Cycling UK Forum

I've got just over 100 miles on them and they're bedded in. They don't have the stopping power of the old worn blocks so I will be swapping them out for one of the suggested types, or some SwissStop ones.

Bmblbzzz wrote: ↑21 Mar 2025, 7:24pm In what way have you found the new Aztec blocks to be unsatisfactory? Stopping power, wear, ... ?

There's no branding or any other identifying marks like the original Aztec blocks, so could be from any supplier. They're narrower, so don't distribute wear as much across the rim. Friction material depth is considerably less. More secure grip on old type due to groove pattern on post being more effective. Sadly, no longer made in the UK.

Mine use an unthreaded post, so it looks like I'm out of luck. I wish I'd known before ordering that they're no longer made in the UK. I may be wrong, but these now seem to be the kind of parts I see in discount shops alongside clothes pegs and mouse traps, or fitted to a £75 full suspension MTB.

Update: just scrolled through and they do have some post mount blocks and possibly the Alpine ones may be OK.

I've just worn out the last of my old Aztec Control Block supply. These had 'Aztec' moulded in and 'Made in the UK'. I ordered a set of replacements and there's no marking at all to indicate they're Aztec - could be any generic part. The only reference is on the instruction sheet and the box label says made in Taiwan. Is this how they are nowadays?

cycle tramp wrote: ↑19 Mar 2025, 9:12pm Glad to hear it's all sorted, the Biopace chainrings were sent today and should be with you in the next 24 hrs...

Thank you - very much appreciated.

The biggest problem with refinishing is to get a paint that's hard enough when dry/cured. Cellulose used to be the preferred choice for DIY and it had a lot of advantages, one being that it can be melted in (fresh paint or lacquer softens existing paint). The problem with cellulose nowadays is the lead chromate has been removed and the solvents reformulated. I had 1/2 litre of 'industrial cellulose' mixed last year to try out and superficially it sprays and behaves like the old cellulose, except it stays soft for a long time. I found that leaving it a couple of days and applying a clear coat of Upol 2085 lacquer hardened it considerably. Previously I wouldn't have clear coated solid colours but it now seems to be necessary.

Isocyanate-activated 2-pack can be had in rattle cans and sprayed outside but it's expensive and you still need a respirator (a dust mask is no good). You need to use it up fairly soon after activation, as it soon sets in the can. An issue with this is any subsequent requirement to touch in or repaint a section means either buying another can, or using an acrylic to overpaint.

I've had really good success with non-isocyanate activated 2K acrylic in rattle cans, but the hardness and durability vary a lot depending on colour. White is worst, and darker colours can go as hard as powder coat or epoxy and cure quickly. I sprayed some grey/blue outside on a warm still day and after a cup of tea it was hard enough to handle and reassemble.

Most of the brush paints that still contain solvents are alkyd. They dry initially through evaporation, then cure over 2+ weeks, but remain relatively soft which is a problem when you want to clamp anything to the frame (such as the front derailleur). There are some better paints; skip paint is excellent and can be baked at low temperature. It contains anti-corrosion compounds as it's formulated to apply directly to steel and not rust through. I've used this with a primer coat of ZG90 with good results. Machinery paint and tractor paint can also be good choices, depending on brand. On steel I still use an etch primer (I used to use Upol Acid #8 but more recently been experimenting with E-Tech Technik self-etch primer, which appears to be much better) to give a good bond to the surface.

For spraying I use an Italian ANI GF/3 gravity feed gun from Spray Guns Direct which has a nice small cup that's perfect for small jobs. If you're stuck to using rattle cans though I'd go with the non-isocyanate acrylic 2K.

Just come back from a ride and happy to report that it now shifts very smoothly without any problems at all. I have some reservations regarding the lifespan of the Biostrong rings, as the alloy is very soft compared to the harder (and anodized) Shimano rings. The more extreme changes in chain tension is also quite alarming to watch as the rear derailleur oscillates back and forth due to the pronounced ovality. I think that's probably a reason to return the rings back to my standby parts once the rings kindly offered by cycle tramp arrive. At least now I know the Biostrong set will work and fitting them has raised questions regarding optimum orientation of non-round rings for me personally, which I want to further experiment with.

Something I'd overlooked was the ring spacing. On the Stronglight crank it's 6mm, but the Biopace is 7.5mm. Experimentally I've fitted the Biostrong rings onto the Deore crank and this has given them 7.5mm spacing. I think I prefer the Shimano cranks anyhow but the spacing may be irrelevant. I also went over the rings with a needle file and removed any burrs.

It's all back on the bike but will need reindexing tomorrow. I'm too cold to do any more today.

