Servicing Procedures
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This page is written as a guide to servicing the most common families of vintage Gilson Snowblowers. It relates best to the following machines:

These machines cover that vast majority of units in the field and are the styles I'm most fond of. A lot of what should be done is the same for all of the models and I will point out the differences where they exist. For machines not in these families and those of other makes altogether much of the following material is still applicable. In time I'd like to illustrate this with many pictures but for now I will concentrate on the text. This section reflects what I do to a vintage machine when bringing it up to snuff as a working piece in my collection. It does not reflect work that must be done each and every year although a full inspection and some things should be done yearly. In many cases these bullet items will begin and end as inspection tasks. Finally I must point out that Gilson built many variations of these machines and you may have a unit that differs from those that I know. Use your common sense, if what I say doesn't make sense then don't do it!

General Service Procedure (Tune-up)

When I service or rejuvenate a machine I sometimes skip around depending on what I feel like doing and where the risks are. For this presentation I'm going to start at the front and work my way back. This is also the triage procdure I use when evaluating a newly acquired machine. It's a great "getting to know you" exercise if you are new to your Gilson.

By now you should have a fair idea what your machine is all about and what it's condition is. Some of the common repairs needed are covered on this page.

ADJUSTING a 3 SPEED UniTrol SHIFTER

3 SPEED UniTrol BELT CHANGING

NOTE: This does not apply to the 2 piece UniTrol models commonly exported to Canada. These machines commonly carry decal designations of Gilson 500, 800 and 1000 for 5, 8 and 10 HP models respectively. For these machines consult your documentation for the procedure.

  • Remove the top belt cover.
  • LOOSEN the 3/4 inch bolt on the engine that holds your belt guard, just loosen it a enough to pivot the guard.
  • Look down near the big impeller pulley on the left side, use a 7/16 wrench to loosen the little belt retaining finger.
  • Look in the same place on the right hand side. If you have a similar finger loosen it. Newer machines have a brake mechanism, leave it alone.
  • Tip the machine up on it's nose, if the drift cutter is not there or good enough to support it then position wood blocks to support the top lip of the bucket.
  • Remove the bottom cover
  • Look at the base of your handle assembly on the left hand side, there should be a hair pin cotter.
  • Remove the pin and release the linkage from it's hole.
  • You should now be able to reach into the machine and lift the friction wheel from the platter far enough to pass your belts through.
  • Mark your belts in some way so you won't get them confused, B for Blower & T for Traction for instance.
  • By rolling the pulleys slowly you will be able to get them off and on the pulleys. You will also move the idlers so they are behind the belts and then place them back on top in the end. This part is mostly common sense and defies verbal explanation!
  • This is a real good time to grease your idler rollers if they are the solid steel type held on by retaining rings, they should be opened up and greased every year or 2. If you have the sheet metal idlers with sealed bearings held on by a nut then you're all set.
  • With the belts in place reset the belt guides for 1/16- 1/8 inch clearance when the blower is engaged.
  • Reverse the balance of the procedure.
  • That's about it, the hair pin cotter is the key.

3 & 4 SPEED UniTrol IMPELLER and IMPELLER BEARING CHANGE

Given the age of these machines and some of the typical operating conditions having the main bearing or impeller seized on the shaft is common. Occasionally I encounter a unit that just slides apart but these are the exception. In the end, this procedure often amounts to precision destruction. Exercise patience and remember to do no harm.

The actual impeller removal for the 5 speed units is similar though dealing with the drive train is different.

