skipping chain on single speed mtb

Me said:

Hi, a buddy just coverted his old GT mtb into a single speed.

It includes:

1 a new deore chainring on front 2 new sach BMX chain 3 DMR chain tensioning device (screws into
where the derailler went) 4 bmx cog on rear wheel 5 bolt on dmr rear wheel dished/spaced for
singlespeed

Hes got the tension fairly tight, but when hes really pedaling hard up a hill the chain slips and
makes a noise and then allows him to keep pedalling.

He describes it as the feeling you get when a chain is worn and it skips off a multispeed
cassette. Except in this case all the componants are brand new.

Anyone have any suggestions as to what might be the problem? Do you think if he bought a sach mtb
chain instead of a BMX it would work better?

cheers for the help...

I'd wonder about the chain -- is it the right size and does it have any stiff links. The sachs
chains that I've used have been great and also used a quick link which gets rid of the most common
source -- pressing the pin in and leaving the plates tight against the link making it stiff there.

David

Me said:

Hi, a buddy just coverted his old GT mtb into a single speed.

It includes:

1 a new deore chainring on front 2 new sach BMX chain 3 DMR chain tensioning device (screws into
where the derailler went) 4 bmx cog on rear wheel 5 bolt on dmr rear wheel dished/spaced for
singlespeed

Hes got the tension fairly tight, but when hes really pedaling hard up a hill the chain slips and
makes a noise and then allows him to keep pedalling.

Anyone have any suggestions as to what might be the problem?

Sounds like a case of insufficient chain wrap on the rear sprocket. SS freewheels are notoriously
crude with short nubby teeth (ACS are the worst with Dicta close behind), and require plenty of
engagement with the chain if they are not to cause it to "climb" the teeth. A BMX bike does not
allow this because its slot-tensioned chain can't give up any slack like a tensioner can.

I'm nor familiar with the DMR tensioner you mention, but I had a similar experience with a Surly
Singleator once. The Surly is furnished with two springs, a "pushing down" spring and a "pulling up"
spring. When I used the "pushing down" kind, the chain wrapped maybe
1/3 of the circumference of the freewheel, and the chain would slip under hard pedaling. Switching
to the "pulling up" configuration allowed the chain to wrap a little over 1/2 of the freewheel and
the problem was solved for good.

Quoted message said:

Do you think if he bought a sach mtb chain instead of a BMX it would work better?

No, but a freewheel with taller and more precise teeth would certainly help. That means a NOS
Suntour model (hard to find), a Shimano unit (limited sizes), or the breathtakingly expensive White
Industries ENO freewheel.

Chalo Colina

Me said:

Hes got the tension fairly tight, but when hes really pedaling hard up a hill the chain slips and
makes a noise and then allows him to keep pedalling.

He describes it as the feeling you get when a chain is worn and it skips off a multispeed
cassette. Except in this case all the componants are brand new.

I'd be suspicious of the freewheel. Those BMX cogs can be pretty cheesy. Try cleaning it out, and
oiling it, and maybe that will help. My guess is a pawl is sticking or a spring is missing.

Quoted message said:

Do you think if he bought a sach mtb chain instead of a BMX it would work better?

Nah. I've used BMX chains on my track bike, which now has a MTB chainring, for years.

--

David L. Johnson

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