Chassis Special: Part 5 – Troubleshooting and Basics

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Chassis Special: Part 5 - Troubleshooting and Basics
Jahn

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landing gear & Spring elements

Suspension special: Part 5 – Troubleshooting and basics

Suspension special: troubleshooting and basics
All-round check for the motorcycle chassis

Content of

If the box turns stubbornly around the corner or stumbles more than walking cleanly in a straight line, there can be various reasons. A thorough all-round check is required before extensive setup changes.

Volkmar Jacob

October 13, 2012


Chassis Special: Part 5 - Troubleshooting and Basics


Jahn

Sufficient chain slack forms, among other things, the basis for a perfectly working suspension. A small laser measuring device checks the chain alignment.

The world is complicated and sometimes it seems like it is getting more confused every day. Fortunately, things are a little easier with motorcycles. They are complex structures too, and the interaction of the individual chassis components in particular often raises questions. But cause and effect are often clearly linked here. Sometimes it’s the little things that affect driving behavior. Before the pilot completely messes up the set-up when the vehicle is driving lousy, he should first check various things. Only when these sources of error have been eliminated do changes to the setup follow: How do you adjust the chassis for which problem? More on this in the next issue.

tire

It may sound banal, but tire pressure has an immense effect on driving behavior. For example, if it is too low at the front, the bike will turn in with difficulty and require high steering forces. In addition, feedback and steering precision suffer, and the machine stands up clearly when braking, even at a slight lean angle. A slightly lower air pressure than prescribed in the front and rear usually improves performance because the larger contact area (“Laces”) means more grip. In addition, the so-called fulling, i.e. the deformation of the tire, increases, which means that the rubber reaches temperature more quickly. In addition, the self-damping increases. Particularly on the racetrack, the air pressure is sometimes significantly reduced – even on approved tires. In case of doubt, you should definitely fill the soles with the manufacturer’s recommended air pressure – especially when troubleshooting. Another important aspect is wear and tear. Depending on the skin, the properties deteriorate noticeably in a worn condition. If the box behaves strangely, check the tires first!

Check screw connections, frame, swing arm

One of the first steps in the chassis check is to check screw connections. Relevant to the chassis – here are: front and rear wheel axles, swing arm axles, engine mountings on the frame, screw connection of the rear to the main frame, suspension strut, deflection, handlebar clamps, central nut of the upper and the clamps of the lower triple clamp. Important: check the lower clamps with a torque wrench. If the screws are too tight, this can have a negative effect on the response of the fork. During this work it is advisable to examine the frame and the swing arm for possible cracks.

Steering damper, steering head bearings, wheel bearings

Completely relieve the front when checking these components. The front wheel must not touch the ground and the steering must run freely. If necessary, a helper can lift the machine over the side stand. Racing bikes require a special stand that does not attach to the underside of the steering head or fork feet. First step: check the steering damper. To do this, check the freedom of movement on the screw connections. If the damper is correctly installed, the ball heads can move a little despite the screws being tightened. With rubber covers (example: Suzuki GSX-R models) make sure that the thin spacers are inserted and that the sealing lips do not press too hard on the ball joint. Then swivel the steering back and forth minimally (two or three degrees). There should be no resistance during this exercise.

It is different when controlling the damping. To do this, remove the steering damper and move the damper rod several times over the entire stroke. The part must not hook and must also dampen evenly at the reversal point. Otherwise have it revised or a new damper installed. Now relieve the load on the front again and slowly swivel the handlebars several times from stop to stop. The steering should run completely freely, easily and without resistance. If it doesn’t, the steering head bearing may be too tight and needs to be corrected. If you can even feel the rolling elements raster around the straight-ahead position, this indicates a defective bearing – replace it! When checking the steering head bearing again, grab the undersides of the fork feet and move them back and forth in the direction of travel. The bearing must have no play. If necessary, tighten carefully. To check the wheel bearing, grasp the front wheel sideways and with both hands on opposite sides and move it back and forth. No game may occur here either. The bearings on the rear wheel are checked in the same way.


Chassis Special: Part 5 - Troubleshooting and Basics


Jahn

Both inner tubes of the fork and the damper rod of the shock absorber must be dust dry. Leaks falsify the damping behavior.

Air cushion fork

The air cushion is an empty space between the fork oil and the upper sealing plug. The size of the pad affects the way the fork works; it is checked without springs.

However, expanding them requires a certain amount of screwdriving skills. Unfortunately, explaining the individual steps is beyond the scope of this story. So at this point only: With the springs removed, the front is lowered to the lower stop of the fork. In this position, measure the space between the oil and the upper edge of the fork with a depth gauge or folding rule. In both spars, the dimensions should correspond to the information provided by the manufacturer or tuner. If necessary, adjust the air cushion by drawing off or adding oil.