  • Remove the auger shaft bushings on the sides of the bucket. On some models you will need to remove the grease fittings to get them through the side panels
  • Remove the belts. See Here
  • Tip the machine up on it's nose. If you have the original drift breaker it will act like a kick stand. Otherwise use a 4X4 wood block or something similar to support the top lip of the bucket depending on your exact model. If gas flows from the cap you will need to drain some gas.
  • Remove the bottom cover plate, click pins, wheels and any thin shaft spacers. Make notes of any spacer placements. normally 2 thin spacers will be on each side.
  • Disconnect all of the linkages to the mechanisms. Unbolt the "boomerang" bell crank mounted to the inside of the big dimple on the back of the machine. It has a lock-nut so you will need to hold the nut with a wrench while turning the bolt with a socket on an extension.
  • Unhook the extension spring that is hooked into the back panel.
  • Remove the bolts securing the side plates that the axle bushings are in.
    • Do not remove the hex head sheet metal screws for the inner gear cover on the left, this can stay together. However as part of this job it's suggested that you disassemble this final drive gear case to clean and re-grease. The grease has probably lost a lot of it's oil content and there may be considerable sand in there.
  • Grab it all by the axle ends and pull the whole transmission from the machine. The dimple plate will remain. All of the guts, axle, and side panels will now come off as one. How thoroughly you clean and re-lube all of this is up to you but it's a great opportunity to get it moving like new or better.
  • Remove the internal retaining-ring that secures the drive platter to the main shaft, slip it off and keep track of the spacers above and below it.
  • Loosen the 2 blower pulley set-screws then use a puller to remove the blower drive pulley. Pull from the center hub, not the outside diameter.
  • Remove the black locking collar from the impeller shaft bearing. See this procedure for details.
  • Now remove the 2 nuts that secure the flange of that big center bearing and remove the flange.
  • Prop the auger leads so that the bearing rises up away from it's seat and remove the bearing from the shaft. See this procedure for details. Replacement bearings are found here.
  • Lay the remains of the machine back down and the auger/impeller assembly will slide right out!
  • Note the distance between the tail end of the worm drive case and the end of the impeller hub and write this down for use when reassembling..
  • Loosen the 2 square headed set screws on the impeller . As time goes on these get harder and harder to remove. You may need to use a small disc grinder to strip the impeller down to the core. Then slit the core lengthwise with the grinder to release it. Be careful to limit nicks to the shaft. Once slit a cold chisel driven into the slit may be needed to open the bore. Again avoid shaft contact. If you have access to a hydraulic press and tooling this will often work. Be very careful to have a straight set-up. If things are askew the shaft may fold over under pressure where it steps from 3/4" down to 5/8". The impeller is on a key. Be sure to allow it passage when setting it up on a press. Sometimes you need to cut some of the blades away to get press plates where you need them. Never strike the shaft end. Doing so will mushroom the end and may ruin the retaining ring groove.
  • You have now turned the corner!
  • Dress the shaft with a file to remove any screw divots, keyway distortion or corrosion. The new impeller should smoothly slide onto the shaft.
  • Mount the impeller on the shaft using the key and tighten the set screws lightly.
  • Once reinstalled including auger bearings and main bearing you can loosen the set-screws and position the impeller such that the blades are central to the discharge port. Tighten the impeller set-screws.
  • Reverse the rest of the procedure and you're done! Consulting other topics on this page such as friction wheel replacement and shifter adjustment will be helpful.
  • New impellers are available here.
I did this exact job for a friend some time ago. We started at 9:00 PM and were blowing again by midnight and we did some other tweaking along the way too. This is a great time to replace the friction wheel if it's cracked or worn.

