Dodge Diplomat Engine Timing Set Replacement Guide: 1977-1984
Keep your classic Diplomat's Slant-6 or V8 engine running strong and in-time with the right parts.
- If you have the original timing set, especially on a V8, plan to replace it as preventative maintenance.
- Always upgrade from a factory nylon gear to an all-metal timing set.
- A 'double roller' chain is a worthwhile durability upgrade for both Slant-6 and V8 engines.
- Always replace the chain and both gears as a complete set, along with the timing cover gasket and front crank seal.
Is Your Diplomat's Timing Chain on its Last Legs?
For 1977-1984 Dodge Diplomats, especially those with the 318 or 360 V8 engines, the original timing set is a known weak point. Many came from the factory with a camshaft gear that had nylon plastic teeth. After decades of heat and age, this nylon becomes brittle, cracks, and can break off. These broken pieces fall into the oil pan, where they can clog the oil pump pickup screen and starve the engine of oil, leading to major damage. Even without breaking, the timing chain itself can stretch over time, causing poor performance.
Symptoms of a Failing Timing Set
- Engine Rattle: A rattling or scraping noise from the front of the engine that may quiet down as the engine warms up.
- Poor Performance: The engine may feel sluggish, lack power, or hesitate during acceleration.
- Engine Misfires: A stretched chain can jump a tooth on the gears, throwing off the engine's timing and causing it to run rough or misfire.
- Metal Shavings in Oil: During an oil change, you might see small, shiny metal or plastic bits in the used oil. This can be from the chain or gears wearing out.
- Engine Won't Start: If the chain breaks completely, the camshaft will stop turning, and the engine will not start.
Choosing the Right Aftermarket Timing Set
Since original OEM parts are largely unavailable, the aftermarket is your go-to source. The good news is that many aftermarket options are significant upgrades over the original factory parts. The most important choice is to get an all-metal set and get rid of the old nylon gear.
Good: Standard Replacement (OE Quality)
These brands offer reliable, all-metal replacements that are perfect for a daily driver or stock restoration. They are a solid upgrade over the original nylon-toothed gear setup.
- Melling: A highly trusted name in the Mopar community for timing sets and oil pumps. Known for consistent quality and durability.
- Cloyes (Standard): A long-standing brand that makes reliable OE-style replacements. For a stock engine, their standard kits are a dependable choice.
- INA: A well-known manufacturer of quality parts, though less commonly discussed for classic Mopar engines. Generally considered a safe bet for OE-level quality.
Better: Heavy-Duty & Performance
For added strength, durability, or high-performance engine builds, these are excellent choices. They often feature stronger chains and more precise gears.
- Melling Select Performance: Melling's premium line, offering enhanced durability for engines that work hard.
- Edelbrock: A top name in performance parts. Their timing sets are known to be durable and are popular for mild performance builds.
- Cloyes (True Roller / Billet): Cloyes' premium offerings, like their "True Roller" sets, are highly regarded for strength and timing accuracy in the Mopar community. These are a step up from their standard kits.
Estimated Costs for Timing Set Replacement
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Timing Set | $32 - $168 |
| Shop Labor | $450 - $700 |
| Total Estimated Cost | $482 - $868 |
Cost estimates are for reference only and can vary based on location, the specific parts chosen, and shop labor rates.
Frequently Asked Questions
Do I have to replace the gears with the chain?
Yes, always replace the timing chain and both gears (camshaft and crankshaft) as a set. A new chain on old, worn gears will wear out very quickly. All kits come with the chain and both sprockets.
What other parts should I replace at the same time?
Since you have to remove the timing cover to access the chain, it is highly recommended to also replace the timing cover gasket, the front crankshaft oil seal, and the water pump gasket. It's easy access and cheap insurance against future leaks.
What's the difference between a single roller and double roller chain?
A double roller chain has two rows of rollers, making it stronger and more resistant to stretching than a single roller or a stock link-belt chain. For the V8 engines in particular, upgrading to a double roller is a very common and recommended modification for improved durability.
How do I know which timing set fits my Diplomat?
You must buy the timing set that is specific to your engine. The 1977-1984 Diplomat was available with the 225 Slant-6 engine and the 318 or 360 V8 engines. A timing set for a Slant-6 will not fit a V8, and vice-versa. Always verify your engine before ordering.
Technical Specifications
Vehicle engine must be identified before ordering (225 Slant-6, 318 V8, or 360 V8). Key types include standard replacement 'silent' chains and upgraded 'double roller' chains. Camshaft gears are available in cast iron or billet steel.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.