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Technical Q&A with Lennard Zinn – Repair, replace, restore?

  • By Lennard Zinn
  • Published Oct. 8, 2003
  • Updated Aug. 29, 2010 at 10:47 PM EDT

By Lennard Zinn

Technical Q&A with Lennard Zinn – Repair, replace, restore?

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Preservationist
Dear Lennard;
I have several repair books including your “Art of Road Bike Maintenance,”and I can’t find the answer to this question. I have a nice late ’80s Stronglightcrank that has the threads stripped on the drive side where you put thetool in to extract the crank. Is there anything I can do to get the crankoff and save the BB and crank?
–Drew

Dear Drew;
Were you ever a trumpeter or other brass instrument player? I was,and I frequently managed to get my mouthpiece stuck in my trumpet. To removeit, you had to slip two notched steel plates around the tube of the mouthpiece,one against the bowl of the mouthpiece, and the other against the tubeof the trumpet itself. You put a fulcrum between the plates and squeezethem together to pry the mouthpiece away from the trumpet. Seems like Itried something like this with a crank once. I don’t remember if it worked,but it might be worth a try. A mechanic’s gear puller – a threaded screwattached to three hooks to pull on the gear – could work, too.

One time, I removed a carbon crank with the claw of a hammer. The crankhad a self-extracting bolt, but rather than pushing the arm off of thespindle, the bolt of the head pushed out through the face of the carboncrank. Anyway, prying it off with a hammer claw worked, but it was hardon the crank.

Now comes the real question: Why would you want to save that crank,though, if you can’t remove it anyway? I would think that you would justwant it off and not run the risk of installing it again.
–Lennard

Repair or replace?
Dear Lennard;
Recently, I was involved in a bike accident which resulted in a damagedfork (cracked steerer tube) and a possibly damaged head tube. The bikeis a 2002 LeMond Zurich, and the frame material is 853 Reynolds steel.

When I took my bike to my local bike shop to diagnose the problem, theyconcluded that my head tube was ovalized because when the lower cup ofthe headset was placed against the bottom of the head tube, you could seevery tiny flecks of light when you looked directly down into the top ofthe head tube. Their recommendation was to replace the frame or if possible,get the frame repaired.

In my opinion, the head tube does not appear to be so badly ovalizedthat it requires a costly frame replacement. I will take my frame to otherbike shops to get a consensus opinion of the severity of the problem; however,if the head tube is definitely ovalized, what would you recommend me todo? Do you think it is possible to have my head tube repaired, or is thisnot recommended and the frame should be replaced? If the head tube canbe repaired by a professional framebuilder, how much will the repair cost?(approximate ballpark figure)?
–Elton

Dear Elton;
There is no way to replace a head tube on a welded frame like that.The only thing a framebuilder could do is build up some brass inside theend of the head tube and ream it out to the proper size. That would probablywork just fine, but it would required stripping the bike’s parts, repainting,and reassembling–probably $250 for all of that.
–Lennard

A blast from LZ’s past
Dear Lennard;
I have an old steel Pinarello (in fact this bike used to be yours,a Denver Spoke team bike issued to you but never used because you got injuredor something. I bought it from Bruce Whitesel). Anyway I crashed and bentthe fork and it has never been the same. I am thinking of buying a Pinarellocarbon fork for it. But before I spend almost as much as I paid for thewhole bike I’d like to know if a new carbon fork is compatible with a “vintage”bike and will it add some zing to her. Or should I try to re-straightenthe old fork (second time), buy a new steel fork, etc.

Any advice you can offer would be appreciated. There are probably plentyof us out there with old road irons thinking about an upgrade who wouldbe interested in your response – hence the thought about the Q & Asection.
–Dave

Dear Dave;
Well, first off, I think the Pinarello carbon fork only comes in 1.125-inch-diameter steering tube. So, no, that would not work, but there are plenty of forks you can get with a 1-inch steerer.

Your (my?) bike should ride all right with a carbon fork – at leastnot any worse. You know, come to think of it, I remember despising theride of that bike’s predecessor, since it had a 76-degree head angle, andI doubt that one is any different. The frame must have come from the oldschool Italian framebuilding method, which I will abbreviate for you. MyPinarellos from that time (1981) were 64cm, and bikes that big of thatera tended to have this same problem, other than a great Masi I had backthen.

