but don't know how to attach to here.

Lease use this link for video of engine noise:

That's a new one for me, The bearings really should have been measured when torn down, since they are non replaceable they can make or break an engine build, granted a good machinist could machine the case and install a bushing, but that may drive the $$$ up..............first i would check to be sure there is proper clearance between the ignition coils and flywheel and that they aren't rubbing, as for the Flywheel side plain bearing, see if you can move the flywheel side to side any.

Scrubcadet10 said:

That's a new one for me, The bearings really should have been measured when torn down, since they are non replaceable they can make or break an engine build, granted a good machinist could machine the case and install a bushing, but that may drive the $$$ up..............first i would check to be sure there is proper clearance between the ignition coils and flywheel and that they aren't rubbing, as for the Flywheel side plain bearing, see if you can move the flywheel side to side any.

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Thanks for your reply, I've checked both coils and flywheel play.

Those old FH engines had a habit of wearing out the top main bearing. Grab the fly wheel and try moving it from side to side to from and to the ign modules. You might move the ign modules away from the fw first since if you set the air gap the fw would pull the magnets to the fw and not move the crank shaft.

use a small hose, stethoscope or long screwdriver to isolate the sound if you can safely. Typical safety measures, no long hair near moving belts etc, no long loose sleeves, no hanging dog tags,chains etc..

Thanks, I'll try to isolate tomorrow. I don't feel nor see any movement with flywheel.

I tried the long screwdriver around the engine and could not tell anything.

now use a long piece of fuel hose - long enough to hold one side to your best ear and follow to the whistle. I've used that to find sounds that are not internal to the engine like a vacuum /air / exhaust leak etc.. You did put an air filter back on it?

I did not put the air filter back on.

To me that sounds like metal hitting metal, not bearing squeal. I would grab my feeler gauges and recheck the air gap. Take a measurement as normal, then have someone push the flywheel toward rage coil and recheck for any change. Another thing I would try is resetting the air gap .002 “ wider and see if it changes. Might need a shot of carb cleaner to riches the mixture to start.

your whistle may be the air cleaner off. Air going into a carb makes that sound. Part of an air cleaners job is to stop it.

I tried the fuel hose. I could hear a pinging on cyl #2 that I don't hear on cyl #1. I went around the engine and can't hear anything else. I pulled rocker covers off and reset valves after it cooled down. They were bad out of spec on cyl#2.

I reset air gap to .012 (.002 more) and it didn't seem to help. New carb hasn't been adjusted.

Rivets said:

To me that sounds like metal hitting metal, not bearing squeal. I would grab my feeler gauges and recheck the air gap. Take a measurement as normal, then have someone push the flywheel toward rage coil and recheck for any change. Another thing I would try is resetting the air gap .002 “ wider and see if it changes. Might need a shot of carb cleaner to riches the mixture to start.

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pinging and whistling are two totally different sounds. If the air cleaner is off something could have been sucked into a cylinder causing noise. Might have to pull the head on that cylinder to be sure the noise is not something rattling around, or use a small camera thru the plug hole to look around. Amazon sells a small one for about $20 that plugs into a laptop, some phones etc.. https://www.amazon.com/gp/product/B07PBF6DX5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

sgkent said:

pinging and whistling are two totally different sounds. If the air cleaner is off something could have been sucked into a cylinder causing noise. Might have to pull the head on that cylinder to be sure the noise is not something rattling around, or use a small camera thru the plug hole to look around. Amazon sells a small one for about $20 that plugs into a laptop, some phones etc.. https://www.amazon.com/gp/product/B07PBF6DX5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

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I've pulled the heads off already checking head gasket for leaks. While listening with the hose, it sounded like metal tapping in time with exterior noise. ?? valve tappet and cam, maybe ?

I purchased a stethoscope today and definitely heard noise better. The loudest, most distinct I heard it was on the back side of the block, opposite from cylinders. I don't feel any slack in the PTO or flywheel shafts nor oil leaks. Before I break into this engine again, what would be the most likely to make that kind of noise ? Cam rubbing to hard on governor ? Something to do with the oil pump ? Still could be crank bushings ? I've spent way too much time and money on this project already ...