Fork and shock absorber tightness

If the fork and / or shock absorber lose oil, this can in extreme cases lead to massive suspension problems. Regardless, the load may slip on your own oil. Therefore check both inner tubes of the fork and the shock absorber rod of the shock absorber. Everything has to be bone dry. Otherwise seal (let)!

Play in the deflection, swing arm bearing, tension struts, deflection lever, upper and lower strut mounts: everything is directly or indirectly connected to one another. However, many connections may mean a lot of play between the components. If it is too big, it can lead to restlessness (rattling, rear wheel punches). Especially if the bike lifts off one after the other and touches the road again, as happens, for example, when anchoring sharply over bumps. Completely relieve the rear wheel and swing arm when checking. Use a special stand or pull the bike back over the side stand. Then move the swing arm up and down at the rear end. Two millimeters of play on the rear axle is already too much on a super sports motorcycle. Here, precisely fitting bearings and connections (special parts) provide a remedy. The swing arm bearing is also checked with the rear wheel unloaded. To do this, grasp the swing arm at the rear end and try to move the swing arm transversely to the direction of travel. The swing arm bearing must not have any play. A slight axial play on the bearings of up to 0.5 millimeters, on the other hand, is harmless.

Chain slack, chain alignment

Secondary chains need slack. This ensures that they do not interfere with the work of the rear suspension. In addition, the chain slack protects the transmission output bearing and the chain wears out less quickly. The sag is usually checked under load, for example with the driver sitting on the vehicle. In this condition, the lower part of the chain between the pinion and the sprocket must have a play of around 20 to 30 millimeters (observe manufacturer’s information). This ensures that the links are not stretched too much, even when the compression is strong. The chain is tautest when the axes of the pinion, swing arm and rear wheel are in line. With sporty bikes, however, this rarely occurs when driving. In addition to the slack, the chain alignment is also an issue: Do the pinion and sprocket run exactly in one line? If there is a misalignment, the secondary drive wears out more quickly, and the increased friction also has a performance-reducing effect. For the check, the trade offers easy-to-use laser measuring devices (example: Louis, 40 euros). If there is a misalignment, the secondary drive should be distanced – a job for advanced users or professionals.

Offset of the wheel contact points, track

Are the center lines of the front and rear wheels exactly in line? Experience shows that this is not the case with all series machines. If there is a significant offset, the aiming accuracy, steering behavior and driving stability suffer. There are also measuring tools with laser technology for checking. However, they cost a few hundred. If you want to save yourself the bills, you need two measuring rods about two meters long – preferably made of steel or aluminum. Mutual application checks whether the slats are completely straight. Place the measuring rods flat on the right and left of the outer rim of the rear wheel so that they extend to the front wheel. Dismantle both tires for accurate measurement results. In addition, the steering must be exactly in the middle. To align the steering, measure the distance between rim and crossbar at two points on one side. The wheel is only absolutely straight if the dimensions are identical. Similarly, measure the corresponding points on the other side of the rim. Ideally, the four dimensions match. If not, the wheels are offset or the chain tensioners on the rear wheel are not aligned. Professional racing teams distance the rear wheel even if there are deviations of a few millimeters. That too is a job for professionals.

ergonomics

Those who feel comfortable on the bike have more fun burning. In addition, the lap times tumble. Here is the list of questions: Are the handlebars height and spread? Are the hand levers set correctly? Is the seat height correct? Does the seat offer enough space for hanging-off and for folding behind the paneling? Does the knee angle fit? Are the footrests in a comfortable position or are they too far forward or backward? Do the shift and brake levers fit? Sometimes accessories such as adjustable handlebars, footrests or levers help. Trying it out is worth it!


Chassis Special: Part 5 - Troubleshooting and Basics


Jahn

Also works: checking of track offset and wheel contact points without an expensive measuring device. A large offset of the front and rear wheels has a negative effect on driving behavior.

Specialists

Complete measurements:

Herbert Strassmaier
83052 Heufeld / Bruckmuhl Telephone: 0 80 61/9 36 92 20 www.strassmaier.de

Scheibner Limited
38126 Braunschweig Telephone: 05 31/79 02 59 www.scheibner.de

Partial measurements:

Alpha Racing
83071 Stephanskirchen Telephone: 0 80 36/30 31 30 www.alpharacing.com

Koster Motorcycle GmbH
89358 Goldbach Telephone: 0 82 25/8 35 www.motorrad-koester.de

Zupin Moto-Sport
Trostberger Str. 26 83301 Traunreut Telephone: 0 86 69/84 80 www.zupin.de

Precision parts / bearings:

Emil Schwarz
73660 Urbach Telephone: 0 71 81/99 52 90 www.emilschwarz.de

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