Nomad BB bolts

[Bippers]

I was doing some fine tweaking of my BB this morning. I had slackened off the two pinch bolts did my adjustment and was re-torqueing a bit at the time the two bolts, using a torque wrench. One of the threads then stripped...whoops!
Now, I'm an engineer, so like to think I know what I'm doing. Why do Thorn use such a fine thread rate for. I have ordered two new bolts, I think I will get away with it, but tempted to tap out to a coarse 8.0m thread and fit new appropriate bolts. Has anyone done this before?

[Danneaux]

One of the threads then stripped...whoops!

Oh, dear.

Why do Thorn use such a fine thread rate for.

Most likely to facilitate fine adjustment and the tighter, more shallow pitch discourages the bolts from backing out. As I recall, it is a 0.75mm pitch.

tempted to tap out to a coarse 8.0m thread and fit new appropriate bolts. Has anyone done this before?

I would resist for the reasons cited above. The coarser bolts will drive home more quickly and it will be difficult to get them to hold as well.

I would suggest drilling out and heli-coiling the threads. Have you checked...are the bolt threads stripped, the BB posts, or both? If it is a faulty bolt or threads, a replacement bolt of the same size may well do the trick.

A general caution, not aimed at you 'cos you used a torque wrench: I have seen eccentric BBs with grub screws of this design ovalized by overzealous tightening. It can happen, sadly.

Best and sympathetically,

Dan.

[Bippers]

after the screw stripped out I ran the better of the two screws through and feels ok but I'm not sure I will ever be happy

[Danneaux]

after the screw stripped out I ran the better of the two screws through and feels ok but I'm not sure I will ever be happy

There's a couple alternatives. One is a thread-insert kit, example here:
https://www.amazon.co.uk/PowerCoil-3523-8-00K-0-75-Thread-Repair/dp/B00MV1PE02

The other is to use a thread-repair compound, essentially an etching polyamide/polyamine epoxy resin -- and retap through it. I would avoid it in preference for the helicoil insert. Reviews here: https://www.amazon.com/product-reviews/B000WSEUII

Even better would be if the new bolts were a good match and you could achieve a nice, sound fit in the existing bosses. Fingers crossed for your good luck.

Best,

Dan.

[Bippers]

Hi Dan. I think the heli coil idea is good. Still don't like this fine thread malarkey, just feels bad to me. Never stripped a thread in my life, so a warning out there to anyone torqueing up these bolts.
I love my Nomad but this eccentric boss is the downside of a brilliant bike.

[Bippers]

Well Dan, just ordered a helicoil kit on Amazon, with 20 coils. May be interested at flogging on when finished with it, although one day my partners Raven may need the same treatment. Thanks for your help. Bippers

[mickeg]

I do not use a torque wrench on those bolts and there have been a few times that I did not tighten them as much as I should have.  I once noticed that one was loose, I concluded that I was lucky that I did not lose it.  I added blue loctite but decided later that was a mistake so I cleaned off the loctite.  Now I wrap a rubber binder around the bolts to keep them from unthreading if one gets loose.  Someone on this forum suggested I instead use rubber bands cut from inner tube rubber, it was suggested that it will last longer, I have done that after the photo was taken.

Last time I ordered supplies from SJS I put one spare bolt on the order too, that is in my bag of spares to take on tours.

[Danneaux]

I had slackened off the two pinch bolts did my adjustment and was re-torqueing a bit at the time the two bolts, using a torque wrench...Never stripped a thread in my life...

It might be worth checking your torque wrench. I have a number of them and send the click-type to be recertified annually, as their accuracy can vary with use. In-between, I check the click-type against my beam wrenches.

As a general caution, it is good practice to slacken the tension on click-type wrenches every time they are put away for storage. Even so, they can sometimes get out of adjustment and their construction means they almost always read low so failures can occur if they are out of range.

This will sometimes cause the sudden onset of broken or stripped screws.

I used to have an automotive repair business and so had to deal with torque settings on a regular basis. This resource might be useful:
http://www.boltscience.com/pages/quality.htm
Don't forget, lubed (wet) torque values must be lower than clean, dry torque values; the kind of lubricant used can make a difference of between 15% and 50%. See: http://raskcycle.com/techtip/webdoc14.html This caution also applies when initially torquing bolts with still-wet thread-locking compound (i.e. Loctite).

Best,

Dan.

[Danneaux]

Well Dan, just ordered a helicoil kit on Amazon, with 20 coils. May be interested at flogging on when finished with it...

I hope it will work out well for you. I'd still try the new bolts first to see how tightly they fit. It would be nice if that solved the problem completely without further intervention.

By the way, M8 x 0.75mm is the same diameter and thread pitch as chainring bolts.

Best,

Dan.

