Changing a chainwheel - Mercury

[quilkin]

Hello, I'm a  first-time Rohloff user with a second-hand Mercury about 10 years old. I'm going to change the 47-T chainwheel into a 39-T tooth one (the rear is 17 teeth). Since I've not used (or adjusted) an EBB before, I wonder if someone could check my proposed method of making this change?

• Remove old chainwheel
• adjust EBB to give smallest distance to hub
• Fit new chainwheel; shorten chain (probably by 4 links?) and fit
• adjust EBB to give sensible tension

I'm hoping this will give me the max time before the EBB needs adjusting again (the chain is almost new, btw).
Thanks
Chris

[PH]

That's pretty much it.  There's just one catch - If your Mercury has a mini EBB (Gold colour) which it almost certainly does, there are only certain  Chainring/Sprocket combinations which work.  It was detailed in the original brochure, but I don't seem to have a copy, maybe someone else does, otherwise a call to Thorn will probably get the answer. The gearing you want, might require a change of sprocket as well as, or instead of, a change in chainring.

[JohnR]

See page 16 of the Thorn Owner's Manual http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf .

Is a half link one way of getting the chain length within the range provided by the EBB?

[quilkin]

That's pretty much it.  There's just one catch - If your Mercury has a mini EBB (Gold colour) which it almost certainly does, there are only certain  Chainring/Sprocket combinations which work.  It was detailed in the original brochure, but I don't seem to have a copy, maybe someone else does, otherwise a call to Thorn will probably get the answer. The gearing you want, might require a change of sprocket as well as, or instead of, a change in chainring.

Thanks. A 47:17 combination is shown on page 47 of 'Living with a Rohloff' which also (at the bottom) says it should be OK for a Mercury (if I understand correctly!)

[PH]

Thanks. A 47:17 combination is shown on page 47 of 'Living with a Rohloff' which also (at the bottom) says it should be OK for a Mercury (if I understand correctly!)

Yes that was probably the chart I was thinking of, your proposal looks fine. Along with the linked instructions posted by JohnR, you're good to go.
While you're at it, take the EBB insert out, give it and the frame where it inserts a good clean and slathering of grease/copper-slip, they have an inclination to seize, sometimes even if they've been greased and it's washed out, it's no big deal to free it, and Thorn have provided a useful video
https://www.youtube.com/watch?v=XdFLDSeK7LY

[quilkin]

Thanks for help so far. I have changed the chainwheel but can't get the EBB to rotate. I have used the suggestion with coins to open up the slot, but no luck. Two questions: (a) is the special 'Thorn Mercury Eccentric Pin Spanner' essential? Maybe one is supplied with a new Mercury. (b) is it necessary to remove the BB itself? Photos show no BB installed, but maybe that's just for clarity?

Probably a different thread needed, sorry!

[JohnR]

I've rotated an EBB by inserting the end of a long Allen key of suitable diameter into one of the holes and then, while holding the free end of the Allen key, pushing it with the crank. However, if it's really stuck then you might need the proper two prong EBB tool. Alternatively, you might be able to knock the EBB sideways to remove it for lubrication. Before you do that check if the end of the EBB are flush with the frame. If not, note any offset as this is your reference when replacing in order to get the right chainline.

[PH]

I wouldn't force it, my next step, with the coins in, would be to squirt some Plus Gas in there and leave it a day.
The pin spanner isn't really necessary, even if it was it needn't be a specific Thorn one.  As well as the allen key method John suggests, you could use two screws/bolts (M5 I think) in the holes and a flat edge, like a spanner,  between them.
It should rotate with or without the BB in, but if you're going to remove the BB to grease it, then it's out of the way to deal with the EBB.

[quilkin]

Thanks, PH.
I've now tried PlusGas (had to wait for it to come into stock) and waited nearly 24 hours. Still nothing moving. I have made a copycat pin spanner from Meccano parts (4mm rods fit nicely!) but that doesn't help. Tried tapping it sideways as well, with a rubber hammer.
The coins are in place and the shell has opened enough to get a  thin card into the area underneath the shell bolts (about 5 Nm); I don't want to risk opening it too far and breaking something.
Also, I have removed the crankset and the 'floating' BB cup from the EBB but cannot shift the  BB itself, even though I have the correct spanner and have tapped that with a hammer. Since the BB doesn't shift either, any force on it should transfer to the EBB in its shell. But it still doesn't move

All this is most disappointing. I was planning to go off on a week's tour on Tuesday. Any ideas? I was wondering about asking for a 'used' chain from my LBS (the existing one is almost brand-new) and adding a half-link if required (It's currently about 1/4 inch too long, and the up/down movement is far more than the 60mm that Thorn recommend).

