For Abikerider & 2Door's above posts: I recently built my first MB using a Huffy Stone Mountain 26" and a 66cc China Doll engine kit. This little engine has so much compression, that when I go to pedal the bike to start it, the lower run of the drive chain tension is so great, that it pulls the chain tensioner roller towards the spokes! When the engine starts, I stop the bike and with some difficulty, re-align the tensioner with the chain. I am using the kit tensioner and I have it bolted very, very tight! I have both aluminum and steel in my metal scrap at the farm, and all the tools that I need for fabrication; I will make the chain tensioner that Abikerider made. Since the chain tensioner pushes up on the bottom run of chain, it provides more tooth contact with the engines drive sprocket; better for the sprocket and chain wear in operation. When I first put this engine kit in use, I had to adjust the new chain many times in the first few miles as it was "wearing in" along with the new sprockets. For me, re-adjusting the tensioner is much easier than re-justing the bikes rear wheel and brake pads! That's my two cents worth on this matter--now I am heading for the barn and my metal scrap pile! BMF
Chain tensioners
- Thread starter Bikeman08
- Start date
Bicycle frames are not designed to have holes drilled in them. You risk frame failure whenever you do this. I would never do this, especially on a bike that goes 30+ mph. If you do drill holes, please make them as small as possible.
The pros and cons or drilling holes in bike frames have been discussed her many times. Personally I would not want to drill a hole in an aluminum frame. The stress factors involved and metallurgical characteristics of aluminum warn against the practice.
As for mounting engines, there too I would shy away from a drilled frame, even a steel one, for that purpose.
However, when we're discussing a steel framed bike you need only look at the holes that are drilled into them from the factory. On nearly every bike I've worked on I've observed holes drilled in critical areas such as chain stays near the drop outs, down and seat tubes, head tubes for rivets to hold a badge, etc. The reason for the holes varies. Some are for mounting such things as water bottles, air pumps, luggage carriers, and in some cases the holes are drilled to relieve internal expansive pressure during the welding process of closed frame members.
I've seen warnings against drilling a hole to secure the chain tensioner over and over and I have challenged the folks who warn against it to show me one photograph of a steel chain stay failure caused by this practice. To date no one has produced any evidence to prove the theory. In reality the area of the chain stay where a hole would need to be drilled is not a high stress region. Structurally, the seat stay is under much more stress during normal riding than the chain stay.
For esthetic purposes I prefer a welded one piece tensioner bracket that spans the seat and chain stay but I realize that welding and machining a slot might not be an alternative to many builders. In defense of the drilled chain stay my first motorized bicycle built in the summer of 07, which has accured a little over 1800 miles has the kit supplied tensioner bracket mounted with a 10/32 cap screw through the bracket and chain stay through a hole drilled through the frame. There is absolutely no evidence of fatigue or cracking at the point of that hole. That bike is now retired and hanging from the garage ceiling but not due to a frame failure. It just is an uncomfy bike to ride.
As for the potential of structural failure and injury from a broken frame; I have to realistically compare that threat to what could happen if the tensioner bracket rotated into the spokes at 30mph. I will say with conviction that there is more potential for that to happen than the frame letting go do to a 3/16" hole drilled through it.
We have to assume also that the bike will be used for normal riding on relatively smooth surfaces. A bike that will be subjected to abuse, jumping curbs, hitting potholes, railroad tracks, off-road at speeds that might be well above what the manufacturer intended, could fail structurally. Read the owners manual for any bike and you'll see warnings against abuse and over stressing. And those warnings do not consider it has been motorized but for pedal power only.
In conclusion I will stand behind my opinion that drilling to secure a chain tensioner bracket is a safe practice that many have found caused them no problems and did in no way compromise the bike frame.
Tom
As for mounting engines, there too I would shy away from a drilled frame, even a steel one, for that purpose.
