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Discussion Starter · #1 ·
For the past several years I have been using my 18538 Snow Caster to remove the snow in my driveway and on several occasions have experienced the roll pin that retains the smaller gear to the input shaft breaking. This usually happens at a most inconvenient time during the snow removal process and to replace it is time consuming as it requires removing the gear case, draining the oil and disassembling it to insert a new pin. I used to experience the same thing in the gear case on my 42" mower deck which is very similar. Several years ago I purchased a new gear case with the updated spiral cut gears for the mower deck and installed it and I have not sheared a pin since using the mower deck (knock on wood that this trend continues). Last February the pin in the snow caster gearcase sheared so at that time while I was replacing the pin I noticed the teeth on the two original straight cut gears were worn as well as the pin hole in the input shaft. At that time I decided to order two new gears, a new bearing and seal kit and a new input shaft from Bolens Parts and Supplies so that I would have them on hand the next time the pin sheared - from experience I knew it would be a matter of when and not if. This winter season has been rather strange and up until last week the snow had been coming and going on its own which made me quite happy. Last Thursday we got a good dumping of the white stuff (6" to 12" where the wind had piled it) so it was time to put the tractor and snow caster to work. About two hours into snow removal duties the pin sheared again so things came to a halt and I parked the tractor back in the shed and removed the gear case to begin the upgrade.
 

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A Little Off Plumb
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Discussion Starter · #2 · (Edited)
Decided I would do a thread on this since the newer gears have a different tooth count which changes the output shaft speed slightly in relation to the input shaft. Attached is a image of the original gearcase set up and the two gears - the smaller gear has 16 teeth and the larger one has 23 teeth. The input shaft (unlike the mower deck applications) has the smaller gear mounted to it and the output shaft has the larger gear mounted to it resulting in a speed reduction. In the mower deck applications the large gear is on the input shaft and the smaller gear is on the output shaft resulting in a speed increase. Using the 18 and 23 teeth gears the reduction ratio is approximately .782 meaning that one revolution of the input shaft will result in the output shaft turning .782 of a revolution resulting in a speed reduction. The newer style spiral cut gears have a tooth count of 20 on the smaller gear and 24 on the larger gear resulting in a reduction ratio of .833 meaning that for one rotation of the input shaft the output shaft will turn .833 of a rotation which will make the output shaft turn slightly faster. At 3500 rpm engine speed the PTO shaft rotates at approximately 3343 rpm from the research I have done. This would mean that with the original gears the output shaft speed of the gear case would be approximately 3343 X .782 or 2614 rpm. With the new spiral cut gears the output shaft speed of the gear case increases to 2784 rpm (3343 X .833) - a difference of 170 rpm. In my opinion this is not a major concern but it does increase the auger speed slightly which I wanted the reader to be aware of if they chose to do this upgrade as it will probably require a little bit more horse power in heavy snow conditions.

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Discussion Starter · #3 ·
Attached are pictures of the new gear set, the bearing kit and the new input shaft. The shaft had a bit of surface rust but cleaned up nicely with a light wire brushing and the key for the PTO yoke had already been installed - I think that Brian told me when I ordered it that it was a new shaft that had been removed to convert a gear case to a different application. Unfortunately I did not take any pictures when I did the upgrade but I will try and walk the reader through the process that I used to remove the two shafts from the gear case which is necessary to install the new gears. I also installed the new thrust washers and bearings at the same time - the two seals and the needle bearings still appeared to be in good shape and a nice fit on the shafts so I did not change them as I was in a hurry to get the snow caster up and running again to get the rest of the snow removed. I have also included a picture (the last one) of the remains of the roll pin that held the smaller gear to the shaft. I find that the coiled style roll pins seem to last longer than the regular split style so I inserted a new one of the coiled style in the picture top retain the smaller gear to the shaft. As you can see the original small gear has worn teeth and the pin holes in it and the shaft were slightly worn so I am hoping that by replacing the gears and also installing a new input shaft that the roll pin will not have to replaced as often - time will tell.

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Discussion Starter · #4 ·
In order to access the inside of the gear case to either replace the shaft roll pin or to do the gear set upgrade it is necessary to remove the gear case assembly from the snow caster. Since I do not bend well I find that removing the snowcaster from the tractor and then flipping it up so that the hitch assembly is pointed skyward works best for me - you may find that you can remove the gear case with the snow caster still attached to the tractor. Whichever method you choose it will be necessary to unbolt the gearcase support (10) - it is attached with three bolts - two at the bottom secure it to the housing at the bottom and one at the top holds it to the gear case cover assembly (28). It is also necessary to remove the shear pin (or drive pin) (70, 71) so that the drive coupling (67) can be slid off of the rotor drive shaft (69) - the drive coupling is secured to the output shaft of the gear case. I find that the top cover mounting bolts and the outer bolt that secures the chute control support (10) must be either removed or loosened so that the gear case cover assembly (28) will move enough to allow the gear case to clear the tunnel area where it sits and slid out the rear opening. Once the three mounting bolts are removed the gear case assembly can be slid forwards so that the PTO shaft (31) can be slid out of the U Joint slip yoke (30) and also sideways to the left so that the drive coupling (67) slides off of the rotor drive shaft (69). Once this has been done the gear case assembly can be slid out the rear opening and placed on a suitable work bench. Note: if the roll pin has sheared then the input shaft may try and slide out of the gear case and gear oil may leak out depending on how you are holding the gear case assembly.

