Drilling chainstays to fit chain tensioner ?

unityjon

My donkeys year old Saracen has rear chain stays that are about 1.5" tall and oval shaped T7 aluminum, i picked up a basic chain tensioner the other day to prevent some chain slap and suckage when giving it some beans down the trails but the tensioner will never fit a chain stay that large, I've searched for larger tensioners but can't find any, dabbled with the idea of a bottom bracket fitting one but they are so expensive for very basic kit?? perhaps i should machine a billet one up for £15 rather than fork out £60 on a name ?

My simple and quick solution appears to be to drill and tap the chainstay and screw the tensioner direct to the frame there for by passing the need for the bracket, has anyone else gone this route ?? It seems a simple engineering job to me. :?:

nicklouse

and as the rear mech is actually the iten that add tension to the chain you will get just as much slap as before if not more as you have moved the chain closer to the chainstay.


re drilling etc dont bother as you will most likely find it is in the wrong place or does little for the noise. also that you will seriously weaken the stay.

if you must try fitting it some other way to see how it works first.

but some old inner tube on the chainstay is a much better way or reducing noise. and for chain retention a BB mount device is better.

paulbox

I'm no expert, but that sounds like a great way of weakening your chainstays to me.

unityjon

Thats interesting as the guys i have started riding with have noticed far less if any slap when using a very simple cheap tensioner, hence why i bought one, but hear what you say about the rear mech as thats the only part that moves to allow the slack in the chain in the first place, i thought the idea was to put the tensioner in the place of most slack chain travel which then moves that point further back reducing the length of slack chain making the amount of free movement less preventing the possiblity of slap ?.

Would a M4 (3.2mm) hole filled with an ally bolt really weaken a chain stay ?

Not sure why anyone would drill a hole in the wrong place LOL ? Measure 2times mark once measure again and drill once !

The other option i could weld a short threaded tube to the stay and screw into that.

If i had a new bike i wouldnt entertain welding or drilling the frame but for this old thing its part of the fun of upgrading.

rhialto

Holy crap! Are you seriously thinking of drilling a hole in your chainstay instead of spending a paltry £17 on a Superstar chain device?! Check it out:
http://superstar.tibolts.co.uk/product_ ... cts_id=336

Never mess with the frame. You can't reverse the process if you change your mind later. Another way to look at it: I would never buy a frame into which someone had drilled a hole.

paul20v

dpaulett wrote:

Holy crap! Are you seriously thinking of drilling a hole in your chainstay instead of spending a paltry £17 on a Superstar chain device?! Check it out:
http://superstar.tibolts.co.uk/product_ ... cts_id=336

Never mess with the frame. You can't reverse the process if you change your mind later. Another way to look at it: I would never buy a frame into which someone had drilled a hole.

couldnt have put it better my self
and also a +1 on the chain device i have one and it pretty good for the money and i have not dropped a chain since fitting or even heard a slap 8)

cooldad

unityjon wrote:

The other option i could weld a short threaded tube to the stay and screw into that.

Randomly welding aluminium is probably even worse than drilling a hole.

unityjon

cooldad wrote:

unityjon wrote:

The other option i could weld a short threaded tube to the stay and screw into that.

Randomly welding aluminium is probably even worse than drilling a hole.

I'm qualified engineer and I'm a coded welder LOFL.


The bottom bracket mount chain tensioner looks good i'll investigate that, just need to count the teeth of the outer and measure up the diameter of the BB to make sure it'll fit there and that'll do, thanks for the link, much appreciated.

I'm not scared to modify stuff, been engineering shizzle for ever and I like it, and the challenges it produces.

Anonymous

unityjon wrote:

I'm qualified engineer and I'm a coded welder LOFL.

Qualified engineer eh? Wow, that sounds good.
And it's good that you're a welder, too. All the good welders I've known have known everything about heat treating aluminium to remove stresses.

Er, why do you need to know the diameter of the BB?

nicklouse

unityjon


you must have done the engineering after you did the Geography then.

and if you are then why are you asking? just do what you know works.

BBs are a number of standard sizes so get the right one to fit.

Or if you are making something then get the Verniers out.

unityjon

to make sure the damn thing fits lol its a very old frame and many new components dont seem to be compatible.


