The Yamaha YZ85 is a popular motocross bike for young riders to experience the thrill of motocross racing.
The YZ85 is a lightweight, agile, and powerful machine known for its reliability across various terrain and challenges.
But the Yamaha YZ85 isn’t immune to performance issues. This article lists the 7 most common problems with the Yamaha YZ85, their causes, symptoms, and solutions.
Table of Contents
1. Lowering the Bike Causes Front End Head Shake
One of the most common causes of front head shake or wobble on a Yamaha YZ85 is lowering the bike too much or unevenly. Front-end wobble or head shake is when the front wheel starts to wobble from side to side, making the handlebars shake uncontrollably.
This can be very scary and dangerous, affecting your steering and balance and may even cause you to crash.
While some claim that the Yamaha YZ85 shakes as soon as it hits high speeds, others theorize that the head-shaking issues indirectly stem from the bike’s tall stature.
The YZ85 is intended to be a kid’s motocross bike, and children around ages 10-13 vary in size. Various kits are available, allowing parents to tailor the bike’s height to their child’s body type and stature.
“My boy loves his new YZ85/105. I put a DeVol lowering link on it and lowered the forks as much as possible. I can’t lower them anymore because of the fork’s tapper. He came off the bike Friday, going flat out 5th on flat ground, tank slapping like I have only seen on a street bike. He is 4’10”, weighing in at 70 lbs. He is 12 this week. The head shake seems to follow him around all day.”
Many riders lower their bikes to fit their height or preference, but this can negatively impact the bike’s handling and stability.
For example, if you lower the forks too much in the triple clamps, you will change the bike’s geometry and reduce the rake and trail. These angle settings determine how stable your bike is at speed.
Lowering the forks also reduces ground clearance and suspension travel, affecting your performance and comfort.
Lowering your bike more in the rear than in the front will create an imbalance in the motorcycle, leading to oversteering and stability loss.
So how can you fix or prevent front-end head shake on your YZ85?
- Avoid lowering your bike too much or unevenly. If you have to lower your bike, do it proportionally on both ends and keep the original geometry as close as possible.
- Check other things that may cause a head shake, such as tire pressure, wheel alignment, steering stem bearings, fork oil level, and suspension settings.
- By keeping your bike in good condition and properly adjusted, you can reduce the chance of front-end head shake and enjoy a smoother ride.
2. Tight Gear Ratio
Another common problem with the Yamaha YZ85 is its tight or close gearing ratio. Gears that are close in proportion require constant shifting for optimal engine power. While this suits some aggressive motocross riding styles, other riders complain it’s tiring or distracting.
- The standard transmission for a YZ85 has six gears with these ratios:
- 1st: 2.666 2nd: 1.937 3rd: 1.556 4th: 1.333 5th: 1.150 6th: 1.043
- These ratios are very close together, giving your YZ85 tight gearing.
Some riders like the tight, aggressive gearing because it gives them more control and responsiveness. They can use the clutch and the throttle to adjust their speed and power, and they can always find the right gear for any situation.
Tight gearing also helps the engine rev faster and produce more power.
However, some riders don’t like tight gearing because it makes them feel like they are always between gears, and they have to shift more often.
Tight gearing also limits the top speed and acceleration of the bike, and it can make the engine run hotter and wear out faster.
So how can you change the gearing on your YZ85? The easiest way is to change the sprockets. The sprockets are the toothed wheels that connect the chain to the engine and the rear wheel. By changing the number of teeth on the sprockets, you can change the final drive ratio of the bike.
Changing the gearing on your YZ85 can make a big difference in how your bike performs and suits your riding style. Whether you prefer tight or loose gearing, you can find your ideal setup by changing either the sprockets or the transmission.
Just remember to do your research before making any changes, and always test your bike carefully after any modifications. If you’re unsure, leave the upgrades to the pros.
3. Subframe Problems
Yamaha YZ85 owners and reviewers sometimes complain about the bike’s subframe. Yamaha updated the 2022-year model with an aluminum subframe to shave off weight. Riders complain that it’s fragile or bulky, and their boots can get stuck.
“The YZ85 switched from steel to an aluminum subframe to drop over 1/2 a pound and help make room for a straighter intake tract…” (Source: Motocross Action Magazine)
“… some of our test riders’ boots got caught on the lower subframe bolt.” (Source: Motocross Action Magazine)
While the boots getting stuck isn’t the most common problem, it can happen if you have large boots or if your Yahm’s subframe bolt is too long or loose.
To avoid this problem, check the subframe bolt regularly and ensure it is tight and secure.
Cut off the excess bolt or use a different bolt that does not protrude as much, and adjust your bootstraps or buckles to prevent them from catching on the bolt.
Another possible problem with the newer aluminum version of the YZ85’s subframe is bending or breaking.
This can happen if you crash hard or land awkwardly on the bike’s rear end. A bent or broken subframe can affect the alignment and stability of your YZ85.
A compromised subframe also risks damage to other parts, such as the airbox, the seat, or the rear fender.
To avoid this problem, ride carefully and avoid hitting obstacles or landing flat on jumps.
Inspect your subframe regularly and look for any signs of cracks, dents, or deformation.
If you notice any damage, replace your subframe as soon as possible – you can buy a new subframe from Yamaha or an aftermarket supplier.
4. Fork Lugs Drop Too Low
Some riders have complained that their Yamaha YZ85’s fork lugs drop too far below the front axle, causing them to drag when riding through ruts. This can affect the steering and handling of the bike, making it harder to turn.
Fork lugs are the parts of your Yamaha’s forks that connect to the front axle and the brake caliper.
