Have any of you got any ideas why my stupid chain keeps derailing?
Ive built up an 06 enduro with a single 38 tooth renthal ring up front on shimano hone cranks, an 11-34 cassette at the back with a long cage xt rear mech, an e13 ss chainguide and a hope bashring.
This is the first time ive run a single ring set-up, and my thinking was that it would be simple to use and maintain and that my chain would never fall off.
Well, the opposite has been true. Before i fitted the bashring, the chain would often fall off the outside of the ring onto the crank arm on rough downhills and over jumps, it would do this irrespective of what gear i was in. Today was my first rough run with the bashguard on, and i lost the chain on the inside twice. GRRRR!
As far as I can see, ive covered all the bases. The chain, cassette and renthal ring are new, the Hone cranks seem to run perfectly true, in fact the only item thats not mint is the chainguide.
Any ideas, anyone? Before i go nuts!!

You won’t need more than a short cage mech. Replace it with a new ‘clutch’ model.

Long cage rear mech will allow it to flap about too much. Either tighten it up a bit and / or get a medium / short cage mech.

Also check you dont have a bent tooth that throws it off.

Shorten your chain.
Set your chain guide up properly.
Buy an SS specific chainring if you dont have one.

good work so far!! i always believed that a long cage mech would be necessary to allow me to run such a wide spread of gears at the back, 11-34 is a pretty big cassette? or have i got that completely wrong? could i run a shorter mech with a cassette as big as that? anyhow, i have a long cage rear mech on my other bike with a 38/28 double set-up, and the chain never comes off that 38 tooth ring. im not discounting this theory though. i will check for a bent tooth, but as the whole drivetrain is as good as new i dont expect this to be an issue.

david- the renthal ring i have is one of the gold downhill rings, so its designed for a single ring application. i have done a lot of messing about with the guide, and i reckon ive got it pretty good, although i will continue to make subtle adjustments. its a 38 tooth ring, so as the guide is for 36-40 ive got both top and bottom guide set up in the middle and the chain seems to run pretty straight in the middle gears.

shorten my chain, to take up some of the slack. now we`re talking. i will try this tomorrow. cheers!!

11-34 is a pretty big cassette? or have i got that completely wrong?

Yes. If you’re only using one ring at the front then a short cage is fine.

Your chain shouldnt be able to slip off the inside, the guide should stop it. There shouldnt be a gap for it to fall into.

When I used shimano hones and an E13, I had to file the granny ring tabs off to get the guide close enough.

I bet you havent set the guide up correctly.

have you put the 38t ring on the old “middle” tabs (assuming it was a triple intially)

the cassette has a really small PCD compared to crankset, thats why you need long cage -not number of teeth per se its the relatively large front diameter that takes so much chain. Long cage wont help, too much chain to slap about.
I reckon your problem is definitely its not set up right. Read the setup stuff online and start from scratch starting with chainline.
Dont get a clutch mech because that is 10sp and you have 9sp….

david, it sounds like youre right on two fronts. there is too big a gap between the guide and the ring, even though the ring is on the “middle” ring tabs. i had almost considered removing the bb spacer so the cranks sit closer to the frame..

how would i best sort this issue? can i remove the 5mm bb spacer? or should i add washers between the iscg tabs and the guide maybe?

and i found a link that explained why i would need a short/medium/long mech, so i apologise for being stupid!!! here it is, maybe it`ll help somebody elsehttp://forums.mtbr.com/drivetrain-shifters-derailleurs-cranks/when-use-long-cage-vs-short-cage-derailleur-205890.html

http://singletrackworld.com/forum/topic/any-reason-i-cant-remove-a-drive-side-spacer-from-my-htii-bottom-bracket

theres always a previous thread if you look hard enough. i actually think ive got the same issue on my enduro as this guy has on his bike. can any of you confirm whether or not it is ok to move the bb spacer from the right to left side, or if this will cause any detrimental issues? it would make my chainline run better in gears 1-4, and would bring the ring closer to the chainguide. i might try this tomorrow, unless any of you have any good reasons why it wont work??

Honestly, if your chain is set-up as short as it can the mech length makes little difference. Sounds like you need to spend time on the guide. Removing cranks spacers is not usually a good idea, tho always good idea check the instructions and make sure it was installed right in the first place before spending time faffing with the guide. Spacers behind the guide is an option if needed.

EDIT: you can move the spacers if you have no other options, tho make sure youve checked the cranks wont hit any part of the frame (including when the suspension is moving).

how would i best sort this issue? can i remove the 5mm bb spacer? or should i add washers between the iscg tabs and the guide maybe?

You want to set your chainring so it gives you the best chainline. You may not get it bang on, for example it may favour the lower or higher rear gears slightly. But set the chainline first. This may mean you use BB spacers, or it may mean you dont need any (on the drive side)

After you’ve sorted your chainline, set up your chain guide. There should be some spacers that go between the guide and the ISCG mount. Any washers will do if you dont have the ones that came with it.

Set it so its nice and close. I bet you’ll need to file off your granny ring tabs.

right, im in a much better mood now. my chainline looks like its about one bb spacer out, the ring is too far away from the guide and theres a huge clearance between the crank arm and the frame, so im going to start by shifting the bb spacer over to the other side (if i need a washer at all). then if the guide is still too far away ill try iscg washers (there arent any, david!), and ill take a link out of my chain. if all that doesnt work i`ll try a short cage mech.

thanks a lot everybody for helping with this!!!!

Chainguide setup is a black art, tbh the other suggestions are worth following up but getting the chainguide right will sort it so should be the priority.

ok, ive just spent an hour and a half messing about with this set-up. I dispensed with the bb spacer, and didnt add it to the other side. the hone cranks knocked right in and now feel far more secure than they did before, and the chainring lined up nicely with the 4th or 5th gear rather than 9th as it did before. there is still plenty of crank arm clearance on both sides.

with the crank further in the guide almost lined up, so i took out all the washers that i (and the previous owner) had packed it out with, and fitted thin washers between the frame and the guide to force it out a couple of mil. i then rebuilt the guide, which all lined up very well without needing any surplus washers, and the chain sits very snug between the guide and the bashring at the top and the bottom. also, the chainline looks great now.

the last thing i did was take a link out of my chain. i did try two links, but the rear mech was coming up too high in 1st gear with the suspension fully bottomed out, so i put a link back in. time will tell whether one link makes that much difference.

so the only suggestion from here that i havent done yet is to fit a short cage mech. ill take it for a thrash down a rocky hill and off some jumps and see how i get on, if the chain still derails then ill buy one.

thanks very much to everyone who helped on this, espescially davidtaylforth who came back to the thread 3 times with suggestions and tips. david, i havent had to file my granny ring tabs yet, but they are VERY close, as are the back of the middle chainring bolts (which are actually just scuffing). i reckon im onto a winner now, but the proof will be in the thrashing!!