The Italian old school method started with establishing the bottom bracketheight, building the seat tube onto it at the desired angle (72.5 degreeson that bike, if memory serves). Then, the top tube length was establishedto find the upper end of the head tube. A fork was installed (and all ofthem had the same rake, regardless of frame size) along with a front wheel.Then the distance from the bottom bracket to the front wheel was checkedto make sure that there would be no toe clip overlap (with a 180mm crankand long toe clip, on a frame this big). This clearance alone was the determining factor in the head angle! Handling did not even figure into it! Amazing to think of now. So that is how I surmise my bike ended up with a 76-degree head angle. It tended to oversteer and it shimmied like mad on descents.I did ride the Coors Classic and the Tour of Ireland on it, but that bikewas one of the main reasons I became a framebuilder focusing on tall riders!

A deeper question might be related to what sorts of problems you orothers might encounter switching forks on an old frame. First, you needa one-inch steerer. Secondly, if you want to use the old components, youneed a threaded steerer. If you get a threaded steerer, you have to ensurethat it is not only long enough, but that after you cut it to length, youhave at most 2 inches of threaded section left. That way, there is no wayyou will be expanding the stem in the threaded section, a dangerous proposition.

Furthermore, Pinarello had an Italian headset, which is the same diameteras an English one but differs in thread pitch. You can screw one onto theother in a class B fit. It’s not a big worry with a headset, but this wasthe cause of many a stripped hub back in the day – namely guys interchangingItalian freewheels on English-threaded hubs or vice versa. You do consumesome thread in the forcing of one onto the other.

Finally, there is the fork rake. Other than the new Seven carbon forks,which come in a wide range of fork rake from 3.8cm to 5.6cm, you generallyare stuck with a rake between 4.2 and 4.5cm, hardly enough difference toeven notice. A Pinarello of that vintage had 4.5 to 5cm of rake, as closelyas I was able to measure it back then. That 76-degree head angle wouldhandle better with less rake so the trail would be larger, and 2.5cm ofrake is what it would take to get 6cm of trail with that head angle. Thatis not only less than you can find in a fork, but reducing the rake willmake the shimmy worse.Now, what are you doing, crashing my old bike anyway?
–LennardShock updates? Dear Lennard;
I have a 2001 Sugar1 with a Cane Creek air shock on it. I know Fisherhas updated the rear end of the bike quite a bit since then as shock technologyhas moved forward. I like the way the bike rides, but wouldn’t mind a moresophisticated shock. My question is this: can I put a newer shock (5thDimension, FOX with lockout) on the frame, maybe even with a bit more travel?
–Chris

Response from Gary Fisher:

Chris;
Get a new Fox Float RL. It will make a big improvement in keeping unwanted bob out while sucking up the hits. Fox has quietly improved the valving on this shock (ProPedal yes!), the lock out lever barely ever gets used. Be sure to measure the eye to eye and get the right length. It’s a worthyimprovement, you will think you have a new bike!Two reasons not to use the new 5th element stuff on the old Sugar design:
1) The Sugar has a “falling rate” on the rear shock. The 5thelement (Swinger SVP) wants a rising rate.
2) The original short travel Sugar design was made to be riddenpretty much “topped out” with almost no sag, The 5th shocks allow you toride with 30 percent sag and be able to hammer out of the saddle and notbe bobbing; it’s amazing. Sag a short travel Sugar 30 percent and you havea stupid low BB that’s under 11 inches when you’re just riding along.
–Gary Fisher

Feedback:
Dear Lennard;
Regarding the question on shimmy from September 23, I wanted to letyou know that Serotta built me up a new bike with a stiffer down tube andtop tube (tubes for overweight folks) and a different carbon fork thathad more rake. I have tried it out and it is doing fine and the ride isstill great – smooth, comfortable and still responsive – and those tubesdid not really add any additional weight.
–Peter

Dear Lennard;
In one of your past Q&A columns, you stated that you haven’t heardof a Shimano splined crank breaking. While mind didn’t technically break,it did crack. I noticed a crack develop in the left crank arm (Dura-Acesplined) at the top where it connects to the bottom bracket. The crackstarted from the inside, went about half-way across where it formed a “T”that went about 1/3 around the top circumference.Unfortunately, I noticed the crack while unpacking my bike after aflight to Paris to ride the Paris-Brest-Paris event. I don’t think it couldhave been damaged in shipping. It was packed in a Tricor Iron Case, andthe wheels were true. Can’t imagine anything putting enough force on thebike box to break a crank without damaging the wheels.The worst part, I couldn’t find a bike shop open in Paris. Saturday was, some sort of national holiday. One mechanic was available Sunday for P-B-P support. I paid approx. $230 for a Shimano 105 crank (without chain rings-used mine) in a 170mm length. (I had been riding 172.5′s)
-Vince


Technical writer Lennard Zinn is a frame builder, a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / / / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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