Cycling UK Forum

I've just replaced the bottom bracket on my Wife's 2017 Boardman Comp 650B and I thought a description may be helpful to others. The first job is to clean the bike and remove the chain from the chain wheel. This bike is fitted with a Suntour XCM HTII crank with a 73mm BB width and the first difficulty encountered was removing the LH crank, which is a self-extract type. The theory is to slightly loosen the lock ring with a peg spanner (it's left-hand thread and a decent circlip plier will slacken it) and use an 8mm allen key to unscrew the centre retaining bolt to draw off the crank. I quickly realized that the lock ring thread would possibly strip due to the extreme force required to remove the seized crank from its taper. A full kettle of boiling water was run slowly over the area to expand it and the crank then slowly came off without excessive force.

Take a note of the preload arrangement - there's a wavy washer, then a serrated lock plate (serrations face the BB). The serrations engage with a threaded preload adjuster, which has serrations that face away from the BB. Remove these items and withdraw the axle from the drive side.

After some research I decided that a Shimano XT BB-MT800 would be a good replacement. Removing the old BB took some difficulty. I had already got an Icetoolz HTII tool but couldn't apply enough pressure to remove the bearing carriers. As the old ones were scrap anyhow, I used a large stillson and it still needed a fair bit of effort even with penetrating fluid. Water had got inside the BB past the seals and corroded the threads because the centre plastic tube was too short to engage the O rings at both ends. The drive side bearing had completely rusted up and seized. This bike has never been pressure washed and always carefully looked after.

I cleaned up the surface of the axle with 500 wet & dry. Fortunately no serious damage had been done. The BB threads in the frame cleaned up with steel wool.

The new BB came with a plastic adapter tool. The BB-MT800 has a smaller diameter than the old HTII - the same as a SM-BBR60 (41mm/16 spline) but the adapter did not fit my tool so I machined it down in the lathe. In retrospect I would have bought another tool, so that's one to get to add to my growing collection. I measured up the shoulder of the old unbranded bearing carriers and they were very close (within 0.03mm) of the new ones. The drive side originally has a 2.5mm plastic spacer and looking at the Shimano dealer instruction sheet it shows this is correct for a 73mm BB. The new assembly comes with three metal spacers so I used one of these.

Reassembly is straightforward. I lubricated the axle before fitting and everything went together smoothly. The threaded preload adjuster only needs to be finger tight, then orient the serrated locking plate to give the best engagement. Fit the wavy washer, then the crank and tighten the 8mm centre bolt and finally tighten the lock ring. After reassembly I didn't even need to reindex and the whole thing is much smoother than its ever been.

Thanks - that's just the information I was looking for.

Mick

Quality can be a misleading word because from a customer perspective it's highly subjective and based on personal expectations, whereas in manufacturing it's a reference to materials, processes and assembly. I prefer references to standards, as this provides a defined baseline for comparison.

The basic retail price of a consumer product is roughly 5 or 6 times the burdened manufacturing cost - that is, the entire costs involved in a manufacturer making and selling a product. But certain goods - often leisure goods - have a much higher multiplier because the price is based on perception of exclusivity, performance, branding, or other characteristics that consumers are prepared to pay for. In economics there are goods where demand increases as the price rises - a Veblen good - where the actual manufacturing cost can be detached from the selling price. So you have to be careful linking price to value (or 'quality').

So, a £15 helmet is likely to have been made for maybe £3. But when considering this you have to look at the manufacturing process and volume of production. The machinery and investment involved may be far more than (say) a small manufacturer with low-volume and comparatively inefficient production systems. Buy a £2 jar of jam from a farmer's market. Now, how much if the seller hand-crafted the jar and lid? Would that be a higher quality item than a jar from a supermarket?

When looking at any safety equipment it's important to determine what standards are met, whether these are statutory, and whether the item has been tested to that standard. Sometimes this is stated as "Meets or exceeds", which is not the same as "Tested to". Also, you have to be aware of cheap products have fake standards labeling. Once a standard is met, how does a perceived 'higher quality' item justify the price - is there a redundancy overhead that does not contribute anything to the basic safety aspect? It may come down to an impression of luxury, feel or finish, packaging, brand kudos etc. Because (say) a Lidl helmet is sold by a supermarket chain and has a house-branding, it does not mean it doesn't perform as well as any other much more expensive helmet that passes the same basic standards. A critical aspect of a helmet is how it fits: Regardless of price, a poorly fitting, insecure helmet is no good and equally, so is an uncomfortable helmet where strap adjustment is compromised to ease the discomfort.

How does Dawes measure their frame sizes for the Nomad? The range is 16",18",20" but is this measured the old way - centre of bottom bracket to top of seat post, or some other method?

I was wondering why there's mention of 610 frames for the raven, when the 2015 brochure I have only goes up to 600. I didn't know they changed the geometry. I'll also take a look at the rest of the range.

I'll keep a lookout for a 60cm frame (600L). I think I could be looking for a while.....

Yes, the Cougar is an ATB design with a level top bar and more of a road-biased geometry. It has a nice 531 double-butted lugged frame in the old Dawes style. I have an extended seat post and stem, both at their limit. It does work pretty well for gentle touring holidays, but loaded up it needs a lower gear or two for hill climbing (lowest is 22.5" in old money, which on my post-surgery knees is a bit too high for me). I like the look of the Thorn/Rohloff combination and took a look at the current mega-brochure but the Raven is not listed. I did find an older 2015 brochure for this particular model and they list a 600L. It looks like they've now changed their sizing from mm to cm. A larger frame than I already have would maybe be more comfortable. The problem is I've ridden the Dawes for so long and never looked at anything else.

