i blew my rear mech up last weak as it was a little to short when my rear shock was fully compressed,

i had crc post me a new rear mech and a pc991 chain (as before ) as i had binned the links so couldn’t
get the chain length correct,

i fitted the new rear mech today and the chain and let the shocks air out ,strapped the wheel in against the seat post and cut the chain etc, fitted a new cable, set the tension, stuck it in top and bottom sprockets set
the limit screws, job done,

bit of background, the blackspire front chain ring has only had two rides, max 40 miles. and is in no way showing any burrs or signs of wear or elongation of the tooth form.

the chain is new as stated, the rear mech is new straight etc, the hanger is not bent, the chain line is fine
as this is not changed,

the rear cassette is 6 months old, it’s done max 15 rides out all at woburn i think, a total of around 300 miles ?

is this my problem ?, it hardly shows any wear, the chain seems to slip over the cassette ..

help please

Possible.

Does it skip in all gears? Does the chain have any stiff links?

Very concerned you strapped the wheel to the seatpost with the shock at max compression.

You are supposed to measure the chain as large + large +2 rivets with the suspension set to the maximum effective chainstay length, wherever that may be in the suspension stroke (but probably not at max compression). The suspension paths are often very complex, with chain ‘growth’ then ‘shrinkage’ as you move through the travel.

I cannot see that you have left enough chain….

Final note: Write down the correct number of links used with a certain bike and the Cassette + Chainring combo for next time.
Not easy to compare when your old chain is 1% worn.

PaulD

the chain length is fine, followed advice on the forum last week,

big chain ring to big cog, through the mech and leave enough for plenty of movement all with no air in
shock on max compression,

http://www.pinkbike.com/news/World-Cup-Tech-Video-Setting-Chain-Tension-2011.html

i gave it a few more links than this.