If i was engineering the space shuttle i would indeed dunk the frame in the heat tank then artificially age the chain stay to bring it back to spec, but its a bike frame. I'll get on it and have fun.

Sorry for just pushing an idea out there, you never know there may have been other people that have had similar issues and they could have shared their experience/solutions, after all, isn't that what forums are for?

Anonymous

Have fun when the chainstay breaks then.
Honestly, you don't sound like a very good engineer.

unityjon

yeehaamcgee wrote:

Have fun when the chainstay breaks then.
Honestly, you don't sound like a very good engineer.

Have you had a chain stay break because you sound like your typing from experience? do share the tail there's obviously lots to learn here and you can help other people.

Anonymous

Er, yes, actually. I've had a chainstay break right at the union with the BB shell.
It was not a pleasant experience, since the bike no longer held itself together, and it happened as I was landing a drop to flat from a stair set.

Go on then. What kind of engineer are you?
Software engineer? Chemical engineer? Social engineer?

unityjon

yeehaamcgee wrote:

Er, yes, actually. I've had a chainstay break right at the union with the BB shell.
It was not a pleasant experience, since the bike no longer held itself together, and it happened as I was landing a drop to flat from a stair set.

Go on then. What kind of engineer are you?
Software engineer? Chemical engineer? Social engineer?

Sounds nasty, what caused it what type of break was it ?

Mechanical.

Anonymous

It seemed to be either the weld, or some kind of impurity in the material. There seemed to be a boundary layer there, which was either remnants of bad welding, or a material fault.

cooldad

yeehaamcgee wrote:

It seemed to be either the weld, or some kind of impurity in the material. There seemed to be a boundary layer there, which was either remnants of bad welding, or a material fault.

Or someone who knows you did a bit of sneaky sabotage.

juz69

For what its worth unityjon, I am also an engineer and have had exactly the same thoughts as you in the past, with regards to drilling or welding a tensioner to the chain stay - great minds hey?

I decided against it but still think a tapped hole, with a solid bolt would not weaken the stay as much as others may have you believe, depends on what you intend on using it for I guess.

Let us know what you come up with, I'm sure you'll make it work.

Anonymous

juz69 wrote:

For what its worth unityjon, I am also an engineer and have had exactly the same thoughts as you in the past, with regards to drilling or welding a tensioner to the chain stay - great minds hey?

I'd put money on the "fools seldom differ" part of the saying.
Seriously, you need to really think hard about what causes chainslap, and where the possible cures for it could be.

I'll give you a clue... Years ago there was a bolt on chain tensioner which was a strong spring that sat behind the rear mech, pulling it taught.

juz69

yeehaamcgee wrote:

juz69 wrote:

For what its worth unityjon, I am also an engineer and have had exactly the same thoughts as you in the past, with regards to drilling or welding a tensioner to the chain stay - great minds hey?

I'd put money on the "fools seldom differ" part of the saying.
Seriously, you need to really think hard about what causes chainslap, and where the possible cures for it could be.

I'll give you a clue... Years ago there was a bolt on chain tensioner which was a strong spring that sat behind the rear mech, pulling it taught.

It depends on the indended application, a rat bike that is just used to rattle back and forth to the shops twice a week and I think it would be fine, anything more and I wouldn't trust it.
However, I dont think its quite as bad as you make out. Yes you are removing metal, and strength when you drill the hole but filling it with a solid bolt means it can't really go anywhere unless the bolt fails....in theory!!

Northwind

Filling it with a bolt might help if the only stresses are in compression. Can't really visualise exactly what you're trying to do here but it doesn't really sound like it'll only be in compression- filling the hole won't help at all when the arm gets stressed in other directions and bikes get stressed in loads of interesting ways.

If you think a little hole'll make no difference, I've seen a motorbike swingarm snap in half because it had been drilled for a sharksfin... An M5 tapped hole in an extruded beam swingarm that had about as much metal in it as your entire bike. Just created a nice stress riser I think and unzipped the arm from there.

Anonymous

juz69 wrote:

It depends on the indended application, a rat bike that is just used to rattle back and forth to the shops twice a week and I think it would be fine, anything more and I wouldn't trust it.

