Mercury slight pedalling resistance - Bottom bracket worn or loose ?

[CAM]

Hello
I'm getting a slight feeling of resistance/lack of smoothness when pedalling through part of the pedal revolution.
On investigation there is the smallest amount of play in the crankset.
Is this likely to be a worn out BB or a loose BB ? Is there any other potential cause ?
The crankset is a Thorn 130 PCD EX Bearing single crankset with integral BB, SJS part 24749L170 and was replaced when the bike was serviced 3 years ago. It hasn't done excessing mileage since.
I'd be happy for any advice before I start to dismantle....

[JohnR]

I see that SJS offer replacement bearings for that crankset https://www.sjscycles.co.uk/cranks/165-thorn-130-pcd-ex-bearing-single-crankset-with-integral-bottom-bracket/ but first I would check (i) that the bottom bracket is tight in the frame and (ii) the chain tension is not too tight - see page 12 of the owner's guide http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf . If the chain tension is variable then try to adjust the position of the chainring on the spider.

[CAM]

Thank you - tightening the crank seems to have worked. Although it needed someone stronger than me to do it!

[martinf]

Thank you - tightening the crank seems to have worked. Although it needed someone stronger than me to do it!

Or you need a tool with a longer handle for extra leverage. Even better, a big torque wrench. 

Typical torque values for square taper crank bolts are 35 to 50 Nm

[Moronic]

Thank you - tightening the crank seems to have worked. Although it needed someone stronger than me to do it!

Hope that's a permanent fix.

If not, you might find some info in a thread I started on a similar issue, here:

http://thorncyclesforum.co.uk/index.php?topic=14416.0

My crank issue was an occasional click, and some play that seemed to be at the bottom bracket. Turned out that the nut securing the BB had worked loose.