mrkano

I've been posting a few questions about my new bike I'm building, and I'm very grateful for all the answers I'm getting...
My bike is slowly getting built...

Just a few teething problems...

Here's the pics..





The issue is when I spin the wheel there's a clunking / clicking sound coming from the rear cog area... Everything is brand new... The chain and cogs are all the same as in teeth and chain etc....

The 2nd pic is the rear cog and chain ring, could it be that the rear cog needs spacing out?? How can I do this if so???

Or any other ideas on what it could be??

DannoXYZ 

1. Chain is too loose.

2. Typicaly ou want to install a 5-10mm shorter BB-spindle when converting to single-speed. Quick way around chainline issue is to mount the chainring on the inside of the crankarm spider. Make sure the chainring-bolts are the short kind for single chainring.

3. Also use 3-6 wraps of teflon plumbing-tape around the BB-cups when installing. This fills in the gaps in the large-tolerance threads and prevents fretting/squeaks.

4. Make sure you have the crankarm bolts tightened to 25-33 lb*ft torque. What are they currently at?

hueyhoolihan

looks like your crank is a little too wide. chain alignment issue. it can be critical as regards noise.

mrrabbit 

Chainline looks better than mine actually...

Did notice though you are using the el cheapo Novatech/Dimension/Raleigh/Godspeed/SOMA/AllCity hub...hopefully it's not a bad cartridge bearing putting up with misaligned dropouts....

=8-)

FBinNY 

Before I looked at the photo, my first reaction was CHAIN TOO TIGHT. That's almost always the cause of the kind of sound you're describing.

So before abandoning that theory, is the photo showing the chain in the same position when it makes noise? And did you check for chainring concentricity?

Backpedal slowly and watch the chain and see if it gets tight at any point. At the tightest position there should be a vestige of slack, that you can transfer between the upper and lower chord by pushing the crank back and forth.

If, there's a significant variation in chain slack with the lower loop rising and falling as you pedal, then your chainring isn't concentric. On many cranks there's a bit of float, so loosen the chairning bolts, and retighten to just firm. Then rotate the crank to find the tightest position, and hit the chainring at the 3 o'clock position to drive it back toward the axle. Keep doing this, finding the tightest spot, and tapping the ring back, working by degrees until the chainring is as concentric as you can get it (lower loop doesn't rise and fall), then tighten the chainring bolts to keep it there. Then pull the rear wheel back so that at the tightest place there's about 1/8" of sag that you can move to the upper loop and back.

mrkano

the chain isnt too tight, the wheel is only slightly tightened on just to roll it, its not in a riding state yet..

when I roll it, it looks like the chain sort of jumps a little as it approached the teeth, as in rises up 1mm or 1.5mm or there about?

The only thing I can think of is that the chain is not right, but it's a 1/8th chain (for single speed or fixed)..

I'm going to try a different back cog and see if that does anything...

mrkano

Hi guys..... Thought I would just quickly upload a video of what's happening...

It looks like the chain isn't catching, but like I said it's quite weird as 1. all the parts are new, and 2. all the parts are meant to be matching in terms of size (1/8TH etc).. ??

Please turn up the volume and you will hear it.. ?? The same thing is happening with the chainwheel..

FBinNY 

watching and listening, I suspect that the rear sprocket itself is the problem. The chain seems to hang a bit high on the teeth before settling in. You might check it by taking the wheel and chain off and looping the chain onto the sprocket to see if you can feel any roughness when winding it on and off.

Sometimes there's a slight pitch error in the sprocket in which it's trash. More often it's a matter of burrs or some surface roughness which will resolve with wear, or can be dressed off quickly by spinning the wheel with a file against both faces of the sprocket.

Spoonrobot 

Your chainline is was off, that's why it looks like the chain is jumping a little when it engages the teeth.

What bottom bracket/crankset are you using?

mrkano

Hi....

I'm running Miche Crankset, not 100% sure on the model.... But they are in very good condition, and the guy O bought them off is a fixed gear rider who rides some of the best gear.... So I'm guessing the cranks/bb are ok....?

If the rear cog is as you call it 'trash' and cheapish, would this also affect the chain and it's relationship with the chain wheel?? ?

FBinNY 

No, you have to use a bit of diagnostic logic.

There's the relationship between the chain and the rear sprocket, and the relationship between the chain and the chainring. If it runs badly on both, either the chain, both sprockets, or the overall system has issues. If the chain runs badly on the rear sprocket, but fine on the chainring, that pretty much narrows it down to the rear sprocket itself, something that's easy enough to confirm.

Sometimes, what you hear is the tips of the sprockets touching on the edges of the inner plates before sliding in. This is easily fixed by filing the tips of the sprockets to more of a point which can slide in without touching the edges of the plates. The chains can affect this also, some have bevel on the insides of the inner plates to act as funnels and guide the teeth in if coming from a slight angle. Most derailleur chains are beveled this way because they're designed to accommodate varying chain angles, but many 1/2x1/8 chains aren't because single speed and IGH chainlines are assumed to be nearly perfect.

Retro Grouch 

I was thinking just the opposite. Back off the chain tension just a skosh and see what happens. If the chainring isn't perfectly concentric with the bottom bracket it will create tight and loose places as the crank rotates. St. Sheldon has a method for centering the chainring but often it's hard to get them absolutely perfect.

mrkano

Well I dont think its about the slackness of the chain, as the video shows, that the chain 'rises' as it hits the beginning of its revolution around the cog..... My only guess is that its the cog, I have just oprdred one from TOKYO FIXED..... A proper one dare I say.. haha... should be here tomorrow..

mrkano

Well I dont think its about the slackness of the chain, as the video shows, that the chain 'rises' as it hits the beginning of its revolution around the cog..... My only guess is that its the cog, I have just oprdred one from TOKYO FIXED..... A proper one dare I say.. haha... should be here tomorrow..

DannoXYZ 

Sheldon's chainring-centering technique is for getting an optimally tight chain for fixed-gear braking. You can leave chain loose to account for wobbly chainring. Doesn't need to be that loose though. Even with Biopace oval chainrings the chain doesn't have to be that loose.

Since the issue here appears to be that the chain isn't falling down into the valley between the rear-cog's teeth, a little more tension on the bottom will help push the chain down the teeth to engage. Filing the sides of the teeth's tips will help. Straight chainline would probably fix all of this.

hueyhoolihan

at first glance, the pic shows what appears to be a straight chain-line, but i have found that, if the chain is reasonably tight, a picture, from the rear at low angle will not show an alignment error very well. in that most of the pic is showing the chain from the top of the cog to the top of the chainring. and on a reasonably tight chain it will always be straight. on a properly straight frame a straight chainline can only be determined by careful measurements of center of cog and center of chainring to the center of the vertical axis of the frame. which is a PITA to do. and even then, if the frame is at all out of alignment, you're still SOL.

so what i usually do is get it close by sight, then fuss with it until the noise goes away.

BTW, there are, of course, other possibilities. recently i was using a hyperglide cog with a wipperman SS chain. the ramps were banging on the large sideplates of the chain. fix was a Surly SS cog.