Khb

Just picked up a pretty original beastie, but she's missing a couple of the crank bolts (at least that's what I think they are called).

Other than looking for broken Motobecane's hanging around, where's a good source of bolts?

Thanks in advance (new to vintage bikes; but I grew up with a Motobecane, and couldn't resist revisiting my youth ;>)

noglider 

They are standard size and thread, except that old bolts had 15mm heads and new ones have 14mm heads.

smontanaro 

If you don't have a ready source, I think I have some spares of the 14mm variety Tom mentioned. Let me know. Also, if you have a bike co-op nearby, this is exactly the sort of stuff they will have.

Khb

Cool, good to know! Threading on old French bikes has bitten me before ... so I figured best to ask ;>

Ideally, I'd find a couple that would match, they seem rounded in a not so common fashion, but I need to hit the shop Friday anyway, so I'll see what they've got hidden away.

noglider 

Bikes are a weird mixture of English and metric. This is where metric won.

cdmurphy

By "Crank Bolts", do you mean the two bolts that hold the crank arms to the (bottom bracket) spindle, or some of the (usually 5) bolts that hold the chain rings to the right crank arm? Usually if you lose the first ones, the crank arm falls off within a few miles of riding. You can lose 2-3 of the "chainring bolts" without issue as long as you aren't putting out some serious power going uphill.

juvela

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+1

was wondering this as well.

always good to make sure everyone on the same page prior to jumping into the unknown.

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verktyg 

When you say "crank bolts" do you mean the bolts that hold the crank arms onto the spindle or the small nuts and screws that hold the large chainring onto the crank arm or the hollow screws that hold the small chainring onto the large one (see pictures)?

In the early 70's Motobecane Grand Touring bikes used Stronglight 49 cranks. The domed nuts that held the large chainring onto the crank arm were on the outside with the hex headed screws in the rear. Those nuts and screws are hard to find but they're a standard size diameter so you can get something to work.

The hollow chainring screws/bolts are also a standard size. You can buy packs of 5 Sugino chainring bolts that look identical to the Stronglight originals.

BTW, Stronglight used crank bolts with 16mm hex heads until at least the late 70's (Zeus too). They switched to the more standard 15mm heads when they changed the extractor threads in the crank arms from the bâtard 23.35mm to the industry standard 22.0mm size.

You will need to get a Stronglight specific crank arm puller to remove the cranks. TA used 23mm threads but using a TA puller can damage the slightly larger Stronglight threads.

I attached the Grand Touring page from the 1970-72 Motobecane catalog and also the spec sheet.

verktyg

juvela

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1977 was the year for this change.

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verktyg 

Are you saying that Stronglight changed the bolt head size from 16mm to 15mm in 1977?

Not questioning your info, but:

The 1982 Stronglight catalog shows that the model 106, 104 and 2nd generation 99 (99NM) and all later models used 14mm bolt heads on the crank bolts.

They also switched the extractor threads on those newer model cranks to 22mm.

The older model 105, and 49 cranks still used the bâtard 23.35mm extractor threads. Same with the Mod 93 as well as the original Mod 99 cranks from in mid 70's.

I've never been able to figure out the rational for using the totally non standard 23.35mm extractor threads.

Is it wrong ...or just French?

verktyg

JaccoW

I have a Stronglight 49 cyclotouriste 50/40/30 crankset with a mismatched 170/175 crank arm but all the screws and chainrings are fine. I was thinking of selling it anyway.

Show us some pictures and we'll be able to tell you what you need.

juvela

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Chas.

My error in not being more specific.

1977 was a big changeover year for Verot.

Models 104 & 105 were launched.

Model 93 was discontinued.

Model 99 was revised.

For new models introduced chainwheel teeth were cut from both sides of the stock as opposed to from one side of the stock only as for all previous models.

Chainwheel teeth continued to be cut from one side of the stock only for older models such as 49D & TS.

Fixing bolts and removal threads stayed the same for older models.

If any of this conflicts with your much great knowledge am delighted to defer.

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JohnDThompson 

Stronglight invented the square-taper cotterless crank, so they were free to use anything on the extractor threads. I suspect they got a good deal on some 16mm 8x1 bolts, and then decided a 23.35mm opening would provide clearance for the 16mm socket to install and remove the bolts.

What's more puzzling to me is why Zeus chose a 16mm 8x1 bolt along with a 22mm wide extractor.

juvela

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+1

Yes, and what's more, unlike Verot, Arregui stayed with it to the end.

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3alarmer 

...because of the above mentioned crank cap and puller threading issue (larger than the now standard 23), if the protective cap thingies are missing on yours they can be difficult and expensive to replace.

I use a lot of this sort of crank bolt in that situation, and they seem to work fine, even if not "authentic period correct".

xiaoman1 

[QUOTE=3alarmer;20308250]...because of the above mentioned crank cap and puller threading issue (larger than the now standard 23), if the protective cap thingies are missing on yours they can be difficult and expensive to replace.

I use a lot of this sort of crank bolt in that situation, and they seem to work fine, even if not "authentic period correct".

Source please?
Thanks, Ben

3alarmer 

Brand new ones:

Truvativ Crank Bolts | Jenson USA

https://www.niagaracycle.com/categor...0aAiftEALw_wcB

But they often show up in a co-op environment, stripped from 80's-90's mountain bikes.

They were popular even on some lower end stuff for a while, and then the technology moved on to Hollowtech and other sorts of cranks on most bicycles.

Khb

Thank you all. Great information!

verktyg 

What I know of French frugality: A centime saved is a Croissant earned!



It's possible that maybe Stronglight started off with a 24mm tap for cutting their crank extractor threads and through many resharpenings it ended at 23.35mm???

The outside diameters of the 16mm/15mm sockets on the extractor tools may have been made close to the minor diameter of the extractor threads so that they don't damage them if the tool moves of center while loosening the crank bolt.

verktyg