problems with my singlespeed mtb drivetrain
 

So I have an MTB converted to single speed with a pyramid tensioner, surly cog and I've tried two different cranks. The problem has been the same each time.

As I put pressure on the pedals to accelerate the drive train skips and makes a "KLUNK KLUNK!" I can't figure out what it could be. I figured maybe the chainline was off so I got a narrower bottom bracket. The chain line seems to be alright and the chain isn't too slack or too tight. What do you guys think is doing this?

Oh, I'm also going to post this to mountain bikes too

Thanks
= ]

Is it skipping on the cog or the chainring? Well either way, you have a worn out drivetrain. Go out and buy a new chainring, cog and chain and you'll be all set

the chain and crank are new, the cog was bought used but appears verryyy lightly used (a little grease residue but thats about it?

what type of chain are you using. If you have chain made for multiple gears it may be too thin for the surly cog. I may not be seating well onto the teeth of the cog, as single speed cogs are fatter than the cassette cogs. Try a single speed chain (if you haven't already).

got a 1/8" chain on there thanks for the try though = ], keep the suggestions coming people

You can easily check your chainline. Shift the chain off to the inside and then use a long straightedge or known straight yardstick. Push the straightedge up against the face of the chainring with the other end extending back to the rear cog. The end of the SE should be in line with the same side face as the chainring. If it's not it'll show you how far out it is pretty quickly. If you're within an 1/8 inch you're likely fine and there's some other reason it is skipping.

Are the ring and cogs you're using single speed types where the teeth are fully shaped or are they intended for multi speed setups so the teeth are tapered so they can shift easily? And if they aren't SS/Fixed rings or cogs did you double check to ensure they are mounted so the reliefs are facing the right way? (shot in the dark since it sure seems like you know what's up)

Could be a number of things.

Right off I think it may be your cassette.
The pawls may be worn or are not engaging.
Clean and oil them.

There could also be a kink in the chain somewhere.
You can check every link to see if there is a tight one.

I had the exact same problem with a Forte (Performance) tensioner. I used a 1/2 link, took the tensioner off, & everything worked great. I wonder if the tensioner(s) did not have enough tension to hold the chain?

I've often thought that the tensioners should not be a spring style tensioning arm. Instead they should be a clamping fixed arm that is adjustable. Also the arm should not hold the chain down at an angle but rather up toward the chain stay so that the wrap around the cog has more teeth in engagement.

In fact come to think of it perhaps you have too much chain so that the wrap isn't as long as it could be? Can you take out one more link pair and still fit the chain on? If it is that loose then you'll have a lot more wrap working for you.

My bike does the same thing when the chain isn't tight enough. Take out a link and try again.

When I was setting up my bike with a cheap Nashbar tensioner in push down operation I had bad skipping under hard pedaling. As best as I could figure, eventough the chainline was fine the frame would actually flex slightly causing the downward hanging tensioner to feed the narrower link plates on to the top of the teeth of the rear cog. About half way around they would drop back in and cause a skip. I added a half link, took out a full link, and removed the spring and rigged my tensioner with a wire tie to push up on the chain. No more problems.

Anyway, I'm sure you have your chain as short as possible, but could a half-link allow you shorten it slightly further?

Also if your tensioner is pushing down it may help to make it pull up for more chain wrap.