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General Category >> Rubber Side Down! >> Loose Flywheel - How does it sound?
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Message started by DragBikeMike on 08/17/22 at 15:31:10

Title: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/17/22 at 15:31:10

This post is intended to document the sound you can expect from an LS engine with a loose flywheel.

I recently had my flywheel come loose. I was going to include the loose flywheel in my Wiseco Flat-Top Piston 10,000 mile report, but Rob++ currently has a noise problem so I thought I would do a mini-report on the flywheel.

I started hearing a pronounced rattling noise at about 8500 miles. I figured it was piston slap or possibly the rod bearing. That noise got worse over the next 1500 miles. At 10,000 miles it was time to take a look.

You can hear the noise in this YouTube video. Note the very loud metallic rattle when I twist the throttle open.

https://www.youtube.com/shorts/KUhN_OHQhmo

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/17/22 at 15:32:35

I did an inspection of the cam chain tensioner. It was fine.

I checked valve clearance. It was .005” to .007”. Not a problem IMO.

Visual inspection of the flywheel nut indicated that all was normal. Don’t be fooled by a nut that looks tight and can’t be rotated with your fingers. The nut was loose. I estimate it took no more than 10 ft-lbs to move the nut (probably less).

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/17/22 at 15:34:04

I’m pretty anal about critical torques. I view this nut as a “critical torque” item. It’s supposed to be tightened to 110 ft-lbs, and I know for sure I applied 110 ft-lbs to this nut when it was installed. So, the nut came loose even though it was major-league tight.

The factory service manual does not specify thread locker for this nut, and I don’t advise using thread locker on this nut. The nut is so thin, and the tightening torque is so high, you run the risk of rounding off the corners if you use thread locking compound. Get it glued on there tight enough, and you might end up wrecking things in an effort to remove the nut later on.

The flywheel was clearly moving on the crankshaft. You can see the scoring on the face of the flywheel. I was lucky, no wear on the splines (male or female). I fixed it and the engine is quiet now. The noise was a loose flywheel, no doubt about it.

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/17/22 at 15:37:27

I’m not suggesting that every loose flywheel will sound exactly the same. Mine still had some tension being applied by the Bellville Washer. If it had continued to loosen, the noise probably would have changed. But the YouTube vid should give you an idea what to expect.

Hope this helps some of you.

Title: Re: Loose Flywheel - How does it sound?
Post by justin_o_guy2 on 08/17/22 at 18:56:51

When I have a thin nut that needs to Tight,I look at the socket. If where the sides meet isn't where the socket stops, I grind the socket until the radius is gone and the inside corners of the socket are going all the way to the end of the socket. On impact sockets the start of the sides is sometimes almost an eighth of an inch up inside the socket. That doesn't sound like a lot, until you have a nut that is around 3 sixteenths thick, knowing it needs plenty of torque and then that difference matters.

Title: Re: Loose Flywheel - How does it sound?
Post by Ruttly on 08/17/22 at 19:48:43

Good point JOG. I see no problem using loctite on that nut. I’m looking at the location , no problem using a small torch to heat it when it’s got to come off. Loctite is just glorified candle wax heat it and it becomes liquid again !

Title: Re: Loose Flywheel - How does it sound?
Post by Ruttly on 08/17/22 at 19:53:00

I’m swapping flywheels soon and I’m definitely using loctite. Think mine is loose too. Putting stock flywheel back in.

Title: Re: Loose Flywheel - How does it sound?
Post by justin_o_guy2 on 08/17/22 at 20:01:41

Little stuff like that can be the difference between winning it quickly and cleanly
And struggling.

Title: Re: Loose Flywheel - How does it sound?
Post by Armen on 08/18/22 at 06:37:21

A million years ago I build 250 Bultacos for a dear friend that raced them in AHRMA vintage. By the time we were done, we were about double the stock horsepower. The primary sprocket on the right side would loosen up no matter what I did. I finally cleaned up the splines as well as possible, and put some Blue Loctite on the splines. Always needed heat and a puller to get the sprocket off, but we never had one loosen again.

Title: Re: Loose Flywheel - How does it sound?
Post by Ruttly on 08/18/22 at 12:27:45

Yup , I look ahead and make sure it’s a place I can use a torch for heat , a place free of wiring , seals , etc. Then glue it with the blue.