However, when we're discussing a steel framed bike you need only look at the holes that are drilled into them from the factory. On nearly every bike I've worked on I've observed holes drilled in critical areas such as chain stays near the drop outs, down and seat tubes, head tubes for rivets to hold a badge, etc. The reason for the holes varies. Some are for mounting such things as water bottles, air pumps, luggage carriers, and in some cases the holes are drilled to relieve internal expansive pressure during the welding process of closed frame members.
I've seen warnings against drilling a hole to secure the chain tensioner over and over and I have challenged the folks who warn against it to show me one photograph of a steel chain stay failure caused by this practice. To date no one has produced any evidence to prove the theory. In reality the area of the chain stay where a hole would need to be drilled is not a high stress region. Structurally, the seat stay is under much more stress during normal riding than the chain stay.
For esthetic purposes I prefer a welded one piece tensioner bracket that spans the seat and chain stay but I realize that welding and machining a slot might not be an alternative to many builders. In defense of the drilled chain stay my first motorized bicycle built in the summer of 07, which has accured a little over 1800 miles has the kit supplied tensioner bracket mounted with a 10/32 cap screw through the bracket and chain stay through a hole drilled through the frame. There is absolutely no evidence of fatigue or cracking at the point of that hole. That bike is now retired and hanging from the garage ceiling but not due to a frame failure. It just is an uncomfy bike to ride.
As for the potential of structural failure and injury from a broken frame; I have to realistically compare that threat to what could happen if the tensioner bracket rotated into the spokes at 30mph. I will say with conviction that there is more potential for that to happen than the frame letting go do to a 3/16" hole drilled through it.
We have to assume also that the bike will be used for normal riding on relatively smooth surfaces. A bike that will be subjected to abuse, jumping curbs, hitting potholes, railroad tracks, off-road at speeds that might be well above what the manufacturer intended, could fail structurally. Read the owners manual for any bike and you'll see warnings against abuse and over stressing. And those warnings do not consider it has been motorized but for pedal power only.
In conclusion I will stand behind my opinion that drilling to secure a chain tensioner bracket is a safe practice that many have found caused them no problems and did in no way compromise the bike frame.
Tom
The whole drilling the chain stay thing seems easy to test. Someone who has lots of old bike frames laying around could weight a chainstay to failure, and compare holed to non holed. Someone test it please.
It's not that easy to test. The failure would likely occur from repeated loading and unloading. This is called dynamic loading. Applying a static load that is applied only once would not prove much when it comes to real world use. That's why when manufacturers test bicycle frames and forks for durability, they use dynamic load tests.
@2Door
I was not aware of any discussions about the hazards of drilling holes in chainstays, I'll check them out. I agree that drilling into aluminum frames is more risky then steel. I also agree, I would NEVER make a hole in the downtube to mount the engine. If the downtube fails, you're probably going to end up in the hospital. If the chainstay fails, most likely it will only cause the rear wheel to start rubbing the frame and not be catastophic. It will still end the ride but the consequences will be much less. Now it is true that chainstays are probably the least`stressed frame tube but it's also true that it still carries a load proportional to the strength of the tube. They usually have a very small single hole near the dropout for water drainage but the hole is 1/8" or less and only in one side of the tube. I just don't think any bicycle designer ever imagined that someone`would drill a larger hole through both sides of the tube. Besides, it seems so unnecessary when a simple bolt-on solution is so easily fabricated. This isn't rocket science, it's a piece of metal with a slot and some holes drilled in it. If you have the skill to drill a hole through both the tensioner and the chainstay then it's within your grasp to make the bolt-on tensioner I made. I think I even saw something similar being sold on one of the vender websites, can't remember which.
In the end, I think it just comes down to this. I just cringe at the thought of doing irreparable harm to my bike. I become emotionally attached to my bikes when I work on them and don't want to see them (or me) get hurt.
