squirtdad

I just noticed a small crack in the spider of a ~84 Ofmega cranset that is original to my torpado supper strada

it is a crack, not a scratch and goes all the way through

I am going to replace it....wtb post in for sale coming soon

in interim....what do you think? ok to ride or don't take a chance?

thanks

crack




whole crank

Ex Pres 

I don't think failure would be catastrophic, more along the lines of losing a chainring bolt than the seriousness of having a crank arm break/losing a pedal; but it might prevent you from pedaling home, so why take the chance? And if it's failure started a chain reaction where you lost the entire spider at once, that could cause a crash.

Plus, if it breaks you won't be able to sell it on ebay

SJX426 

Hmmm... strange. I would not have expected a crack in that location with that orientation! Are your chain ring bolts uniformily tight?

There is a nick just inside (below) the radius on the edge where the failure is. Do you know where or how it was created? That may have been the location of the force that caused the crack.

repechage

I would not ascend and 11% grades, or sprint to victory, do a "kilo" start when the light turns green…
No other bikes to ride?
I would see it as an excuse to do an overhaul, and buy a replacement.

repechage

I think it is at a location that might get the initial torque transfer when the RH pedal is at 3 "o'clock" or so, not a huge surprise. Squirtdad just does massive fast starts.

squirtdad

I don't know where that was created. I was given this bike for helping with some charity work. It had been sitting outside for several years. And a previous owner had done work like putting a shimano BB on (which was not a perfect taper match) and putting an english headset on.

I did have some loose chaing ring bolts, and lost one, but it wasn't the one on this locations....so hard to say

Bianchigirll 

I wouldn't hammer on it but I would likely ride it.

gaucho777 

I would not ride it. If that spider does crack through and fail catastrophically, I could envision the chain ring folding and you toppling to the ground. If you must ride it--say, in the interim while you are waiting for the replacement to arrive--I would stay in the saddle.

squirtdad

Of course i have other bikes but this one is so darn fun to ride

repechage..... Massive maybe.... massive fast not so

It is now on hiatus until I find a replacement

SJX426 

I think it is important to identify that one, it is a torsional load and two, it is distributed through all the spiders and through all the teeth engaged with the chain. There is no single point of the force vector from the crank or ring but a system of 5 force vectors distributed through the spiders which in turn impacting a distributed area of the ring and then through ring teeth. I would not be surprised if the variation of the force from the pedals was reasonably uniform at the ring bolts at any given time, if they are uniformly torqued. Then we get into the details of the tolerance of each of the holes and fastners relative to each spider and the resulting impact to the force distribution at the interface.

Nominally, the spiders see a cyclical load based on the force applied to the pedals in a given location, like a sine wave. Granted, the spider with the crack can only tolerate a load less than the others due to the failure on one of two spider sections, but the other four will pick up the difference while the remaining one will continue to work with the load until it fails. When it does the other four will have to pick up the difference. So initially the spiders distributed the load into 5 spider, with the complete failure of the 5th the load is distributed through 4. Note the resistance force vector is pointed counter-clockwise (your trying to get the ring to move clock-wise and the rear wheel and ground are resisting it), forcing a compressive force on the crack.

So squirtdad, experiencing the risk is your call. As little as we know of the design parameters of the crank and the load (s), what is the impact of the risk event of the second section of the failing spider? Are the remaining spiders up to the task of eduring your mashing? Is the failure of the second section truely catestrophic (one stroke) or will it propogate over time (n+1 strokes)? When it fails, what is the likelyhood of the ring folding with a distributed load around 180 degrees of teeth and being supported by the internal ring (would have to "fold" both rings)? Do you want to find out?

repechage

If the bike was sporting the older "webbed" chainrings…one could just remove the one chainring bolt, back in the day we saw a number of bikes arrived in the shop with a missing bolt and no catastrophe.

Creaking, yes.