I'm 194.5cm tall with a step over of 92cm. I'm looking to replace my venerable Dawes Cougar with a used Thorn - maybe a Raven with Rohloff hub. Now, I never took any notice of the frame size of my Dawes until I checked today and it's 21". That seems to be a small frame for my height and much smaller than perhaps most sources would recommend.

So, looking at Thorn frame sizes, they use (for example) 565L. Just to be certain - is this the frame size in mm - 565mm/56.5cm? and this would be a long top tube?

My present bike would be 533 if that was the case. If there are any taller Thorn riders out there, what size frame do you have and is the size a good comfortable fit?

Thanks. I removed the RD and did what you suggested. There were two issues - the hangar was slightly bent outwards, and the parallelogram slightly out as well. I've just had a session of slightly tweaking and reassembling and the second attempt has got it working perfectly. The L screw is now in the centre of the range and the RD maintains its alignment. The next step is to make a proper alignment tool, but for the time being the bike has never changed and run as smoothly as it does now.

I did some checks with a straightedge this morning to re-check. Whilst it looks OK, it does angle outwards slightly by 1mm throughout the range, except that at the extreme of travel (largest rear cog) this is just a little under 2mm. Measurements are taken comparing top and bottom of side plates compared with vertical. The cassette sits closer in than it did previously and now the RD is at its extreme of travel the outward angle looks to be the problem because if I apply gentle pressure to align it truly vertical it goes into gear (though the L screw still has to be backed right out).

Gregoryoftours mentioned this distortion in an earlier post with SRAM RDs. Mine is an X5. Very low mileage, never dropped and no pivot wear. Just looking at it again and the main hanger pivot looks as though it may be at a slight angle, which would account for the overall misalignment.

Chainline is 46mm front, 44.5 rear.

Some experiments with shimming fixed the problem, but because the shim is so narrow and it has to sit in a machined recess in the 13T cog I decided it may not be reliable. So this morning I went and bought a new SRAM PG-1050 cassette to replace the original PG-1020. Same x10 11-36 gearing. Immediately the original problem was resolved and the bike no longer rubs on the 11T and shifts really smoothly. There's a difference in the machining on the face of the 13T - it doesn't have a recess and the spacing is equal right the way across the cassette.

However, there's now insufficient travel in the RD to shift onto the largest rear cog (with the 24T front chain ring). I eliminated the cable from the equation and even with the L screw right out and with considerable hand pressure it's only just able to go into bottom gear. This has never previously been an issue and the L screw is usually about halfway out. Because the RD is mechanically at the end of travel no amount of cable tension can pull it over that last bit. The cassette is torqued up to 40N/m as per specification. There are no spacers or shims between the free hub and cassette, just like the PG-1020. Any spacer there would throw out the 11T and leave me back where I was.

Any ideas?

The agricultural paint I've used is Corroless and Corrofast and it lasts well and is tough but colour chioce is limited. It can be wet flatted but needs a cure time after the original drying time. I also have some paint sold for painting skips and this contains a phosphate rust inhibitor. I've used this over zinc primer and it's held up extremely well.

Just about the best product I've used is an moisture catalyzing automotive paint. It's made up in a rattle can and has a good shelf life, is really tough and can be wet flatted. I first used a brush version years ago on a motorcycle swing arm and it didn't show any marking after years in service. The rattle can stuff hardens really quickly - I did a spray job outside in the summer, took the can back into the house and when I went back out it the finish had cured enough to reassemble. It's easily as hard as powder coating.

I have some friends in the motorcycle trade who use 2-pack rattle cans quite a lot. The finish is really hard and tough but once activated the whole can needs to be used up before it sets in a lump. You really need an air-fed respirator to use it safely. No time for between-coat flatting and you need to get a good finish off the can.

The bike is the MTB Comp that came out in 2016 and the chainset and cassette are original. I can screw the H screw out enough to get clearance, but by then the chain starts hunting to try to jump off towards the chainstay. I can get it nearly there, but not quite and I'm coming to the conclusion that the answer is to shim out the 11T as it is closer spaced than the rest. I can't figure out why this would be the case unless there is a shim missing there. I think 0.5mm would easily fix the problem if the RD would tolerate this and still shift OK. The chainline looks fine, otherwise though I've just used a straightedge to check. It is a SRAM rear mech so I'll make some further checks to see if it gets skewed.

It's certainly the rear that's rubbing. I just took another very detailed look and can see the chain catching on the adjacent 13T. At the rear of the cog the chain is nicely centred, but the chain angle is just a little but too acute to clear the 13T. If I release the skewer and push the axle over towards the opposite side slightly (to effectively shift the chainline) the problem completely disappears. I'll try a temporary shim on the 11T and if that works I'll machine a shim out of some stainless sheet as a longer-term fix.

The front chain rings are 38/24 and the problem occurs in the highest gear (no cross chaining) - 38T front and 11T rear. When I adjust the RD I make sure there's slack in the cable so that the H screw isn't limited by cable tension and then adjust the H screw for best running in the highest gear. Then adjust the cable tension to set the indexing The clearance on the front cage is 1mm from the outer edge of the chain. The FD changes quickly and smoothly.