I was not aware of any discussions about the hazards of drilling holes in chainstays, I'll check them out. I agree that drilling into aluminum frames is more risky then steel. I also agree, I would NEVER make a hole in the downtube to mount the engine. If the downtube fails, you're probably going to end up in the hospital. If the chainstay fails, most likely it will only cause the rear wheel to start rubbing the frame and not be catastophic. It will still end the ride but the consequences will be much less. Now it is true that chainstays are probably the least`stressed frame tube but it's also true that it still carries a load proportional to the strength of the tube. They usually have a very small single hole near the dropout for water drainage but the hole is 1/8" or less and only in one side of the tube. I just don't think any bicycle designer ever imagined that someone`would drill a larger hole through both sides of the tube. Besides, it seems so unnecessary when a simple bolt-on solution is so easily fabricated. This isn't rocket science, it's a piece of metal with a slot and some holes drilled in it. If you have the skill to drill a hole through both the tensioner and the chainstay then it's within your grasp to make the bolt-on tensioner I made. I think I even saw something similar being sold on one of the vender websites, can't remember which.
In the end, I think it just comes down to this. I just cringe at the thought of doing irreparable harm to my bike. I become emotionally attached to my bikes when I work on them and don't want to see them (or me) get hurt.
I thought of that too. That only works when you have horizontal rear dropouts with enough room for adjustment. Mine on my derailer equipped bike are vertical with no front to back adjustment. I have no choice but to use a tensioner. on the engine side.
Though I do have a machine shop at my disposal, nothing about mounting my engine was done at the shop, it was all done with hand tools and a die-grinder - in my kitchen. I don't even have a vice or a bench. That's rubbish that you can't mount your engine in a good way without a machine shop.
As far as not being able to utilize drop-outs as a tensioner; The main problem I see here is people mounting their engines so high in the frame. Why? Why would I want my engine jacked up 4 inches off the downtube? I want my engine LOW. Instead of bending up all these goofy brackets to raise the thing up, I ground down my engine block(with a dremel) so I could sling that sucker as low as possible. Now my clutch cover is less than 1/4" from the chainring. Perfect. Lower center of gravity is always better.
As far as not being able to utilize drop-outs as a tensioner; The main problem I see here is people mounting their engines so high in the frame. Why? Why would I want my engine jacked up 4 inches off the downtube? I want my engine LOW. Instead of bending up all these goofy brackets to raise the thing up, I ground down my engine block(with a dremel) so I could sling that sucker as low as possible. Now my clutch cover is less than 1/4" from the chainring. Perfect. Lower center of gravity is always better.
Mike,
I never said that an engine couldn't be mounted properly without specialized tools. You misunderstand me. My argument is when people tell newbies that the only fix is custom fabricated parts such as engine and tensioner mounts.
What we try to do here, because of the number of people who attempt to install an engine kit without the proper tools or skills, is to offer advice that will help them build a successful, reliable bike using simple methods available to most everyone.
It would be nice if every member had the equipment/skills/materials to fabricate one-off mounts, brackets and modifications but unfortunately that's not the case judging from the questions and content of many of the posts from new members. Even those with extensive backgrounds in mechanics often need help to work out the little kinks that inevitably occure during an installation.
Our goal here is to offer advice to those who need it most and suggest alternatives that can be accomplished with a minimum of specialized tools and skills. If a guy has access to a machine shop and has the knowledge to use what's available as well as the materials then he's fortunate and will undoubtedly build a strong reliable bike that features custom parts. Good for him and congratulations. Nevertheless, there are those who will benefit from gaining some knowledge here in spite of their lack of mechanical experience or the tools necessary to fabricate parts.
Therefore we strive to offer help in ways that the newbie can use to get themselves on the road without resorting to cobbling together a bike that might prove to be not only unreliable but potentially dangerous.
I hope this explains our position.
Tom
I never said that an engine couldn't be mounted properly without specialized tools. You misunderstand me. My argument is when people tell newbies that the only fix is custom fabricated parts such as engine and tensioner mounts.
What we try to do here, because of the number of people who attempt to install an engine kit without the proper tools or skills, is to offer advice that will help them build a successful, reliable bike using simple methods available to most everyone.
It would be nice if every member had the equipment/skills/materials to fabricate one-off mounts, brackets and modifications but unfortunately that's not the case judging from the questions and content of many of the posts from new members. Even those with extensive backgrounds in mechanics often need help to work out the little kinks that inevitably occure during an installation.