3 and 4 SPEED UniTrol FRICTION WHEEL REPLACEMENT

    Quickie Method
    OK for simple friction wheel replacement but it can stress the axle bearings.
    • Tip the unit up on its nose. (Drain some fuel or seal the cap if you have over 1/3 of a tank to prevent leaking.)
    • Remove the bottom cover plate.
    • Remove the right hand side wheel, keep track of any small spacers. If the wheel won't come off see here.
    • Note: Sides are always described from the operating position.
    • Remove the 5 bolts that secure the right side plate this is the plate the axle bushing is in.
    • Loosen the same 5 bolts on the left side.
    • Pull the right hand end of the axle towards you to get the right hand side plate out from under the lip that retains it at the top.
    • Slide the RH side plate off of the axle.
    • There will be a cotter pin on the RH side of the friction drive module, remove it and any spacer washers. Keep track of them.
    • There is a small carriage bolt on the RH side of the friction drive module remove it. NOTE: If your machine is from the first years of this model (1969, 70) you will not have this feature. You will need to remove both side plates and everything in between them and release the hex shaft from the bearing to slide it clear to allow removal and replacement of the friction wheel.
    • There is one more thing that has to go right before you're home free, if you're so inclined say a prayer.
    • Wiggle the end plate that you removed the carriage bolt from. The bearing at the top end has to slide off of where you removed the cotter pin. Don't force or distort it.
    • Did it come off? If yes take a deep breath.
    • If not here's where you have to be careful and clever with pullers and such. Odds are very good it will come right off. See below for what I use.
    • Hold the hex shaft with a closely set big adjustable wrench.
    • Remove the 3 bolts that mount the friction wheel.
    • Remove the friction wheel
    • Clean all sliding surfaces with WD-40 or some solvent that will cut gummy old oil.
    • Clean the platter/pulley with brake cleaner, denatured alcohol, lacquer thinner or anything else that will leave it absolutely clean. If it's rusty sand it first. If it is work polished smooth sand with coarse emery cloth in an orbital pattern to promote friction. Platters that have work polished smooth can slip when a little snow blows in to wet the surface.
    • Reverse the procedure to put it back together
    • Lightly oil the sliding surfaces including the hex shaft, wiping them with oily fingers will help prevent over oiling. I like to use Mobil-1 5-30 oil for this. I think the synthetic behaves better in the cold and over time.
    • Reclean the drive platter as needed.
  • Preferred Thorough Procedure
    This method provides a thorough cleaning and servicing of the transmission. It is also the procedure required to replace the reduction gear bushings.
    • Tip the unit up on its nose. (Drain some fuel or seal the cap if you have over 1/3 of a tank to prevent leaking.)
    • Remove the bottom cover plate
    • Remove both wheels and note the sides they come from, keep track of any small spacers .If the wheel won't come off see here.
    • Note: Sides are always described from the operating position.
    • Loosen the bolt that secures the bell crank at the base of the left side handle bracket. Remove the cotter pin from the rod that emerges from the back of the machine to free that rod.
    • Remove the 2 small carriage bolts securing the ship lapped shifter linkage.
    • Use a 9/16" open end wrench to engage the nut on the inboard side of the big dimple. Use a 9/16" socket on a 6" extension to reach into the dimple and remove the bolt. Note the order of the stand-off, and large washer.
    • Release the spring that is hooked into the top left corner of the back panel. A tool like an old long scewdriver with a V notch ground in the end of the blade is a nice tool especially to replace this spring.
    • Remove the 5 bolts that secure the right and left side plates.
    • Tug on the axle to free the whole transmission assembly. Manipulate the rods to get them out of the chassis.
    • This is a good time to start taking digital pictures. The parts can be hard to visualize when not oriented in the machine.
    • Remove the right side chassis panel by sliding it from the axle.
    • Remove the cotter in from the outer surface of the left side chassis panel.
    • Slide the friction wheel module out of the left side reduction gear housing.
    • Open the reduction housing by removing the sheet metal screws.
    • The axle and inner reduction housing will remain an assembly unless you bother to knock out the axle roll pin.
    • Degrease and clean everything
    • Inspect/replace the flanged oilite bearings in the reduction gear.
    • Now we go after the actual friction wheel. There will be a cotter pin on the RH side of the friction drive module, remove it and any spacer washers
    • There is a small carriage bolt on the RH side of the friction drive module remove it. NOTE: If your machine is from the first years of this model (1969, 70) you will not have this feature. You will need to remove both side plates and everything in between them and release the hex shaft from the bearing to slide it clear to allow removal and replacement of the friction wheel.
    • There is one more thing that has to go right before you're home free, if you're so inclined say a prayer.
    • Wiggle the end plate that you removed the carriage bolt from. The bearing at the top end has to slide off of where you removed the cotter pin. Don't force or distort it.
    • Did it come off? If yes take a deep breath.
    • If not here's where you have to be careful and clever with pullers and such. Odds are very good it will come right off. See below for what I use.
    • Hold the hex shaft with a closely set big adjustable wrench.
    • Remove the 3 bolts that mount the friction wheel.
    • Remove the friction wheel
    • Clean all sliding surfaces with WD-40 or some solvent that will cut gummy old oil.
    • Bolt the new friction wheel in place, replace the end cap, washers and cotter pin.
    • Butter the reduction gear and axle gear teeth with wheel bearing grease.
    • Place the inner reduction housing against the friction drive module, mount the reduction gear cluster on the stub shaft mating its big gear with the friction drive module output gear. Slide the axle gear in to mate with the small gear of the reduction cluster. Slide the left side chassis plate onto the axle and then onto the stub shaft. Install the cotter in in the stub shaft. Close the reduction housing with the sheet metal screws.
    • Slide the axle bearing onto the axle.
    • Orient the rods and spring for reinsertion in the machine.
    • This is a good time to mop out the transmisison cavity. Degrease and wipe away belt and friction drive framents.
    • Clean the platter/pulley with brake cleaner, denatured alcohol, lacquer thinner or anything else that will leave it absolutely clean. If it's rusty sand it first. If it is work polished smooth sand with coarse emery cloth in an orbital pattern to promote friction. Platters that have work polished smooth can slip when a little snow blows in to wet the surface.
    • Ease the transmisison assembly back into the machine. Be sure to get the side plates under the lips of the main chassis. Push it full up and secure with the 10 bolts but to not tighten them yet.
    • Reconnect the spring into the notch in the top left corner of the back plate
    • Remount the boomerang to the inboard surface of the dimple. Remember the stand-off and fender washer.
    • Install the 2 small carriage bolts securing the ship lapped shifter linkage. Adjustment comes latter.
    • Reassemble the bellcrank assembly at the base of the left handle bracket.
    • Lightly oil the sliding surfaces of the friction drive module including the hex shaft, wiping them with oily fingers will help prevent over oiling. I like to use Mobil-1 5-30 oil for this. I think the synthetic behaves better in the cold and over time.
    • Reclean the drive platter as needed.
    • Install the bottom cover and snug the bolts.
    • Tighten the 10 bolts securing the chassis side plates.
    • Remove the bottom cover.
    • Adjust the shifter using this procedure.
    • Replace the bottom cover.
    • Replace the axle washers, wheels and klick pins.
    • Work your way up the linkages putting a drop of oil on each pivot point.
    • Remove plastic from the gas cap if used.
    • Test run.
    • The transmission should shift easily with the lever held between your thumb and forefinger. With decades of break-in, a good cleaning and fresh grease the drive reduction should sound like a fine sewing machine when you push the machine.

