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Gary Fisher / Bontrager crank problem
#1
I recently purchased my 1st bike in many years - a 2005 Gary Fisher Marlin. Very happy with this overall, but after about 8 3 mile rides I started hearing an annoying clicking sound.

I found the left crank arm was just a little loose. So I pulled the center bolt out, not realizing it took a tool to remove the crank arm. No tool, so I just reinstalled the bolt. No matter how much I tighten it it seems to loosen again after about 1/2 mile. Can I do anything about this without having to visit the LBS? If I have to replace the whole crankset, how do I know which one to get?

Sorry for what may seem like silly questions. It's been 32 years since I had to work on a bike.
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#2
I've had this happen to me. Most of the time I just got a little grease on the spindle so it makes the crank slide off easier. It still does it to me sometimes though. And ya I have a bontrager crank set too.
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#3
Yes if you want to take the crank arm off you do need a special tool. It helps.

If you just want to try to make the bolt stay, clean it with a good solvent, clean the crank threads too, than use some blue locktite thread locker (automotive stores) on the bolt to keep it firm. That is if the threads are not stripped. Do not over tighten as you will strip it . Use fingertips, let sit overnight.
Never Give Up!!!
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#4
If you don't have any LockTite and the bolt is 1/4" in size or larger, you can also use teflon tape thread sealant; the same teflon tape that you use on plumbing pipes. I use it all the time and it does keep bolts from loosening up unless there is a lot of torque or constant vibration on the part, then LockTite is your best bet.
HCFR Cycling Team
Ride Safe...Ride Hard...Ride Giant
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#5
Fairly common problem, if the lh arm is not tightened enough on first assembly, it works loose, if you continue riding with it loose, the square taper becomes rapidly bell mouthed and no amount of further tightening will work. The only solution is a new arm, which can be bought separately, and fitted really tight.
This should? be done under warranty if a new bike, but as yours was sh? you may have to visit a LBS and pay for it to be done.
If properly installed, you should not experience further problems and loctite etc. is not required.
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#6
Its true that if the problem is with the crank arm hole than you do need a new arm. However from your description I am not sure if that is your issue or if the loosening of the bolt allows the arm to move.

Since it does hold for a while and than loosens up, its a question needing more DATA. Carefully examine, threads, arm hole, and crank shaft for wear.
Never Give Up!!!
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#7
Thanks to GeorgeET & everyone for the input. This forum rocks!
I will try tonight to clean the threads very well (using brake cleaner) & inspect as much as I can without removing the arm (since I do not have a puller). I'll also try to swipe the wife's digital camera & post pics of the arm & bolt. Oh, when I pulled the bolt out the first time, some small, hard, half round pieces came out with it. Not aluminum, more like a dark plastic. Couldn't tell if it was some really grungy Loctite or some other type of locking material - but it wasn't threads.
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#8
Took a day longer thanks to camera & computer not wanting to communicate. Damned technology. Anyway, here are some pics of the crank bolt, the pieces that came out, the grease / dirt I cleaned out of the hole and the arm. At my wifes request, I have waited to try using the Loctite until you guys get a chance to see what I see and make recommendations. Before our last ride I tightened the dog-snot out of it. It still got loose after just over 1/2 mile. Any additional thoughts are appreciated. Thanks to all.[attachment=1947][attachment=1948][attachment=1949][attachment=1950][attachment=1951][attachment=1952][attachment=1953]
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#9
Cannot tell too much from crank shoots. Did you use macro focus? Set the ASA high(400+) if the shutter speed was under 100 , to get higher shutter speed to prevent shake. Do not use flash for close ups. I use a clip on light with a PAR for close up photos. Set camera for indoor light if using light indoors.

Anyway the arm looks OK (hard to see) look for gap and rounding at shaft, the bolt looks OK. No telling what the threaded hole looks like. I suspect that that was stripped and the particles you found are a repair with epoxy or thread repair epoxy.
Try a magnet on the particles if not sure. Some look metallic like in stripped threads. Do not over tighten your your next crank. See LBD.
Never Give Up!!!
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#10
I have removed hundreds of these in my time, both with the correct tools and ad hoc methods when the removal thread is stripped.
If the arm works as loose as you say, it should come off fairly easily.
Grip near the pedal and pull, at the same time lightly tapping on the back with a hammer, as close to the axle as possible and fairly rapidly to set up a vibration, do this with the bike upside down and the arm vertical, this usually works with loose arms.
If not, a blunt bar applied at an angle to miss the chain ring and again as close to the axle as pos. and hit with a hammer.
Then carefully examine the inside of the square taper, if this is at all bell mouthed it will never lock up again and a new one will be required, if you cannot find a bontrager one, any will do as long as it is the right length and the orientation of the square is the same ( there are 2 types, yours is classed as "square" the other is "diamond") This must be fitted very tight or the same problem will repeat.
I suspect that the debris you have removed is the previous owners attempt to solve the problem!
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#11
(02-24-2011, 05:52 AM)GeorgeET Wrote:  Cannot tell too much from crank shoots. Did you use macro focus? Set the ASA high(400+) if the shutter speed was under 100 , to get higher shutter speed to prevent shake. Do not use flash for close ups. I use a clip on light with a PAR for close up photos. Set camera for indoor light if using light indoors.

