Bicycle Mechanics - Bit off more than I could chew

Oh, I have done it again. I am always turning routine repairs into such ordeals. What I am trying to do is replace the crankset. I have a Shimano Alivio, which I am replacing with the same make, but I just can't get the derailleur lined up to work.

FYI...this is unrelated to my earlier problem concerning derailleur placement. I haven't even starting working on that one yet.

The problem with the Alivio is that the chain won't stay on the second chainring. It slips back onto the first one. When it is in first gear it seems as if the angle is too sharp for the chain to stay on the 2nd chainring, but it works fine with the old crankset. I do not know what else I can adjust to rectify this. Since it is the identical crankset I would not think there would be too much difference.

Any suggestions?

Perhaps you installed the wrong size bottom bracket? Maybe your chain is too short? You really haven't given much info, so all I'm doing is guessing.

Was your old crankset for an 8 speed drivetrain? Is the new crankset for a 9 speed drivetrain? If both are true and you are running your old 8 speed chain, I would point to this as the most likely cause.

Is the front mech rotated correctly about the seat tube. It should be aligned straight with the chainwheels. If it is at an angle, you will never get it working properly

The only thing I replaced was the 8 spd crankset. I replaced it with an identical one. I did not replace the chain as I just did that last month. The front derailleur is lined up.

This one might be a tough one to fix (with my limited knowledge). Would it help if I put a new chain on, even though the other one is only a month old? Is is possible the new cranset sits out just a little bit further on the BB spindle?

Who know?

The chain shouldnt make a difference.
Is your gear lever indexed? If it is, then you may have to adjust the location of the indexing, with the cable tension adjuster.
Individual cranks often fit onto a bottom bracket spindle differently, so you may have shifted the rings by a few mm.

You are assuming that the casting of the arms is identical, which is rarely the case. If this is a cheaper crankset, there is a likelyhood that there is some "flash" on the place where the crank seats to the BB spidle. You haven't said which type of BB you are using, but I'm assuming that it is the tapered-square style. You may need to file any burrs and flash on the seat down with a file. Also, do you have the crankbolt all the way down? Were there any washers from the old crank?

I had a similar problem a few months ago. It turned out that I hadn't tightened the crank bolt enough. You really have to lean on that thing - I now use a large shifter to help push the allen key around. The few millimetres difference this made was enough to put the derailleur out of alignment.

Did you replace both crank arms? Did you put them on one at a time so that the arms are on the same bb surfaces? You more knowledgable guys - would this make a difference? Is my question clear? Is it possible that wear on the bb axle surfaces could affect the angle of the chainwheels enough to cause this? I am a real novice at this so I am just asking. Along the same lines, is there a specific way the cranks should be oriented on the axle or does it not matter as long as they oppose each other? Any other orientation would sure play hell with a smooth pedal stroke, wouldn't it? :)

Steele-Bike, is your bb cup and cone or sealed cartridge? If cup and cone, did you service the bb when you did this? If so are you sure you installed the axle correcty? One end is a little longer from the cone to the end to accomodate the chain rings. The difference is not obvious to the naked eye but could be enough to position the small ring too far inboard.

I replaced the both arms and I have a sealed cartridge BB. Last night I put the old crankset back on so I could go for a ride. The old one still works fine. I adjusted the derailleur as much as I could, both at the mech and shifter, but to no avail. I have not had time to take a closer look, but soon I will, and hopefully will figure it out.

Shimano has a nasty habit of changing stuff all of the time so you have to buy more stuff to make the replacement stuff work.
Check the dementions on the cranks and BBs to make sure they're the same. Then check for tightness, chainring wear, "chain stretch" etc.
Ride soon
Pat

There should be a BB length printed on the bearing body. The first # should be 2 digits, and that tells the diameter of the BB threads. The second # is the length of the spindle. Common #'s are 109.5 (road doubles), 114.5 (?) (triples), etc. If the bike was a department-store bike, however, who knows what the original length was? Non-standard parts on these bike cause all kinds of problems.

Only thing I can add to all of the above is to check that the chainring or teeth aren't bent.

I'd be tempted to use the old chainset, and mount the new chainset in a glass jar with vinegar to preserve it for the future generations.

But that's just me.

Rich

OK, I think I am getting somewhere now. I was just looking at the crankset again and decided to count the teeth just to make sure everything was the same...

(The crankset I am replacing is off my 1998 Mongoose NX7-1, which has an Alivio crankset. Well, I count the outer chainring and came up with 42 teeth and decided I would order a new Alivio that I saw on sale at Nashbar.)

...Well, due to my laziness I never counted all three chainrings (until now). The old Alivio is 42/34/24. And the new one is 42/32/22. So, I think that is where my problem is. Do I have to shorten the chain? What else can be done?

Thank you much!

Here's how to get the right chain length:
Put the chain on the large ring/ large cog combination (but don't ride on this setting). Pull together the slack on the bottom. Find the tightest possible length, then add 1 linkset to that length. Count the # of linksets you need to remove, then break the chain, and remove those links.
While you atre at it, check the chain for excessive stretch. 1/16" over 12" is considered the maximum allowable.

