The Yamaha TDM 850, a motorcycle that dared to be different, blended the upright riding position of an adventure bike with the punchy parallel-twin engine of a sport bike. It offered a unique riding experience, and for many, it was a fantastic machine. However, like any motorcycle, the TDM 850 wasn't without its quirks and potential problems. Understanding these issues is crucial for potential buyers and current owners alike, ensuring a smoother and more enjoyable riding experience.

What's the Deal with the TDM 850 Anyway? A Quick Recap

Before diving into the nitty-gritty of potential problems, let's briefly revisit what made the TDM 850 special. Produced from 1991 to 2001 (with slight variations and regional differences), the TDM 850 boasted a torquey parallel-twin engine, a comfortable riding position, and decent handling. It was often praised for its versatility – capable of handling daily commutes, weekend trips, and even some light touring. The TDM 850 filled a niche, offering something different from the inline-four sportbikes and the heavier, more cumbersome adventure bikes of the time. Its distinctive styling also made it stand out from the crowd.

The Elephant in the Room: Cam Chain Tensioner Woes

One of the most frequently discussed and well-documented issues with the TDM 850, particularly the earlier models (4TX), is the cam chain tensioner (CCT). The original design was prone to failure, leading to excessive cam chain noise, potential engine damage, and ultimately, a headache for the owner.

  • The Problem: The original CCT design relied on a ratchet mechanism to maintain tension on the cam chain. This mechanism could wear out or fail, allowing the tensioner to retract and the cam chain to slacken.
  • Symptoms: The most obvious symptom is a rattling or clattering noise coming from the engine, especially on startup or at lower RPMs. This noise can worsen over time.
  • The Fix: The good news is that this issue is well-known, and there are readily available solutions. The most common fix is to replace the original CCT with an upgraded, manual cam chain tensioner. Manual tensioners allow you to manually adjust the cam chain tension, providing greater control and reliability. Another option is a later model OEM Automatic Cam Chain Tensioner from Yamaha. Several aftermarket options are also available.
  • Preventative Measures: Regularly checking the cam chain tension and listening for unusual noises is crucial, especially on older models. If you're buying a used TDM 850, inquire about the CCT history.

Carbs Out of Sync: A Common Complaint

The TDM 850 uses two Mikuni carburetors, and like any carbureted engine, maintaining proper synchronization is essential for smooth running and optimal performance. Carburetor synchronization ensures that both cylinders are drawing the same amount of air and fuel, resulting in a balanced and efficient engine.

  • The Problem: Over time, the carburetors can fall out of sync due to wear and tear, vibration, and changes in atmospheric conditions.
  • Symptoms: Common symptoms of out-of-sync carburetors include:
    • Rough idling
    • Hesitation or stumbling during acceleration
    • Poor fuel economy
    • Uneven throttle response
  • The Fix: Carburetor synchronization is a relatively straightforward procedure that can be performed with the right tools and knowledge. A vacuum gauge is used to measure the vacuum in each carburetor, and the carburetors are adjusted until the vacuum readings are equal. It's often recommended to have this done by a qualified mechanic, especially if you're not comfortable working on carburetors.
  • Preventative Measures: Regular maintenance, including cleaning the carburetors and checking the synchronization, can help prevent these issues.

Fuel Pump Frustrations: When the Engine Starves

The fuel pump on the TDM 850 can sometimes become a source of frustration. While not as prevalent as the CCT issue, fuel pump problems can lead to stalling, poor performance, and difficulty starting.

  • The Problem: The fuel pump can fail due to age, corrosion, or debris in the fuel system. The electrical contacts can also corrode, leading to intermittent operation.
  • Symptoms: Symptoms of a failing fuel pump include:
    • Engine stalling, especially under acceleration
    • Difficulty starting the engine
    • Poor fuel economy
    • Hesitation or lack of power
  • The Fix: Replacing the fuel pump is the most common solution. Aftermarket fuel pumps are readily available and often more reliable than the original. Cleaning the fuel tank and fuel lines can also help prevent future problems.
  • Preventative Measures: Using a fuel stabilizer, especially when storing the bike for extended periods, can help prevent corrosion and fuel degradation. Regularly inspecting the fuel lines and connections can also help identify potential problems early on.

