I have shimano rd6500 rear derailleurs. when chain is on small chain-ring and smaller rear sprockets the derailleur cage is rubbing against the chain.How do i tension chain to hold cage away from chain, help,Martin from Dublin

I'm not sure what you mean by "shifter blade", but I might assume it might be the cage of the derailleur. On the front derailleur there is either a rivet or a small bolt at the trailing edge that holds the two halves together, if it is a rivet then it is not repairable and the derailleur will need to be replaced, if it is the bolt, it is probably a 8mm socket head, tighten to the right. If it keeps loosening up from road vibration then the threads could be stripped (replace the derailleur), or else put a drop of Blue Loctite on the threads to prevent it from backing out. If you are talking about the rear derailleur cage that holds the two pulleys in place, these have two Allen type bolts, probably 3mm or 4mm Allen wrench size. The bolt slides through a small bushing inside the plastic pulley wheel, the bushing is slightly wider then the pulley to prevent over tightening the cage plates against the pulley, thus preventing the pulley from spinning freely, use the Blue Loctite if the bolts keep coming loose. Blue Loctite (also known as 242 Loctite I believe) is the removable type and provides some extra friction to prevent bolts from backing out. Now if by "shifter blade" you are referring to the shift/brake levers, these have a small amount of "play" in them from the factory, a little bit of wiggle. They basically are not serviceable. Try adjusting the derailleur cable to see if that removes excess play. If they still have an excessive amount of play in them, then you will need to replace the shift/brake levers as a unit. If you do this, make sure you get the shifter that is designed for the number of cogs you have in your gear cluster and front chain rings. I would recommend also replacing your chain and rear cluster at the same time so that all part wear evenly for optimal shifting performance.

This may be to do with the replacement having a shorter cage, so it can't go on the big sprocket and big chain ring at the same time.

Try to not use the big rear sproket and the the big front chaining at at the same time,

Snagging? Like hooking on the teeth in a bad way? Go through all the rear derailleur adjustments.

http://www.parktool.com/blog/repair-help/categories/derailleur-systems

Look for worn parts...

http://sheldonbrown.com/chains.html

Get out your wallet.

the system was not designed to have rub.

If your chain is too long, there can be enough slack to rest on the front derailleur. Also may want to make sure you have the B-tension screw set correctly on the rear derailleur.

If you still getting rubbing, swing the bike by your local bike shop to have them take a look (thats free) and make sure you installed everything correctly. it's very difficult to diagnose properly without seeing a picture or the actual system.

The outer limit is too close in or the cage is misaligned or the BB is too short or....

http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

You don't say if this happens in the BIG ring, small ring or both. If it's just the big ring I'd suspect there isn't enough chain length.

Cross chaining is unnecessary and bad for your drivetrain. I never go more than one cog past the center of my cassette opposite the chainring I use.

http://www.parktool.com/repair/readhowto.asp?id=26

Set the rear derailleur to the lowest gear (big cog) and the front to the lowest gear (small chain ring). Disconnect the derailleur cable. Screw in the adjuster for the cable tension all the way (this adjuster is on the shifter of a mountain bike or the down tube of a road bike). Pedal to make sure the chain is not rubbing on the derailleur cage. If it is, adjust the "L" setting on the derailleur until the chain moves by without touching the cage. Now pull taut and reattch the cable and shift the front to the big ring while pedaling. If it does not shift up well or completely, hold the shifter past its normal shift and adjust the "H" screw so that the derailleur allows the shift. Shift into the highest cassette gear and keep pedaling. The chain should not be touching the front derailleur's cage when you pedal. Adjust with the barrel adjuster until the chain moves freely without touching the derailleur cage.

