Impeller shaft and bushing clearance - Snowblower Forum : Snow Blower Forums
 
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post #1 of 10 Old 12-05-2014, 10:54 AM Thread Starter
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Impeller shaft and bushing clearance

Hello all,

Working on Craftsman model 842.242560 snow blower attachment. Have found many of the walk behind snow blowers have the same gear box.

Impeller shaft was bent and wore the auger gear box bushings egg shaped. Also wore the impeller shaft where it contacted the bushings.

Had impeller shaft straightened. Filled with scatter weld, and machined down. Left the bushing area of the shaft a little over sized (0.760") until new parts arrive.

Old Craftsman part numbers from Sears direct are no longer found anywhere except at Sears.
But Sears had newer sub numbers listed for moving parts that show up in newer Murray gear boxes.

Same gear box and internal parts can be seen here:
Lawn Mower Parts, Small Engine Parts & Much More! | PartsTree.com - Briggs, MTD, Toro, Cub Cadet, Husqvarna, Troy-bilt...

Parts in this drawing are the same on mine, including the housing halves, except the actual impeller shaft and the auger shaft. (Same diameters, but different lengths and configuration.)

The impeller shaft I am working with did not have a C clip inside the gear box.
Sears direct parts diagram and the owners manual parts break downs do not show a C clip inside the gear box. (Although now I begin to wonder if there was one originally and the groove for it was wiped out when the shaft was worn.)

I need help with three things.

No. 1 My main concern, how much clearance should there be between the shaft and the bushings?
Flange bushing is suppose to be 0.0753" ID, and Sleeve bushing is suppose to be 0.752" ID. (I am waiting on new parts to arrive.)
I am thinking between .001" to .002" of clearance. Anyone here worked with this before?

No. 2 The old Helical (worm) gear slipped off the impeller shaft easily. Hi-Pro Woodruff key for the gear was tight and hard to remove from the shaft.
Is this suppose to be this way? Is that gear suppose to slide on the shaft? Or is that gear suppose to be press fit to the shaft? It seems to me it is suppose to slide. Shaft area that was inside the gear did not look worn at all.

No. 3, If this shaft set up had no C clip, and Helical gear slides on the shaft, what keeps the shaft in place in the gear box?
I realize that once the gear box is in place, bolted in and the mid bearing set screws tightened it will stay in place. At least it is suppose to.
I can see by the drawings that once the gear box is assembled if I were to try and pull the shaft out of the housing, it would move a short distance, but the woodruff key for the helical gear would run into the thrust washer at the end of the helical gear and stop it from coming out.
I am just not sure if this is the way it is suppose to be, or if I am overlooking something.

Any input would be appreciated.
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post #2 of 10 Old 12-05-2014, 03:13 PM
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number 1. you are right on that. number 2 it should be a snug as a bug in a rug fit. number 3 I forgot already I will have to recheck that 1. ohhhh yeah ALOHA to the forms..: cool:

Long LIVE THE POWERSHIFT!! MAY IT NEVER RUST IN PEACE!!
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MAHALO!!!!!!!!!
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post #3 of 10 Old 12-05-2014, 03:15 PM
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number 3 I will divert to someone more up to date with those machines.. they will show up sooner or later here.

Long LIVE THE POWERSHIFT!! MAY IT NEVER RUST IN PEACE!!
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post #4 of 10 Old 12-05-2014, 09:16 PM
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Welcome, and from the Sears diagrams, it does appear that they had it designed without a c-clip.

Does it make sense? Probably not, but it does allow for flex in the design to prevent failure down the process. The shaft is secured from the pulley end, with a bolt. So, if the augers were engage in the middle, the case would be pulled forward. If the shaft were secured inside the case, it may cause that stress to applied to the actual gear set. With the designed slippage, it places it onto an inexpensive washer.

I hope that makes some sort of sense.