I'd pull up the parts pictorial and try to see what might be back in that area before tearing it apart again.

sgkent said:

I'd pull up the parts pictorial and try to see what might be back in that area before tearing it apart again.

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I did look and the oil pump is the only thing in that area. I've never heard an oil pump sound like that ?? I haven't tested oil pressure. Yet !

Hayward51 said:

I did look and the oil pump is the only thing in that area. I've never heard an oil pump sound like that ?? I haven't tested oil pressure. Yet !

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I have a new problem with oil pressure - 66 PSI at idle after engine warms up. Started up at 72 PSI. Could this noise still be coming from the oil pump ?

general rule is that bearings need 10 PSI minimum per 1000 RPM.

That is quite normal.
Cold oil is thick so holds pressure much better & longer than hot oil
Cold engines have smaller clearances than a hot one when the parts have expanded .

bertsmobile1 said:

That is quite normal.
Cold oil is thick so holds pressure much better & longer than hot oil
Cold engines have smaller clearances than a hot one when the parts have expanded .

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I changed out oil pump and pressure relief spring/ball. Didn't help noise or oil pressure.

Is your stethoscope solid on the end like the one I have? If so, listen to the case in that area, then use a hose in the same area to see if the sound is louder or softer near the case or touching the case. Try to determine if the sound is coming out of the case or just in that area.

I would remove the spark plugs and the drive belt and clutch if it has one and the engine shroud. Then i would slowly rotate the engine checking for a tight spot or anything rubbing. Then spin a little faster and listen for the noise.

sgkent said:

Is your stethoscope solid on the end like the one I have? If so, listen to the case in that area, then use a hose in the same area to see if the sound is louder or softer near the case or touching the case. Try to determine if the sound is coming out of the case or just in that area.

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Yes, it is solid on the end. I'll check it out again tomorrow. Thank you for your help. I can't think anymore for the frustration.

Hammermechanicman said:

I would remove the spark plugs and the drive belt and clutch if it has one and the engine shroud. Then i would slowly rotate the engine checking for a tight spot or anything rubbing. Then spin a little faster and listen for the noise.

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I have the engine 'uncovered' but no noise with spark plugs out. I only hear it after it starts.

If the engine is working fine then don't go chasing ghosts
It could be the crankcase vent or the vent gasket, the fuel pump vent or any one of 1/2 dozen gaskets that are a tiny bit too big / too small or out of place
Could be the dip stick tube , could be a missing / out of place blade on the fan , a crack in the blower housing etc etc etc

bertsmobile1 said:

If the engine is working fine then don't go chasing ghosts
It could be the crankcase vent or the vent gasket, the fuel pump vent or any one of 1/2 dozen gaskets that are a tiny bit too big / too small or out of place
Could be the dip stick tube , could be a missing / out of place blade on the fan , a crack in the blower housing etc etc etc

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Thanks for that ! I'm really tired of chasing ghosts. I've practically rebuilt this engine twice looking for this strange noise. The engine seems fine other than, who wants to buy an engine that sounds like that ?

Thanks to all who tried to help. I can only hope the engine stays together until I get it broke in. I need to sell it for the parts money, at least, whistling and all ...

maybe if you recognize the tune it is whistling it will reveal itself.

Hi . sorry I saw this post late. i just did a Kawasaki FH601 that was showing the same symptoms your having with your engine . It was making a distinct Train Whistle / grinding sound . Especial when it was revved up and the rpms started to level out . What I found was the lower PTO Clutch bearing was beginning to seize up . You could still rotate it with the clutch on the crankshaft but upon checking the bearings closer the lower bearing was super hard to rotate when spun with my fingers . I started the engine with the clutch removed and the sound was gone . We replaced the PTO clutch and it cured the problem . If you still have this you might want to check and see if yours has the same issue . Good luck !