HerrKaLeun

I have an old Schwinn Mesa LT withe a " Truativ Isoflow" 3-ring crank. Crank is bent and I want to replace it.

I watched the Park tools videos and think it is a 3-piece crank. But I can't get that 8 mm allen nut to open. The videos make it look easy. I have the feeling I must have a different type of crank. could one of you see the attached pictures (with and without what i think the dustcover is) and tell me what tuype that is and what removal method (and tool) I would need? i researched a lot, but conclude there are dozens of crank styles with dozen of BB. that dustcover is all plastic and was kind of threaded, but not really. I had to bull it out with a screwdriver.

I haven't tried violence to loosen that nut (hard to do when crank is on the bike), but thought before I damage something I ask here. all youtube videos work without violence, so i think I'm doing something wrong.

My next problem is I want a replacement crank that is better. One of the ones i like is the shimano alivio T4060 (because of the 48 teeth).

How do I know if my BB will work with that? I realize if I had the crank removed I had a better idea what is inside. I would also be willing to buy a new BB if this is needed, but again how do i know what will fit? All I know the frame width at the BB is 65 mm measured outside. i saw many BB are 68 mm. mmmmmhhhh.

This isn't a very valuable bike, so i don't want to spend a ton. just some decent component on Alivio level will do.

thanks in advance for any hints or recommendations. Had to make the pictures quite small to upload here. Sorry. Also can't post links yet.

bargainguy

If you can't break that 8mm bolt, can't replace the crank.

Is it frozen? A P-handle hex wrench with a fairly long lever or a long ratchet with a 8mm hex might help with leverage. Align said wrench about 2 clock hour positions clockwise from the crankarm so you can apply leverage by squeezing the wrench handle and the crankarm together counterclockwise (mechanical advantage). If that doesn't work, could try spraying/soaking with penetrating oil, let sit overnight, try again.

Once the 8mm is removed, you'll need a crank puller. Screws into the crank threads surrounding the 8mm and pushes the crank outward from the BB spindle.

I'll let the experts decide on the best crank to replace your TruVativ. By the way, what's the bike/saddle with the funky paint job in the background?

Andrew R Stewart 

Motorcycles for years used impact wrenches to help loosen tight fasteners. Shock often overcomes torque.


But I notice that the 8mm socket is still in very good shape. To me this means that not enough torque has been tried. Andy

JanMM

Socket wrench with hex adapter might help
(As previously mentioned)

wesmamyke

I can tell you that bottom bracket is not compatible with anything Shimano makes. Shimano has it's own Splined standard called ocatlink, they have never used isoflow. So you will certainly need a new BB as well.

grizzly59

I would soak it in penetrating oil and leave it sit for a day. Soak both bolts again and turn it over for another day. If you mess up the bolt heads you're in for a lot of work and headaches. After a good soak, use a good tight fitting hex key and take the bolts out.

HerrKaLeun

OK, thanks for the tips. i didn't use full force since i wasn't all sure there isn't some secret way. so force it is.
sounds likeyou all are sure what it is. which Removal tool will i need? i saw Park has many different ones...

that colorful bike in the back is my daughter's :-)

Can i just buy any 68 mm Shimano BB? Or what Cranks could I install in this one?

CliffordK

Shimano has several crank standards, including TWO different Octalink standards.

They have used square taper cranks in the past. I don't know if they are still making them, but the technology is widely available. I wouldn't be surprised to see Shimano branded square taper cranks on Department Store bikes.

There is always the angle grinder approach if the bottom bracket doesn't need to be spared.

But, as Andrew R Stewart mentioned, the bolt head isn't stripped, so it isn't time yet to give up hope. You can buy ordinary socket Allen Wrenches that should fit on your favorite breaker Bar. You should be able to get anything off with a good breaker bar. If not, it isn't meant to come off.

HillRider

Is "Isoflow" just Truvative's brand name for the generic ISIS design? If so, there are a few ISIS compatible cranks around and I think Nashbar still sells one.

Otherwise, the replacement crank is going to require it's own bottom bracket. I assume the frame is English threaded so the whole world of cranks can be used.

Ronno6

Yours is a self-extractor.
With the dust cover in place, if you can break that allen bolt loose, backing it out will remove the crank arm.

corrado33

That was my first thought as well.

If the part you've already removed looks like this.



Then you have a "self extracting" set of cranks. Which means you won't need an extractor tool. Just reinstall the "ring" around the bolt then remove the bolt. (Yes, it seems counterintuitive, and YES, the bolt will seem to get TIGHTER as you remove it (lefty loosy). This is all normal. And yes, the bolt won't come OUT of the crank, it'll just pull the crank off and stay put.)

By the way, even if you've already taken the bolt off, you can still "reinstall" it, then reinstall the ring, then take out the bolt and it'll still work fine.

