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What ever happened to…? No 1 Sintered Chains

This is the first in an occasional series of articles about biking technology that seems to have sunk without trace.

First up is the sintered chain.

Now, riders with bikes equipped with shaft drives or belts look smugly at bikes with chains. Old fashioned, primitive technology, they say, technology that should never have left the machine shops where they drove engineering equipment.

Of course, whilst a shaft drive and belt should be maintenance-free, that doesn’t stop them wearing out, at which point replacement can be time-consuming and expensive. Shafts also sap power and are heavy, and finally you can’t change final drive ratios with shafts or belts, which is why chains are still fitted to many bikes. Chains are easy to replace, and cheaper too, an important consideration for budget bikes.

For those of you with long memories, back in the days before O and X ring chains, you’ll recall how keeping chains well-maintained was a black art – literally. The most complete solution to lubricating chains was to remove from the bike then immerse in a big circular tin of molten grease. After a good soak in the hot grease, you removed it with a bit of wire then hung it up to drip the excess back into the tin. It would cool overnight, the grease would harden and you refitted the chain. The results were reasonable and given average weather, the fresh lube might even stay on the chain for, oh… all of a week!

You’ll spot the obvious problem here. It needed a split link to get the chain off. Split links and increasingly powerful bikes didn’t go together, so for safety’s sake manufacturers started fitting endless chains.

The need to lubricate the chain without removing it led to the explosion of aerosol lubes we know today, but to drive the bike, the front sprocket pulls the chain over the rear sprocket. This means there’s friction in two different locations:

  1. externally between the rollers and the teeth on the chain which causes wear mostly to the sprockets

  2. internally, between the rollers themselves, the bush and the pins which hold the whole chain together which wears the chain itself and causes it to stretch

Whilst spraying lube on the outside of the chain lubricates the surfaces where the chain and sprockets rub together, which reduces wear to the teeth which reveals itself by the change of shape (hooking), it does little to prevent wear internally to the chain, which is what causes the chain to appear to stretch.

The manufacturers were aware of this and packed the rollers with a high viscosity grease in an effort to maintain internal lubrication. The problems were twofold. The grease would soften and be lost as the chain got hot (again, a function of increased power output of the machine and increased loads on the chain) and in the harsh operating environment of the back end of a motorcycle, water would wash the grease away and grit would get into what was left of the grease and turn it into grinding paste!

The result was that by the early 80s, some bikes had chains that needed frequent adjustment (sometimes daily!) and lasted only 5,000 or 6,000 miles!

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Clearly a better solution was needed.

The solution the chain manufacturers came up with was something called ‘sintering’. The steel bushes of the chain were manufactured in a way that meant they were porous and able to contain lubricant actually within the metal. As the chain moves, the lubricant “spins out” of the bushes towards the rollers, to form an incredibly thin load-bearing layer between the pin and internal roller surfaces. The outward movement of the lubricant carries contaminants OUT of the bearing surfaces. This all combines to reduce wear. It’s actually a very elegant solution to the problem.

The hitch was that these chains were supposed to run dry on the exterior, to prevent externally applied oil carrying the grit into the chain internals.

Motorcyclists, long used to coating their chain with thick layers of grease, found it difficult to understand that all that was needed was an light application of a light grease to the outside of the chain to reduce sprocket wear, and so tended to use too much, producing the gritty grinding paste which in turn still destroyed the chain internals all too soon.

Nevertheless, sintered chains were a big step forward. My single cylinder bikes which destroyed a conventional chain in just 6000 miles managed around 12,000 on a sintered chain.

But development didn’t stop there. Almost as soon as sintered chains appeared, they vanished again, replaced by the ‘O-ring’ chain.

In these chains, a simple mechanical barrier formed from a rubber ‘O-ring’ between the plates seals the factory-applied lubricant on the inside of the bush and pin, also preventing grit and water from entering the inside of the chain linkages, improving the durability of the chain once again.

Whilst O-rings do a good job of sealing the chain internals when new, the pressure needed to create the seal flattens it out – think what would happen if you pressed down on a doughnut – which creates friction, which in turn has two problems:

  1. it causes wear to the O-ring (and subsequent failure of its sealing properties)

  2. it causes power loss

The result was the development of X-ring chains we still have fitted to bikes today, where the rubber seal is shaped (oddly enough) like an X, resulting in two smaller contact points touching the plate on either side of the ring. The result is reduced friction, better sealing and less wear.

As long as the rings are in good condition, the chain won’t wear internally to any significant extent – it’s quite possible now to go months without adjusting an X-ring chain and they can easily last 30,000 or more miles. With a chain oiler I’ve achieved 50,000 miles from a chain used in all weathers. But when the rings do fail, which they will sooner or later, wear is rapid, tight spots develop and stretching is sudden and spectacular – now’s the time to change your chain.

The three things that cause wear are no lubricant at all (which increases friction and accelerates wear to the O / X rings), dirty lubricant with a lot of grit in it (because that’s effectively grinding paste) and rust (a combination of no lubricant, water and salt on winter roads!).

So, chain lube has to do two things. Prevent excessive wear to the teeth of the sprockets and most importantly stop the O / X rings destroying themselves. Applied to a CLEAN chain, a good lubricant will prevent all three.

So, are modern chains old-fashioned, primitive technology? Hardly!

If you’ve enjoyed reading this, there’s more about chain maintenance in my “mini-eBook” ‘Back on the Chain Gang – drive chain maintenance’ available to download in PDF format for just £1.99 from www.motoonline.co.uk (illustrated, 32 pages approx 3.4Mb), and more about the joys of old-fashioned chain care in my paperback ‘Riding with the Devil’ along with a lot of other tales of biking in the 70s and 80s, available for just £8.49 including P&P.

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