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/18/22 at 23:27:23

I agree Justin. These suckers need a modified socket. This picture shows just how much engagement you lose with a standard impact socket. Looks close to 1/8” to me.

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/18/22 at 23:28:03

After the mess I had with the failed transmission and excessive crankshaft runout, I got serious about making every effort to limit any sort of bending or twisting moments on the crank. I ordered a 46mm deep socket to give me a good solid fit on the nut. Then I put that socket in the lathe and faced off the chamfer to provide maximum engagement with that thin nut (some folks refer to the engagement as “purchase”). Oooooooo! These sockets are tough, but where there’s a will there’s a way.

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/18/22 at 23:28:40

Finished product. That sucker fit like a glove, and I had no problem hitting the 110 ft-lb mark.

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/18/22 at 23:29:54

Sneezy, I changed direction on the mini flywheel. After hours of fiddling with my Big Bore 4-Speed project, I really couldn’t find any connection between the 3-inch flywheel and the bearing bore fretting. It pretty much boiled down to the excessive crank runout. So, when this loose flywheel reared it’s ugly head, I had to take a second look.

Seems to me that when you bump up the squeeze two points, you increase crankshaft angular velocity on the power stroke, and decrease crankshaft angular velocity on the compression stroke. Of course, there’s a difference in the angular velocity on the power and compression strokes on the stock engine too, but that difference is probably much greater on the high compression motor. Throw in the DR cam with it’s earlier closing intake valve and the spread goes up a bit more.

I’m thinkin that the continuous change in angular velocity gets the heavy flywheel rockin back & forth within the clearance limits of the splines. That overcomes the torque eventually and things get loose. Hey, it lasted 8000+ miles before it manifested in a rattle.

I installed the mini-wheel. This clamping tool ensures that I can achieve the correct torque without bending or twisting on the crank. The mini-wheel has much less inertia and isn’t gonna work that nut loose (I think).

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/18/22 at 23:30:29

I guess I could live with the Loctite 242 (blue), but the 262 or 272 is brutal stuff. I’m not a fan of throwin heat on the crank, plus the big ole flywheel is gonna make a great heat sink. You’ll need to pump a lot of BTUs into that sucker to get the whole mess up to 400°F. I’m good with the mini-wheel solution. If it turns out to be a bad decision, yooz guys will be the first to hear about it.

Title: Re: Loose Flywheel - How does it sound?
Post by justin_o_guy2 on 08/19/22 at 07:45:46

I didn't know about the difference between the Loctite colors and I was putting a clutch in a John Deere tractor. I was uncomfortable about everything staying where I had it and I had some red Loctite... Which would not be a problem, except for the fact that the only way to get To that part with heat and a good angle on it you would have to split the tractor again. In the FWIW department, I did that job without a hoist,on an uneven dirt floor in a barn with no fan in the heat of summer. Yeah, split the tractor, did the job and stabbed the transmission input shaft in the clutch with Zero help.
I used my floor jack to lift on the tread of the tires to roll it. Right now I don't remember exactly how I supported the transmission. The front of the tractor was on jackstands,,
It's been a few years,, but I've cringed a few times thinking about what kinda cussing someone would be giving That Idiot who did that. If it ever needs a clutch adjustment,, someone is gonna have a really bad day.

Title: Re: Loose Flywheel - How does it sound?
Post by TheSneeze on 08/19/22 at 07:50:21

Good to know, Mike. I am looking forward to more feedback on this. Not sure if I will have my motor back together and in the bike before you report back, though.

Title: Re: Loose Flywheel - How does it sound?
Post by Ruttly on 08/19/22 at 22:00:51

DBM , We’re you feeling any vibration and did it get worse as noise got louder ?

Title: Re: Loose Flywheel - How does it sound?
Post by Ruttly on 08/19/22 at 22:10:37

I’m gonna order a new nut & washer , just in case !

Title: Re: Loose Flywheel - How does it sound?
Post by DragBikeMike on 08/20/22 at 17:55:48

Ruttly, no discernable change in vibration. Mirrors were the same as always. Grips same. Pegs same. Seat same. Only thing different was audible noise, and it was loud & scary.

I was hoping to see some comments from others who experienced a loose flywheel. Curious if they heard the same thing I did, and just how loose their flywheels were. Were the flywheel nuts backed off noticeably, or did they have to apply a wrench to determine that the nut was loose?