Don't shorten your chain as the largest chainring is the same size as the old one. What you need to do is fine tune the front derailluer. You will have to do one or a combination of the following:
1. Adjust the limit screws (side to side action)
2. Adjust the mounting position of the derailluer vertically
3. adjust the angle of the derailluer (make sure it is parallell with the chainrings)

My guess is #1 will take care of it. Only make one adjustment at a time, and note how much you adjusted (for instance, 1/2 clockwise screw turn on upper limit screw) so you can make changes back if you need to. Be methodical and patient and you should be able to get things working.

To clarify the above post, which I must have been writing at the same time as Alex:

You should not have to shorten your chain, since things were working properly on your old crank. However, follow Alex's advice and check anyway. I see a lot of bikes with chain's that are too long.

Hold the presses!!!

I have just figured something out. To simplify things, I am only going to talk about the Mongoose in this post. I just measured the 42t chainring on the old Alivio and it measured 7 1/2 inches; The new Alivio 42t chainring measures in at 7 inches. I am including the URL for Nashbar to show what exactly I bought...

http://www.nashbar.com/profile.cfm?category=81&subcategory=1031&brand=&sku=2958&storetype=&estoreid=

The text in the above link says the Alivio is 8 spd compatible. Does compatible mean something different than "yes it will work"? How is it a compatible chainring with the same number of teeth could indeed have a smaller diameter. The crankset says to use Shimano IG chain, which is what I have, so that is not the problem. Can someone clarify this?

Hey Steele-bike,

RiderX has a good point; Things worked properly on the old one!
I had the same problems with a new crankset and my old F-derialleur.
The point is that the old one is bigger than the new one, so if you mount the new set; check your F-derialleur hight!

If it won`t work dispite all the advices from us, you could try this;

http://www.parktool.com/repair_help/howfix_frontderailleur.shtml

Good luck :thumbup:

Does anyone have the answer to my above question?

How could two 8spd chainrings with the same number of teeth have a different diameter? I would think that on the smaller chainring, the teeth would be closer together, thus not interchangeable.

I am thinking this may be why my new crankset isn't shifting well and the chain rides very rough on the chainring.

First off: are they BOTH 8speed chainrings? Are you SURE?
secondly: Which diameter are you measuring? The only diameter that matters is the 'minor' diameter, the one from the inside of the tooth to the crank.
Teeth are always the same distance apart, and that hasn't changed for many, many years. What is often different, though, is the tooth profile. Older style rings have longer teeth, with round profiles. Newer teeth are shorter, often ramped, and sometimes have non-round profiles. Shorter teeth make quick shifting easier, but are also easy to junp out of. For that reason, profiles are often non-round, and just a small amount of wear will cause the chain to jump out, as your rear cluster seems to be doing. Also, hyperglide-compatible teeth are unidirectional, for this reason. If you want more detailed info, check out Sheldon Brown's site. He explains all of this, in great detail.
This is the risk you take when you delve into things you don't fully understand. In the end, you won't save any time or money, but maybe you will learn a few new skills (and add a few tools to your kit). If you are looking for quick, sure repairs, though, you really ought to go to a decent bike shop.

Originally posted by D*Alex
This is the risk you take when you delve into things you don't fully understand. In the end, you won't save any time or money, but maybe you will learn a few new skills (and add a few tools to your kit). If you are looking for quick, sure repairs, though, you really ought to go to a decent bike shop.

If one never delved into anything they didn't know, not even the bicycle would have ever been invented. The reason I am trying to fix this myself is mainly because I am on a three month paid leave from my job and I need something to occupy my time.

The thing about fixing ones own bikes is this: How often would the average rider have to replace his/her crank, BB, chain, wheels? More likely never. Most bikes can be rode for many years with out anything other than minor tune-ups. I am not talking about pro-racers or century riders, I am talking about the average rider who puts a few miles on here and there.

My point? I am 28 years old and have been riding bikes since I was 5, but I am just now beginning to learn about the mechanics of the bicycle. When I was 12, I can remember sitting in the garage with my bike torn apart, wondering where all the bearings rolled to...and things really haven't changed.

Here is the situation I am dealing with now. I have a 1998 Mongoose NX7-1, which came stock with a 8 spd Shimano Alivio crankset. I decided to replace it. I found a new 8 spd Alivio in the at Nashbar, so I bought it as a replacement. Now, this is where it is not working out. Maybe a trip to the LBS is in order, but if I do, I shall lower my head in shame.

On the bikes which have sealed bearing BB's, I replace them about every year. Cassettes likewise. Chains, at least every year, but my touring bike gets enough use that sometimes I need to replace it twice a year.
It seems, from the type of questions which you are asking, that you need to learn more about bike repair. I would suggest getting one of the "Zinn" books, as well as checking out Sheldon's site.
From what you've written, it sounds likre you probably have a worn cassette. You also sound like your chainline is not where it should be. Put the chain in the middle gear on the cogs. and middle ring. The chain should be dead straight. If not, then you have the wrong BB length for that crank.
The rings, unless defectively cast, are not the problem. It seems that the chain is compatible with your rings. Did this problem start only after you changed the chain? If so, then there's the casette issue again. Have you changed the casette? You really have to every time you change the chain on most new bikes.
Bikes are not as simple as they look.

