72vintagebiker

Hi
I am new to this forum. I am wondering what problems I will incounter if I change my crank set. I need a new chainring but have found it difficult to find a steel one and aluminium does not seem a good option. I found a slightly used crank set on ebay. My bike is a 21 speed (3 x 7) with a shimano exage biospace crank 46/36/26 Teeth. The crank I want to buy is the same model but with
50/40/30 teeth. Any thoughts etc. is my chain length okay.

dsbrantjr

Depending upon how much extra length your existing chain has, it may very well be too short for a 4 teeth-larger big chainring. The Biopace ring further confuses the matter. Probably the best is to replace your chain with one which is correctly-sized for your new crankset. If there is much wear on your cassette the new chain may skip, requiring it to be replaced also. You will also probably need to move your front derailleur higher to accommodate your new crankset.

72vintagebiker

thanks
I ordered this slightly used crank set and have decided to use my existing old outer chainring which is still good. That way I don't have change the chain. The middle chainring was the worn and cracked one.

70sSanO

It depends. Unfortunately there is no good answer to your question. If your current chain is old and stretched, then no you shouldn’t use it. If it is new, it shouldn’t be an issue.

I’m always leery when someone has worn (cracked) chainrings and wants to use the old chain. Chainrings wear, but a stretched chain really accelerates the problem because that stretched steel chain will find a way to seat on aluminum rings.

But there is a domino effect in that you should also check the freewheel/cassette and replace that if the new chain skips.

But you will get a lot more miles out of your bike over continuing to use a partially worn out drivetrain.

John

Edit added: There is a chance you can’t use your 46t on your new crank. The old crank is a 110 bcd and the new crank might be a 130mm bcd.

72vintagebiker

Thanks
The cassette and chain are fairly new. So John, I do not understand why the chain would not work on my replacement crank set if I used my 46 t outring instead of the replacement 50 t. The chain, I believe is suppose to be for a 7/8/9 speed arrangement.

mack_turtle

are you certain that the new crankset will play nice with your existing bottom bracket spindle length? I'd check that as well.

70sSanO

If your “fairly new” chain hasn’t stretched, sure you can use it.

John