Then send the whole frame to Thorn for a service later.

[Aleman]

Stupid question, but you have removed the bolts on the frame, holding the EBB in place??

Don't ask why I would ask that question? You really don't want to know, suffice it to say, it IS possible (on a Dawes Supergalaxy Twin) to adjust the EBB without doing so ... You just need a very long lever

[PH]

How frustrating!  Steel is very elastic, right up to the point where it isn't!! I'm inclined to be a bit on the cautious side, the consequences can be severe.
I'd keep going, you're trying to break the bond, so I'd be working it back and forth on whatever limit you feel comfortable with, tighten it back up, loosen again, squirt some gas, tighten again.... Whatever you're using as a pin spanner, leverage is your friend, as long as it's securely in the EBB a long bar on it ought to help.
Good luck.

[JohnR]

First I would open the clamp a bit more and give it a few more whacks with a hammer (perhaps a proper one - a rubber one doesn't give enough sudden impact. Another possibility would be use a hair dryer or heat gun to heat up the frame around the EBB. If the frame gets hotter then it should expand more than the EBB.

Also, if there's a bit of a gap between EBB and frame in the area of the clamp bolts then I would be tempted to replace the BB and cranks and then give the cranks a very firm tap with a big hammer towards the clamp which might get the EBB to release from the frame on the side away from the crank.

[quilkin]

Thanks for all suggestions. I've now tried a heat gun (almost started to discolour the paint), and hit parts as hard as I dare. Still nothing moving.

So, for the short term I have fitted a slightly worn chain from another bike. It's 3/32 rather than 1/8" but seems to sit nicely enough on the sprockets. I have refitted the cranks but have not replaced any of the EBB bolts, and I'm going to ride it like that for a while, hoping that repeated pressure from turning the cranks may loosen something up..... it isn't a long-term solution because if the chain stretches too much (or breaks) I can't just fit a new chain, I need to find a part-worn one.

Maybe I'll change my planned tour next week to go via Bridgwater.....

[later] after a short test ride, the 3/32 chain doesn't feel right, all gears now feel like 1-7 only worse. Need to find a part-used 1/8" chain.

[JohnR]

Slightly off topic but Rohloff recommend a 3/32 chain https://www.rohloff.de/en/service/handbook/faqs#c9457

"All 1/2"x3/32" eight speed chains are suitable for use with the Rohloff SPEEDHUB 500/14.

Both the eight and nine speed versions can be used. This is because the chains are less elastic, and therefore, causing less wear on the chainring and sprocket (2mm) due to their identical link plates.

All 1/2"x1/8" bicycle chains are compatible with the Rohloff SPEEDHUB 500/14 sprockets.

However, these thicker chains are by no means stronger and not recommended for use with the Rohloff SPEEDHUB 500/14 due to their relatively short lifespan

In addition, these chains are too wide to pass through the Rohloff chain tensioner if in use."

So maybe your part worn chain isn't sitting as comfortably as you thought.

[quilkin]

Slightly off topic but Rohloff recommend a 3/32 chain https://www.rohloff.de/en/service/handbook/faqs#c9457

"All 1/2"x3/32" eight speed chains are suitable for use with the Rohloff SPEEDHUB 500/14.
Both the eight and nine speed versions can be used. This is because the chains are less elastic, and therefore, causing less wear on the chainring and sprocket (2mm) due to their identical link plates.
All 1/2"x1/8" bicycle chains are compatible with the Rohloff SPEEDHUB 500/14 sprockets.

......

Ah, thanks for that FAQ. The chain I found is from a 10-speed So I need a slightly worn 3/32" 8 or 9-speed, not a 10-speed. That's probably why it felt terrible on my half-mile test run.