Riding Mtn Bike with rear derailleur only

Hi, I've set my Mtn bike so I only use the rear derailleur, which gives me a choice of 8 gears. I didn't bother fitting the front derailleur as I never need to move off the large chainring. I thought this would reduce weight too.

However, a problem I've encountered here is that the chain keeps jumping off. Initially, I thought this was just because there were too many links on the chain and so I just reduced the number. However, now the chain is shortened so it can't even reach the largest rear chainring. BUT, the chain keeps jumping off at least once on every ride! So, the problem doesn't seem to be the number of links!

So, the solution to this problem, I thought, would be to fit the front derailleur mechanism to keep the chain in place on the largest front chainring. However, to do this, it needs to be fitted with a cable and 'pulled' with the handlebar front gear lever over the front large chainring. I think the default position for the front derailleur mech is to sit over the middle front chainring.

Anyway, I hope that's clear. I'd appreciate any tips on solving this...Thx.

Johnny, the front derailleur should have some adjusting screws which will allow you to set it to stay in one position without a cable.

I run a 7 speed rear and use the front d as a chain guide ove the middle ring for just this problem.

Dog fang and bash guard.

Just fit a chain keeper. Either via the BB axle, or the seattube.

http://superstar.tibolts.co.uk/product_info.php?cPath=56&products_id=362
http://superstar.tibolts.co.uk/product_info.php?cPath=56&products_id=475

Great, thanks!

Or swapping the chainring to one without shifting ramps might do it.

"Or swapping the chainring to one without shifting ramps might do it."

So you mean like a chainring on a fixed wheel bike?

what size ring you using, it would work out better for chain alignment purposes (cross chaining isn't good from big to big) & pretty much eradicate your problem by fitting the ring onto the middle fixing point.
Likely you wouldn't need a dog fang (et al) at all.
ATEOTD there must be something up because your chain wouldn't normally unship like that derailleur or no derailleur/with or without shifting ramp chainrings.

Or swapping the chainring to one without shifting ramps might do it.

I've ridden a lot with a single ring with a 7/8-speed rear. You can't avoid the chain coming off, mainly due to chain resonance during shifts, and the occasional pot-hole.

I'd recommend fitting a chain keeper.

what size ring you using
It's a standard Deore 26.36.48t. I only use the 48t ring.

Would a dog fang alone do the job? It looks a bit flimsy!

Or swapping the chainring to one without shifting ramps might do it.

This

I used to run this ring http://www.tredz.co.uk/.DMR-Saturn-Chain-Ring_26728.htm

back in the day with 9spd on the rear. Chain never fell off. I moved the chainring to the middle ring position.

Hi, I still haven't solved this problem.

I wondered if this'd be a better option: http://www.chainreactioncycles.com/Models.aspx?ModelID=10137

no that won't work, your chain falls off from the top, it's effectively already 'fallen off' by the time it reaches that type of device. I'm running 1x8 on my big full sus with just the front derallieur, chain's not dropped yet. Can't you fit a cheap front mech and use the sdjusting screws to hold it in place?

I run 1x9 with the superstar BB mount guide as posted by smallfurry above, never drop the chain out on the trails only when wheeling the bike backwards but I suspect that's because I'm using a very worn ramped inner 32t ring. Highly recommend the superstar guide