Extremely broken chain!

GoldenMotor.com

baD mR fRosTy

New Member
Sep 14, 2011
28
0
0
Halifax
Hi...

OK.
My first "build"...a 80 cc Chinese kit on an 18" aluminum mountain bike.

After perusing this forum for a few days, and taking into consideration the 'tips', e'g' stonger bolts, careful sprocket centering, rubber under the mounts etc etc...I finished up last night.

Unable to wait until daylight, and against the better judgement of my wife - I set out on the driveway for guts and glory!

We have a quite steep drive, but after 5 or six tries, I could not get the engine to continue to run on its own. The hill part of the driveway is not long though, and probably just before it "started", I was already braking.

Back to the forums this morning, where I read that, particularly on the FIRST start, it may be becessary to pedal along at 10 MPH for quite a few seconds until the engine comes to life. Also, I read that it's a 'tickle valve' that primes the engine, NOT a "pump" (d'oh)...and that 2/3 choke might be enough.

Sure enough, after holding the "tickle valve for 3-4 seconds, and putting the choke lever to 2/3 up...I pedalled like mad on the level, and slowly she began to fire...and then by using full throttle burst into life!

In fact, I had TOO much acceleration for ME (on my 56 tooth sprocket) and backed off, easily keeping up about 15 MPH...the engine was purring along nicely...

...but I got about 100 yards up the drive, on the level, and WHAM! - my chain broke - a peice flying up and hitting me in my smug ass, the rest trailing on the ground, and still wrapped around the drive sproecket.

I have done a search...and cannot find any examples of what might lead to this...my sprockets seem pretty well aligned...the chain tensioner gave me only 1/2 "play" in the chain...I thought I was good to go.

The "good" news if the motor worked...choke, throttle, clutch etc...but the chain failed after 30 seconds or so.

Any ideas? I mean this chain broke BIG TIME, not just one link...here's a pic.

Thanks
 

Attachments

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
"my sprockets seem pretty well aligned" This makes me suspicious. Sprocket/chain alignment is not to be taken lightly. They must align and the rear sprocket must be installed correctly which means no wobble or out of concentricity with the rear hub. A sprocket that isn't centered will cause the chain to loosen then tighten, sometimes dramatically depending on how far off it is.

Go back and take a good look. View from the rear of the bike looking forward and see that the chain path is an absolute straight line. That includes the tensioner wheel. Some will tell you that the kit supplied #415 chain is junk and prone to breaking but it's been my experience that the Chinese chain will perform just fine if everything is as it's supposed to be in terms of alignment and tension.
Let us know what you find and good luck.
Tom
 

Greg58

Well-Known Member
May 1, 2011
5,353
2,575
113
65
Newnan,Georgia
I don't know if you are using a chain tensioner, if so make sure the chain is rolling as close to center as you can get it. On most bikes the tensioner wheel is not inline with the sprocket, what I like to do is push the bike with the clutch lever locked in and watch the chain as it rolls over the tensioner wheel. If it moves to one side I bend the mount till it runs straight.
 
Last edited:

baD mR fRosTy

New Member
Sep 14, 2011
28
0
0
Halifax
OK..will check that again tomorrow.
I must admit, putting the sprocket and chain on took me longer than the hole rest of the build!

My supp-lier had forgotten my 'half-moon' backing plates...and when they bcam the other night, there seemed to be TWO sets. I tried using both sets...in the order(from the inside) plates, rubber, spokes, rubber, plates, sprocket....but that seemed to put the chain out too far from the axle. I took the outer plate off, so that the sprocket contacts the rubber...even then it was out too far, so I then turned the sprocket around to that the teeth were closer to the spokes....that seemed to be the only was to get the chain not to rub against the frame.

Could that be a problem?

I will try to check the alignment tomorrow, with the chain off, with a straight edge.

Could a 'too-loose' chain cause it to break? Perhaps because of all the starting, semi-running, braking...it seems like it might put quite a shock, but I never expected a breakage! It almost looks "chewed" a bit.

Will check. Now I have to find where to buy chain...we don't have stuff like harbour freight et...is this a motorcycle chain or something? Industrial "roller chain"? It's way larger than the pedal chain on the other side. I guess it's the next size up.

Thns!

At least I know she runs!
 

