|Author: Jim Brink May 2000 Photos by: Scott Wilson||
|Typical 22R Single Row Timing Gear (Cam Sprocket)|
It's no secret that the "R" series of Toyota engines is renowned for their durability and longevity. True stories are told of engines lasting upwards of 500,000 or more miles with "routine maintenance."
Just what exactly constitutes routine maintenance varies from one individual's opinion to another but we can pretty much agree that this includes basic oil changes, tune-ups, valve adjustments, and proper cooling system maintenance. One item often overlooked (until it is too late) is timing chain maintenance. While the factory has no recommended replacement interval for the timing chain and related components for these vehicles, it is this author's opinion otherwise that attention should be paid to the timing components at 100,000 mile odometer readings. Even if this attention is in the form of a simple visual inspection, early detection of chain failure is key to long engine life.
The timing chain is not the weak link in the system, it is the related components that cause the inherent problems. Beginning with the model year run of vehicles in 8/83 (1984 model year), Toyota switched from a double-row timing chain to a single row with plastic chain guides. Plastic guides are less expensive to produce and are quieter. The drawback to plastic guides is breakage. Over many miles and temperature cycles, the plastic fatigues, becomes brittle, and ultimately breaks away. The timing chain loses tension resulting in less static timing control. Broken plastic guide pieces floating around in the engine's oil pan can cause additional problems. These pieces can block the oil pump pick-up screen and starve the engine of oil. If let go too long, chain wear and stretch is accelerated. Several things can occur at this point. The chain can gouge the aluminum timing cover, opening a water passage dumping coolant directly into the oil pan. If this ingestion of water into the crankcase wasn't bad enough, the chain can break all together and in an "R" engine, serious engine damage will take place. This is because these engines are what is known as an "interference" design. This means that if the camshaft and crankshaft are thrown out of time, the pistons will hit the valves.
|Stock Broken Plastic Chain Guide (top)|
The fix for this situation comes not from the factory but the aftermarket. DOA Racing Engines, known for building efficient, reliable race motors, has taken a serious look at what can be done to prevent breakage of timing chain guides while not compromising dependability or longevity.
DOA manufactures it's own metal-backed guides that address the common breakage problem. These guides are a direct bolt-in upgrade and include mounting hardware. DOA is so confident in their metal-backed guides, they offer a guarantee of the guides for the life of your engine.
|DOA's Metal Backed Guides|
Recently, DOA has expanded it's line to include their guides in a complete timing set. This is perfect for someone reconditioning a high-mileage engine or one that is due for an overhaul. DOA's kit comes complete with the metal-backed guides, cam and crank sprockets, pre-stretched chain, tensioner, gaskets, oil pump o-ring, and two crankshaft oil seals.
|DOA's Complete Timing Set|
DOA's Tim Jenkins explained that the only real drawback in installing their kit is the tightness of the chain supplied with it. Upon installation of the chain and guides into our 1986 2WD pick-up, we too noticed how the installed chain was more difficult to install than original equipment pieces. Jenkins commented that this was due to the design of the chain itself. He said that the chains in his kits start tight to prevent slack after the run-in period. This is important again not only for a long-lasting engine but in high horsepower applications, more efficient timing control means more power gets to the ground.
|Stock, Plastic Guides (L), DOA Metal-Backed Guides (R)|
In addition to the chain and guides in the DOA kit, all of the other parts were first rate in quality. The gaskets and seal appeared to be original Toyota pieces. As a courtesy, DOA provides two crankshaft seals to cover the "oops" factor that sometimes occurs while installing this seal in the oil pump housing.
As mentioned above, DOA's metal backed guides can be purchased individually for $65 or in the complete timing set for $201 (1985+ 22R) and $150 (-1984 Double Row Chain) plus applicable shipping charges.
Next month, we'll cover the installation of a new timing chain in a 1986 pick-up equipped with a 22R engine using a complete timing kit supplied by DOA. Be sure to check back for helpful tips and installation hints.