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Trek 820 (1998) Crank and Deraileur Replacements
#1
I'm refurbishing my Dad's old 1998 Trek 820 with the following OEM
specs for the crank and bottom bracket - first bike I've ever done this to but thought it would be an good entry into bike repair (since I just got a bike tool set and XMAS $ to do the project)

Shimano Altus CT92 (24/34/42 Square Taper) 170mm crank length paired with a
BB-CT91E, 68mm / 118mm spindle length bottom bracket

Its easy enough to crossover (and find online) the BB to a UN55 (68mm/118mm/English). The questions revolve around the crank (which seems to be harder to find a replacement)

1. Remedial question . . . I don't have to match the # of teeth exactly . . correct? This would only seem to effect bike performance and not the alignment of components as long as I match chain size (1/2 x 3/32" for a 7-speed)

2. What is giving me fits is that the cranksets that I find (with the matching teeth specs) have different BB spindle length requirements (i.e., 123 mm) Since my plan is to try to replace the derailleurs with the original OEM components, is this possible or do I have to match spindle lengths exactly? I could foresee issues with the front derailleur especially.

3. And since I'm asking, the OEM front derailleur is a Altus FD-CT92-E, which is fairly available online (it's not an EE). Taking it on faith that the rear (RD-CT92) will be reasonably available as well. OR I'm I better off replacing both with something more current? FYI, will be replacing the busted SRAM MRX -170 grip shifters with what looks to be a apples-apples replacement from Performance (SRM MRX Comp that includes the grips and cables)

Thanks so much!

Keith
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#2
1. You don't have to match # of teeth, but the gear range will of course change if you do. "Performance" is the wrong word - the bike won't perform any better or worse with a different tooth count (in particular it won't be faster or slower). It's just a matter of whether one needs a higher or lower gear range. If you don't anticipate true off road riding you MIGHT consider a slightly higher range on the chainwheels, but as the 42-11 top gear is already a 100 inch gear (good for 30+ mph) don't go overboard. Higher gears don't mean higher speed unless you have the power to drive them at the same RPM.

2. The cranks have different BB spindle requirements because the crank design is such that the spindle sits further out in relation to the chainrings, requiring a longer spindle to place the rings in the same lateral position relative to the frame and the cassette.

3. A current derailleur will do pretty much the same thing as the old one. Any front derailleur would need to be a top pull, same as the old one.

**4. (The question you did not ask) No, you should not replace parts just because they are old or out of date. You state no reason why the crankset or derailleurs should be replaced, which is a major expense in both parts and tools, and is especially questionable on a bike that sold for the $300 range. Unless there is some issue such as damage or extreme wear you would be better off putting your effort and money into overhauling wheel bearings, cleaning or replacing the chain (Google chain wear) and if necessary cassette, and maybe overhauling the headset, checking brake pads for wear or hardening.
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#3
sounds like you want to freshen it up nice even if parts may not 'Need" to be replaced.
If you want to to make it sweet, Chain Reaction Cycles has a great sale going on right now. you can upgrade the components on the bike and make it nicer than it ever was if you are willing to spend around $150. Here is what I would put on it for the that price range.
KMC X8-93 8 Speed Chain..........................................$10.49
SRAM PG730 7 Speed MTB ........................................$12.99
Shimano Acera M360 Top Swing Front Derailleur...........$14.49
Shimano Alivio M410 7-8 Speed Rear Mech...................$28.99
Shimano Altus M310 7 Speed Trigger Shifter.F...............$10.99
Shimano Altus M310 7 Speed Trigger Shifter.R...............$10.99
Shimano Acera M361 Triple Chainset Square Taper.........$29.99
Shimano UN55 Square Taper Bottom Bracket.................$11.99
Total.......$130 or so
ad some grips, some new cable/cable housing and you are good to go.
certainly a mountain "Mix" set up. but will work together fine. and the prices are
good. these components you would find on $600 bikes today. One note. get the bottom bracket length spec'd by the crankset. I replaced the gripshift as you can see,
you cannot beat the price. The Mrx ones are garbage in my book compared to the triggers. but that would be your call.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#4
Painkiller does list some very good prices, but again you will likely be unable to detect very little difference in performance with most of the changes. 80-90% of the difference in higher end components is finish and weight. It's your money and time, of course so up to you. I have little experience with mountain shifters, and none recently, so I'm sure if Painkiller says the the trigger shifts will be more reliable and better operating than what you are considering that he is correct.
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#5
"you will likely be unable to detect very little difference in performance"
Other than night and day he probably will not notice. I think you are a bit of the mark on that quote. I do not mean to be rude or snarky however, I actually do builds every day with these products and have tons of data of what works the best together. Half of what I do for fun is to purposely test and run various chain/cluster, model to model. and brand to brand combinations of components to achieve the optimum level of performance @ various price levels. I kept pricing in mind on my recommended list. But not @ the cost of performance. Should the OP deviate from that, then its all him.
I would mention again that he also needs to check and align his rear derailleur hanger also. This is a must, and that tool did not come in his kit more than likely.
Cny has a good point about servicing/inspecting the bearings.It also may be a good time for a pad replacement too. And then you will have a fresh rebuild that will make your Dad proud!
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#6
Keith;

why do you want to replace the cranks? I can understand the BB bracket, but not the cranks (or for that matter the derailleurs).

Bob and I have slightly different tastes - I like grip shifts, he doesn't Smile I also tend to use modern components, and he uses NOS.