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post #5 of 10 Old 12-06-2014, 12:41 AM Thread Starter
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Quote:
Originally Posted by db9938 View Post
Welcome, and from the Sears diagrams, it does appear that they had it designed without a c-clip.

Does it make sense? Probably not, but it does allow for flex in the design to prevent failure down the process. The shaft is secured from the pulley end, with a bolt. So, if the augers were engage in the middle, the case would be pulled forward. If the shaft were secured inside the case, it may cause that stress to applied to the actual gear set. With the designed slippage, it places it onto an inexpensive washer.

I hope that makes some sort of sense.
It does.
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post #6 of 10 Old 12-13-2014, 12:05 AM Thread Starter
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New bearings came in, and impeller shaft done.

New Bearings were 0.752" ID.Had the shaft machined to 0.751"
Machinist did a really nice job. But did tack another $10.00 on to the price. So $85.00 total to get the shaft straightened, worn spots filled, and machined back down.

Installed it in the gear box today. Once all was in place I found the shaft, as suspected, would move towards the tractor 3/8". Not quite far enough that the 7/8" dia. part would slip past the quad ring, but close. White grease line in the picture is the edge of the 7/8" part of the shaft. Tip of pencil shows were the quad ring will ride.

A C clip installed between the sleeve bearing and the worm gear would stop that. Must be why they added one to the later builds of this gear box.

Heavy duty well built snow blower, but this gear box is the weak link in the whole thing.

That and people that do not put Loctite on the bearing set screws.
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post #7 of 10 Old 12-13-2014, 12:10 AM Thread Starter
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Now the picture

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post #8 of 10 Old 12-13-2014, 07:03 AM
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Can't you shim the front to stop it from sliding up? Either that or the front bushing is shot.

Please direct all snow blower questions to the forums and not to me with PMs.
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post #9 of 10 Old 12-13-2014, 12:37 PM Thread Starter
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New parts installed.

Quote:
Originally Posted by Shryp View Post
Can't you shim the front to stop it from sliding up? Either that or the front bushing is shot.
Thanks for your thoughts.

I replaced with new the Flange bearing, sleeve bearing, thrust bearing, 2 x thrust washers. Parts diagram did not show any other spacers.
I had thought about adding 2 more of the thrust washers behind the worm gear, as spacers, but worried about alignment of the two gears. Didn't know if it would make a difference. Thinking about it now, it was operational with one thrust washer and the thrust bearing destroyed. Adding two more thrust washers as spacers probably would not affect the gear alignment.

My original question was about how the the impeller shaft was kept in place when there is no C clip in front of the worm gear as there is in other parts diagrams of this gear box. What kept it from being pushed backwards too far?

I am thinking now that when the blower is running, the worm gear is being thrust towards the tractor. So thrust on the shaft, what little there is, must be the reverse. Pushing the shaft away from the tractor, not towards the tractor. The set screws in the main (Mid) bearing must be enough to hold the shaft in place. So not having a C clip on the impeller shaft is not really a problem. Just something they must have added to later builds of this gear box.
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post #10 of 10 Old 12-13-2014, 11:31 PM Thread Starter
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Put the auger and impeller assm. back into the housing today.
From the back after I had it all in place, and the auger bolted in. I lightly tapped on the impeller shaft to make sure it was sitting in the gear box as far forward as possible.
Then I used Loctite and tightened up the set screws on the mid bearing.
Put the large chain sprocket on the impeller shaft and found the hole for the 1/4" bolt did not line up with the hole in the sprocket collar.
Had to loosen the set screws and bring the shaft out toward the rear about 3/16" in order for hole in sprocket collar and hole in shaft to line up. After that I checked and both sprockets lined up quite nicely.
Glad I knew I had the extra play the gear box.

Finished putting the blower back together and fired it up. Can not believe how quiet it is compared to before.
Even compared to the old Agri-Fab 32" red blower I had on the Murray.
Only noise that stands out is a little some chain noise. May need to change out the chain. But that will be for another post.
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