Snapper Mower Deck Repair

I was given a heavily used snapper lawn mower a few years ago and it has been a great riding mower!  However, it was made in the mid 90's and has several parts in need of attention.  Lately the deck belt has been jumping its pulley system every time I disengage the blades.  Apparently 20 years of the tensioning pulley pivoting on its hinge has caused some wear.  This turned out to be a perfect job for the lathe.  Here we go!

old pin vs new pin

 

For the snapper-curious, this is a snapshot of the mower deck removed.  The small pulley located inner-right is designed to function as a clutch.  Pulling on a lever results in this pulley tensioning, pivoting back, and engaging the belt with a drive pulley attached directly to the engine shaft.

snapper mower 28 inch deck

 

Next we have a close up view of the clutch pulley.  You can see that the pivot pin and bushing are quite worn.

pulley and hinge

hinge pin

 

The badly worn pin was fastened to the deck with a nut from underneath.  Also the pressed bushings were badly worn and so I started by locating approximate center (relative to the wear) and drilling out until the hole was returned to round (or close enough).  Here is a shot of the final drilling operation.  Note that the wear was off center and so the new hole will be as well.

drilling out the bushings

After drilling out the bushing, I measured the hole and moved on to making the replacement pin.  I started by cutting off roughly 3.75" of 5/8" steel round.  I'm not sure exactly what type of steel it was, but it cut nicely.  I deburred and mounted in the 3 jaw.  Next is a facing cut on each end for cleaning up.

5/8 inch steel in taig 3 jaw chuck

 

Here you can see layout dye was applied and then the depth stop was set for a turning operation.

setting the depth stop

 

Action shot!  The turning operation went well.  I roughed it with 0.020" cuts (0.040" dia per pass) and then finished with a 0.005" pass.  Note that taking more than 20 thou would have proven difficult.  I used cutting oil with each pass and the HSS cutter held up well.

turning operation on taig lathe

 

Now to test the enlarged bushing with the freshly turned pin.  It fits!  Actually it was pretty tight the first attempt and so I took another couple thou off and polished it up a bit with sand paper.  You can cut a piece of sandpaper and polish your parts removing a half thou or so while leaving a nice finish right on the lathe.  Unlike when using the larger machines, in my experience it is difficult to get more than a minor cut on the Taig.

pully pin fit check on lathe

 

pin in bushing

 

Next step is to flip the part around and turn down the section of the pin that mounts the pin to the deck.  Note how the rough cuts do not look as pretty as the final passes.  You can get a very nice finish with the round nose tool but then you are limited on how sharp the corners will be.  I wanted a 90 degree flange so I used the right hand cutter.

turning operation taig lathe steel pin

Ready for 5/16-18 threading! 

turned pin for 5/16 in threading

 

Threading on the Taig is accomplished via taps and dies held in the tail stock.  Regular taps can be held dead center in a Jacob's chuck while 1 inch button dies are held dead center in the die holder tool.  Caution here - all threading is recommended to be done by hand turning the chuck (and reversing to break chips every turn or so).  Threading under power is not recommended (but feel free to experiment and let me know how it goes)!  Ok, so why aren't we threading yet?

centering pin in 4-jaw chuck

And what's with the 4-jaw?  I've found that attempting to use a die for larger (relatively) external threads on steel doesn't go so well in the 3 jaw chuck.  The soft jaws can only grip so tight and what tends to happen is the pin will begin to spin in the chuck once the thread die gets a full bite.  There are workarounds (e.g. start with hex) but I favor going straight to the 4-jaw chuck.  It has steel jaws that can maintain a much stronger grip.  If I was thinking ahead, I would have setup in the 4-jaw before the turning operation but no big deal.  Using a dial indicator mounted as shown, you can get the runout down to less than half a thou pretty quickly.

taig threading attachment

Threading was only required to a depth where the nut seats under the mower deck and so as shown below, the new pin is ready to go!  You can see how much larger the new pin is and how badly worn the old one was.  I used a center drill and 7/64" twist drill to add the cotter pin hole but forgot to take photos.

old vs new pin

 

Here is the new pin installed.  It pivots nicely with a few drops of way oil, which will hopefully last because it's almost certain I will fail to add more oil in the future.  I remembered to add the washer after taking this photo (and after bending the cotter pin to a near unremovable shape).

snapper pin installed

So there it is, no more excuses to avoid mowing the lawn one more weekend...  More projects soon.  Take care!  -Keith