Pulling the End Bearing on a UniTrol Transmission.
The spanner is made from 2 lengths of 1/4 X 1 flat steel bar and two 5/16 bolts. It lets you get behind the bearing plate and attach a commercial puller. Works great! Install the puller so it mates up with the hex shaft, center it and tighten the nuts just finger tight. Install a common small gear puller and remove the end plate and bearing with the puller. Be sure to touch up the shaft so it's a clean fit for next time.

REPLACING THE ROPE IN A RECOIL STARTER

This is written based on the Briggs & Stratton L Head engines that are commonly found on these vintage machines. The procedure is similar on most small engines.

Adjusting your carburetor

This is written based on the Briggs & Stratton L Head engines with FloJet carburetors. These are bowl type carburetors with a visible adjusting needle at a 45-degree angle.

Well assuming that the ignition is good and the carburetor is free and clear here is what I do...

If you are starting with an engine that is hopelessly tinkered with here are some starting points. For the high-speed (diagonal) needle run it in (CW) and gently seat it closed. Now back it out 1-1/2 turns. The low- speed needle is up where your fingers can barely reach it in the heater box. This wants to be similarly seated and backed out 1 turn. In general the high speed will determine how the engine runs at full speed. The low needle will effect how the engine responds and accelerates when you pull up on the throttle.

Replacing a Gear Drive Impeller or Main Bearing

In general the gear drive machines split in 2 tight behind the impeller. This makes impeller / bearing service quite easy. The hardest part is dealing with the effects of aging that tend to make certain things not want to come apart. I always replace the main bearing if I'm in this deep.

