Hollowtech 2 XT 760

vespapete

Have 73mm bracket, says fit 2.5 mm spacer on drive side with new XT crank set. if you do this the crank is so far away from the chainstay you cant adjust front mech enough .plus it then makes the crank arm twice the distance away compared to the non drive side. So fitted with no spacer all seems to be ok. anybody had this problem? If 761 chainset fitted do not need spacer? only difference as far as i can see is larger rings.

Dirtydog11

vespapete wrote:

Have 73mm bracket, says fit 2.5 mm spacer on drive side with new XT crank set. if you do this the crank is so far away from the chainstay you cant adjust front mech enough .plus it then makes the crank arm twice the distance away compared to the non drive side. So fitted with no spacer all seems to be ok. anybody had this problem? If 761 chainset fitted do not need spacer? only difference as far as i can see is larger rings.

It depends on the type of front mech your running . If you are using a standard band type front mech then 2.5mm on the drive side is correct.

http://techdocs.shimano.com/media/techd ... 638324.pdf

Have you tried adjusting the high/low stops on your front mech?

Whats the frame and what model mech is it?

dave_hill

vespapete wrote:

Have 73mm bracket, says fit 2.5 mm spacer on drive side with new XT crank set. if you do this the crank is so far away from the chainstay you cant adjust front mech enough .plus it then makes the crank arm twice the distance away compared to the non drive side. So fitted with no spacer all seems to be ok. anybody had this problem? If 761 chainset fitted do not need spacer? only difference as far as i can see is larger rings.

What's more important than which side the spacers go on is checking what your chain line is like. With the chain on the middle ring and middle sprocket, it should be dead in line all the way along , with no deflections.

As long as that's correct and your cranks aren't fouling anything, then where the spacers are is irrelevant.

nicklouse

vespapete wrote:

Have 73mm bracket, says fit 2.5 mm spacer on drive side with new XT crank set. if you do this the crank is so far away from the chainstay you cant adjust front mech enough .plus it then makes the crank arm twice the distance away compared to the non drive side. So fitted with no spacer all seems to be ok. anybody had this problem? If 761 chainset fitted do not need spacer? only difference as far as i can see is larger rings.

761 or 760 the use of the spacers is the same.

check your chain line measurement.

and what is the front mech?

vespapete

HI, bike is Trek front mech is XT770 band on. the mech wont adjust to take up the amount 2.5 mm adds on!

nicklouse

a Trek you say. they do make one or two, and have been making them for a few years.

the Mech and crank should work fine with the spacer fitted and the stop screws set correctly.

cant comment about the bike as you dont say.

vespapete

Hi, Mr nicklouse. Loads of Treks yes! Anyway Trek 7000. Even if adjustment works ,as i say it still pushes the drive side further away from the chainstay , in fact doubling the crank gap, compared to non drive side surely the distance should be equal? all this spacer does is to stop the inner plastic sleeve from being crushed yes/no? Chain line on middle ring and middle sprocket correct (10 speed) All this is still no positive answer to why the need for spacers.

supersonic

What is the width of your bottom bracket shell?

vespapete

Hi, 73mil.

supersonic

Try the spacer on the non drive side.

vespapete

Yep, allready tried it , works ok but as i have said pushes crank arm twice the amout away from chainstay.?

nicklouse

Well i believe we have a spare 7000 frame in the shop and some HT2 cranks so i will set one up for you.

Oh and do you have a pic of your set up so i can see if there is any obvious problem.

supersonic

vespapete wrote:

Yep, allready tried it , works ok but as i have said pushes crank arm twice the amout away from chainstay.?

You said that for the spacer at the other side.

How about two 1.25mm spacers, one either side?

nicklouse

Paul: i bet it is just a mixture of cable tension and stop screws.

hoathy

vespapete wrote:

All this is still no positive answer to why the need for spacers.

spacers are there because if you are running an e-type front mech then it would go there instead, so to make it compatible with everthing they use a spacer... right?

nicklouse

Hoathy
which he would have known if he had looked at the fitting info

supersonic

I wopuld imagine omitting a spacer would not allow the correct preloading of the bearings.

vespapete

As requested pics.et.com/albums/jj3/vespa210/th_IMGshim3.jpg[/IMGucket.com/albums/jj3/vespa210/IMGshim3.jpg]s/jj3/vespa210/IMGshim2.jpg

supersonic

I can't view the last 3 images.

hoathy

my advice is: just put the spacer on the non drive side and get on with it, probably be fine.

