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.

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.



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.


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.
  • You will now see a bearing with a retaining collar, loosen the set screw in the black collar and use a drift pin and hammer or spanner in the plain hole to release the eccentric locking collar, try CCW but it could be the opposite. Remove the collar. If it is seized then you may have to grind one side away to free it. For this I use a 4 inch disc grinder and take a swipe out of the collar, much like trimming sideburns. When you see a paper thin layer of remaining metal a pair of pump pliers will probably wiggle it off. The use of Kroil, PB Blaster or Liquid Wrench along the way or well in advance can't hurt.
  • 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 use a puller to remove it from it's shaft. If you have a pickle fork (tie rod end tool) that's worth a try. If you cannot get a puller in there you can take an air hammer or punch and striking hammer to shatter the bearing outer race. Wear eye protection. It is suggested that this bearing be replaced when doing this job so wrecking it is of no consequence. This will leave the race on the shaft which can be split with a small disc grinder just like the prior collar.
  • 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
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.


The alternative is to unbolt both side plates and disconnect all of the linkages grab it by the axle and haul the whole pile of guts over to your bench, for a simple friction wheel change this usually does the trick.

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.


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 set-screw.
  • Find the drift pin hole in that collar, whack it CCW and it should loosen. If all else fails try CW. It could have been tightened in either direction.
  • Remove the collar and touch up the set-screw divot
  • Now its' time to get that bearing free......
  • 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.
  • If you can get a puller on the bearing, do so and remove it. You might get lucky carefully prying. If not you need to get rough.....
  • Put on some safety goggles. Using an air hammer or cold chisel and striking hammer shatter the outer bearing housing and dissect the bearing. This will get it out of the bucket assembly!
  • Now you just need to remove the inner race from the shaft, try tapping it. If that doesn't work you can gently grind it with a small disc grinder until it splits open. Don't cut into the shaft.
  • 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. Use a lawn mower blade balancer if nothing else.
  • 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 November 30 2008