msa969

I am doing up a vintage racing bike, I always liked them, anyway the peddle crank is broken and has come off,
i have a number of questions, how do i know which one to purchase and the size of peddle crank?
It is the left sided one that I need to purchase. The right crank brand is custom.
In terms of difficulty to put a new crank peddle, what is it out of 10?
Any more suggestions will be much appreciated
Thank you.

Pompiere

Your best bet to find a single crank arm and pedal would be to look for a used one at a bike co-op. Normally cranks and pedals are sold in pairs, but bike co-ops salvage a lot of bikes to scavenge the good parts. A co-op could also help you with installation. It isn't very difficult, but it would be helpful to have someone show you the first time. If you end up replacing both sides to have a matched set, they will have the tools to get the right side off.

jimmuller 

ebay often has a slew of single arms if you aren't too picky about the styling being identical L to R. Just check the length. There are different spindle tapers too but those that aren't JIS or ISO are quite rare.

Charles Wahl

I'm not an expert, but the crank you have looks like it may be an SR Custom model with the arm swaged to the spider, which is integral to the large chainring. That's not a very typical/popular arrangement. You might be able to find an SR Custom non-drive-side crank arm; or you might not. You should measure the length of the existing crank arm, and match it, though it's probably 170 mm. If removing crank arms, you need a "crank arm extractor tool" -- 22 x 1 mm by far the most typical. To replace them, all you need is a 15 mm thin-wall socket for the crank bolt; but the bolts really should be torqued, so a torque wrench is advisable -- 350 in-lb or 29 ft-lb is about right. Whether or not to remove all oil from the crank spindle tapered end and the inside mating surfaces of the crank arm is a matter of religion:
https://www.sheldonbrown.com/tooltips/cotterless.html
You should, however, definitely remove the rust from the exposed spindle end.

It's about a 99% certainty that if you're replacing with a non-matching arm, a JIS taper is what you want: Japanese-made crank that is not Sugino Mighty-anything. Almost anything that's fairly modern will also be JIS, unless it says it's ISO.
https://www.sheldonbrown.com/bbtaper.html

Hudson308 

You can easily identify the left (non-drive) side crank you need by the lack of any chainrings or provision for attaching them. Your existing crank will have a length marking cast or stamped into the back side, likely a 170. This would mean the crank is 170mm long from center to center, and you will want to match that length.

JohnDThompson 

It doesn't appear to be "broken;" just that the left side arm retaining nut fell off and the arm is missing. As mentioned above, you could likely find an orphan left arm on eBay or a local bike co-op, just match the length. The retaining nut should be easily sourced from the bike co-op or bike shop at minimal cost. 14mm socket will install the arm on the spindle. Then you'll need to find a pedal, also available (usually in pairs) from the co-op or bike shop or even eBay.

Cute Boy Horse

Oh this is an easy one as everyone has said.

Your crank is almost certainly 170mm long as that's the normal size for adult bikes. Square taper fitting, also the normal way. You can buy a left side crank arm and the crank nut off ebay. Then you just push it on and screw the nut on very tight using a ratchet.

That last bit about putting the nut on very tight is important otherwise it'll work itself loose and ruin the arm when it falls off.

thinktubes 

One word: Torque Wrench

denny1969

Worst case scenario. You could always replace the whole crankset. SR/Sakae or Sugino cranksets can be found rather inexpensively.

Dennis

Cute Boy Horse

you mean coward ratchet?

The Golden Boy 

It's interesting- I think that front derailleur is a more 'upper end' piece, but the crank is a 'lower end' piece.

As everyone has said, the brand is SR (Sakae Ringyo), and "Custom" isn't exactly the model- it might have been a series for SR.

Look on the back of the arm, the length will probably be stamped/cast into it. It'll probably be 170 as everyone has said. But check! It would suck to have one side of your crank longer than the other.

There is one of those cranks on eBay right now (165 length), but I wouldn't buy the whole crank. If you're not too concerned about being matchy-matchy- there's a few that will go with your crank, but won't exactly match.

Left Crank Arm Square Taper 170 mm SR Low Profile Used | eBay