Chain issues with Explosif

[Pointer]

I have transfered lots of old kit onto a 2006 Kona frame, everything worked well on my 1993 Saracen frame, but now I have a really annoying problem where the chain is jumping off (to the pedal side of the crank - not chain suck). Setup:

Sugino XD cranks, unworn rings,
Newish Sachs chain, Shimano rear cassette, DX thumbies (on friction)
1995 LX rear mech
I have no front mech - but am running all three rings.

I have tried:
shortening the chain, checking the spring tension on the rear mech. I have never had an issue with not running a front mech before and the chainline looks fine...it's driving me mad! Any ideas?

 

[cchris2lou]

chainline between a 1993 saracen and a 2006 Kona must be different .

 

[Pointer]

Thats what I thought. I used a wider BB than is fitted to the Kona as standard so that the chainrings will clear the chainstays, but the chainline looks fine to me. It happens say hopping off a kerb, under tension uphill.
I was also worried about the rear wheel fitting into the frame, this was fine also.
I guess I could use a chain tensioner but I don't really want to.

 

[Pointer]

Thinking about it, my chainrings are actually further away from the BB than a standard Kona (I have a wider BB) the chain should (if the chainline is wrong) jump towards the frame?! But my issue is the chain jumping away from the BB.

 

[cchris2lou]

if you have been running your transmission always on the big ring at the front , and then using all the cassette at the back , your rear mech is probably worn out by having to stretch so much all the time .

 

[Pointer]

Yeah I guess I do tend to do that (bad habit). Thanks - might try a new mech first off

 

[kaiser]

Could it be derailleur hanger alignment ? How is the indexing?

 

[Pointer]

good point, I haven't really studied that and using friction shifting on the thumbies I might not have noticed it being out.

 

[Anthony]

Providing you're using the same bb and cranks, it shouldn't make any difference what frame you put them on, the rings are going to be in the same place relative to the centre line. Ditto the sprockets are going to be in the same place relative to the centre line.

I know you say that you're confident that the chain length and spring tension are fine, but I can't help thinking that the sliding dropouts on the 2006 Explosif might be an issue. Are they set to a standard chainstay length?