Our goal here is to offer advice to those who need it most and suggest alternatives that can be accomplished with a minimum of specialized tools and skills. If a guy has access to a machine shop and has the knowledge to use what's available as well as the materials then he's fortunate and will undoubtedly build a strong reliable bike that features custom parts. Good for him and congratulations. Nevertheless, there are those who will benefit from gaining some knowledge here in spite of their lack of mechanical experience or the tools necessary to fabricate parts.
Therefore we strive to offer help in ways that the newbie can use to get themselves on the road without resorting to cobbling together a bike that might prove to be not only unreliable but potentially dangerous.
I hope this explains our position.
Tom
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I go along with the above posted thoughts. I don't have any fabricating tools and no where to put them if I did have them. All I have is basic hand tools. We should all go by K.I.S.S. when explaining things to people. At least at first.
Terry
Terry
Tom,
I understand your position. For someone with limited resources or skills, drilling holes in the chainstay is better than having the kit tensioner rotate into the wheel and causing a catastrophic failure. I guess I'm being too much of a perfectionist. We all need to find the solution that works best for our own situation. My solution was to make my own tensioner.
Have a safe and happy new year.
Mike
I understand your position. For someone with limited resources or skills, drilling holes in the chainstay is better than having the kit tensioner rotate into the wheel and causing a catastrophic failure. I guess I'm being too much of a perfectionist. We all need to find the solution that works best for our own situation. My solution was to make my own tensioner.
Have a safe and happy new year.
Mike
While on the subject of chain tensioners or chain stays, I see a few of the builders that use them substitute the plastic wheel that is usually furnished with the engine kits, for a sprocket. I am wondering if that is an improvement or have any advantages? BMF
As an alternative to the kit supplied plastic wheel many of us use a modified skateboard wheel. You'll have to cut a groove in it to accomodate the chain but if you use a good quality polyurethane wheel with bearings it's a big advantage over the kit part.
Just a word of caution: When you look for a skateboard wheel, look for ones that are one piece. Some of the cheaper ones are laminated with an outer layer that will come apart when you're trying to groove it.
The sprockets work well too but alignment is more critical.
Tom
Just a word of caution: When you look for a skateboard wheel, look for ones that are one piece. Some of the cheaper ones are laminated with an outer layer that will come apart when you're trying to groove it.
The sprockets work well too but alignment is more critical.
Tom
Another way is to just remove the tensioner all together.
I created my own shims that fit between the rear of the engine & the engine mount to move the engine forward to correctly tension the engine side chain... Something similar can easily be made at home if you have a little fabricating skill.
This is what they look like...
I created my own shims that fit between the rear of the engine & the engine mount to move the engine forward to correctly tension the engine side chain... Something similar can easily be made at home if you have a little fabricating skill.
This is what they look like...
Thanks for another idea VMB on this subject! I suppose a fella could fabricate a "quickly adjustable" rear engine shim that would accomplish this with, let's say, a turn of a single screw. I will make a chain tensioner for my bike, I haven't decided yet as to whether I will bolt it on or weld it on. Welding will burn some paint of the bike frame, but on the other hand, it will never get loose either. Again, when I first put my engine kit together, I had to adjust the loosening chain quite a few times until it finally had stretched and maybe wore the two sprockets in as well. I'll post my results here in the weeks ahead on what I have decided to do. BMF
I just drilled two 1/8 inch holes threw the out side of my chain stay and chain tensioner and pop riveted her on. That frame lasted over a year and 1000 miles till I got a truck and stored the bike.
That's good that you managed 1,000 miles but the chain-stays are under tension and they're the most stressed tubes on the bike. Drilling holes in them weakens them greatly so if anyone on here is fairly heavy, like 200+ lbs, and is riding a hard-tail bike, don't expect to get the same amount of reliability. The seat-stays, on the other hand, are under compression and small holes in them won't have any adverse affect.
I ordered a phantom bikes chain tensioner that goes from seat stay to chain stay. Hopefully that will make my chain tensioner dreams come true.