Anyway the arm looks OK (hard to see) look for gap and rounding at shaft, the bolt looks OK. No telling what the threaded hole looks like. I suspect that that was stripped and the particles you found are a repair with epoxy or thread repair epoxy.
Try a magnet on the particles if not sure. Some look metallic like in stripped threads. Do not over tighten your your next crank. See LBD.

Sorry George, guess I'm not much of a camera guy. I checked the camera tonight, but don't think it has a macro setting. But I did use a flashlight to light the pieces, turned the flash off & for the arm shots set the camera on the table with the arm in front of it to eliminate any shake. Hope this helps...
(02-24-2011, 12:00 PM)trevgbb Wrote:  I have removed hundreds of these in my time, both with the correct tools and ad hoc methods when the removal thread is stripped.
If the arm works as loose as you say, it should come off fairly easily.
Grip near the pedal and pull, at the same time lightly tapping on the back with a hammer, as close to the axle as possible and fairly rapidly to set up a vibration, do this with the bike upside down and the arm vertical, this usually works with loose arms.
If not, a blunt bar applied at an angle to miss the chain ring and again as close to the axle as pos. and hit with a hammer.
Then carefully examine the inside of the square taper, if this is at all bell mouthed it will never lock up again and a new one will be required, if you cannot find a bontrager one, any will do as long as it is the right length and the orientation of the square is the same ( there are 2 types, yours is classed as "square" the other is "diamond") This must be fitted very tight or the same problem will repeat.
I suspect that the debris you have removed is the previous owners attempt to solve the problem!

Trev, thanks for the tip - only took a few taps with a ball-peen and it came right off.
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#12
[attachment=1954][attachment=1955][attachment=1956][attachment=1957][attachment=1958][attachment=1959][attachment=1960][attachment=1961][attachment=1962][attachment=1963]

Above are the pics with the arm removed. My guess is the arm shows what you are calling "bellmouthed". The first pics, none of the pieces that came out with the bolt were metallic. But there were some metallic (alloy) specs that came out when I cleaned out the hole with solvent. I cannot see any damaged threads inside, but ...
the crank end itself ( the worst pics of course) appears to me to be okay. You can see some gouging in the inside of the square in a couple of the pics.

Now, I am going to reinstall the arm, tap it on to the crank, then Loctite the bolt. I imagine this won't last very long and I will have to get a replacement arm. But the funds are super tight right now (rent time) & both my Labrador & I need to get out. I'll hope it holds for awhile. How do I measure the arm for replacement? Center to center??
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#13
You will be very lucky if it lasts any length of time, however, if you ride with most of the effort on the right side, you may extend its life.
Yes, centre to centre, probably 170mm. it may be stamped on the back.
Try your LBS, they may have a good sh one, but don't forget the square orientation!
The axle looks ok, it is rare for these to be damaged as they are hardened steel.
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#14
The crank arm does look distorted at the hole. You also want to be absolutely sure the threads in the shaft are OK.

Ye try a hail Mary Pass.

Good Luck
Never Give Up!!!
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#15
Looking at your photos, it does look like one end of the crankarm is belled and because of it, the play in the crankarm is what keeps loosening the bolt. I earlier suggested teflon tape, but looking at the new photos, that will probably not work in this case. After doing what George suggests, as an extra precaution, when using the LockTite on the threads, you can also use a lock washer between the crankarm and the bolt head. It will cause the bolt head to stick out some and won't be the nicest looking crankarm on the block, but it will also keep it from coming loose during your ride until you are able to get a new crankarm.
HCFR Cycling Team
Ride Safe...Ride Hard...Ride Giant
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#16
Wish I had thought enough to put a lock washer on last night. Just didn't occur to me. Duh. I'll let you know how long this lasts. Meanwhile - off to search for the replacement since I know it won't be long. Thanks for all the input. Like I said, this forum rocks!
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#17
tydy. If you can ID that Bonty crankset, I might be easily able to tell you the exact part number that you need, or at least a similar one.
On the back of each arm will be the length; 165, 170, 172.5, 175 etc. I'll need this as well as any other info that you may find. Is there proud lettering on the outside of the arms announcing to the world what they are? If you're lucky, you may even find a small decal on the inside of the arms with a long part number. It may also be forged into it like the length is.
I am a Trek Dealer and have privy to that kind of GF archive info. Wink
Wheelies don't pop themselves. (from a QBP fortune cookie)
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#18
(02-26-2011, 01:00 AM)RobAR Wrote:  tydy. If you can ID that Bonty crankset, I might be easily able to tell you the exact part number that you need, or at least a similar one.
On the back of each arm will be the length; 165, 170, 172.5, 175 etc. I'll need this as well as any other info that you may find. Is there proud lettering on the outside of the arms announcing to the world what they are? If you're lucky, you may even find a small decal on the inside of the arms with a long part number. It may also be forged into it like the length is.
I am a Trek Dealer and have privy to that kind of GF archive info. Wink

