Replacing worm gear in Craftsman snow thrower model 247

I have a Craftsman 26" Snow Thrower, Model No. 247.88691, purchased 2009. The worm gear on the auger shaft stripped a few months ago and needed to be replaced. I got help from the forum about it, and I promised to post this after I replaced the gear, because I couldn't find instructions for it from Craftsman or online. I hope this will help some other people who have the same problem.

How I replaced a stripped worm gear, in the gear box at the center of the auger shaft.

When the augers on the snow thrower do not turn under load (they do not turn when the auger control on the left handle is pressed down and the snow thrower is run into snow), then the first thing to check is whether any of the shear pins have broken. If necessary, see “Replacing Shear Pins” on page 16 of the OM (Operator’s Manual).

If the shear pins are intact, and the augers do not turn under load (or if they turn but stop when run into snow), check to see if the impeller (#2 on page 26 of OM) is rotating as normal when the auger control on the handle is pressed down. If the impeller is turning but the augers are not, then the 20-tooth gear (#46 on page 26 of OM) in the gear box (#s 37 & 38 on page 26 of OM) has probably stripped and needs replacing. This is an MTD part used in Craftsman and some other brands of snow throwers. It is part 717-04449 in the OM, but the replacement part now (March 2014) is 917-0528A ($65).

You will also need a low temperature lubricant, and an RTV silicone gasket maker. I got the RTV sgm from a local auto store, but couldn’t find the lubricant locally. MTD Lubricant part #737-0300A is highly recommended. Read through the steps below first for a few other things you’ll need.

I made these notes and took these photos when taking the snow thrower apart, and used them pretty much in reverse to reassemble it. Plan on taking your time and doing this slow. Plan on taking several hours at least just to get the auger and impeller shafts out of the machine.

These notes are typed up afterward as ‘best recollection’. If something doesn’t quite make sense, just slow down and think things through for yourself.

When removing screws and bolts, line them up them up in removal order along something like a window ledge where they will not be disturbed, and/or mark them so that you will use the right screws and bolts as you reassemble. Some are very similar and they can easily get mixed up if you’re not careful.

1. Remove the black plastic upper belt cover – 2 screws. This is between the engine and the black plastic snow chute that the snow shoots out of.
2. Remove bottom frame cover (#39 on page 30 of OM. (This might not be absolutely necessary, but I think it will make it easier to reassemble the snow thrower when you’re putting everything back together.) To remove the bottom frame cover, drain most of the gas and tip the snowthrower 90 degrees so that the machine rests on the front edge of the auger housing – wheels in the air and handles top most. I needed help with this step. Don’t leave the machine in this position any longer than necessary, because after a while the oil will begin to leak out around the yellow oil fill cap. Remove the 4 bolts that hold the bottom frame cover on, remove the frame cover, and tip the machine back to resting on its wheels.
3. You’re going to separate the front section (impeller and auger section) from the back section (motor, wheels, handle section). First remove the nuts from the 4 bolts that hold the black plastic chute adapter in place (#13 on page 26 of OM). 7/16 hex.
4. Work the front (auger) V-belt (#71 on page 30 of OM) forward off the small grey center wheel (about 2 3/4 diameter). To get more slack in the belt, manipulate the spring-loaded black pulley wheel (#63 on page 30 of OM) that’s to the right of center as you look at the area from the front (auger side) of the machine. The pulley wheel is about 3diameter. (See e ST Photo 1.)
5. Remove the cable from the Auger Control on the left handle: push the spring-loaded black pulley wheel (see step 4 above) toward center to slacken the auger cable. At the same time, there should be just enough slack to remove the cable’s goose-neck fitting from the Auger Control on the left handle. Lay the cable down carefully and always be careful not to kink or snap it.
6. Now you’re going to remove the bolts that connect the two sections of the machine. When these bolts are loosened, the weight of the back section (motor, wheels, handles) will cause it to tip backwards, so first chock in front of the wheels and put something under the handles, such as an adjustable sawhorse or something you improvise. Remove the four bolts and washers (1/2 hex).
7. Gently tug and wriggle the auger housing (front) section out and up away from the back section. Keep an eye on the auger cable and give it more slack as the auger housing pulls free of the back section. (See e ST Photo 2.)
8. Tip the auger section 90 degrees – giving the auger cable more slack as needed, so that the housing rests on the front edge, with the auger V-belt topmost.
9. Loosen the bolt at the top center (#48 on page 30 of OM); ½ hex. You’ll need to insert a stout stick of wood through the chute hole to keep the impeller paddles from turning while you loosen this bolt. I used a piece of .75 x 1.5 (actual) wood about 16 long; you may be able to use a 2x2x16 or so. (See e ST Photo 3.) This bolt is on very tight, and on re-assembly it must be put back on very tight. For the bolt, I used some blue threadlocker gunk on reassembly; you’ll also have to use the stout stick to keep the impeller paddles from turning when tightening it on reassembly. A spring loa
10. Continue to loosen this bolt until it is free (it screws into the end of the impeller shaft). Lift off the V-belt and wheel assembly (#s 46-48, 66 &71 on page 30 of OM) and put safely aside until reassembly. For reassembly you’ll have to move a spring-loaded part to one side for the belt wheel to go back on.
11. Loosen first and then remove the four bolts (1/2 hex) that hold the auger shaft to the sides of the auger housing. When the bolts are removed the impeller and auger shafts should drop down to the floor, about 1.
12. Tip the auger housing back. (See e ST Photo 4.) Remove the impeller from the impeller shaft. Remove the shear pins from the auger shaft and then slide the augers and spacers off each side of the auger shaft onto dowels or rods so that you don’t lose the order and spacing of the parts.
13. Remove the five bolts from the gearbox (3/8 hex) and the blue plastic plug (part #48 on page 26 of the OM). Insert a small blade in the plug hole to carefully loosen the silicone gasket’s hold and to pry the two sides of the gearbox apart. (See e DT Photo 5.) Clean out the gearbox and its interior parts using old gasoline, scrape off all of the old silicone gasket. Take careful note of the order the parts are in.
14. There are several good Utube videos by donyboy73 for how to clean out and reassemble the gearbox after replacing the stripped gear. For example, see his Utube video on 4HP Noma Snowblower Auger Gear Box Repair Part 1/3
Basically after cleaning everything up, you put the left side of the auger shaft into a vise with the left side of the gearbox resting on the vise top. You fill that half of the gear case with lubricant, being careful to keep the lubricant off the surfaces where the silicone gasket will go. After inserting washer and new gear, you insert the impeller shaft and prop up the loose end while you fill the other half of the gear case with lubricant and smear on a little over an even 1/16 layer of the silicone gasket material. After putting in other washer, bolt the two halves of the gearbox together, tightening bolts in criss-cross pattern until mostly tightened and the silicone is starting to ooze out of the seam. Wait a minute and then tighten the bolts another ½ turn. The gasket needs about 24 hours to cure.
15. Reassemble using the above in reverse order to extent practical.

