sheared key in flywheel for 2nd time!

[choretime]

ugh! first off its a 50hp johnson (ESL72c)
i have replaced both coils,stator,timing sensor,and power pack. this resoleved its origanal issue (once again thanks to all who helped) then after 3 successful short fishing runs it died due to a sheared key. so got a new one and this time i made sure to use some loctite. now im a big guy using a 3/4 drive with a 2 1/2ft breaker bar (dont have torqe wrench with large enough drv) to tighten the nut down so i figured i should have got to 100 mark and that the loctite should have held. in the end she sheared the key a 2nd time (barely made it back to the dock) so maybe im not as strong as i think i am or theres something else wrong that im missing.

 

[HighTrim]

Re: sheared key in flywheel for 2nd time!

Torquing that to spec is extremely important. If you do not have a wrench, I would invest in one, or bring to someone that does. The taper also needs to be clean and dry. This means no loctite, oil, anything!

 

[choretime]

Re: sheared key in flywheel for 2nd time!

hi! only used loctite on the nut threads and made sure to use solvent to clean the shaft and flywheel then air hose.

 

[ezeke]

Re: sheared key in flywheel for 2nd time!

Sounds like you have the torque number (100-105 ft lbs), but I would still try to check it with a good torque wrench.

 

[F_R]

Re: sheared key in flywheel for 2nd time!

Every time it shears, it destroys the crankshaft and flywheel a bit more. Or a lot more. If the tapers are messed up or the keyslots wallowed out, it is too late now.

As said, tapers must be clean and dry and nut torqued to 100-105 ft lbs. NO Loctite!! If that stuff gets in the tapers you never will get it back off.

 

[BigB9000]

Re: sheared key in flywheel for 2nd time!

what happens when you shear the flywheel?

and what does sheat the flywheel mean?

and couldnt you just hit it with an impact wrench?

 

[choretime]

Re: sheared key in flywheel for 2nd time!

Every time it shears, it destroys the crankshaft and flywheel a bit more. Or a lot more. If the tapers are messed up or the keyslots wallowed out, it is too late now.

As said, tapers must be clean and dry and nut torqued to 100-105 ft lbs. NO Loctite!! If that stuff gets in the tapers you never will get it back off.

ok no loctite. next ? should i be using a lock nut or a lock washer may be or is the torq alone enough to keep the nut tight?

 

[choretime]

Re: sheared key in flywheel for 2nd time!

what happens when you shear the flywheel?

and what does sheat the flywheel mean?

and couldnt you just hit it with an impact wrench?

1. it went out of time and was firing funny and then not at all.tracked it down to a sheared key.
2. im a bad speller
3. dont know if an impact would wreck the threads.

 

[HighTrim]

Re: sheared key in flywheel for 2nd time!

and couldnt you just hit it with an impact wrench?

To tighen it? Absolutely not. Torquing it to spec is critical. Overtightening is just as bad.

 

[ezeke]

Re: sheared key in flywheel for 2nd time!

Torque is the key to keeping the flywheel from turning and breaking the key. Simply preventing the nut from turning will not do that.

This series of motors had problems from the start with proper torque and the torque was increased to 100-105 ft lbs for that reason. If you could go higher without breaking something they probably would have done it, but you definitely don't want to go any less. Reference is SB 1273.

 

[jay_merrill]

Re: sheared key in flywheel for 2nd time!

If you torque the nut correctly, there is no reason to use a lock washer or loctite. If you don't have a 3/4" torque wrench, check your local auto parts stores to see if you can rent one.

I think F_R is probably right, though. If the taper and the inner surface of the flywheel were absolutely clean and the woodruff key was installed properly, you may have a problem that isn't fixable.

BTW, you did use an OEM woodruff key, instead of a hardware store key, didn't you?

 

[choretime]

Re: sheared key in flywheel for 2nd time!

thanks guys. i will try again and this time i will try to do it all right and hopefully there isnt some hidden problem. let you know some time between mon and nxt weekend.

 

[jbjennings]

Re: sheared key in flywheel for 2nd time!

I was going to ask if it was a hardware store key, too, but I see Jay already asked.
Good luck,
JBJ

 

[clanton]

Re: sheared key in flywheel for 2nd time!

Lap the flywheel/crankshaft contact surface with valve grinding compound, clean all contact surfaces to perfection, then install key and flywheel dry. No loctite, grease or snake oil. OMC gasket sealer on nut threads. Must use a torque wrench. Most good 1/2 torque wrenches should go this high.

 

[BigB9000]

Re: sheared key in flywheel for 2nd time!

how would you keep the flywheel from turning while torquing it down?

 

[jay_merrill]

Re: sheared key in flywheel for 2nd time!

With a strap wrench.

 

[CharlieB]

Re: sheared key in flywheel for 2nd time!

Lap the flywheel/crankshaft contact surface with valve grinding compound, clean all contact surfaces to perfection, then install key and flywheel dry. No loctite, grease or snake oil. OMC gasket sealer on nut threads. Must use a torque wrench. Most good 1/2 torque wrenches should go this high.

After you have lapped the parts together and clean them perfectly, use a black felt marker to coat the taper of the crank with ink. Leave the key OUT and install the flywheel, remove the flywheel and look at the ink patterns, you are hoping to find as close to 100% contact between the parts. You might settle for better than 95%, but NO LESS. KEEP LAPPING and retest contact until you are there. Any decent solvent, alcohol, carb cleaner, lighter fluid, will remove the ink from both surfaces prior to final assembly.

 

[choretime]

Re: sheared key in flywheel for 2nd time!

thanks guys. I did use the oem key from my johnson dealer both times. i think that as the crank heats up the aluminum expands just enough to "F" things up.
the lapping and checking the fit with the ink sounds like a great idea. i'll give it a shot. thanks too all and keep the ideas coming,ill try just about anything to get back on the lake so i can rip some lips.

 

[Joe Reeves]

Re: sheared key in flywheel for 2nd time!

If you're going to be working on your own engine(s), you'll need to tool up properly. The torque wrench is a must. Not tight enough..... keys shear, bolts loosen, etc. Too tight.... tapers spread, bolts break, etc.

The flywheel can be held by using a Spanner Wrench, used by mechanics to turn a flywheel when installing a clutch and pressure plate on a manual shift automobile, available at any automotive part type store.

The flywheel key must be installed vertically with the engine, that is straight up and down, NOT in line with the crankshaft taper. See the following diagram. Tapers must be clean and on that model a nut torque of 105 is essential.

 

[Dhadley]

Re: sheared key in flywheel for 2nd time!

Just be very very careful with the lapping compound. Don't get carried away.

Now, is the nut loose after the key shears or still tight?