Hi there,

Ive been given a peugot talisman ph8 as a hand me down . Through the great help of some users on these forums Ive figured out that the threading for the Bottom Bracket . The BB was loose and needed servicing , I managed to get the cotters off . My original intention was to fix up or replace the bb and put the cotter on with fresh pins . I`ve now decided against it as Cotterd cranks and pins seem like a headache and I dont ever fancy tackling them again . Im planning on ordering a square taper 52t ,42t double chainset which matches the cottered one I removed and installing a cartridge BB which is compatible with the new chainset . Just wanted to run this by a few more experienced people here before I order the chainset and bottom bracket . Do you think this should work out ok or would there be chainline issues ?Thanks for any advice

as long the BB axle is the same length then there shouldn't be any problem with the chain line .

hmmm I thought so , the cottered BB was 136mm but the square taper chainsets that I have looked at all recommended they be set up with 115mm BBs , 136mm seems like an almost absolete spindle lenght so I think this could be a difficult search for a 136 square taper BB and a matching chainset

It ain't necessarily so!

The spindle of a cottered crank extends fully to the outside of the arm, whereas cotterless spindles end roughly 3/8" or so short of the outer face.

Also, the cottered crank is probably of a low or no offset design (straight crank) and so would take a longer spindle than most relatively modern cotterless cranks with curved arms to bring the center in closer (for a stiffer shorter spindle). That too, would mean a shorter spindle.

Unfortunately, there's no real formula for translating spindle length to chain line because cranks have such variance in the chainline offset.

However, most cranks specify a suggested spindle length, and this is the best guide (though not 100% reliable). Most experienced mechanics can eyeball a crank and roughly predict the spindle they'll need, and/or have an off the bike for gauging the offset, so they don't have ti install, then replace BBs (too often).

Can you put the BB back together ? , if you can measure the distance between the smallest chainring and the chainstay . To give you a idea what the chainline should be . The longest axle in a seal unit is 127 MM from end to end . as long there 5 mm between the chainring and the chainstay ,your chainline will be fine .

Put it back together and doesn't seem to be a lot of room to play with between inner ring and frame , definitely no more than 5mm .It seems like a hard one to call as the way the cottered crank fits on the spindle doesn't make for an easy conversion .I'm going to order the square taper crank that matches the teeth on the cottered crank and go with its recommended Spindle length with fingers crossed .

I like your thinking. I struggled with the cotters years ago on my bike until I finally got a nice tight fit. I dread the thought of having to take it apart again!

Wishing you success and a favorable report on this parts update.

-SP

Is the frame English thread ? Sometimes the French like to do things their own way.

The "Classic & Vintage" forum is a good resource for older bikes.

Do check this first, before investing in new parts. Metric thread cartridge bottom brackets are available (e.g. Velo-Orange), and what spindle length you need will depend on the crank you select.

Had a good long chat on these forums about what the thread could be and eventually figured it out , its british , Ill chose the BB based on the new cranke and hopefully Ill have enough positive bike karma to luck out on this one ,

Have to report an epic fail on this . Cartridge Bottom bracket fitted snugly and was ordered at 115mm as suggested for new crankset , no problems fitting it , so we were correct about size 68 and british thread . Found a matching crankset for the cottered crank in square taper 52t/42t here and ordered it

Silver Double Alloy Road Race Chainset 42 52T RRP £34 95 | eBay


Waited giddly for postman to arrive , matched the new crank against the cottered and all dimensions seemed perfect , then put the cranks on and ujnfortunately they are way too far off out from the frame. The old cottered chainset hugged it with a few mill to spare , had over a cm here with new crank,chainline looked way off and deraileur could barely stretch . Strange as my worry was that the new crankset would be too close as I was going down from a 136mm cottered bb to a 115mm square taper . Plan now is to send back the ill fitting crank and just struggle on with the cottered . It seems that this kind of crank conversion would be a lot of costly trial and error as the cranksets vary so much in depth as they sit on the square tapers .

Put the new BB in backwards, to shorten the drive side ? Might be "good enough", although the left arm may sit out too far.
Or try a new front derailleur with more swing ?

As the supplier specified a 115 mm BB and you have the standard 68mm BB shell (correct?) you should receive a refund if that has not been offered. You do have a problem now, as it's difficult to match a crankset to an already existing cartridge BB. It's always best to order crankset and BB as a unit, or at least from the same supplier who has guaranteed compatibility.

Not possible with English threading and cartridge BB.

There are a lot of cartridge bottom brackets significantly shorter than 115 mm so instead of giving up, get the right length. Shimano UN54 bottom brackets are cheap enough to experiment with even if your original supplier won't take the 115 back.

Hey yes its a 68mm bb shell , and the supplier did specify a 115mm bb and I went and ordered it on that ground s so i guess I have a case for a full refund . Not so bothered about ordering the 115mm BB as I can use it on another bike that needs a BB so not such a loss .

Im in two minds now about sending back the new crank . I have measured the distance between the inner chainring and the frame with the crank fitted on and its a whopping 11 mill , Ive worked out that if I order a 102 mill BB that I can cut that down by 6.5 mill (115milBB - 103mill BB = 13mill/2 = 6.5 mill) so that I can reduce that distance to 4.5 mill . Would 4.5 mil be an acceptable chainring to frame clearance ? Im not looking for tour de france perfection here but Id like it to be someway correct .

4.5 mm is plenty of clearance.

Ok just going to post this for the benefit of anyone who searches this thread in the future and is attempting a pug bb conversion . Ordered a 102 mm BB but a new problem has arisen . There is a slight ridge in the inside bottom of the BB cup . It starts when the threading ends on either side and it continues until it reaches the beginning of the threading on either side . Its about 1 mill in height and 1 mill in width and it runs straight .The BB I ordered has a slight lip going around it so that it contacts with this ridge and I cant push it through . The BB is a token 68 x 102 mm BB . Dont know if this inner ridge is on most peugots . Next plan is to attempt filing the ridge down without damaging the threads which should take a long time , and/or hacksawing a small notch into the lip on the cartridge BB .

Not clear about the "ridge" you're speaking of. It's time for a pic. Typical BB shell machining procedures just might take care of it.

Sounds like it could be a seam from when the BB lug was welded together, as I believe a lot of cheaper lugs were. Maybe the BB shell was made at the same time as the rest of the BB lug, or maybe it was just a piece of seamed tubing that had the rest of the lug welded onto it, or maybe you don't even have a lugged BB joint and it's just that your BB shell is made from a short length of seamed tubing. A picture would help confirm.

I've encountered a similar issue on a bike that came with a cup-and-cone BB when converting to a cartridge one, in my case the cable guide under the BB was held in place with a rivet which protruded into the BB shell and got in the way of the BB cartridge. The manufacturer probably didn't forsee the cartridge retrofit in either of our cases, so they never designed for it.

Hi , I am delighted to say that I have filed down the lip that extended out around the cartridge BB so that it could pass through into the shell and thread in . It was the last small hurdle on what has been a tricky pug renovation . The ridge was about 1 mill high ,1 mill wide and ran the lenght of the shell , starting right after the threads ended on each side . This bike was made back in a time when there were no such things as cartridge bottom brackets and may well have been a seam of sorts .Luckily a bit of elbow grease with a file and the BB could fit . The bike runs like a dream , took it out for a spin and very happy with it Thanks for all the help , great forums here .