 

Nice pictures. I've added the following one to my stored pics here on the site. I've also shown what I did. I added a grease fitting to the gearbox and fill it once a year.

 

Correction: in step 4 it should say that the black pulley wheel is to the LEFT of center, not right of center. Sorry for mistake.

Thanks, PJMax for the grease fitting suggestion - great idea!

 

Nice job. I prefer a liquid lube instead of grease, as grease tends to get wiped away from the gears. I see it as a major problem on the blogs

 

How long does this job take? Is this an hour long job or an all day job?

If it can be done in an hour than. It is worth paying the shop at 75 bucks an hour to replace my worm gear but if is going to take 4 hours it may be cheaper to buy a new one. I looked and the gear gasket grease and new auger belt will. Be a hundred bucks alone. I have not opened up the gear box yet and I am only assuming the brass side needs replacing it could be both the steel and brass side which would be more parts. It broke this year during my last snow but It might of got damaged the year before when it hit something that actually broke the auger blade and I had it re welded.

A brand new one snow blower is 900 bucks mine is now 12 years old. Pleas let me know what kind of effort this job is. Thanks!

Mike

 

Great! Nice job and good suggestions. This is a keeper.

 

I'd think a 12 year old snow blower is built better than a lot of the models today and would probably be worth the repair.

How long it would take one of us or a shop to do that project is two different things. A repair shop would have a somewhat fixed price on a repair like that as they do them all the time.

I can see at least four hours for a DIY'er to do that repair.

 

It took me a long time to do it because I was working in a cramped space and had never done a repair like that before. It was time consuming, but I don't remember how long it really took. After it was over I felt that it was worth it - it was more satisfying and cheaper to fix it myself. I think it's more the quality of time than the amount of time that matters. It's best if you're doing it without distractions and without time pressure. I can't imagine doing it with noisy interruptions -- something like that would throw me off and I'd make mistakes.

 

On complicated projects, I find that I need an exit strategy.

I have taken some equipment apart one year and tried to put it back together the next year after I've obtained all of the necessary parts and tools . . . . that doesn't work so well because I sometimes get selective amnesia and don't remember how things came apart.

I have a lawnmower transmission partially disassembled right now while I took all winter to find a replacement gear . . . . not something I'd recommend to others.

But I have to do most repairs myself as repair places are 20 to 50 miles away, and transit of bigger pieces of equipment would eat me alive.