They’re located at the bottom of your YZ85’s fork legs and have holes for the axle and the brake bolts.
The fork lugs affect the handling and suspension of the bike as they determine how much the forks drop below the axle.
The YZ85 has adjustable fork lugs that allow you to raise or lower the forks in the triple clamps.
By doing this, you can change the ride height and geometry of the bike and fine-tune its performance and feel.
Raising the forks in the clamps will lower the front end and increase the rake and trail, making the bike more stable at high speeds and less responsive in corners.
Lowering the forks in the clamps will raise the front end and decrease the rake and trail, making the bike less stable at high speeds and more responsive in corners.
To avoid this problem, don’t lower the forks too much in the clamps, and keep your lugs nice and tight so they don’t loosen and drop the fork settings while you ride.
Adjust the fork lugs by loosening the triple clamp bolts and sliding the forks up or down as desired.
Measure both sides to ensure they are even, and securely tighten the bolts.
Check your sag and suspension settings after adjusting the fork lugs, as they may change due to the new rider height.
5. Faulty Head Gaskets
While this doesn’t indicate a design flaw with the YZ85, any high-revving dirt bike is susceptible to worn engine head gaskets. This can lead to overheating, power loss, white exhaust smoke, or milky/foamy oil. A worn head gasket left untreated can cause engine failure.
“I have a problem I would like some opinions on. My buddy has an ’04 yz 85 that had a bad head gasket, so anti-freeze leaked inside the motor.”
“[With a] bad [head] gasket, coolant can enter from the water jacket into the cylinder on the down stroke of the piston. As for flushing it, if it is a head gasket, then once you replace it, simply running the bike should burn out any residual coolant.”
The head gasket is a thin metal seal between the cylinder head and the cylinder block. It prevents combustion gases, oil, and coolant from mixing.
The head gasket is exposed to high pressure and temperature and can wear out or crack over time. This can cause a leak that allows the coolant to enter the cylinder and contaminate the engine oil.
To replace a bad head gasket, you’ll need to remove the cylinder head and inspect it for cracks or warping.
Clean the mating surfaces of the head and the block and install a new head gasket.
Torque the head bolts to the correct specifications, and reinstall the other parts, such as the spark plug, carburetor, radiator, and hoses. You’ll also need to refill the coolant and change the oil and filter.
Replacing a bad head gasket is a complex and time-consuming process that requires special tools and skills. If you need more confidence or experience in doing it yourself, you should take your bike to a professional mechanic.
6. Water Pump Failure
A Yamaha YZ85’s water pump seal can wear out early and fail due to weathering, corrosion, or contamination. This can cause a leak that allows the coolant to mix with the transmission oil, causing problems such as overheating, loss of power, poor shifting, and clutch slippage.
If left untreated, a water pump seal leak can damage the engine and the transmission.
Your YZ85’s water pump circulates coolant through the engine and the radiator. It is driven by a gear that meshes with the crankshaft.
The water pump has a shaft that rotates inside a housing and a seal that prevents the coolant from leaking into the transmission oil.
Fixing a water pump seal leak is a relatively simple and inexpensive process that requires essential tools and skills, though there’s no shame in taking her to a po if you’re unsure.
To fix a water pump seal leak, drain the coolant and the transmission oil and remove the right-side engine cover.
Remove the water pump impeller and inspect it for damage or wear.
Replace the water pump seal and gasket and reinstall the impeller and the cover. Refill the coolant and change the transmission oil and filter.
7. Gas Cap Hard to Remove
Another common complaint regarding the Yamaha YZ85 is that its gas cap is hard to remove, requiring more force to unscrew it than on similar models.
The gas cap is the part that covers the fuel tank opening and prevents dirt, water, and debris from entering the tank. It also helps maintain the pressure and the vacuum inside the tank.
The gas cap has a thread that screws onto the tank neck and a vent that allows air to escape or enter the tank.
Riders complain that the thread pitch on the Yamaha YZ85’s gas cap is too fine.
This means that the thread has too many turns per inch, and it takes more rotations to unscrew the cap.
A fine thread can also be more prone to cross-threading, which means that the thread is not aligned correctly, and it damages the cap or the tank neck.
What Are the Pros and Cons of the Yamaha YZ85?
- Lightweight chassis
- Readily available and replaceable parts
- Agile handling
- Durable and reliable
- High-revving engine power
- Lack of low-end torque
- High maintenance
- Tight Gearing
- Subframe Problems
- Gas cap hard to unscrew
- Fork lugs drop too low
What Do the Reviews Say?
-“The mini riding and racing world is alive and well, and manufacturers like Yamaha are taking notice. The YZ85 has been a staple in the minibike scene since, well, practically since the beginning of time. It’s the bike that catapulted careers for champs like Josh Hill and Chase Sexton and continues to be a platform for riders and racers alike.”
– “The chassis received several improvements, and the result is a stable ride. Yamaha reworked the rigidity and strength of the steel frame with new swingarm bracket thicknesses and changes in the lower motor mounts. There’s also a new one-piece aluminum swingarm and solid rear axle.”
– “The YZ85 is a legend in the youth motocross scene. It’s the bike that inspired many of today’s top professional racers and helped them on their path to MX glory. And with its punchy performance, the YZ85 is the dirt bike that can turn young riders’ dreams into reality.”
What Are Some Alternative Models?
|KTM 85 SX
|Husqvarna TC 85
Note: These are estimations. The actual MPG for these models is unavailable because they are two-stroke dirt bikes that use premixed fuel and oil. The fuel consumption may vary depending on the riding conditions, the fuel-oil ratio, and the jetting settings.
What’s the Resale Value of the Yamaha YZ85?
|Used Listing Price