CannedPakes

I recently bought a Raleigh SC-30 for a family member. When I test rode it everything felt fine, but when we took it out for the first major ride there was apparently an issue. He said that the chain skipped when starting up in the middle ring occasionally, so after getting home I decided to take a look. Now I know manufacturers like try all sorts of weird things with chainrings so I just wanted to make sure... is this part of the design or is it severely broken? I would have just assumed it was broken but it looks like there's 3 of these notches across the middle chainring so I thought maybe it's something to assist shifting. I've ridden it and haven't noticed any issues but he's much heavier so maybe that affects something.

techsensei

I'm pretty sure what you are seeing is not damage. Those are shift gates. If you look on the opposite side of the ring (180º), you will see the same exact pattern of teeth.

fietsbob

I think the base of 1 tooth lost a chip of <guess> steel .., if the chainrings are all riveted together (which is done for economical Bike Parts )

Could be a tear (Worn Tooling on the Punch Press), as the whole chainring was Punched out at the factory by the Millions.

(But not Ruined, just less than Pristine.)


then look to new crank BB chain & probably cassette ( worn giving way to new for the whole drivetrain to work... like New!)

FBinNY 

Other than dirt and dried grease, the ring seems fine. As pointed out above the teeth are thinned and sculpted this way to make shifting crisper and smoother. It's what puts the glide in Hyperglide (or is it the hyper?).

HillRider

+1. The first thing it and the chain need is a good cleaning.

CliffordK

It is rare to skip on a chainring, and you need a lot more wear than that to have it happen.

Those hook shaped teeth look odd, but having at least 2 of them would indicate that they were intended from the factory (notice several shift ramps/gates around them).

For skipping chain, consider a few possibilities:

• Overly worn chain.
• Worn Cassette of Freewheel (probably freewheel on that bike).
• Stiff link in the chain. Watch as it goes through the derailleur to see if it jumps, or run through your fingers bending it.
• Poorly adjusted derailleur

Why it would be specific to the middle ring? More force? Maybe a poorly adjusted derailleur making it try to shift.

See this for measuring the chain.
Easy Way To Check For Chain Wear | CyclingTips

It says, replace at 12 1/16. Heavily worn if it hits 12 1/8.

AlexCyclistRoch

Those tooth profiles are so obviously shark-toothed and one on the middle ring is damaged. Replace them. Probably your cassette and chain, as well.

techsensei

I'm sitting here at the co-op looking at an FC-CT92 Altus crank that has the identical tooth profiles. It is not damaged, it is part of the design.

techsensei

Reynolds 

That's not a super-precision crankset, those teeth are OK for probably thousands miles more.

RoadGuy

Check, adjust or repace if necessary in this order: rear derailleur alignment, chain wear, freewheel or cassette and lastly chainrings (crankset if chainrings are riveted together or to the crankarm).

CannedPakes

Thanks everyone.

I ended up cleaning/lubing the drivetrain and going for a ride and there was no "skipping" so either there was really nothing wrong in the first place or that fixed it. The back wheel started clunking really loudly under weight at the end of the ride though, so I guess I have something else to try to fix tomorrow.

Andrew R Stewart 

This thread is a good example of how old, well used, bikes can have a few different problem at the same time. Fix one and the next problem is made known. This is why a comprehensive assessment is a good investment (not that this should cost much.) andy.