Dirtydog11

With your current setup............ i.e. no spacers, whats the gap between the center of the seat tube and the middle ring.


Look here for an explanation.

http://www.sheldonbrown.com/chainline.html

For Shimano triple cranks it should be between 47.5 and 50mm. Now just use whatever spacers are required to give you the correct chainline.

The spacers are there for different front mech setups/ bottom bracket widths as long as yours is between 47.5 and 50mm you shouldn't have a problem.

supersonic wrote:

I wopuld imagine omitting a spacer would not allow the correct preloading of the bearings.

I don't think it matters super as 73mm shell with an e type front mech doesn't require any spacers.

supersonic

But the etype front mech acts as a spacer.

This system uses a set width of 75.5mm, I assume for correct preloading purposes ie 68mm shell plus 7.5mm of spacers (2 on driveside), 73mm shell plus 2.5mm of spacers (one driveside).

It may work without, but the non drive crank arm would have to be installed 2.5mm further down the spindle. Does it go that far? Would some of the splines be exposed reducing contact? I could check with mine lol, but I think Shimano has their reasons here.

Dirtydog11

supersonic wrote:

But the etype front mech acts as a spacer.

This system uses a set width of 75.5mm, I assume for correct preloading purposes ie 68mm shell plus 7.5mm of spacers (2 on driveside), 73mm shell plus 2.5mm of spacers (one driveside).

It may work without, but the non drive crank arm would have to be installed 2.5mm further down the spindle. Does it go that far? Would some of the splines be exposed reducing contact? I could check with mine lol, but I think Shimano has their reasons here.

Mmm I never thought of that. There's only one way to find out............... Fit it and see if he can get any preload.

There's something not quite right here though, he shouldn't be having the problems he's having. It's like he's got some sort of none standard offset BB or something.

I've fitted a couple of Hollowtech cranks to 68 and 73mm BB's without a problem, I just followed the instructions and everything lines up. Very strange!

clanton

I think it will preload just fine - but then work loose. That was what was happening when I fitted an old HTII BB to my On-one, I moved it from a 73mm shell to a 68mm but it didn't occur to me to check the shells were the same and so I forgot the spacers.

Took me a while to figure it out and it drove me crazy till I did!

vespapete

will check seat tube to ring measurement tomorrow. Thanks for help so far, just to let you know i am not new to this game and have loads of experience and have tried all i know but the fact still remains if you set up like Shmano says i am still ending up with either crank arms an unequal width from chain stay? This cant be right? And yes i think without spacer left arm is further down axle, not the same gap as on my other tech2 bikes. Have owned this bike from new so know its history.

supersonic

What about other HT2 cranks on this bike?

Also some chainstays are asymetrical.

hoathy

is the distance between the inside of the crank (where it touches the bb) and the out side of the crank (where you fit the pedal) between the left and right side cranks? to achieve true equidistance you would need to have 2.5mm of difference, unless that bb cups are different (i don't think they are).

It could be a manufacturing defect in the frame, probably wouldn't have noticed with a square taper bb.

Also, it could be due to the front mech (can of worms)

vespapete

Dirtydog11 measures correct between 47.5 & 50mil. Bike was fitted with square axle when new , but has been fitted with HT 1 for years no problemo. front mech was old XT now brand new XT, all very strange? Question if "faced" would this affect spacers? and how much metal does facing remove, tool looks quite aggressive.

hoathy

you shouldn't really be running HT2 without facing the shell, it may damage the bearings of the BB quite quickly. Facing dosen't take off much metal, just enough to make sure the surfaces and flat.

nicklouse

Hoathy wrote:

you shouldn't really be running HT2 without facing the shell, it may damage the bearings of the BB quite quickly. Facing dosen't take off much metal, just enough to make sure the surfaces and flat.

from

http://www.bikeradar.com/forum/viewtopi ... 7&start=60
before

during

done

Dirtydog11

vespapete wrote:

Dirtydog11 measures correct between 47.5 & 50mil. Bike was fitted with square axle when new , but has been fitted with HT 1 for years no problemo. front mech was old XT now brand new XT, all very strange? Question if "faced" would this affect spacers? and how much metal does facing remove, tool looks quite aggressive.

You can see from the pictures Nick has posted that very liitle material is removed, not enough to effect the spacing.

Well at least you know the chainline is correct although I'm still at a loss as to why the non drive side doesn't match up.