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Discussion Starter · #5 ·
With the gear case removed the first step I would suggest is to remove the drain plug and drain the gear lube out of the gear case. Once that is done you can remove the four bolts (12) that secure the gear case (3) to the gear case support (10). Be careful that you do not damage the gasket (14) if you are planning on reusing it - I would suggest that you install a new gasket but I have reused the old gasket a couple of times without encountering serious leaks. If the input shaft roll pin has sheared then you can slide the input shaft (5) out of the case - watch that there are no pieces of the old roll pin that may catch and damage the needle bearing or the seal lip. As you slide the input shaft out the smaller gear (7) and the two thrust washers (8) and thrust bearing (9) will drop off the shaft into the gear case. The washers sometimes stick to the gear face or the gear case and may have to be slid sideways so they loose their surface adhesion created by the gear lube. The opening of the gear case can now be set on top of a pail so that the remaining gear lube and any roll pin pieces can drip out. While the case is dripping the input shaft, thrust bearings and washers can be inspected for wear and damage - if you are upgrading the gears I would strongly recommend installing a new input shaft and new thrust bearing and washers. If the roll pin on the input shaft was not broken then you will have to remove it before the input shaft can be removed. Please note that there is not enough room to drive the roll pin in enough for it to clear the shaft and it will become engaged with the inner gear case wall if driven too far. What you may wish to do is drive it in so it protrudes a bit out the gear and then rotate the gear so that the pin may either be pulled if you have some method of grabbing it or cut or grind the pin so it is shorter so it can be driven in enough to clear the shaft without contacting the case wall. Note: I did the gear upgrade because the roll pin was breaking frequently which is not normal - if your roll pin is not breaking then the gear set is probably ok and upgrading the gears may not provide any advantage for you.

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Discussion Starter · #6 ·
If you are replacing the input shaft (5) it will need to be removed from the U joint (31) - it is retained with a 3/16" diameter roll pin that must be removed with a punch. Once the roll pin is removed the U joint (31) will still be a light press fit on the shaft. The easiest way I have found to remove the shaft is to clamp the shaft gently in the vise and drive the U joint off the shaft with a punch. For those afraid of marking the shaft you may wish to clamp 1/4" diameter bolt in the vise with the end sticking up and set the gear roll pin hole over the bolt. This should work to hold the shaft from moving as you drive the U joint off of the shaft. The woodruff key that is in the shaft may now be removed - you can usually catch the end with a punch and start the key to roll out of the seat it sits in. Once this has been done the key can be installed in the new shaft (a pair of vise grips can be used to push the key into the seat) and the shaft can be driven back into the U joint with a block of wood - make sure the keyway in the U joint aligns with the key in the shaft. Once you have the shaft aligned and started into the U joint continue driving the shaft in with a block of wood until the roll pin holes in the shaft and the U joint align. This can be checked with a 3/16" diameter punch or drill bit and then the roll pin can be started into the U joint and driven through the shaft. I usually place a punch partially in the holes on the other side so that the holes remain aligned until the roll pin pushes the punch out as it engages with the shaft. I then set the gear on the input shaft the same way as it would mount in the case and insert a 1/4" punch through the roll pin holes in the shaft and the gear. Take a hacksaw blade or a scribe and put a light mark on the shaft surface (not deep - just has to be visible) where the inner edge of the gear sits. This mark will assist in aligning the roll pin holes in the gear and shaft during assembly as the pin hole in the shaft should align with the roll pin hole for the U joint. During assembly the shaft can then be rotated to the correct position to align with the hole in the gear and the shaft can be slid in so that the mark is flush with the inner face of the gear - the holes should now be aligned. For now the input shaft can be set aside as it is now time to tackle removing the output shaft (1) from the gear case (3).
 