My measurement is just under 126mm

Here's the condition of the rings;

https://www.flickr.com/photos/202426071 ... ed-public/

https://www.flickr.com/photos/202426071 ... ed-public/

Any thoughts on the chainline? Could it be that as it was an early (for them) MTB that they stuck with their existing 45mm? I guess the only way to know is if someone had an original bike they could check, but there can't be too many of those around.

I've tried to observe the process by which the chain comes off but am still puzzled as to how this occurs. As the chain moves over to the middle ring, as soon as the minor diameter of the 28T passes bottom dead centre and begins to rotate towards the major diameter it comes off towards the chainstay. I'm missing what mechanical force pushes the chain off in the opposite direction at the bottom to which its moving at the top. This is something new to me that I'd like to better understand.

The chainline is 44.96mm. I suppose nominally 45mm. Hmmm, Sheldon Brown shows this as a road triple measurement, not MTB.

The old BB was replaced with a Shimano cartridge type in the late 90s, though I remember taking the old setup into the bike shop for measurement to ensure I got the right one. Could it have been wrong for all those years and thousands of trouble-free miles? No asymmetric ring wear, chain wear or changing issues with the Biopace setup.

I've tried posting photo links from Flickr, but they won't open - any recommendations (just get a circling arrow).

I've only just got in and read the latest replies - will take some pics tomorrow.

Most of this morning was spent looking at the problem. I'd tightened the cranks fairly lightly in case they needed to come off a few times. When fully tightened the chain line is now 0.7mm outboard of what it was with the Biopace setup. As an experiment I fitted the original 28T well-worn Biopace ring and this fully cured the problem, so perhaps the chain line isn't too far off. Going back to the Biostrong ring and the problem is back.

I can now see a pattern in the behaviour and it happens only when the 28T chain ring is at it's smallest diameter and only when pedalling. It occurs more during considered shifting (somewhat necessary because the front is not indexed and easily overshoots) and less if the shift speed is increased. At my usual shifting speed the problem is very frequent.

There's a fair bit of play in the rear mechanism and the spring tension on the lower run of chain feels quite relaxed. This is the original mechanism and 38 years old. Given that there isn't a problem with the 28T Biopace changing, I'm wondering if the more extreme geometry of the Biostrong is showing up the wear. Shifting on the cassette is excellent, though.

I've had the Biostrong crank set for a good number of years as a standby set in case the Biopace rings became unavailable. It taken from a little-used Dawes Cougar donor bike that had a very small frame that was no use to me. These would have been a contemporary replacement, as the Cougar came with Biopace from the factory. I replaced the whole crank set, but the BB is the existing one. The chainline is as far as I can measure 1.2mm further out from the centreline than the Biopace setup. I'm not sure whether the steps in BB sizing would over correct for this, though if I went to a smaller size.

My ideal situation would have been to replace the Biopace rings like-for-like, but they're either expensive or too worn to be any use. I do however really like the feel of the Biostrong rings when hill-climbing, so I'd like to get them to work.

I recently replaced the Biopace x3 chain rings on my Dawes Cougar with Biostrong and am having persistent problems when changing up from the front 28T to the middle 38T ring. I see that as the upper chain run properly moves across, the lower run comes off the small ring and wraps up in the gap between the ring and chainstay. The chain rings run fairly true (within 0.005") - better than the old Biopace rings, in fact. Chain is a new genuine Shimano HG40 and the NOS UG x6 cassette was recently fitted and unworn. The Biostrong rings are in excellent condition.

The bike changes perfectly otherwise, and shifts down very smoothly onto the 28T. The Biopace set never had any problems, but I notice that the Biostrong rings have quite an extreme symmetric oval shape by comparison. The front Derailleur needed raising a lot to clear the 48T ovality compared to the Biopace.

The chain suck happens about once every 10 shifts, no matter how careful I am. Is it unusual to see this happening when changing up, and what should I be looking for to fix the problem?

If the retainer is tight against the extractor bolt head there's additional friction to overcome between the contact faces of the extractor and crank, and the extractor and retainer, especially if there's some corrosion. You have the bolt tight against the crank, and the retainer tight against the bolt.

Ensuring that the ring is just slackened off (not removed or unthreaded) means that the bolt is free to rotate. I slackened off the ring just enough to remove the pressure on the extractor bolt. It's probably worthwhile slackening the ring a turn or so and testing to see if the extractor start to unscrew to make sure it isn't rusted in. If it's free, then screw it back in and rotate the retainer so it just barely touches the extractor bolt.

The basic requirement is to make sure that the effort needed to remove the crank is not being masked by other friction.