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odd driveshaft wear pattern

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AC710

A P.O. had replaced the driveshaft coupler disc on my project 7016 with a 3/16" steel plate (pic). While replacing it, I noticed a strange one-sided wear pattern on the driveshaft from rubbing on the rockshaft. It is worn nearly 1/8-inch deep on only one side of the shaft. Any ideas on how this could have happened? And more importantly, how to keep it from happening again?

More facts:

The tractor has major wear from using a snowplow for a long time. One PO replaced the spring in the plow lift rod with a piece of pipe, making it rigid. This had many effects including beating the rockshaft bushings loose, twisting the rockshaft lift tab, shredding the lift lever mechanism and ratchet, wearing out the holes and rod, and oval-ing the front axle mounting.

The driveshaft is straight, not bent.

The rockshaft has wear, but not as obvious as the driveshaft.

The two shafts rubbing together must have made a heckuva racket, and continuing for some time to make such a worn spot.

The steel coupler "disc" is off-centered across the holes. It's not obvious from the photo, but drawing circles  using the edge of the holes to find center shows about 1/8" offset between the engine holes and the driveshaft holes. The holes are not at a 90-degree angle either. I don't believe the  two shafts have been scraping since the steel coupler was installed, based on the rust patterns.

BGB and engine bearings are tight (thank heaven).

SO, what happened???

 

 

 

 

driveshaft 7016.jpg

shaft coupler.jpg

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PhanDad

I'm surprised the driveshaft wasn't rubbing something with the steel plate holes being so much out of line.

As to why the  past rubbing; I'm guessing one of more of the nuts holding the driveshaft to one (or both) of the fiberglass couplers came loose enough for the bolts to start cutting through the fiberglass and become off-center.  It progressed unit the driveshaft rubbed the rockshaft.  

PS - It may be an optical illusion, but it doesn't look like you have the rounded side of the "special washer" against the flex disk on the upper bolt it the pic. (Maybe the bottom one too?)  The rounded edge helps prevent failure of the fiberglass at the edge of the washer.  

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AC710
2 hours ago, PhanDad said:

I'm surprised the driveshaft wasn't rubbing something with the steel plate holes being so much out of line.

As to why the  past rubbing; I'm guessing one of more of the nuts holding the driveshaft to one (or both) of the fiberglass couplers came loose enough for the bolts to start cutting through the fiberglass and become off-center.  It progressed unit the driveshaft rubbed the rockshaft.  

PS - It may be an optical illusion, but it doesn't look like you have the rounded side of the "special washer" against the flex disk on the upper bolt it the pic. (Maybe the bottom one too?)  The rounded edge helps prevent failure of the fiberglass at the edge of the washer.  

That pretty much agrees with my theory about the rubbing.  Also, I think the rockshaft mounting bolts were so loose that  it probably beat on the driveshaft when getting pushed around by the snowplow and that may have broken the disc or at least started it out of alignment. The PO must have ignored it for quite a while to get so much wear. Since the driveshaft is solid, I would think it would still be okay to use.

The damaged holes on the steel plate look like re-drill efforts of the PO trying to get it aligned rather than wear patterns. That 16 hp B&S engine really vibrated when revved up!

I'll check on the 'rounded side' issue on the washers - I was not aware they served that function, but it makes sense. I've been doubtful about the "poor man's" engineering of those u-joints, but Simp/AC used them forever, so it seems to work. Thanks for the advice!!!

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wwbragg

Sounds to me like the PO didn't properly center the metal disk when he drilled the bolt holes.  That threw the drive shaft out of line and cause it to knock on one side against that cross member.  

Nothing wrong with the disk used as a u-joint.  It only has to absorb vibration from the engine and minimal shaft imbalance. 

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AC710
8 hours ago, PhanDad said:

PS - It may be an optical illusion, but it doesn't look like you have the rounded side of the "special washer" against the flex disk on the upper bolt it the pic. (Maybe the bottom one too?)  The rounded edge helps prevent failure of the fiberglass at the edge of the washer.

You are exactly right. I checked and I got about half of them wrong (50/50 chance, correct?). Now it's fixed. Even trying to follow the repair manual, you still "don't know what you don't know" - the amateur mechanic's nemesis - Thanks again.

While fixing my goof, I discovered some more driveshaft damage next to the steering gear. That thing must have really been flying around for a while.

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