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
Any well stocked bicycle shop should be able to get you a KMC 410H bicycle chain.
Be sure that is has the "H" suffix in the name. "H" stands for heavy duty.
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
You can also try Ace Hardware, if they have them in NS. An industrial #41 chain is what you want to ask for. Grainger is another possibility. Most of the vendors listed down the sides of this page will also be able to supply you with chain.
And, yes, a too loose chain can get you into trouble. It can bunch up around the engine drive sprocket, and do other weird things that might account for the breakage you have.
Take GearNut's advice and roll the bike forward and backward with the clutch disengaged and watch the chain carefully. It should roll over the sprockets smoothly and remain straight. That tensioner wheel being aligned is critical too. The bracket that holds it might need to be twisted slightly to get the chain to run across the wheel centered, and not be pulled off to the side.
Good luck.
Tom
 

baD mR fRosTy

New Member
Sep 14, 2011
28
0
0
Halifax
Good advice all round. What I think I discovered today was definetly an alignment problem...and with my new chain, I think I have it sorted out. I have about 5 miles/runs perfect anyway, knock knock...

My engine, I think, was "torquing" or twisting to the left while running, and starting. Those two operations both torque the engine to the left...but the forces are alternating from "engine pulls top of chain from sprocket" (acclerating) or else ""sprocket pulls bottom of chain from engine"" (starting).

The reason mine broke, I think, is that when the engine twisted, even just a bit, the BOTTOM of the chain was moving over to the very edge of the bottom sproket, and then the links were getting chewed by the sprocket teeth.

So, as advised, a good tight chain...I got a replacement "41 Industrial roller chain" which was wayyy tougher than the way in the box. Although it too might have broken with the misalignment caused by the torque/twist, who knows. I know it is tougher, simply because the kit chain, I was able to punch the link pin out with a single blow of my punch....the new chain, I had to grind the end of the pin off first, and it was MUCH harder to bend the outer link joiners out on the new chain....like a proper motorcycle chain.

Additionally...just the way my chain links started out...I have had to use almost the full tensioner, at least until my chain stretches a half link or so. But, also on advice, I have "twisted" the plate to make sure that the roller "centers" the bottom of the chain...to prevent it "wobbling" and entering the bottom of the sprocket too far off to one side...and leading it straight into the sprocket, the chain nice and centered on the teeth. (A proper motorcycle sprocket 'self'centers' the chain by being wider at the base of the teeth.)

Anyway, thanks again for the advice...

To stop my torquing/twisting, byw, I removed some rubber gaskety stuff under the mounts, leaving some...tightened the bolks (I hate the idea of breaking the motor mounts though!), so just about 5 ft/lbs...and, awkwardly, I strapped the exhaust pipe, about n3 inches from the manifold, to the frame.

I hope this will not break the manifold bolts, but it really isn't much force. When experimenting, I was able to hold the engine from torquing by HAND, so I bet it's not a great deal of force. I did not clamp the pipe right TO the bike frame...just made a "preventer" metal strip from it moving further away ...it's about a 1/4 inck gap.

I hope this makes sense, lol...

At least "broken chain" will show up in the Search...so any and all more opinions/anectdotes are welcome, I'm sure!
 

Attachments

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Congratulations. We're glad you got this one solved. It's just another argument against using rubber or any resilient material between the engine and frame. The engine needs to be attached solidly with no attempts to reduce vibration.
Ride safe, have fun.
Tom
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
replace cheap chinese junk chain with high-quality 420. It fits fine despite being a tiny bit wider. No more chain breakage!
 

Cyclin

New Member
Jul 4, 2011
118
0
0
California
Also, you may want to take out the rubber under your mounts. It was pointed out to me and after a little searching I found this practice to be unsafe.
 

Ibedayank

New Member
Oct 29, 2011
1,171
0
0
Columbia Tennessee
the stock chains that come with the kits from gasbike are just junk.
had it break just trying to start the motor

replaced with KMC bmx chain ...end of problems
 

toddrobert38

New Member
Nov 6, 2011
5
0
0
Miami Beach
this is a great thread on chain breakage. mine has been popping off then broke today. bike/scooter shop fixed it and it popped again tonight. i will sure look for that heavier chain tomorrow and hopefully they can check the alignment. i am guilty of using wd 40 on it last week when i was having problems getting the chain to move at all. turned out that the back wheel hub bearing, cone and whatever else is in there needed to be replaced. will probably go for the heavy duty 30 lb wheel soon as i dont know how long it will hold out this way, but gotta fix the chain first!

thanks for this thread full of info