i hope this helps
-matthew

Wash, degrease and scrub the chain and derailleurs with a good degreaser (like Simple Green). Dry the chain and relubricate it with an appropriate bike chain lubricant (not oil or WD-40). Shift the derailleurs to the smallest chain ring and cog on the cassette (low front gear, high rear gear) and then loosen the cable at the derailleurs, pull the cables taut and reattach them. If the derailleurs still need adjustment, here is a procedure for it:
Flip the bike over (so you can pedal the bike manually while you shift) and shift the front to the middle chain ring. Shift the rear to the highest gear (small cog). Release the cable from the pinch bolt on the derailleur. Adjust the screw marked "H" on the derailleur until the jockey wheel on the derailleur is aligned perfectly over the small cassette cog. Set the cable adjuster on the derailleur to the middle of its range (find this by screwing it all the way in and then count how many revolutions it makes until it screws out completely. Screw it back in one half of the total revolutions). Reattach the cable and shift to the lowest gear (the biggest cog). Over-shift and hold on the shifter, then adjust the "L" screw on the derailleur until the jockey wheel sits just past the last cog. You have to hold the shifter to do this. Now shift into the middle gear (or one of the two middle gears if the bike has an even number of gears) and adjust the derailleur using the barrel adjuster you previously set to the middle of its range. Adjust it so that the derailleur is sitting perfectly over the appropriate gear. Shift up and down the cassette while pedaling and in every gear, reverse pedal (freewheel) to make sure the chain does not hop. Adjust as necessary until all gears are smooth.
Now the front:
Set the rear derailleur to the lowest gear (big cog) and the front to the lowest gear (small chain ring). Disconnect the derailleur cable. Screw in the adjuster for the cable tension all the way (this adjuster is on the shifter of a mountain bike or the down tube of a road bike). Pedal to make sure the chain is not rubbing on the derailleur cage. If it is, adjust the "L" setting on the derailleur until the chain moves by without touching the cage. Now pull taut and reattch the cable and shift the front to the big ring while pedaling. If it does not shift up well or completely, hold the shifter past its normal shift and adjust the "H" screw so that the derailleur allows the shift. Shift into the highest cassette gear and keep pedaling. The chain should not be touching the front derailleur's cage when you pedal. Adjust with the barrel adjuster until the chain moves freely without touching the derailleur cage.
That should be it, unless there is another mechanical problem causing the missed shifts, like a bent derailleur hanger or damaged teeth on the cassette cogs or a bad derailleur. If it is still problematic, come back for further information.

i hope this helps
-matthew

Try this first:
Shift into the small ring and release the cable. Pull it tight (with pliers) and re-tighten the cable. It should shift now. If it doesn't, the solution is a little time consuming, so i apologize in advance.
First, flip your bike onto the bars and saddle. Now shift into the small chainring and your lowest cassette cog (the largest in number of teeth). Release the cable from the front derailleur and set the adjustment knob for the front derailleur to its center point. You should find it on your shifter. Now adjust the "L" setting on the derailleur while turning the crank so that its stop sets it in a position where it just skims the chain but does not touch it. Now pull the cable taut and re-clamp the cable. Shift into the middle ring and shift the rear derailleur to its highest and lowest gears, making sure the chain does not rub the front derailleur. If it does rub (it will be in either the lowest or highest cog on the cassette), adjust the front derailleur by way of the adjustment knob to clear the rub. Then shift into the big ring and you should have no problem. Set the "H" stop if necessary.

Try this first:
Shift into the little ring and release the cable. Pull it tight (with pliers) and re-tighten the cable. It should shift now. If it doesn't, the solution is a little time consuming, so i apologize in advance.
First, flip your bike onto the bars and saddle. Now shift into the small chainring and your lowest cassette cog (the largest in number of teeth). Release the cable from the front derailleur and set the adjustment knob for the front derailleur to its center point. You should find it on your down tube. Now adjust the "L" setting on the derailleur while turning the crank so that its stop sets it in a position where it just skims the chain but does not touch it. Now pull the cable taut and re-clamp the cable. Shift into the middle ring and shift the rear derailleur to its highest and lowest gears, making sure the chain does not rub the front derailleur. If it does rub (it will be in either the lowest or highest cog on the cassette), adjust the front derailleur by way of the adjustment knob to clear the rub. Then shift into the big ring and you should have no problem. Set the "H" stop if necessary.