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Thread lock or not on flywheel and clutch?


Spiff

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When you reassemble your engines, what do you do when it comes to the flywheel and clutch assembly? Do you just torque it and leave it be, do you put thread locker on and screw them on or both thread lock and torque it down?

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In the case of the 720 the flywheel securing bolts are 101-116 ft lbs. There are 6 bolts... it ain't coming off.

 

Pressure plate are much less at 16-22 ft lbs.

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It doesn't hurt to do it. Better to do it and not need it. Blue loctite, not red!

 

 

Blue works the best. Red you will have a hard time getting loose. and could damage the threads.

 

 

I always use blue loctite on both the crank and pressure plate bolts. I have never had a problem getting them back apart. The loctite seals out moisture and prevents the corrosion that causes the bolts to stick.

 I use red Loctite on flywheel bolts and clutch pressure plate bolts, have been for years. Never had the Loctite cause a thread to strip. As Engine Room says, it seals out the moisture making a stripped thread less likely.

 

I have had flywheel bolts come loose without using Loctite though.

 

This rumor that red Loctite will make bolts impossible to remove is bunk. It's only a problem when used on set-screws and even then, a light application of heat from a Mapp torch frees it right up.

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I'd guess it depends largely on the application.. But a worn out 80hp L motor... the flywheel bolts are have more torque than the engine does torque or HP. lol

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Mike made a comment about trusting your torque wrench. It frightens me to think about how many people have a crappy torque wrench that isn't calibrated, or worse, how many people don't even use one.

 

On the L motors, if you over tighten the flywheel bolts, or run them on with a rattle gun, the back of the crank can distort.

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The vibration that causes the bolts to loosen is highly unpredictable. You might build an engine and run it for years; and everything goes fine until one little change makes something hit a harmonic and the engine eats itself.

 

IMG_20160524_133637125_zpsyhuhrj3z.jpg

 

This was caused by pairing a harmonic damper on an engine (that didn't have one from OE) with a lightweight flywheel. This caused a harmonic at around 3000 rpm that essentially liquefied the mating surface between the crank and flywheel.

 

This was an extreme example but you do not know what changes will affect the resonance in a system.

 

The thread locker fills the air gaps between the male and female threads and makes them harmonize as one mass.

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I'd guess it depends largely on the application.. But a worn out 80hp L motor... the flywheel bolts are have more torque than the engine does torque or HP. lol

I'll have to remember that one :lol:

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I sheared my 521 bolts off from leaving the L20B block outside for the winter. The threads got rusty and the bolts torqued up fine but were not in holding the wheel properly. Took 6 months of abuse but one evening driving along the engine just revved up like in neutral. I stopped and used the starter to pull me several blocks. Lesson learned.

 

Flywheels coming off is a rare event.

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