new chain ring day

Earlier this year one of my club mates had a tortuous ride when his chain kept slipping, we put it down to poorly indexed gears, but it turned out to be a very badly worn chain ring. So last month, whilst I stripped and rebuilt by my race bike for its annual main service, a check of the chainrings was on the task list.

My bike has done about 12,000km and although I am fastidious about drive chain cleaning, the bike had been ridden though 4 British winters and that was taking its toll on components in general.

After dismantling and a degrease I decided that the small chain ring looked just fine but the big ring had clearly seen better days so I got my credit card out and winced at the cost of a single Shimano 105 outer chain ring.

Despite lock down the replacement ring arrived a week later from SJS Cycles, these guys  stock of all kinds of parts and accessories that you cannot find anywhere else. They have become my “go-to” supplier for hard to find bits and pieces during the rebuild of my bike. They also have knowledgeable staff on the end of their phone line for help and advice.

So interestingly the new chain ring arrived in a general purpose box with just a tick from a marker pen to indicate size, group set etc. Perhaps suggesting Shimano don’t sell too many of these.

I have not taken a Shimano crank set apart before so the other interesting thing to look at is the construction of these chain rings. When separated from the crank it is easy to see the two part Hollowtech construction that makes them look so unique.

With the new and old rings side by side the wear on the old ring was clearly evident, but actually not as bad as I thought it would be. The black paint on 105 chain rings wears off, partially exposing the bare aluminium alloy underneath making them look more worn than they really are.

Clearly the ends of the teeth have been rounded off and they not as sharp as the new ones. Some reduction in tooth height is also evident but overall the wear on the teeth was  not too bad.

I had thought that there was also some asymmetrical wear on the faces of the teeth, with some of the edges on one side having a shallower slope than others. However, when placed side by side with the new ring it is clear that some teeth are cut like this from new, perhaps to aid changing gear.

On balance it looks like my old chain ring actually still has some significant life left in it. I was a bit cross with myself as the new chain ring wasn’t cheap. However without something to compare to it was quite tricky to objectively assess the old ring. It is not made any easier by the black painted finish. I think I could have easily got another few thousand kilometres out of this chap whithout any problem. I guess the good news is that it proves my regular program of chain cleaning and replacement has been successful in keeping wear on the more expensive components to a minimum,

So what to do now? I could have returned the chain ring for a refund but I’m sure I will need it one day so I thought I might as well keep it. But then there seemed no point in putting a brand new chain ring on a shelf and riding an old part worn one so I decided the new one would go on the bike and I would keep the old one as a “crash” spare. The good news is that with the new ring and a spotlessly clean and re-lubed chain the whole drive train is now running particularly smooth and quiet.

The other worry with Shimano Hollowtech cranks and chain rings is the issue of de-lamination. The front a back sides are bonded together and there are stories on the internet of this joint failing.  I checked both over very carefully and there are no signs of either of these comping apart. This of course is really very good news, a new chain ring is one thing but a complete crank set is a whole lot more cash.

 

Finally to the crank axel which looks OK-ish. The bottom bracket bearing has clearly spun on the shaft and left some marks. It is not too bad and I am certainly not going to replace it. As part of the rebuild I had a new bottom bracket fitted so this problem should not get any worse in the  near future. But it is a reminder to keep a close eye on the bottom bracket. These Shimano press fit BB’s with nylon cups are essentially “disposable” items and do not have a long service life.

So that was drivetrain about done. The 105 cassette is made from steel and virtually bomb proof. The chain is part worn so whilst it will do me for a thousand kilometres or so before needing replacement i’ll be keeping an eye on it from now on.