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thebuddhist

I feared some wear on the crank axles and my fears were well founded. What are my options for replacing? The front BB is eccentric to allow tensioning the chain between captain and stoker on the left side. The BB shell and cups are in good condition (see photo below axle photo), the rear BB axle is ok but if I am replacing the front I might as well replace the rear.

One side of the captain's crank axle shows severe wear<br><br>

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Gtane

Welcome to the forum and lovely tandem by the way.

I would definitely replace the axle, without question. It looks like the bearings could possibly be too large as the wear is not in the centre of the bearing surface. The wear appears to be at the edge of the bearing surface. You're fortunate that the cups are without damage. A change of bearings would also be worthwhile.

This type of wear will eventually fracture the axle clean off.

There should be a code stamped in the centre of the axle which will indicate the model and help in matching with a replacement axle.

All the best with the restoration.

Tim

sandranian · Site Admin

The axle should be replaced...as said above. It also might be because of an inaccurate adjustment of the cup...i.e. too loose or too tight.

verktyg

Most cottered axles (spindles) were made of low quality case hardened low alloy steel and a lot of them weren't even precision ground after hardening.

In case hardened steel the zone of hardness ranges from about .005" to about .050" deep ( .13mm to 1.3mm ). Once the case hardening wears away the softer substrate quickly starts to fail as pictured above.

Better quality bottom bracket axles were/are made of through hardened alloy steel precision ground after heat treatment.

An additional factor is the holes in the cups for the axles on inexpensive bottom brackets are usually fairly oversize which allows a lot of grit to get into the bearings.

Also with a crossover drive setup like those on most Gitane tandems - a pair of same sized chainring on the left side of the frame transmitting power to the the chainrings on the rear right side bottom bracket - generates very high forces on the right rear bottom bracket bearings. A pedal pressure load of 150 Lbs. subjects those bearing to 1080 Lbs. of pressure.

The front BB axle will probably be easier to find because it's most like a standard size. The rear is longer than standard and may not be available.

You could check with these online shops, they may have replacement axles. You will need ALL of the dimensions off of the axles including the overall length, the distance between the bearing races, the distance from the end to the bearing races on the chainring sides.

http://www.yellowjersey.org/ (email or call Andrew)

http://sheldonbrown.com/harris/hub.html (Harris Cyclery)

If that fails, keep checking on eBay as these sometime come up.

You may end up having to go with a set of Phil Wood bottom brackets with a tandem set of alloy cotterless cranks which would be an expensive conversion but it would take 3-4 Lbs. off of the bike and remove the constant problems associated with cottered cranks and repacking bottom brackets. Also the alloy chainrings will give much smoother pedaling than with the older steel rings.

If you do find some new or usable axles, we used to put rubber O-rings on them next to the BB cups to keep out dirt. Fuzzy pipe cleaners also work in dry climates.

To add to the complexity, there were at least 14 sizes of cotters used on bikes of that era. The cotters used on Gitanes should be 9mm x 40mm or 43mm long with out the nut. The threads were 7.0mm x 1.0mm.

For best results don't use the ball bearing cages with 9 bearings. Use 11 loose packed grade 25 chrome steel 1/4" ball bearings per side.

Good luck,

Chas.

sandranian · Site Admin

What the heck would we do without you, Chas.

verktyg

Chas.

thebuddhist

Thanks for the tips.

I spoke with Andrew at YJ and he located me a front axle.

I found a rear one matching all the dimensions on ebay.

There were 11 loose bb's per side and I have bought grade 25 to replace them.

What kind of grease should I use? Can I use valvoline durablend axle bearing grease that I have in my garage?

I'll keep the o-ring trick in mind, what about putting a bead of clear silicone around it and after it having dried, slice it off the bb cup with an x-acto?

sandranian · Site Admin

I always use Phil Wood.

vanhelmont

"what about putting a bead of clear silicone around it and after it having dried, slice it off the bb cup with an x-acto?"

Interesting idea. The only negative I can see is that ordinay silicone gives off acetic acid as it cures. You can get non-corrosive silicone. I have a blue silicone that is intended for automotive use, if I recall rightly.