Have you ever thought about the importance of your four-stroke engine’s cam chain – also referred to as a timing chain – and what would happen if it broke? The cam chain is one of those all-too-often glossed over parts that make many four-stroke engines run, but often isn’t discussed from a maintenance standpoint. In this article, we’re going to dive into all things cam chain related, covering topics from what it does, what happens when it fails, what diagnostic checks you can perform, replacement tips, and where to get new cam chains.
The cam chain synchronizes the rotational motion of the crankshaft with the reciprocating motions of the piston, intake valves, and exhaust valves so that each of the engine’s four strokes can be precisely controlled. Most engine manufacturers gravitate to similar architectures to control timing, where one side of the engine is dedicated to valvetrain control. In these types of arrangements, the crankshaft provides power to the cam chain through a gear. From the crankshaft gear, the cam chain is routed to one or two cam gears, depending on the engine, and guided back down to the crank gear. A cam chain tensioner and pair of chain guides are also part of the system. The cam chain tensioner mounts between the crank gear and last cam gear in the system to ensure the chain remains at constant tension.
When the cam chain fails, catastrophic engine failure typically results. The resulting damage that occurs depends on where the engine was operating at, at the time of failure, and whether you’re lucky or unlucky. Usually, failures occur when the engine is under the most stress, which correlates to high RPM and load operation. In the worst case, loss of valvetrain control occurs, and the valves ultimately crash into the piston. Often, the piston cannot endure the damage inflicted upon it by the valves, so it also fails, which causes the connecting rod to flail around inside the crankcases. The crankcases weren’t designed to contain an unconstrained connecting rod, so they also fail, allowing the internals of the engine to see the light of day. All of these events occur in the blink of an eye, leaving the rider helpless in the situation and their wallets dreading the repairs to come.
The cam chain itself doesn’t usually outright fail, meaning the chain doesn’t become unconnected and fall to the bottom of the crankcase or wad up in the gears. Instead, a compromised cam chain usually allows other components to cause failures, such as the valves crashing into the pistons through the loss of timing control.
Many people discuss cam chain wear or failure in terms of chain stretch. The term “stretch” is a bit of a misnomer because the chain links themselves never elongate. To do so, the material, commonly steel alloys, would have to reach and exceed their yield strength. Instead, cam chains elongate because the elements that comprise the chain wear out beyond their normal operating tolerance, including things like the roller pins and their bores. For this article, the terms stretch and elongate are used synonymously.
In many cases, what happens to the cam chain is that it wears locally. This means that across a span of an equal number of chain links, one portion of the chain becomes longer than another. When one section of the cam chain becomes stretched, it creates a local disparity in how taught the chain is when wrapped around the gear train. The local disparity results in less chain tension for the affected section. Despite engines being equipped with automatic cam chain tensioners, the tensioners struggle to deal with the abnormalities in the chain. This allows the chain to operate with varying tension as it navigates around the gears. When the situation becomes severe enough, there won’t be enough tension in the system to keep the chain from jumping gear teeth. Once the cam chain skips gear teeth, this results in a loss of timing control, leading to valves impacting the piston.
Similarly, cam chains can be run too long (no pun intended) and lengthen uniformly. Stretched cam chains can present similar problems for chain tensioners, leading to the chains skipping cam gear teeth and altering valvetrain timing.
One of the main reasons the cam chain wears is due to poor lubrication or lack of lubrication. Poor lubrication occurs when dirty oil lubricates the cam chain. The contaminants in the oil act like sandpaper and cause the chain elements to wear. Lack of lubrication, which occurs if the oil level is low in the engine, may allow the chain elements to make metal on metal contact instead of operating on a thin film of oil.
Inspection of the cam chain can and should occur anytime the valve clearances are checked. A few telltale diagnostic checks can be performed with the chain in place and tensioned.
If you'd like to take the diagnostics a step further to be sure, or even just to learn, the next handful of diagnostic checks require the chain to be removed, and a new chain is available.
Photo: DIY Moto Fix
Photo: DIY Moto Fix
If you’re performing some valvetrain maintenance, installing a fresh piston, or other top end work, it’s always good insurance to replace your cam chain. To replace your cam chain, you should have your machine’s factory service manual on hand. The service manual will precisely outline the necessary steps required to remove and install a new cam chain. Here are some essential tips to keep in mind as you perform the job.
ProX knows just how important the cam chain’s role is and takes its manufacturing seriously. ProX cam chains are manufactured through a partnership with Borg Warner, a highly reputable manufacturer of cam chains and other engine components, and a supplier to many OEMs. While ProX cam chains have the reliability and quality advantage of an OEM supplier, they also improve up on many OE designs. They utilize an 'M-style' link design which results in higher tensile strength and better fatigue life. Improved design, OEM-level materials and manufacturing, and a fair price - how could you go wrong?
