Just like the drive chain, timing chains elongate, fatigue, and wear out. Luckily, they are not subject to dirt and mud, are bathed in an oil bath, and their overall environment is much better. Before I get into it, one misconception I want to clear up right away is that the timing chain doesn’t technically stretch. Instead, the pins and rotating elements of the chain wear. When the pins wear they become smaller and their mating holes grow larger leading to increased clearances and chain length.
When an engine is run with a worn timing chain engine performance is compromised and the likelihood of related failures is greatly increased (think chain tensioner). Cam timings that are off several degrees will result in a loss of power and the cam chain tensioner will have quite a job trying to take slack out of the valvetrain. When a timing chain elongates it may not do so in a uniform way and parts of the chain may be tighter or looser than others. While automatic cam chain tensioners have proven to be reliable on the majority of engines, some model years, brands, and individuals have fared better than others. A worn timing chain which adds extra slop and inconsistent chain tension to the valvetrain certainly won’t make the tensioner’s job any easier. So it makes a lot of sense to keep tabs on the condition of the chain itself from time to time.
When I was working on a Kawasaki KX250F engine build I took the time to do some comparisons which illustrate the differences you will see between a new and worn out cam chain. First, with the worn chain installed I checked the cam timing. Then I installed the new chain and rechecked the timing. In the table below you can see the intake cam timing was retarded by 6.625° and the exhaust by 9.50° when compared to the new cam chain timing values. For the average weekend warrior this may not seem like much but in terms of performance engines this is miles off the mark!
Method 1 - The Pin to Pin Measurement
Once the total number of pins is known a measurement across a set number of pins is taken with the chain installed. I like to span around 6 - 8 pins between the sprockets on a twin cam engine. Unicam engines are trickier and the number of pins you can measure is usually less. It is important to try and measure across multiple pins because the variation between new and old chain measurements will be more pronounced this way. With the new chain installed I measure 1.846” (46.89mm) across eight pins. This is my benchmark measurement and is what I will compare all future measurements to.
8 pin segments which fit into a 114 pin chain = 114/8 = 14.25
Once I have determined how many 8 pin segments fit into a 114 pin chain I can multiply this value by the change in length between the two chains to determine the total length the chain has increased.
Total Chain Length Increase (inches) = 0.014" x 14.25 =0.200"
Total Chain Length Increase (mm) = 0.36 x 14.25 =5.13mm
The calculated increase is accurate since this is about the difference in length I saw when I laid the chains side by side and measured them. If you aren’t familiar with what changes in length are acceptable this example can be considered one on the far end of the spectrum. The engine had been seriously neglected and wasn’t in real good shape.
Method 2 - What Does the Chain Tensioner Say?
In the image below I marked the plunger position with the new chain installed. As you can see the plunger is hardly extended and the second tooth on the plunger is engaged.
Method 3 - Alignment Marks and Feel
Here, with the old chain installed there is roughly 6-8mm of slack when I pull up on the chain.
If you have additional tips and tricks relating to cam chain wear I’m all ears. Be sure to comment below!
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