Thanks RobAR. No such luck on the sticker, though. As far as lettering, yes, it proudly says BONTRAGER on the front (outward) side and SPORT on the thin side. On the back of the arm it has "BP4CCH 175" stamped into it.
I saw an arm on EB that was kind of similar, right length & orientation, but I don't know if there are other considerations with these. Car parts I know - bike parts, not so much. I appreciate the help. We have a semi- local Trek shop but I can never get there with the hours they keep. I hope next week to visit my LBS to check with them. Since you have access to GF archives, can you tell from their info what size (right term?) crankset I would need if I wanted to upgrade? And with the plethora of cranksets out there - what would be a good upgrade? And since I am asking... can you get the replacement head badge for this?

Now for the update: took the wife & dog out for a short 2 mile ride last night (I use a "Walky Dog Bike Leash" for her (the dog, that is) & I think she enjoys it more than I do) and so far no problem. I know this dance ain't over yet & I'll have to replace it soon, but it's the farthest I've gotten yet without having to get off & tighten the bolt. So hooray & thank you to everyone for suggestions.
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#19
Glad to hear you made some progress. As I understood it the bolt was loosening up and now locktite is helping it stay.The arm did have some distortion in it but seems still usable.

Check if the arm has any play in it . Rotate it and pull it. If no play, most of your issue is damaged crankshaft thread. If the bolt loosens up again check the depth of the threaded hole. You may be able to get a longer bolt in there with a large washer( not sure if your current washer comes of or is welded) and catch the undamaged threads deep in the shaft. Measure depth carefully with the washer. Still use loctite blue. BTW there is also red loctite for stud mounting, holds very well but requires torch heat for removal. Do not over tighten.

Do not worry about a lock washer as that would reduce the depth of bolt and you need all the threads you can catch. There are also tapping new threads options but that wont save you money.

I just put in a Shimano UN54 Bottom Bracket in my bike. They are about $25. If you do go to a new bracket than it may be good to get a new arm too and start over. Hopefully the fix will hold till your wallet thickens. :-))
Never Give Up!!!
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#20
(02-28-2011, 06:51 AM)GeorgeET Wrote:  Glad to hear you made some progress. As I understood it the bolt was loosening up and now locktite is helping it stay.The arm did have some distortion in it but seems still usable.

Check if the arm has any play in it . Rotate it and pull it. If no play, most of your issue is damaged crankshaft thread. If the bolt loosens up again check the depth of the threaded hole. You may be able to get a longer bolt in there with a large washer( not sure if your current washer comes of or is welded) and catch the undamaged threads deep in the shaft. Measure depth carefully with the washer. Still use loctite blue. BTW there is also red loctite for stud mounting, holds very well but requires torch heat for removal. Do not over tighten.

Do not worry about a lock washer as that would reduce the depth of bolt and you need all the threads you can catch. There are also tapping new threads options but that wont save you money.

I just put in a Shimano UN54 Bottom Bracket in my bike. They are about $25. If you do go to a new bracket than it may be good to get a new arm too and start over. Hopefully the fix will hold till your wallet thickens. :-))

George- checked the arm tonight after 3rd ride since I "fixed" it with the Loctite. Got about 9 miles + on it now and still no issues. No play, squeaks, crunches; but I am trying to take it easy & not push it.

I didn't think the crankshaft itself really looked that bad, the arm was pretty torn up. Maybe I should have given more detail: when I said I "tapped" the arm back on, well, that was with a 32oz. ball peen! I was pretty determined that I would get it to stay or just have to replace it. If it does come loose again before I can afford a replacement I will use your idea about a longer bolt after I run a tap through the crank to make sure the threads are clean. Can't wait until I have to pull the drive side off. The allen head bolt has been changed to a hex bolt - so I'm pretty sure the right side is fubar'd even more.

I looked at the UN54 BB. Looks good & love the price. Is there a way to know which size I need without ripping the old one out? I would really like to replace the crankset too but really undecided about what I like. So many to choose from & I don't know much about this new-fangled bike stuff. It was a lot simpler when I was young.
Anyway, thanks for the help, input & UN54 tip.
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