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. Total Chain Length Increase (mm) = 0.36 x 14.25 =5.13mm 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. My cam chain totals 114 pins and since I only measured eight pins I will need to divide 8 into 114 to determine my length multiplier.Ĩ pin segments which fit into a 114 pin chain = 114/8 = 14.25 To get a better idea of the total chain length increase and the severity of the problem some math is required. For the average weekend warrior this may not seem like much but in terms of performance engines this is miles off the mark!Ī chain length increase across eight pins certainly isn’t earth shattering at first glance but that is only a fraction of the chain. 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. Then I installed the new chain and rechecked the timing. First, with the worn chain installed I checked the cam timing. 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. So it makes a lot of sense to keep tabs on the condition of the chain itself from time to time. 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. 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. 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.
The remaining problem, which applies regardless of whether the engine is stock or modified when the timing chain has worn, is that the cam chain tensioner will have quite a job trying to take slack out of the valvetrain. The good news is that the majority of folks aren’t running heavily modified engines so worries of valves contacting the piston are minimal with a worn cam chain. However, on performance engines set up with aftermarket cams which reduce the clearance between the piston and valves, lack of valve control and incorrect timing can lead to valves that befriend the piston. On stock engines where clearance between the piston and valves is plentiful less precise valve control normally won’t be a problem nor will severely out of spec cam timing. The three main problems are less precise valve control, cam timings that are off, and increased chain slack within the valvetrain. 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). When the pins wear they become smaller and their mating holes grow larger leading to increased clearances and chain length. Instead, the pins and rotating elements of the chain wear. Before I get into it, one misconception I want to clear up right away is that the timing chain doesn’t technically stretch. Luckily, they are not subject to dirt and mud, are bathed in an oil bath, and their overall environment is much better. Just like the drive chain, timing chains elongate, fatigue, and wear out. I want to discuss and share with you some signs that the cam chain is worn out. This week’s post is dedicated to an engine part that is often overlooked, its importance not totally understood, and its service specs minimal.