Chain tensioner "suggestions"

**BarelyAWake** · #51 (**permalink**) 11-02-2009, 03:02 AM

Sucha beautiful wall of text I hadta steal it

;

Quote:

Originally Posted by 2door

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

Tom

xlite · #52 (**permalink**) 11-02-2009, 06:27 PM

Thanks for posting that. Could not have put it better myself. It is a little more likely chain will come off a mis-aligned sprocket without a guide which is one thing I look for when choosing a bike.

I should mention however that it is preferable to having a tensioner go into the spokes in terms of damage. I've seen several examples of both and can tell you there is a difference in the result.

DCX35 · #53 (**permalink**) 11-02-2009, 09:52 PM

Hi all - I'm a newby to motor bicycling and to this forum. I have been reading your informative threads with great interest. Lot's of great tips there. I am running an 80cc Zoombicycle engine on a 27" Schwinn Cross-Fit 18 speed bicycle. It was a simple installation (slight exhaust pipe bend the only complication) and has been trouble free during the first two hundred break-in miles. I made what I hope to be an improvement over the original kit's chain idler as follows:

The standard chain idler pulley has a single ball bearing set in its center.

Here is an alternative chain idler pulley with two ball bearing sets, one at either side which I have been using with success:

** Purchase a standard 52mm skateboard wheel with the highest hardness available (durometer of 99a or 100a)

** Purchase a set of ABEC 9 (highest quality) skateboard wheel ball bearing sets

** A set of (4) Skateboard wheels with (8) matched ABEC 9 bearing sets are usually available on eBay or the internet for under $20 and will give you enough material for (4) chain idler pulleys.

Chuck up a skateboard wheel into your drill press’ chuck with a bolt through its center, secured by a nut and two fender washers, one at either side. Note: use tape wrapped around the bolt to adjust its diameter to perfectly fit into the center hole of the skateboard wheel to keep the skateboard wheel properly centered on the bolt.

Hold a coarse ½” wide file steadily against the circumference of the spinning skateboard wheel at the middle between the wheel’s sides until the file has machined a ½” wide chain groove (for use with #40, #41 or 415 chain) 0.200” deep, into the skateboard wheel. This will leave 3/16” thick chain guide fences at either side of the new chain groove. Add a slight taper to the sides of the chain groove by slightly tilting the file as the wheel spins so the configuration of the chain groove ends up similar in configuration to that of the original equipment chain idler’s groove. When finished, the chain groove will be 1.66” in diameter which is 0.300” larger than the original equipment idler pulley’s 1.36” chain groove diameter (a good thing - less chain flexing required as it passes over the idler).

IMPORTANT: When using standard 52mm skateboard wheels, there must be a 0.405” thickness steel spacer stack used between the two ball bearing sets. The spacers must have a 3/8” ID and no larger than 0.600” OD to fit inside the center hole of the skateboard wheel. 3/8” lock washers satisfy this diameter requirement. Flatten out five lock washers (placing them part way into a vice and bending them with pliers until totally flat). The 5 flattened lock washers should produce a spacer stack of 0.405” total thickness. If slightly over this dimension, grind several of the washers until the total stack thickness becomes 0.405”.

Press the ball bearing sets into sides of the grooved skateboard wheel with the stack of spacers between the bearing sets such that when the chain idler pulley’s axle bolt is tightened, the bearings will be prevented from pulling together which would cause side loading of the bearing sets and binding. The tightened chain idler pulley should spin freely when its axle bolt is fully tightened.

I have run this type of chain idler for several hundred miles with no problems or noticeable wear.

DCX35 · #54 (**permalink**) 11-06-2009, 11:29 AM

Just wondering . . . some of the chain tensioner ideas are spring loaded which at first would seem to be a great idea but . . . with pedal to start bikes, during the starting process, the lower part of the chain loop (rearward moving chain) is in tension unlike when under power so wouldn't a spring loaded chain tensioner design tend to have its spring compress and back off somewhat, allowing too much slacking of the upper part of the chain loop (forward moving chain) which, if not perfectly alligned would more easily be able to climb over a sprocket tooth and feed off the drive sprocket?

**BarelyAWake** · #55 (**permalink**) 11-06-2009, 11:45 AM

That's possible ofc - good thinkin'

Proper alignment is so critical tho if it was out of line enough to do that - you'd have bigger problems I bet. I'd also not have that much play - the chain could prolly stand to have a link removed should the spring arm bottom out before the chain becomes tight.

I am ofc theorizing as I use the roller to reroute my chain and not just "tension" the free play and so I've not done a spring variant as of yet

Motor Boys · #56 (**permalink**) 11-06-2009, 12:03 PM

Good advice all, I am always looking for ways to improve my builds.
Thanks

DCX35 · #57 (**permalink**) 11-06-2009, 12:28 PM

The best chain tensioner/guide idea(s) I've seen in this forum would be a combination of a 17 tooth nylon chain sprocket as shown on another's thread and a slotted bracket (like an adaptation of an automotive alternator adjustment bracket) which attaches to both the horizontal and angled bike frame members ahead of where they join near the rear axle, as shown on another's thread. It would not be spring loaded and of course would require periodic readjustments but only during the initial chain stretching phase of a new chain and then only occasionally and should prove to be very reliable and trouble free. I'm heading that way (for about $35). Check out the Brewer Tensioner website's nylon 17 tooth sprocket B4017N (4th sprocket to the right) with its DB clevis adaptor bushings as shown at www(dot)brewertensioner(dot)com(slant)nylon-sprockets(dot)html(poundsign). This sprocket is also available in steel but that could be overkill.