Author Topic: Crank offset (Read 5304 times)

windysurfer1 · « **on:** January 20, 2006, 08:32:51 am »

Hi

Need a bit of advice about the crank on my bike.

I'm new to MTB and have just bought an old Proflex to ride when there’s not enough wind to windsurf

The problem I'm having is with the gears.

It is as though the front crank is not close enough to the frame.

The front derailleur will not move over far enough to move the chain on to the largest chain ring and if I have the chain on the middle chain ring and try to go and put the chain on the biggest sprocket on the back block it pulls the chain from the middle chain ring onto the smallest one. In other words the sprockets on the front don’t seem to line up with the sprockets on the back.
I have tried changing it for a Suntour crank and this lined up ok but I would rather use the Shimano one as it is lighter.

The crank is an old Shimano XT.
Can you get spiders with different offsets or is there something else wrong?

Sorry for the lack of technical jargon

Ionit · « **Reply #1 on:** January 20, 2006, 09:10:45 am »

To know for sure if you have improper alignment for an 8 speed cassette stick a strait long ruler between your 4th and 5th rear cog and see if it point directly at the middle chainring. If you have a 9 speed cassette stick the ruler beside the centre ring and see if it points slightly to one side of the centre chain ring in relation to your centre rear cog.

Try tightening your crank bolt on the drive side. If it is tight and what I mentioned above is not true there is no way you can get proper alignment. You will need a smaller bottom bracket axle length possibly 113mm if you have a 118mm.

And about your fron derailleur you need to pull more cable through the clamping bolt tightening your cable. then fine tune the shifting with the twisties on your shifter body where you shift from.

Maybe someone on this forum can help you with the bb size if it your problem. I don't have the BB size for your bike.

There isn't diffrent offset distances they are all alike.

shovelon · « **Reply #2 on:** January 20, 2006, 09:46:32 am »

I just ran into this on my 957. The XT BB fit perfect but the new BB is adjustable in its chainlline by screwing one shell in farther than another. You might look to see if you have an independant lockring on each side. If so, you can move the driveside closer to the frame.

Terry

kiwi · « **Reply #3 on:** January 20, 2006, 01:28:16 pm »

it will also help us if you post the model of your bike and or a pic if your not sure.Different models use different bb,s

windysurfer · « **Reply #4 on:** January 21, 2006, 04:22:02 am »

Not sure which model of proflex it is so heres a picture.Any info on it would be great.

http://server3.uploadit.org/files/windysurferuk-proflex.jpg

I got it from eBay so do not know it's history

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=27948&item=7204541950

Sorry about the stickers but It needed a lick of paint and couldn't find any new proflex stickers and G and T are my initials

It looks like it is a problem with the bottom bracket lenght.

My bottom bracket is an old type (not sealed) which has 3P stamped on it.What size would I need?

Shovelon do you have a link to an adjustable bottom bracket ?

Simon · « **Reply #5 on:** January 21, 2006, 04:37:46 am »

You will be fine using a

108X68 or 110X68 B/B

Check you will be using CD (Compact drive cranks with
this size B/B) the ring combination will be something
like this 22/32/42

Raceface do adjustable chainline cranks but your talking about a fair bit more cash,go for Shimano LX quality for your B/B,good value and won't break the bank.

Simon.

PS Your in the UK,talk to Spucey at UKBike store,they will sort you out.
http://www.ukbikestore.co.uk/acatalog/Secure_Online_Shop_BOTTOM_BRACKETS_169.html
UKBikestore 02392 528 932

PPS That a worldcup style frame eg 855/856/XPX
its a superb frame plus you have an upgrade from elastomer suspension to an Nr4 shock,you have a great base for future upgrades.

shovelon · « **Reply #6 on:** January 21, 2006, 06:26:51 am »

Yeah, what Simon said. He straightened me out.

Windy, here is a view of a BB that has removable lockrings on both sides. The BB must be aligned to match your chainline, so you can do micro adjustments. I think you can alter your chainline +or - 3 mm(I am in the process of doing that right now).

Your BB length must be correct though, and a narrower one that stilll lets your crank clear the swingarm may be first on your list to look at.

http://cgi.ebay.com/Vintage-Syncros-titanium-bottom-bracket_W0QQitemZ7213166866QQcategoryZ56193QQrdZ1QQcmdZViewItem

Terry

windysurfer · « **Reply #7 on:** January 21, 2006, 07:25:25 am »

y crank is a Shimano Deore XT with 22/32/42 rings on.

Would this BB in a 107 or 110 be ok?

http://www.ukbikestore.co.uk/acatalog/info%5fBBUN73%2ehtml

What size is my current 3P bottom bracket?

I have measured its overall lengh minus the threaded bit and it is 120mm.Is this what the measurement on the sealed unit refers to?

Simon · « **Reply #8 on:** January 21, 2006, 07:41:04 am »

Not sure on that but 120mm spindle length is way too long.
get the b/b I mentioned and you will be sorted,
yes the 110mm one will be fine.

Simon

kiwi · « **Reply #9 on:** January 21, 2006, 07:43:41 am »

your x55/x56 frame requires a 68x110 bb.Get hold of sprucey at the uk bike shop,he knows what you need,cos he has (or has had) a 856 himself

shovelon · « **Reply #10 on:** January 21, 2006, 09:59:28 am »

Yes, I agree that 120 mm is too long. I was posting as an example to show how it gives adjustable chainline. I may try for it swap the cups and bearing to use on my american classic BB which has worn bearings.

But the big question is what is on that bike that throws the chainline out of wack. Is it wider that 110mm? Or even 113mm?

Terry

jeffhop · « **Reply #11 on:** January 21, 2006, 10:22:17 am »

that looks very similar to my medium xpx which use a 68mm x 110mm bb or u can get away with 113mm bb depending on chainset, by the way can you take a pic of the left hand side of it as im curious as to your disc set up,as i thought i was the only one to use a link to the rear strut mount for extra strength

windysurfer1 · « **Reply #12 on:** January 21, 2006, 08:32:23 pm »

All the bottom brackets seem to use bolts where as my present one uses nut.
Does this matter?

Jeffhop. I'll post a couple of pictures of the disk setup as soon as I put it all back together again

Simon · « **Reply #13 on:** January 22, 2006, 06:36:56 am »

Quote

All the bottom brackets seem to use bolts where as my present one uses nut.
Does this matter?

YES if the 120mm measurement you gave us included the threaded stud lengths, can you measure the spindle/axle length but don't include the lengths of the threaded studs,
another words the length from one end of the square
taper to the other end of the square taper,
with this info we can advise you more accurately.
Simon.

windysurfer1 · « **Reply #14 on:** January 22, 2006, 07:08:30 pm »

The 120mm is from square tape to square taper

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Author Topic: Crank offset (Read 5304 times)

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