Unique 1996 Force 75HP Flywheel Shearing Keys issue

[doironjd]

Help!!!! I've gone through many threads on this subject and contacted several boat repair people and we cant isolate the cause.

Problem: Flywheel shears the woodruff key within 1 minute of starting. Repeated 4 times.

Background: Traded for a Skeeter boat with the subject motor. First time on the lake the motor seized up in a few minutes after starting. Pulled apart the powerhead and found a needle bearing stuck between the piston and cylinder wall. Something in side must have snapped and threw some bearings. I then bought a used power head from ebay (according to boat shop i bought it from on ebay, the motor ran fine and had 150 psi compression on all cylinders..seemed to be a very honest guy...he's been helping me on this problem too), pulled everything off of my old one and it installed it on the ebay one, including the flywheel, which took 3 guys, a flywheel puller and 2 cheater bars to pull it off of the old one. It was on VERY TIGHT!! Started the new one up and sheared the first key. Taking advice from this forum, I took of the flywheel off, cleaned the taper and inside of of the flywheel and torqued it down to ~150 Ft Lbs. Started it and it sheared number 2 within 20 seconds.

Thinking i may have a timing issue (I'm no mechanic), I took it to a boat shop. They sheared the 3rd key within 30 seconds. They said it was firing on all cylinders. THey pulled the plugs and checked to see if there was any "slop" in the pistons (checking for maybe a bearing problem which could cause vibrations in the crankshaft) and they said it seemed tight in all directions.

Could this be a flywheel issue?? They said the magnets look good, but I could have spun one that may have thrown off the polarity off, thus throwing off the timing. Could it be possible that i warped it when having a hard time pulling it off of the old powerhead?? I just don't want to spend $425 on a new one only to find out thats not the problem....Could it be the stator or another ignition component causing a timing issue and shearing the woodruff key?

I'm thinking that what ever is causing this shearing issue on this powerhead, may have had something to do with my other powerhead seizing up.

Another thing I've noticed is when I put the lower unit in the water when running, the exhaust seems to really throw the water everywhere. It almost looks like the prop is spinning (in gear), when it isn't.

Sorry for the long winded post....Any help/ideas would be greatly appreciated. The guy at the boat repair shop is just guessing at what the problem is and that is scary when he's charging me $70/hr. Hes ordering me 3 more woodruff keys and after that id like to try my own fault isolating.

 

[steelespike]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Did you lap the flywheel to crank taper with valve grinding compound?This seems to be reccomended as normal assembly procedure.Also examine the key ways for wear/damage.

 

[doironjd]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Did you lap the flywheel to crank taper with valve grinding compound?This seems to be reccomended as normal assembly procedure.Also examine the key ways for wear/damage.

 

[doironjd]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

I didn't on the first two keys, but the boat shop said they did for the last 2, to no avail. Thanks for the response.

 

[steelespike]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Under the circumstances I would suspect a mismatch between the flywheel and crankshaft.Considering the cost of a new flywheel I would lap it real good and maybe use prussion blue to check the match.
My book is not up to date but my specs say 90 ft lbs on the flywheel nut.At 150 lbs the flywheel may be distorted.
If there is a lip on the crank or a removeable
cam it may be damaged or the flywheel bottoming before it is tight.

 

[Frank Acampora]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Ok, a couple of hints and questions.

Does the engine tend to backfire when starting? If so, this could be an indication of faulty timing. Timing should be 0 deg at idle ((+or- 2) and a few more at fast idle /start position. If it is significantly greater, re- adjust the timing. Timing at WOT should be 32 BTDC. The relation between the throttle advance cam and timing advance is crucial, Get the manual and set it properly. Too long to explain here. I would check this area before considering a new flywheel.

However, I did work on an Evinrude that had locked up. Unknown to me, the force of the lock up had shifted the hub. I timed it correctly but the first time the person ran it, the hub re- shifted and the timing was off.

These aluminum flywheels have a knurled steel hub cast into them and it is not unknown for the hub to shift, and it cannot be seen by eye. You cannot even feel it by rocking the flywheel. If you set the flywheel to the 0 deg marks and the linkage is not anywhere near the factory setting, then this could be your problem. Factory setting on the trigger linkage adjustment up top near the flywheel should be somewhere near 3/8 to 1/2 inch between the two plastic ends.

Lapping does not necessarily mate the flywheel to the crank. Once the flywheel is lapped to the crankshaft, there must be a MINIMUM of 80% contact. To check this, remove the flywheel, clean both it and the crank taper, and draw numerous pencil lines on the crank taper. Put on the flywheel lightly and rotate on the taper several times. At least 80% of the pencil lines should be rubbed off. If not, re-lap the flywheel. If the second lapping does not correct it, replace the flywheel.

 

[doironjd]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

I started at a lower toque on the initial install (~120 ft lbs), but i noticed after the first key snapping, when I took the flywheel off it came right off by just pulling it with my hands. Compared to pulling it off of my seized motor, it just seemed way to loose. Then i asked a mechanic about the torque and he said between 140-150 foot lbs). Even that one seemed easy to take off. There may be a mismatch. They were both 1996 powerheads though.

Thanks for the inputs guys! After I pick the boat up from the shop i will check this stuff (Mismatch and timing) and let you know the verdict.

 

[doironjd]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

By the way...There was no backfiring observed. It actually started pretty quick and seemed to idle relatively good (for less than a minute anyway), which led the boatshop to think it wasn't a timing issue , but maybe a problem internal to the powerhead.

 

[Frank Acampora]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

That taper should lock and not be removable without a puller at 90 ft lbs torque. Replace the flywheel! Apparently the original torque was so high that it stretched the bore of the hub. Look closely to see if the flywheel nut is bottoming on the threads and land of the taper. I'll bet it is. Look on auctions for a flywheel. You should be able to pick up one for less than 400 bucks.

Go over to Chrysler Crew and ask if anyone there has a flywheel to sell. You might get lucky.

 

[Frank Acampora]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Let's hope your mechanic didn't get too aggressive while lapping and reduce the size of the crankshaft taper. If the nut is bottoming out as I think it might be, you always have the option of putting a large hole spacer under it. As long as the flywheel does not go down far enough to hit the stator windings, you should be OK and save some money.

 

[Matthew A.]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Could also be that the first time the flywheel snapped the woodruf key or, due to overtorquing or damage while removing it, the slot for the woodruf key on the crankshaft and/or flywheel got distorted. Despite the lapping, there is now just enough play that is allowing the crankshaft and/or flywheel to shift slightly to now become a very efficient pair of bench sheers.

 

[bass4brains]

Re: Unique 1996 Force 75HP Flywheel Shearing Keys issue

Gotta agree with the seaman I had a 35hp evenrude that sheared keys every time you slowed to idle turned out the crank keyway was wallered a little. I seated the last key with a little J.B.Weld never had to pull the flywheel again, Don't know that I'd recommend that with a good engine though8) This was like a 30 something yr.old engine I think it was a 53-55 model but would push a little starcarft fast enough to ski behind if you helped it a little coming out of the water! Makes you wonder why they don't last that long nowdays?