Without seeing the bike; I would replace the BB, cassette, chain, cables, shifters and brake pads. I would service the wheel bearings, head set and pedals (if not serviceable, replace). Why do you want to replace the derailleurs?
Nigel
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#7
I’m totally impressed with the response to my post; very collaborative and helpful information. When I made the post, was in FL on vacation so didn't have access to the bike to take pictures or elaborate much further – so wanted to clarify and respond to the group

Would say I’m an intermediate+ rider (recovering triathlete – rode a Felt S22) and my current road bike is a Felt Z100. So I would get value from going with an optimized set of drive components (like Painkiller‘s suggestion) and the Chain Reaction sale is a no-brainer. The Trek bike will be used for greenway path and low-technical trail riding

My goals for this build include having a bike more appropriate for off-road use, learning how to breakdown and rebuild a bike (and then be able to maintain my bikes for most future needs) and I think my Dad would have been impressed with re-purposing his bike. Beside fixing frame paint cosmetics (rust and nicks), my technical goal is to replace, recondition or maintain ALL drivetrain components to include: bearings/cables/pads and also the headset

Finished the total breakdown yesterday. The components that definately need to be replaced include the BB, chain, pedals, crank and shifters (front busted). I’m tired of trying to clean up the front and rear derailleurs and the cassette all have enough surface rust that I don’t feel like messing with it anymore.

What questione is still bouncing around in my head:

The Trek bike specs from Bike Pedia indicates the front derailleur is top-swing/bottom-pull. I think they're wrong about the pull. My research from the 1998 Trek catalog states the part is an Altus CT92 which matches this part http://velospec.com/components/shimano/fdct92e . The actual pull cable is from the bottom (just like my road bike). Picutures are included with this post . Clearly E-mount and top swing. I like the idea of Painkiller ‘s part suggestion of the FD with a top/bottom pull type - I think that takes care of that "concern"

My question is would not having the E-mount change the lateral position of the FD in respect to the chain. Also, don’t want to have to mount the E-plate (wo/the derailleur components) is I don’t have to.

Thanks again!

Keith
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#8
It will be fine, just make sure to order the correct BB for your shell width and spec'd for the crank you choose. The Sale @ chain reaction is over in a couple days. some of the prices are hard to beat and over $100 is free shipping. I stocked up on a few shifters sets, chains, and other stuff myself. I find out next week if my Wife will leave me or not over my stocking up. Smile I will just blame you as I would have never known about the sale til I started to answer your question! Ha
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#9
Gents,

Thanks for the great advice on the rebuild.  Only 7 months to get it close to being done-done!  Work, etc etc etc .  Special props to painkiller; I got the components from Chain Reaction during the sale - even managed to get a jersey within my budget as the prices were so good.  The chain was not available so I ended up getting that part from the local Performance.  I have been learning so much about bikes during this exercise.  Hopefully, only one more question to get to done-done.

Apology please for the photos . . seem to be Iphone challenged today

The first picture shows the bike all constructed; I have been riding it in the 2nd big ring and hooked up the front mech today. The gearing is this picture is 2nd big ring, 7th rear.
[Image: dvfzu1.jpg]http://tinypic.com/r/dvfzu1/8

The second picture is of the rear mech. I really think that the chain is too short; even though I "did the math" it seems very tight and forcing the rear mech in a position it shouldn't be in.  I would never ride cross chaining; but when going front and rear big gear, it locks up the entire drive train

[Image: 2rnh4er.jpg]
http://tinypic.com/r/2rnh4er/8

I do know that the (2) pully gears from the new rear mech are larger than the old (and perhaps add a requirement for more chain?)

The final picture is the remaining chain I have (7 links). Should I add some/all of the links back to the chain?
[Image: 55vyr.jpg]
http://tinypic.com/r/55vyr/8

Thanks,

Keith
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#10
Glad it is coming together for you. Looking at the picture I would say the chain is to short. What I call 1 link = inner and outer plate. To size yours, simply wrap the chain around the big cog in rear and the big ring in front(no rear derailleur involved), and add one link (inner and outer plate worth). Nice looking bike so far. I hope you took the time to have the rear hanger checked and aligned. Hardly a bike I put in the rack that doesn't need some tweaking there. I am ready for another sale from them to stock up again. I doubled my money on most everything purchased. My packages did come a tad beat up shipping to the U.S. though
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#11
Hello.  I found kdbamaman initial request for help with refurbishing a Trek 820 and the great advice on parts.  I am rebuilding a 1997 Trek 720 with a worn drivetrain and it appears most parts are similar to the Trek 820.  It would be appreciated if I could get similar guidance on my rebuild that kdbamaman.  Thanks.

    Tim

1997 Trek 720 Info:
http://www.bikepedia.com/QuickBike/BikeSpecs.aspx?year=1997&brand=Trek&model=720
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#12
Hello Tim, welcome to the Tutor. I would start off with a new thread of your build. Titled something like "19##Trek 720 rebuild". and we can go from there. Post lots of overall condition pics of what you are starting with.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#13
Well Painkiller, you certainly helped me too! I salvaged a hardtail Trek 820 that was bound for the dump, and have followed your advice--except that I DO like grip shifts. I love that you restore bikes--what a noble thing to do.
Thanks for helping us out with your knowledge and experience.
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#14
(06-04-2017, 05:46 AM)Edog1955 Wrote:  Well Painkiller, you certainly helped me too! I salvaged a hardtail Trek 820 that was bound for the dump, and have followed your advice--except that I DO like grip shifts. I love that you restore bikes--what a noble thing to do.
Thanks for helping us out with your knowledge and experience.

Thank you. My favorite shifter's are good old deoreXt top mount thumbies
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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