TMP Gearboxes: Maintenance and Repair Guide

For those navigating the world of marine propulsion, the TMP gearbox is a familiar sight. But who is behind these robust units, and what’s involved in keeping them in prime condition? Thamesway Marine has been the driving force behind the TMP 12000 range of gearboxes since 1982, ensuring that spares, service, and new or replacement units are readily available. This article delves into the specifics of TMP gearboxes, offering insights into their maintenance, common repair challenges, and essential assembly tips.

Understanding TMP Gearbox Origins

Thamesway Marine, established in 1982, is the sole manufacturer and specialist for the TMP gearbox range. Their long-standing commitment means they possess in-depth knowledge and a comprehensive supply chain for parts and expertise. Whether you need a specific spare part or a complete replacement unit, Thamesway Marine is the go-to source.

Is the TMP Gearbox a DIY Repair? The Reality Check

For the seasoned DIY enthusiast, the TMP gearbox presents a unique challenge. While not inherently complex in its design, its practical repairability by an amateur is often limited. The gearboxes are substantial and can be awkward to handle, requiring significant physical effort and careful maneuvering. A key issue arises from the materials used: a combination of alloy castings and steel studs. In the corrosive environment of saltwater, these studs can become 'frozen' into their housings. Separating them often requires considerable heat, a great deal of patience, and meticulous care to prevent damage to the precision-machined faces of the castings.

Furthermore, the gearbox is typically attached to the engine bell housing via internal nuts. This means that to access certain components, the entire gearbox and bell housing assembly must be removed as a single unit. Given that the bell housing often supports the rear engine mounts, it’s usually necessary to safely support the engine before commencing removal. It’s a wise tip to loosen the Output Coupling and Transfer Shaft nuts while the gearbox is still connected to the engine, making the process more manageable.

Specifics of Gearbox Removal

To disconnect the gearbox from the engine, a rearward movement of approximately 2.0 inches is required. However, installations on Mercedes engines might demand around 6.0 inches of clearance, unless the studs are detached from the engine backplate.

When the gearbox features a spline input, disengagement is usually straightforward. The situation can be more complicated with an 8-bush input, common in Perkins and Mercedes installations. Here, rust can seize the bushes into the flywheel. A tell-tale sign of this is when the gearbox housing 'bounces' as the rubber inserts within the bushes stretch under load. A proven solution involves carefully cutting a 2.0-inch square access hole into the housing. Through this aperture, penetrating oil (like WD-40) can be applied, and a lever can be inserted between the gearbox flange and the flywheel, adjacent to each bush, to break the seizure.

Essential Spares and Assembly Hints

Successfully reassembling a TMP gearbox requires the correct parts. Thamesway Marine offers comprehensive kits and individual components. Here’s a breakdown of common parts needed for different configurations:

Direct Drive Gearboxes (e.g., TM 12090)

Reduction Gearboxes

Critical Areas for Inspection During Maintenance

Regular inspection of key components is vital to prevent premature failure and ensure optimal performance. Pay close attention to the following areas:

Area 1: Input Shaft and Oil Pump

• Input Flange / Input Shaft: Check for wear on the surface where the oil seal runs.
• Oil Pump: Inspect the pressure plate face for scoring or wear. Examine the oil pump gears and shafts for ovality or wear in their respective body bushes.

Area 2: Clutch Linings

The clutch linings are critical for smooth gear changes. A common issue is wear on the non-active face of the lining, which can manifest as deep 'gramophone groove' marks on the clutch element. The lining may also become recessed into the clutch element. Note that modern replacement clutch linings often require bonding, unlike older types that might have been riveted.

Area 3: Sealing Rings and Planet Gears

• Square Section Sealing Ring: Ensure this ring is intact and free from damage.
• Planet Gear Bushes and Shafts: Excessive wear in these components can lead to increased noise and a loss of oil pressure.

Area 4: Bearings and Casting Faces

• Bearings: Specifically check bearing TM 12021 (referencing Fig 1, point 3.18 on MK II models) for signs of wear or damage.
• Casting Faces: After removing or replacing bearings, it's crucial to check the faces of the castings for any distortion. Warped faces can lead to leaks and improper sealing.

Area 5: Oil Seal Spacer and Water Drains

• Oil Seal Spacer (TM 12410): Examine the running surface of this spacer for wear.
• Water Drain Holes: Ensure these are completely clear of any blockages to prevent water ingress and corrosion.

Important Cautions for Assembly

When reassembling the TMP gearbox, adhere to these critical guidelines:

• Torque Settings: Be extremely careful not to overtighten nuts. The threads in the aluminium casings are delicate and can be easily stripped.
• Thread Repair: If threads are inadvertently stripped, they can often be repaired effectively using Helicoil thread inserts.

Frequently Asked Questions

Q1: Who manufactures the TMP 12000 gearbox?
A1: Thamesway Marine has been producing the TMP gearbox range since 1982.

Q2: Can I repair my TMP gearbox myself?
A2: While not impossible, DIY repairs are challenging due to the gearbox's weight, awkwardness, and the potential for seized components in saltwater environments. Professional expertise is often recommended.

Q3: Where can I get spare parts for my TMP gearbox?
A3: All spares and service parts are available directly from Thamesway Marine.

Q4: What is a common issue when disconnecting the gearbox from the flywheel on older installations?
A4: Rust can seize the bushes into the flywheel, especially on 8-bush input configurations. This often requires cutting an access hole to apply penetrating oil and use a lever.

Q5: What should I be careful about during re-assembly?
A5: Avoid overtightening nuts, as the aluminium casings have easily stripped threads. Always use a torque wrench where specified and consider thread repair inserts if needed.

Maintaining your TMP gearbox is essential for reliable marine operation. By understanding its origins, common pitfalls, and adhering to best practices for maintenance and assembly, you can ensure longevity and performance. For detailed procedures, a workshop manual is available from Thamesway Marine, providing comprehensive guidance for those undertaking repairs.

If you want to read more articles similar to TMP Gearboxes: Maintenance and Repair Guide, you can visit the Automotive category.