Originally posted by Steele-Bike
How could two 8spd chainrings with the same number of teeth have a different diameter?
I don't think I can answer the "how", but consider this:
A lot of cassettes are coming with a 32 tooth gear. Compare this to a 32 tooth chainring. I am almost certain they are not the same diameter yet they have the same # of teeth.

That said, two 32 tooth chainrings of the same model by the same manufacturer should be the same diameter with minor differences do to tolerences. But, that's Shimano for you (I won't get into a rant here).

So considering all of the above posts I believe you need to adjust the F. Derail. vertically on your seat tube, then possibly tweak the adjustment screws. Between having 2 rings that are different diameters plus a diff. # of teeth on one ring (compared to your old crank) I think this is where your problem lies.

Patience young Jedi. Or, ditch the indexing and grab a set of friction shifters and never deal w/ this indexing non-sense again!!!

What it sounds like to me, is that the new crankset is not seating as far down the bottom bracket spindle as the old one did.

Everytime you retighten your crank with a square tapered bb, you push it every so slightly further onto the spindle. Shimano recommends crank bolts be torqued to about 325 ft-lbs. More than this will cause the aluminum to actually compress and wear, versus the cromoly spindle. After years of use and regularly tightening the crank bolt, the cranks go further onto the spindel and the four sided hole in the cranks get enlarged.

This is a typical problem with the BMX type bikes. Go to a track and just listen for creaky cranks. Those guys are constantly removing and replacing their cranks. That and the extreme forces involved with jumping and sprinting causes the aluminum to wear out and the cranks creak on the spindle.

I've seen this numerous times. The fix, torque your cranks bolts to the recommended, and just readust your front derailleur. I don't think shortening your chain will have any affect on the shifting in this case, because your outside chainring is the same size.

Adjustment tips:

Loosen frnt derailleur cable. Loosen clamp bolt. Align frnt der, so the outside plate is 2-4 mm above the big chainring when looking at it from the side. Then look straight down at it from above and make sure the outside plate of the frnt der. is parrallel with the chainring. (some manufacturers suggest a ever so slight inward twist so the back of the der. is toward the frame)
Did that make sense????

Then re-tighten the clamp and the cable (don't forget to turn your barrel adjuster at shifter all the way in, then out one full turn). I then shift into the middle chainring and the smallest cog in back. Twist the barrel aduster at the shifter to move the frnt der. to the point where the chain doesn't rub the outside plate.

I then shift into the largest cog in back and check to make sure the chain doesn't rub the inside plate. If it does, screw the barrel adjuster back in 1/4 turn and then shift back into the small cog and check the rubbing on the outside plate again. Do this back and forth until the chain no longer rubs, or there is a compromise between the two.

I then drop into the smallest chainring up front and the largest cog in back. I use the limit screw (two little screw on frnt der.) to prevent the chain from coming off the inside of the chainring. Figure out which is the inside limit screw and turn it to the point where the inside plate is barely touching the chain, then back out 1/4 turn.

Then shift to the big chainring and small cog and do the same with the other limit screw. Leave a little more space on the outside limit screw-like 1-2mm away from chain. (when pedaling in the big ring and small cog there is humungous torque and the cranks will actually flex and cause the chain to rub.)

I hope you can follow my directions and if not, well I'm sorry, but I tried. While you're doing all this, I would also recommend replacing the cable and housing. A little grit and grime stuck in the housing can severly affect the shifting efficincy.

L8R G8R:D

First of all, let me thank everyone who has given me suggestions and for being patient with me.

Until now I have not even tried to postion the derailleur, because the main problem was with the chain alignment on the chainring. Well, with a little more tightening on the crank bolts I think I have got it lined up. So, I then decided to re-postion the derailleur. Since this crankset is a little smaller, I am having to lowered it about 1 mm. The problem...the bottom part of the derailleur plate was previously set at 1mm above the chainstay. Thus, lowering anymore is not possible, as the derailleur will hit the chainstay.

Do I need to get a more compact F derailleur?

How right you are D*Alex...bike repair is not as easy as it looks.

Also...

The above mentioned F derailleur is a 1998 Shimano STX top pull

Nashbar.com has 2000 model Alivio F derailleurs, maybe that would be a good match for the new Alivio crankset.

As long as the front derailleur does not hit:
a) the chainstay
b) the chain, either left or right, and
c) the chain, again, at the bottom of the cage, when in the small/small combo,
then it should be o.k. (not optimum, but adequate) at the old height. Make sure that the cage is parallel to the chain, or at least slightly toed inward at the back. This doesn't have to be rocket science. Adjust it until it doesn't hit the chain, then fine-tune the angle. If it is a clamp-on derailleur, this might be a good time to slip some friction tape under the clamp.

I finally gave up and brought the bike into the shop. I am so depressed now. I am a failure! WAH WAH WAH WAH!!!:cry:

Oh, I'll get over it.

Steele-Bike,
This, too, can be a learning experience! Be sure to find out what the problem was and how they fixed it.
Regards,
Raymond