Engine Vibration / Loose Flywheel

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Big Ratfink
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Engine Vibration / Loose Flywheel

Post by Big Ratfink » Wed May 31, 2017 4:11 pm

Ok, we pulled apart a stock dual port engine, inspected it, full flowed the case, and put it back together. Looked like the engine was recently rebuilt shortly before the car was parked years ago.

We fired it up, ran it 20 minutes and changed the oil. Fired it up again, and revved it a bit higher and it made a strange whining sound. We pulled the engine and found a felt spacer strip from the tarboards sucked inside the fan. OK, put the engine back in and run it some more. Seemed to run fine until you rev it up from the drivers seat, you could hear an obvious engine vibration when you revved it. We pulled the engine, double checked end play, rotated the flywheel 90 degrees. That seemed to do the trick.

So I give the kid the green light for some short trips around town (we have other issues to fix) and he has probably 40 miles on the engine now. Today the engine made a screeching noise when he was shifting so he shut it down. We got it home and yanked the engine again, the flywheel had come loose! I know we torqued this. My torque wrench doesn't go that high, but I stood on the engine while my 6'3 kid leaned on the breaker bar with a 3 foot cheater. Any ideas where we might have screwed up? Should I have used loctite on the gland nut as opposed to never-sieze? The flywheel pin holes do not look wallowed out.

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Re: Engine Vibration / Loose Flywheel

Post by Marc » Wed May 31, 2017 4:52 pm

Big Ratfink wrote:
Wed May 31, 2017 4:11 pm
..Should I have used loctite on the gland nut as opposed to never-sieze? The flywheel pin holes do not look wallowed out.
Medium-strength, anyway. It'd be a rarity for the dowelpin holes to not have suffered ANY damage (if they're still pristine, kudos to your son for being alert enough to shut down in time).
Tug on the pins in the crank, they should not slide out (they're supposed to be a light interference fit). Once they've worked loose in the slightest, they'll be prone to getting worse quickly.
Use a whet stone to go over the holes in the flywheel and knock down any raised metal around them; if you don't see any other damage it should be safe to use the same 'wheel again.

It's unusual for a flywheel to be enough out of balance that shifting it 90° would make a perceptible difference - might the clutch cover have been badly centered the first time, and that was serendipitously corrected when you moved the flywheel?

I'm assuming that at no time did you need to add to the endplay shim stack thickness to reduce the endplay. If that's done on a used engine that's thrust bearing is slightly loose in the case (could happen also to a "recently rebuilt" if they didn't do a needed thrust cut at the time) it can be disastrous since the real endplay between flywheel and bearing ends up too tight. That results in seizure, though, not the 'wheel coming loose. But since you're in that area, do have your son push/pull firmly on the pulley while you observe the thrust bearing for any sign of movement relative to the case, and report back if you find any. If not, reassemble (don't forget a new O-ring in the flywheel). Clean any residual lube off the glandnut and crank threads, with the flywheel off run the glandnut in with your fingertips until it bottoms, feeling for any rough spots that might be responsible for a false torque reading. Use a drop or two of medium-strength Loctite on the threads during final installation.

Not having heard it, I can only speculate about the "screech" when shifting. Inspect the bearing inside the glandnut and the nose of the input shaft (polish if req'd) and be sure the bearing is greased.

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Re: Engine Vibration / Loose Flywheel

Post by woodsbuggy1 » Thu Jun 01, 2017 10:00 pm

I only use German flywheels(have seen problems with some of the aftermarket ones) and always torque flywheel to 400ft/lbs with a good gland nut and red Locktite. Never had one come loose even on turbo motors. I always use 8 dowel crank and flywheel too.
Good Luck
Good quality is getting harder and harder to find.

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Re: Engine Vibration / Loose Flywheel

Post by Piledriver » Fri Jun 02, 2017 3:12 am

It's not unusual for the vibration to change if you reindex the pressure plate vs. the flyweel...
I was always taught the balance holes go 180 out FWIW.

A loose FW will vibrate like crazy.

Unless you actually have the crank/FW and pressure plate balanced together and index marked for orientation, you will never be sure what is right.

Ir should really require a tight collet on a slide puller to easily get the pins out.
8 bigger dowels and a HD gland nut are likely in your future.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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