Okay, let me reiterate what I've said before.
Yes. You can run without a chain tensioner...BUT! Assure that the chain alignment and tension is PERFECT...otherwise you run the risk of derailing the chain at the rear sprocket and if you do it will probably be at a speed that could spell disaster for your rear wheel, spokes and possibly your head. Yes, motorcycles do not use a tensioner or a tensioner wheel. What we are riding are not motorcycles designed or built in a factory by experienced designers and builders. Our engines, sprockets and rear wheels are not installed to the critical alignment standards used in motorcycle factories. Our bikes are built in home garages, workshops and driveways by novice hobbiest in many instances who have a limited knowledge of essential mechaincal and engineering practice.
The tensioner serves two purposes. One is to keep the chain at a set tension and the other is to help align or guide the chain onto the rear sprocket. If you run without a tensioner and your chain alignment and tension is not right on, then you run the risk of the chain swaying and disengaging (derailing) at the rear sprocket far more than you would if there was a tensioner to make up for the misalignment that too many people build into their installs. Yes, the tensioner can be and often is a source of trouble with many first time builds. That is primarily due to the tensioner not being installed correctly. This is because the installation manuals provided with ALL kits do not address the need to align (bend) the tensioner bracket so it aligns the tensioner wheel with the chain path. Installed as per the instructions, the tensioner bracket will align the tensioner wheel with the chain stay, frame, not the chain. Because most chainstays are not parrallel with the wheel/sprocket/chain it will drag the chain at an angle to the chain path instead of running true with the chain. This cultivates all kinds of issues; noise, chain derailing, tensioner wheel wear etc. In addition the tensioner bracket has the potential of loosening under load and rotating into the rear spokes with the same results as described above with no tensioner. There has been a lot of controversy regarding drilling a small hole in the chain stay and tensioner bracket and installing a screw to prevent the bracket from moving after is has been properly twisted (bent) to achieve the alignment required. To my knowledge there is not one instance of bike frame failure due to this. Many have warned against it but their warnings are based on conjecture and theory, not fact. If there is anyone who can provide photographic evidence to the contrary, please post them here so I can see conclusive evidence of frame failure due to drilling. Tensioner problems are almost exclusively due to them not being installed correctly. I blame the kit suppliers for this because it is a universal problem which no one seems to address and has caused more problems for the new comer than any other one feature of the Chinese 2 stroke, in-frame engine kits. Let me again repeat: Yes, you can safely operate your motorized bicycle without a chain tensioner. But, if you elect to do so make sure that you understand the elements necessary to achieve perfect chain/sprocket alignment and chain tension. Those who run without a tensioner are experienced, mechanically inclined people who understand the issues involved. The tensioner, correctly installed will allow the new comer, first time builder, the mechanically challenged to enjoy their new hobby without the threat of the chain coming off and wrapping around the rear sprocket which they will quickly learn is the most effective brake ever invented. Whew! How many times have I typed this?
Still love ya, Dan