  • Remove the belt cover
  • Remove the blower belt
  • Remove the 2 side acorn bolts below the belt cover
  • Remove the 2 top acorn bolts and catch the drive end of the machine as it tries to fall away.
  • Next you remove the big pulley, loosen 2 set-screws and use a big gear puller to grab the center hub.
  • Now remove the 2 auger support bearings up front.
  • Use a file to remove any set-screw divots the pulley left behind.
  • On the input shaft there will be a black eccentric locking collar with a set-screw, remove the collar. See this procedure for details.
  • Remove the 2 nuts that secure the bearing flanges. remove the top flange.
  • Get a board to put under the augers. You want to force the augers to the back of the bucket to lift the big bearing as high as possible.
  • Remove the bearing from the impeller shaft. See this procedure for details. Replacement bearings are found here.
  • Mark the augers as left and right. Remove the 2 shear pins and auger assemblies.
  • Remove the 2 impeller set-screws. Get the assembly into a hydraulic press and support the center hub of the impeller. Press on the input shaft. The first few movements may make a frightening snapping sound! Be sure to have something soft to catch the worm drive. Soaking it in something like Kroil penetrating oil in advance can't hurt.
  • Using a file dress the 2 impeller set-screw divots
  • Now you can service or replace the impeller. If you work on the impeller try to maintain the balance.
  • When reassembling make sure you get the auger leads back on the right sides.
  • Install the auger support bearings before the main center bearing. The auger bearings will set the shaft projection. You should now be able to introduce all of the bearing parts in order and reverse the rest of the process.

Replacing Belts in a 1, 2 or 3 speed Gear Drive

This procedure covers replacing belts in Early 1 or 2 speed Gear Drive and 3 speed Gear Drive machines.

  • Be sure that your gas tank is no more than 1/2 full. If it is more than 1/2 full get a lightweight plastic bag (like a Wal-Mart bag). Remove the gas cap, place the bag over the opening and screw the gas cap on. This will effectively plug the fuel cap vent and prevent dripping. Always be careful with gasoline and with the old bag when done.
  • Pull the spark plug wire from the spark plug to disable the engine. You may need to gently twist the rubber boot.
  • Remove the belt cover in front of the engine. This will be either 2 bolts or thumbscrews that may require a nearly closed adjustable wrench or pliers. Do not remove the screws, the bottom of the guard is slotted.
  • Set the controls so both idler rollers are pulled back into the disengaged positions.
  • Around the engine pulley there will be a wire retainer that extends along each side of the pulley you should be able to work around this or you can loosen the bolt on the engine if need be.
  • If your machine has a drift breaker bar in front and it is not bent you may lift the handles and tip the machine up onto it's nose. If you don't have a drift breaker or don't trust yours then get a block of wood and place it to catch the top lip of the bucket when you tip the machine up. Note: If you have an early gear drive with the straight sided bucket your machine may want to roll forward on the augers while you tip it up. Lifting it in one clean motion usually counteracts this.
  • Look at the bottom of the machine to see if there are any belt retainer rods in the way of removing / replacing the belts. These are usually only on early models. If you have any loosen the bolts and back them away.
  • If you look between your 2 lower pulleys you will see clear passage for a belt.
  • Since the blower belt is at the end of the engine shaft you need to move it first. You may have enough slack to just start it off the lower pulley and rotate the pulley to make it climb free. Once off the lower pulley pass it up the center. If it's not happening then get it started and carefully pull the recoil rope to pull it around. You need to start from the correct side of the lower pulley to make this work You will see what I mean when you do it.
  • Repeat the process to free the traction belt
  • Install the new belts by reversing the process starting with the traction belt. on 5, 6, 7 & 8 HP models the belts are identical.
  • Engage both belt idlers
  • If you moved any of the belt retaining fingers reset them so there is 1/16 to 1/8 inch of clearance when the belts are engaged
  • Rock the machine down and check any topside belt guides
  • Disengage both belt idlers
  • Reconnect the spark plug wire. Be sure that the metal terminal is aligned to reconnect to the spark plug terminal
  • Remove the bag from the gas cap if applicable
  • Replace the belt cover
  • Start and test
  • Note I have intentionally omitted running with the belt cover removed for trouble shooting. In some cases it will be appropriate to observe the belts for correct tracking on the idler rollers.


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Created January 2002 **** Updated March 2015