[Dave Whittle Thorn Workshop]

I've genuinely never seen a stripped thread on a Nomad eccentric only ever screws, it take out the eccentric and chase the thread with a M8x0.75 (metric fine) tap just to be sure. Theres allot of thread in there so i'd be truly shocked if all the thread is stripped and a bolt now wont hold. Have you got some new bolts?

[hendrich]

"I was doing some fine tweaking of my BB this morning. "
You are actually referring to adjustment of the eccentric rather than the BB, is that correct?

The Thorn eccentric is of interest. I have experience with the eccentric on our 25 year old tandem. Slippage can be a problem when the previous divots are near the present location and I am sure each time I adjusted the timing chain I created new divots. I was often concerned about stripping the screws because much force is used, but it has not happened in that length of time, with hundreds of adjustments. I presume the screws are a high quality steel, but not a bad idea to carry a spare. I was happy to see that Thorn uses a large external hex nut, rather than an internal hex set screw which is also susceptible to stripping from within and also filling with muck.

After about 15 years the older divot alignments created fine positioning problems, so I machined the indentations away and it fixed the problem. But a better fix would be to just have a spare eccentric stored away, so that in the distant future it can be swapped.

[mickeg]

Someone on this forum (I do not recall whom) suggested flipping the bike upside down and taking out one screw so you can look in the hole and see where the little conical shaped holes are that are pressed into the eccentric (I often call them divots) when adjusting chain tension.  I have done that ever since I read that suggestion and I try to make sure that each new divot that I create is at least 5mm (approximate, I did not measure) apart.  I suspect that if the divots are closer than about 5mm to each other, that is when you run the risk of it slipping and creating a groove.  Now that I have several divots pressed into the eccentric, by looking in one bolt hole when I make my adjustments I can often re-use existing divots instead of creating new ones.

Unfortunately I have a few divots in places on my eccentric that violate my 5mm rule  that were created before I read that suggestion.

[Bippers]

The most annoying thing about all this is ,I was not adjusting my chain tension but trying to eliminate that annoying Thorn click when the pedals/BB are loaded. It occured to me to make sure the front and rear sprockets were running absolutely square. I found the chain was running a tiny tiny fraction off centre of the chain ring so was repositioning the BB eccentric about 1/32, or maybe even less. I'm clutching at straws I know but I'm losing sleep over this!

[mickeg]

Clicking that occurs as you pedal that has a frequency of one or two clicks per revolution are tough to find.  I can remember several:

My Nomad, had a click every time i pushed down on the right pedal, tried lots of things.  Finally was standing on the right side of the bike, standing on my left foot I used the right foot to push down on the right side pedal, held down the right side brake lever (in USA we use the right lever for the front brake), intermittently pressing hard on the pedal and then releasing the pressure to see if I could tell where the click was.  By standing on the side of the bike instead of being on the bike I noticed that the click was not in the bottom bracket area but instead was from the rear dropout area.  From that I figured out that the rear right side rack bolt was tight, but not tight enough as the rack was shifting in position on that bolt from frame flex as I pedaled.

I had a click develop in a pedal, switched pedals and it went away.  Some day I have to rebuild the bearings in that pedal, A530, I think there is a your tube video on it.

My left side bottom bracket bushing that is threaded into my eccentric was not as tight as it should be on my Nomad.  I tried many things until I finally decided to replace the bottom bracket, that was when I started to loosen the left side bushing and it was not as tight as it should be, so instead of removing it I tightened it and put the crank arm back on and gave the bike a test ride, the click was gone.

If one of my eccentric bolts was loose (happened once), I could feel movement in the crankarm as I pedaled.  I noticed that movement but I do not think I heard an audible click.  I suspected that one of my square taper crank arms was loose, but it was tight, next I tried the eccentric bolts and found that one was loose.

I have heard people mention clicks from loose chainring bolts, but I do not recall that ever being an issue to me.

I have heard of a seatpost having an audible click inside of a seattube but never happened to me.  With a Nomad where you need a shim I doubt that could be an issue since the seatpost is so much smaller than the seat tube.

If you have access to a trainer where you put the bike on the trainer and then pedal indoors for exercise, if you can put the bike in that and pedal it while someone else is listening for exactly where the click is, that may help.  But the listener has to be careful around a moving chain and spinning wheel, no loose clothing or loose long hair, etc.

ADDENDUM ADDED A DAY LATER

The bottom bracket bushing that I cited above, that was a Shimano UN55 square taper.

I had a squeak from a loose crank arm once (square taper) but it was a creaking noise, not a click.

[JimK]

I had a tough one years back, a loose seat clamp bolt. If I got off the saddle, the noise stopped. I had to be sitting down to flex the rails and loosen the clamp. It was one click per revolution.