Carlton Pro Am 12 Bottom Bracket

[drgj]

Hello, I am new to this forum. I thought it might suit my old bike interest. I have a Carlton Pro- Am 12 which I think is from about 1980. Without measuring anything or even noticing the spacing, etc, I removed the bottom bracket to clean and grease it. It is an old three piece square type. I'm not sure if it is the original one but it is in fairly good condition compared with some of my previous ones on various bikes. Anyway, when I reassembled it with the longer part on the right where the sprockets/ chain wheels are I find that the smaller sprocket is only about 2mm from the frame, if that. I didn't notice this before but it must have been like this. The bottom bracket spindle/ shaft measure 12.5cm in length. Is this correct? I was thinking of buying a modern replacement non adjustable type but they seem even shorter unless I am misunderstanding the sizes.

Hoping someone can give me the correct measurements or whether my set up is normal.

Thanks

Dave

 

[pigman]

Re:

If it's too close, put a washer behind the fixed cup (right hand side) to bring it out another couple of mm. The washer you want is the same as a cassette spacer, costs about £1.
You then still have the original bearing setup at minimal cost

 

[Midlife]

If it works don't fix it iirc the pro am was launched in Harrogate 1978 as a ten speed so the 12 sped would be a tight squeeze lol.

 

[drgj]

Thanks for those replies. The washer idea I hadn't thought of. I suppose that if there is no play then no harm can come to the sprocket as it is.

Dave

 

[pigman]

If it works don't fix it iirc the pro am was launched in Harrogate 1978 as a ten speed so the 12 sped would be a tight squeeze lol.

I may have misunderstood. I thought the issue was the small chainring was too close to the chainstay, and the crank needed pushing outwards.

Otherwise I don't understand the 10/12 speed comment

 

[pigman]

Thanks for those replies. The washer idea I hadn't thought of. I suppose that if there is no play then no harm can come to the sprocket as it is.

Dave

if it's too close, under load it will flex and catch the stay

And being pedantic, a sprocket is one of the cogs on the freewheel/cassette/block at the back of the bike.
A chainring/chainwheel is the thing the chain runs on at the front

 

[drgj]

Thanks, Pigman. I wasn't sure of the terminology and that is why I wrote Chainwheel/ sprocket in my first post.

Maybe the cranks have worn and go too far on the square tapers.

I could just change to 6 speed and have just one chain wheel but will look into the washer idea.

Any ideas on a correct length modern replacement bottom bracket? The one on there can't be the original. I'm sure I put the spindle back in the right way round as it protrudes more on the right hand side.

Dave

 

[Old Ned]

Are there any markings on the spindle that may point to its length? The method of spacing the fixed cup out using a large 'washer' is perfectly OK. I've used it often.

And, of course, there is always the option of putting a dent (or recess) in the chainstay - as many frame builders did BITD - to create extra clearance behind the small chainring.

 

[ZG862]

One thing that *can* cause issues with clearance is if the cranks were not pressed on to the axle previously. A tiny bit of wobble over the years can easily open out the hole in the alloy crank, causing it to sit closer to the centreline when you re-fit. Alas, if this is the case, it effectively writes off the chainset. Fortunately, it was probably an SR Custom and they are pretty common in pretty good nick on your favourite online auction site. Or, as you say, opportunity to upgrade the lot. Slippery slope...

 

[drgj]

Thanks for the new replies.

The bottom bracket measures 125mm without the threads.

Dave