Ahem...

unityjon wrote:

to prevent some chain slap and suckage when giving it some beans down the trails

juz69

yeehaamcgee wrote:

juz69 wrote:

It depends on the indended application, a rat bike that is just used to rattle back and forth to the shops twice a week and I think it would be fine, anything more and I wouldn't trust it.

Ahem...

unityjon wrote:

to prevent some chain slap and suckage when giving it some beans down the trails

Fair point. Just thought some of the comments questioning the OP's professional ability were a tad harsh, as said I decided against it and for good reason. Engineering is all about solving problems and I prefer someone to have an idea than no idea.

Anonymous

Yes, and in this case, "no idea" is clearly the correct diagnosis.

rhialto

Yes, there was some sarcasm. But honestly, someone who claims to be an engineer and then fails to account for the strength of materials in his solution design is asking for it. Particularly when there are other, inexpensive alternatives to DRILLING A HOLE!

juz69

yeehaamcgee wrote:

Yes, and in this case, "no idea" is clearly the correct diagnosis.

To say he had no idea is just not true, he had two infact. If they are good ones is questionable which is I guess the reason he asked the experts on here. It is clear that opinion is against drilling or welding and I'm sure the op will take the advice given.

Anonymous

It's not just the drilling and welding though. His proposal targets the wrong area.
He wants to reduce chainslap, so he wants a way of moving it closer to the chainstay? Yeah, right.

unityjon

yeehaamcgee wrote:

It's not just the drilling and welding though. His proposal targets the wrong area.
He wants to reduce chainslap, so he wants a way of moving it closer to the chainstay? Yeah, right.

actually i just wanted to fit a little roller wheel 'coz they look cool innit'....

I didnt really expect this sort of reaction when i posted the original question, but then i;ve not been on these forums for very long at all. I expect some sarcasm, i really dont mind it as it makes a dull day laughable and looking at the posts in some peoples profiles it seems inevitable.

My initial post probably gave the impression i was going to run an 8mm drill bit hap hazzardly right through the chainstay to prevent that thinking i tried to explain that i had some idea (Msc in mechanical engineering if it matters?) so i wouldn't be quite so brazen but it was too late as opinions had already been formed.

No biggie, but i still think an intergrated tensioner is a nice idea, the bb ones have already been covered by the ISCG mounts, no point re-inventing the wheel, i could weld some lugs onto my BB to accomplish the same, but to drill and tap a small hole is within the remit of most people (isnt it ?) so may have provided a simple solution to those without but you'd need to factor the geometry of the rear as not all rears are alike.

Holding the rear mech back with a spring (wasnt this used on tandems in the dark ages?) is another way but rear mechs are ugly enough IMO without a further bracket set up.

Real world living has proven that many people 'just do stuff' - you can worry too much, it all depends on the application. Customer stuff - no way, own plaything - go for it, suck it and see.

P.S my opinion of 'giving it some beans down the trails' may well be different from other peoples as i'm now older and i'm no longer wreckless and fearless :oops:

unityjon

Northwind wrote:

Filling it with a bolt might help if the only stresses are in compression. Can't really visualise exactly what you're trying to do here but it doesn't really sound like it'll only be in compression- filling the hole won't help at all when the arm gets stressed in other directions and bikes get stressed in loads of interesting ways.

If you think a little hole'll make no difference, I've seen a motorbike swingarm snap in half because it had been drilled for a sharksfin... An M5 tapped hole in an extruded beam swingarm that had about as much metal in it as your entire bike. Just created a nice stress riser I think and unzipped the arm from there.

sounds nasty, was the arm solid or does it have a cavity ?

unityjon

Found this little Gem on the net... Problem solved but i may opt for a Black cable tie ?



:P

Anonymous

unityjon wrote:

Holding the rear mech back with a spring (wasnt this used on tandems in the dark ages?) is another way but rear mechs are ugly enough IMO without a further bracket set up.

If you're observant enough, you'll realise that all mechs have a tentioning spring in them. Hell it's part of their job.
The springs these days are far stiffer than back in those old days, so those additional springs died a death (although they had a very short lifespan anyway, I only ever saw two in the wild).