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Discussion Starter · #7 ·
Removing the output shaft (1) from the gear case is necessary since the roll pin (6) that retains the larger gear (15) cannot be driven out with the gear in the case. A word of caution - the gear case is fragile around the seal retention area and can be easily broken - do not pry or hammer on the gear case! I found the easiest way to remove the output shaft was to first remove the coupling (67) - it is retained by two 5/16" set screws (56). One screw binds up against the rotor drive shaft (69) and the other binds against the top surface off the woodruff key (33). Fortunately the two screws in mine broke loose ok (no threadlocker) and I removed them both to make sure there were not two more screws hidden underneath. You may wish to observe the gap between the coupling face and the gear case so that you get the coupling close to the same location during reassembly or you can use the marks from the set screws in the shaft surface and the key as alignment aids during assembly. Once the set screws have been removed I would suggest clamping the coupling (67) in the vise ( make sure the jaws are not contacting the set screw hole areas) and then use a large punch or piece of round stock to tap on the end of the output shaft (1) and drive it out of the coupling (67) - be careful that the gear case does not fall as the shaft disengages from the coupling. Once the coupling is removed the outer edge of the output shaft where the woodruff key (33) is located can be gently clamped in the vise and a punch can be used to catch the end of the key to begin to roll it out of the key seat and removed. Once the key has been removed use a flat file to remove any burrs on the outer edge of the shaft and then it can be pushed into the gear case and removed - again watch out for the thrust bearing and washers. The gear (15) is retained to the shaft with a 1/4" diameter roll pin (6) which can be driven out with a punch and then the gear may be pushed off the shaft. At this point you can inspect the output shaft for any wear or damage - mine looked good so I reused it and installed the new larger gear on it with a new roll pin (6). The needle bearings and seals in the gear case may now be inspected and if they are damaged they should be replaced - otherwise the gear case can be cleaned up to remove any remaining pieces of roll pin and things can start going back together.
 

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Discussion Starter · #8 ·
Once the new gear has been placed the right way on the output shaft and a new roll pin installed the thrust washers (8) and thrust bearing (9) can be slid onto the shaft (1) and it can be slid back in the gear case through the needle bearings and the woodruff key (33) installed - again a pair of vise grips may be used to force it into the key seat. I usually put a light coating of new gear lube on the needle bearings, the thrust bearings and washers and the shaft. The coupling (67) can then be slid onto the outer edge of the output shaft making sure that the keyway in the coupling aligns with the key and then it can be tapped on with a block of wood to where it is aligned with the shaft and key marks as viewed through the set screw holes. The set screws can then be started back in the holes - I would recommend that the set screws are left loose until the gear case is mounted back on the snow caster so the coupling position on the output shaft can be "fine tuned" so that the shear pin holes in the rotor drive shaft align with the holes in the coupling. The input shaft can now be lubricated with new gear lube and the shaft can be slid in to the case so that the thrust washers and bearing and the new gear can be slid on to the shaft as it enters the case. I usually start the roll pin into the gear so that it is just flush with the inner surface of the gear before putting the gear on the shaft. The shaft may now be aligned using the roll pin hole for the U joint and the mark on the shaft as alignment aids and the roll pin driven through the shaft so it is centered in the gear holes. As I stated earlier I have found that the spiral wound roll pins seem to work the best for me. Once this is done you can verify the gears mesh nicely while turning freely. A new gasket can now be installed and the gear case can be bolted to the gear case support - make sure that the gear case support is oriented correctly in relation to the support with the single bolt for the support to the top, the input shaft extending to the rear and the output shaft exiting to the right. Once the bolts are tightened the gear case can be set so it sits level the same as it does when mounted, the oil plug (11) removed and the gear case filled to the bottom of the hole with fresh gear oil. I usually take a break about this point and observe for any leaks at the gasket. If things look good the gear case is ready to be mounted to the snow caster.
 

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Discussion Starter · #9 ·
The gear case support can now be slid into place again making sure that the coupling (67) slides over the rotor shaft (69) and also that the drive shaft slides into the PTO yoke if you did not remove the snow caster from the tractor. I usually put a light coating of grease on the rotor shaft where it slides into the coupling. A punch or bolt can now be slid though the shear pin holes in the coupling and the rotor shaft and the three mounting bolts installed and hand tightened. The two set screws that secure the coupling to the output shaft can now be tightened and the distance between the rotor shaft and the rear of the housing measured and verified that it is the same along the length of the rotor shaft as described in the owners manual. This will verify that the rotor shaft and gear case are aligned with the chain and gears that drive the rotor (46). Once the distance has been verified the two lower mounting bolts can be tightened and the upper gear case cover can be bolted back down. Then the upper bolt for the gear case support can be installed and tightened. Rotate the driveshaft and verify that everything turns freely without binding - if things look good the snow caster can be mounted back on the tractor and snow removal can once more commence.

I have used the snow caster three times (about three hours running each time) in the last week since upgrading the gears and so far things appear to be working well. Will try and update this thread at the end of the winter season or sooner if something happens but for now I am happy with the gear set upgrade.
 

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Thank you for the detailed write up. Spiral wound pins or coiled spring pins are definitely the way to go, especially if you're re-using a worn input shaft with out-of-round pin holes.

I've considered upgrading my "square back" Sno-Caster to spiral cut gears, however it's been trouble free for the past five years. I prefer the simplicity of the "square backs" despite them being more apt to clog, which can be largely overcome with some rubber paddles on the auger. Every "round back" Sno-Caster that I've come across has either been broken or in pieces. In my opinion they are bit over-engineered. They were a later design primarily used with the higher horsepower models. Maybe it's simply a case of having too much power for that gearbox.
 
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