Regulator/Rectifier Roulette: An Electrical Gremlin

The regulator/rectifier (R/R) is responsible for regulating the voltage from the alternator and charging the battery. A failing R/R can lead to a variety of electrical problems, including a dead battery, blown fuses, and even damage to other electrical components.

  • The Problem: The R/R can overheat and fail due to age, poor ventilation, or excessive electrical load.
  • Symptoms: Common symptoms of a failing R/R include:
    • Battery not charging
    • Overcharging the battery (boiling battery acid)
    • Dim headlights
    • Blown fuses
  • The Fix: Replacing the R/R is the best solution. Many owners choose to upgrade to a MOSFET-type R/R, which is more efficient and reliable than the original. Relocating the R/R to a location with better airflow can also help prevent overheating.
  • Preventative Measures: Regularly checking the battery voltage and inspecting the R/R for signs of overheating can help identify potential problems early on.

Suspension Sag: Time for an Upgrade?

While the TDM 850's suspension was adequate for its intended purpose, it's often one of the first areas that owners look to upgrade. The original suspension components can become worn over time, leading to a loss of damping and a less comfortable ride.

  • The Problem: The front fork springs can sag, and the rear shock can lose its damping ability. This can result in a bouncy ride, poor handling, and reduced stability.
  • Symptoms: Symptoms of worn suspension include:
    • Excessive front-end dive during braking
    • Bouncing or wallowing over bumps
    • Poor handling and stability
  • The Fix: Upgrading the front fork springs and replacing the rear shock are common modifications. Progressive springs can improve ride quality and handling, and a higher-quality rear shock can provide better damping and adjustability.
  • Preventative Measures: Regularly inspecting the suspension components for leaks or damage can help identify potential problems early on.

Bodywork Blues: Cracks and Vibrations

The TDM 850's bodywork, while distinctive, can be prone to cracking and vibration, especially on older models.

  • The Problem: The plastic fairings can crack due to age, vibration, or impact. The mounting points can also become loose, leading to rattling and vibration.
  • Symptoms: Common symptoms include:
    • Cracked fairings
    • Loose or missing fasteners
    • Rattling or vibrating bodywork
  • The Fix: Repairing or replacing the damaged bodywork is the most common solution. Using rubber washers or other vibration-dampening materials can help prevent future problems.
  • Preventative Measures: Regularly inspecting the bodywork and tightening any loose fasteners can help prevent cracks and vibrations.

Exhaust System Erosion: Rust Never Sleeps

The exhaust system on the TDM 850, particularly the original system, can be susceptible to rust and corrosion, especially in areas with harsh weather conditions.

  • The Problem: Rust can weaken the exhaust system, leading to leaks and reduced performance. The exhaust headers are particularly vulnerable to corrosion.
  • Symptoms: Symptoms of exhaust system problems include:
    • Rust or corrosion on the exhaust pipes
    • Exhaust leaks
    • Reduced performance
    • Increased noise
  • The Fix: Repairing or replacing the corroded exhaust components is the best solution. Aftermarket stainless steel exhaust systems are available and offer improved durability.
  • Preventative Measures: Applying a rust inhibitor to the exhaust system can help prevent corrosion. Regularly inspecting the exhaust system for signs of rust or damage can also help identify potential problems early on.

Frequently Asked Questions About TDM 850 Problems

  • Is the cam chain tensioner issue really that bad? Yes, on the earlier models (4TX), it's a well-known problem. Replacing it with an upgraded tensioner is highly recommended.

  • How often should I synchronize the carburetors? Every 12,000 miles or whenever you notice symptoms like rough idling or poor throttle response.

  • Are aftermarket fuel pumps better than the original? In many cases, yes. Aftermarket pumps are often more reliable and can provide better fuel flow.

  • Is the TDM 850 a reliable bike overall? Despite these potential issues, the TDM 850 is generally considered a reliable bike, especially when properly maintained.

  • Where can I find parts for my TDM 850? Online retailers like eBay, CMSNL, and Wemoto offer a wide range of parts for the TDM 850.

The Takeaway: Knowledge is Power

The Yamaha TDM 850 is a unique and enjoyable motorcycle, but understanding its potential problems is crucial for a smooth ownership experience. By being aware of these issues and taking preventative measures, you can keep your TDM 850 running strong for years to come. Don't let these potential problems scare you away, these issues are well-documented and can be easily addressed with the right knowledge and maintenance.