Preemptive Maintenance For Your Trials Machine


Typically the winter months here in the northern tier of the US are good months to take some time to do some needed or preemptive maintenance on our Trials machines.


Maintenance, whether it be a once a year thorough going over or a quick pre/post-ride check,  can be as simple as a new spark plug, a change of transmission oil and clean the air filter or it can be much more involved.


All Trials bikes require maintenance, most require very little maintenance throughout the season, but bikes are made up of mechanical parts working together and inevitably all moving mechanical parts and systems will wear and require maintenance or replacement.  Some Trials riders also feel that admitting to doing maintenance on their bike is admitting that their bike is inferior to other bikes on the market since it required maintenance, again, all Trials bikes are an assembly of parts moving and working together for our enjoyment; these parts do need a small amount of your attention prior to or after a ride and the bike should be on a more in depth maintenance schedule at least once per year.

While changing the water pump seals on an older Trials bike recently I found that the bike would not start, not a problem, in the shop, but it could be very inconvenient on comp day or on a trail ride.  Upon removal of the air box to remove and clean the carburetor, I noticed that the air box exit port to the carburetor had been crushed and broken sometime in the past and was letting air into the intake system without going through the air filter.

The damage to the air box is very noticeable once the box is removed, but never seen as long as the box is on the bike. Notice the route of dirt into the carb associated with the break in the air box,  you diffidently want to find and correct a problem with a defective intake system before extensive damage is done to the engine.

Another common problem found on the older bikes is the rubber sleeves connecting the air box to the carb and the carb to the intake, these sleeves can be installed improperly, misaligned or folded over allowing unfiltered air to work its way into the carb and engine.  Age, heat and fuel will cause the rubber sleeves to harden, expand, shrink, warp and crack effecting the sealing and operation of the system.  An easy fix for most rubber sleeves that are in good condition other than being hard and out of shape, is to heat the rubber sleeve with a heat gun, once hot slide the sleeve into its proper location in the system, clamp it and let it cool, if the sleeve is not cracked this can extend the life of the old out of shape sleeve.  If the sleeve is cracked, replacement is needed.


Would this problem have been found without taking off the carb, most likely not, but if one time per season, when you are removing the air filter to be cleaned and oiled the air box is also removed and inspected, damage to the box, incorrectly attached intake rubber sleeves or lose sleeve clamps can be corrected before a lot of unfiltered air has a chance to get into the system and damage the intake system and the engine.


Another good thing to do once a year is to remove the fuel tank and dump all of the fuel out of the tank; you will be surprised at how much "stuff" gets in the fuel tank during a season.

This is the fuel from a tank, notice the straw that comes on the end of a WD40 spray bottle of carb cleaner can.  The dark particles could have been in the tank since it was new, but most are probably added over time with each fill up, and the other real culprit that can cause a lot of problems is the water that has collected over time in the tank.


Most riders change a rear tire at least once a year, and more often for most.  Before removing the wheel, check the wheel bearings by moving the wheel from side to side, looking for movement and/or noise coming from the wheel hub, then if the bearings feel and sounds okay, some simple maintenance is all that is needed when the wheel is off the bike, it takes just a few minutes to grease the hub bearings,


The bearing on the top right is new, notice the lack of grease; you can easily work at least a 1/2 teaspoon of grease into a new wheel hub bearing.  The pictured hub and center spacer, between the hub bearings, was taken from a hub that had no maintenance of the bearings and was ridden until the bearing came apart. The grooves in the hub and spacer are from the ball bearing rolling around the hub destroying everything while the bike was being ridden.



When removing and cleaning a spark arrestor and cleaning and re-oiling the air filter, after a day of riding;, take a few minutes to check all of the exhaust system mounting bolts and nuts.  Exhaust system mounting bolts and nuts do come loose,  with time a loose exhaust system will allow the mounting brackets to wear or break.

Both the spark arrestor and air filter were in need of service in a very bad way.  The customer complained about the loss of power on his bike and wanted a new cylinder and piston installed.  When the spark arrestor was removed no light from a flash light could be seen through the arrestor screen and the air filter is self explanatory.  Once the air flow problems were corrected the bike ran as it should without the requested expensive repairs.



A couple of mechanical systems that are out of sight out of mind are the front and rear suspension systems.  Both systems are tough and do an excellent job of taking a beating all season long, but they do need your attention. If not changing the fork oil and/or a rear dog bone linkage bearing or bushing inspection and lube, at least take note of the forks and the rear linkage. Are the forks aligned and moving up and down smoothly, a good crash can tweaked the forks in the clamps, forks that are misalignment can sometimes be noticed by a front fender that does not mount parallel over the front tire.  Also look at and listen for any looseness in the bars or squeaks in the front end, either could be an indication of a loose triple clamp, bars or steering head assembly and/or dry or worn steering head bearings.

This steering/triple clamp assembly was so loose a screwdriver would fit under the top nut.


At least once during the riding season, get down on the ground and look at and put a wrench on each bolt and nut in the rear suspension, especially on a new bike, as these bolts and nuts can loosen with riding. If you do find a lose bolt or nut in the rear suspension then you should check the system more often than not during the season.

Notice the bolt head lodged against the red frame as well as the wear in the bottom of the swing arm from the loose suspension.


While looking the rear linkage over be sure to check the rear sprocket bolts and nuts, these too do come loose and can be a real game stopper on the trail ride or during a comp.  Don't forget the look at and adjust the chain to its proper tension.

This bike was dragged and pushed out of the Utah Mountains after losing a rear sprocket completely on a trail ride.


I have tried to touch on some of the maintenance issues that are surprisingly seen more often than not in the shop.  It is inevitable that our trials machines will need some parts replaced over time, but a simple inspection and a couple of wrenches before or after each ride will help delay the inevitable and when the time comes to replace a worn part it should be only a part replacement and not a new wheel hub, cylinder and piston or transmission rebuild.


As always, don't hesitate to contact Thumbs Up Trials Supply with any questions you may have, if I don't have an answer for you I will help you find the answer. Also go to for the maintenance blogs listed above as well as part catalogs on all brands of Trials motorcycles and much more.