TL;DR: A minor rattle, ticking, or clacking sound at idle and low RPM is a normal issue with sportbikes caused by some minor slack in the cam chain. It is very rarely that the part designed to tighten the cam chain fails but since it is a mechanical part, it can only adjust at certain increments and there's a purgatory period between adjustments where some MINOR slack in the cam chain can cause an audible ticking, rattling, or clacking. This is by design and well in spec and should not be an issue and eventually go away when the cam chain tensioner eventually tightens on its own as it is designed to do.
There's been about 2 or 3 new posts on the infamous rattling sound our bikes make along with another 2 threads that get bumped a lot about the same issue. I figured I'd make a Tech Tip explaining the likely cause of this "issue" to help those in the future that are dealing with this.
I want to preface this with: I am not a mechanic but I've developed enough proficiency that I can basically do all routine maintenance on my bike and have a good understanding of how the entire system works. I've owned Kawasakis, Triumphs, and Yamahas so far in my Sportbike career and one thing they ALL had in common is they all eventually start to "rattle" or "tick". When I had my ZX-6 track bike, it developed a pretty loud rattle and since it was a track bike, I decided to get to the bottom of what was going on and with a mechanic friend who was helping me with my valve adjustments, we checked the cam chain and tensioner and found absolutely no evidence of anything wrong with the bike and he assured me it was fine. Through this experience, his guidance, and my research, I learned about the cam chain and the cam chain tensioner and what the source of the rattle was.
So what's going on?
I'd like to defer to an actual expert on this topic by posting a YouTube video that explains, with visuals, on how various cam chain tensioners work. That link will be at the bottom of the post and I'll do my best to paraphrase the explanation.
Your cylinders are connected to a cam shaft that rotates. The cam shaft is connected to a chain (the cam chain) that is connected to the crank shaft. The spring loaded valves in the cylinder heads are under tension when they reach full compression, they want to "pull" the cam shaft "ahead" as it rotates. A loose cam chain will pick up the slack of this as the camshaft attempts to jerk ahead and the cam chain will cause a clacking sound as it momentarily loosens then tightens that is often referred to as a rattle or tick. The cam chain is just like your regular chain, and will stretch over time due to the forces placed on it, adding slack to the chain and causing a dangerous issue that can throw off cam timing and cause your pistons to hit the valve heads and cause catostrophic engine failure.
To combat this issue, most sportbikes including the FZ/MT-10 have what is called an automatic cam chain tensioner. This mechanical part is designed to take up the extra slack in the cam chain to avoid excessive slack in the cam chain to avoid catastrophic engine damage. The cam chain tensioner is basically a spring loaded plunger with teeth on it that is connected to a guide that rests up against the cam chain. When enough slack develops in the cam chain, the spring in the cam chain tensioner can overcome the loose space that develops as the cam chain slackens and the cam chain tensioner will "grab" the next tooth on the plunger and push the guide further into the chain and tighten up the chain. Below is a picture of the cam chain and the tensioner. Pictured is actually a manual (not an automatic) cam chain tensioner but the basic idea is the same. The video at the end of this post will show an actual automatic cam chain tensioner.
However, the adjustments on the cam chain tensioner can only be accomplished in increments of a certain measurement and it may take some time for enough slack to develop in the chain to allow the spring to overcome the tension in the cam chain and "reach" the next adjustment. When the cam chain is in this purgatory, it may clatter and cause the rattling or ticking that is most often heard.
Fortunately, this purgatory that the cam chain slacks is acceptable and will not cause damage to the engine. But the minor slack in the cam chain will clack a little bit.
So what can you do about it?
The best answer, is you likely don't need to do anything about it. Just learn to live with the clacking until the tensioner eventually takes up the chain slack and adjusts.
If it is still an issue for you, you do have a a few options but I want to make it very clear that messing with the cam chain is a very serious task that if done wrong can cause CATASTROPHIC engine failure. I strongly recommend against messing with the cam chain or tensioner at all. But if you are up to the task, here's a few things you can do"
1. Inspection - You can inspect the tensioner to see if the teeth are stripped. I haven't personally inspected the FZ/MT-10 so I'm not sure if the teeth are visible when you take off the engine cover off but If the teeth are stripped, you may have an actual issue with the tensioner and needs replacement. HOWEVER, I must stress that this is extremely rare especially on a low mileage bike and the automatic cam chain tensioner is a very durable part that should outlive the life of your bike. It is EXTREMELY rare for them to fail.
2. Adjust the automatic cam chain tensioner. You can force the cam chain tensioner to the next position. I've never personally done it and I once again caution against doing so but to my knowledge, you can force the next adjustment on an automatic cam chain tensioner.
3. You can purchase a manual cam chain tensioner. This will replace your stock tensioner and allow you to more easily adjust the cam chain. Personally, I think this is silly because the engineers who designed our motorcycles through decades of research and development invented the automatic cam chain tensioner for the exact purpose so you would never need to adjust it. But if you absolutely cannot live with the clacking and think you're proficient enough not to do it wrong and damage your engine, this is usually your best option.
How do you tell if its normal or if there's a developing engine issue?
If there's an issue with the motorcycle related to the cam chain or a failure of the cam chain tensioner, the issues will likely become more pronounced, at higher RPM. Although I have not personally experienced it, I know from my previous experience that you usually can't hear or notice the normal clatter at higher RPM when the cam chain and tensioner are within spec. I imagine when you are screaming at 10,000 RPMs and you can hear the clattering very distinctively and are experiencing engine surging, this would be a sign of an issue with the cam chain or tensioner and needs IMMEDIATE attention. However, I want to again remind that automatic cam chains are a very reliable part and very rarely fail.
Hope this helps. If I missed something or if there's an inaccuracies, please let me know.