Crank bolts are often seriously difficult to remove. When I teach people to take cranks off they are ALWAYS surprised at how much force it takes to remove them, especially for the self extracting kind. (And many people with weaker grip strength can't remove them at all.)

wesmamyke

Isoflow is it's own thing. It's similar looking but completely different. If you look at the picture of the crank posted there is a sticker with the Isoflow logo and a little picture of the spline pattern. IIRC it uses the square taper end of a crank extractor, it's smaller diameter than ISIS and uses a standard crank bolt and not the M15 or whatever ISIS/octalink uses.

Edit: Also pretty sure that's just a plastic dust cap, not a self extractor.

Picture of Isoflow BB:

corrado33

In my experience, any crank that has an "exposed" allen and screw on ring (accessible without taking the "dust cap" off) is a self extracting kind. The kind that has the easily removable (basically fall off when you touch it plastic rings) are not self extracting. Besides, the bolt in the OP has a "shoulder" that seems to be meant to mate to a self extracting dust cap. (Or am I just seeing things?) You may be right though, I'll check tomorrow when I head into the shop, I know we have a few of these cranks hanging around.

And yes, now that I see a picture of the isoflow, it's completely different than ISIS. ISIS has smooth, concave transitions between the "splines."

AnkleWork

Looks like the OP has this kind of bolt with the plastic trim:


. . . lots of them about.


.

wesmamyke

The Isoflow cranks/BB came with just standard bolts and plastic dust cap that's not supposed to come off the bolt, they have a imprint of the spline pattern around the edges of the plastic, you can just see it in the 3rd picture.

corrado33

Cool, makes sense, I couldn't quite make it out from the pictures.

hairnet

How big of a wrench are you using? A tiny home sized 6" allen wrench won't be enough to get that loose without a 200lb gorilla behind it.

dsbrantjr

Choose a crankset first, then get a bottom bracket to suit.

AlexCyclistRoch

My method is to use an 8mm T-handle, then fit an 8mm closed-end on the shaft, giving you 2 places to apply torque simultaneously.

70sSanO

If you don't have am 8mm socket that will fit on a 3/8-1/2 drive breaker bar you can do what what Dad taught me... get a 3ft piece of 1/2" pipe and put it over the allen wrench for leverage... poor man's breaker bar. You may want to have someone hold the bike and be careful you don't twist the allen wrench out of the bolt.

Good luck!

John

Edir added: In lieu of pipe you can use virtually anything that is long enough and strong enough that you can put over the allen wrench... 1" box wrench, hanging hole end of a large crescent wrench, etc. Keep in mind that the more creative, the more you need to keep the erector set breaker bar straight as it tends to want to slide one way or the other.

dsbrantjr

Put your chain on the large chainwheel and cover it with a rag, to help protect your hands from the teeth.

HerrKaLeun

All: thanks for your input. I bought a set of hex-nuts (to have the 8 mm hex to be used with a 3/8" wrench. i also bought a 30" Breaker bar. Unfortunately i realized at home i don't have a 1/2"-3/8" adapter, so I couldn't use that breaker bar yet.

but I tried my impact driver. It did nothing. i also tried a smaller 10" ratchet. i had difficulty to keep pedal and bike in place. I had soaked it with WD40 all day. I also tried both sides of the crank. My original Allen key is maybe 8" long. the pictures above with the black dustcover and with the dustcover removed (where you see that round around where the 8 mm goes in).

That dustcover didn't have any holes like for the self-extracting cranks (what corrado 33 suggested). It was just plastic and I kind of destroyed it when removing. It was not threaded.

There isn't evidence of corrosion (I know, may not be visible). Is it really that hard? Or is that where I need some sort of removal tool? I kind of think it looks like the 3-piece crank set (where in the Park tool video the guy removes the hex nut and then uses the crank removal tool). The video makes it look easy.

I hope soon I can get my adapter to try my breaker bar. i also could flex it off... but that is my last option and I then really need to know what crank I can buy.
is there anything i can measure to determine what new crank or BB I could use?

Once I know what the existing is, I also could look for one of the same type. My only real requirement is to have at least 48 teeth, Ideally more and of reasonable quality.

How would one know what cranks one needs and what type and dimension they are? When i go to the Shimano website, it barely gives any actual information. it seems even if i had a bike with shimano already, i would not be guaranteed my new Shimano to fit etc.

AnkleWork

No idea what you mean by "nut."
WD-40 will do nothing in this case. Try some actual penetrating oil as mentioned frequently in this forum.
No evidence of corrosion?!? Have you looked at your photos?

HerrKaLeun

I misspoke, I meant hex-bit. an 8 mm to be attached to a 3/8" ratchet.
I'll get some better penetrating oil.

the reason I want to replace the crank is that it is bent. i don't know if i laid it too much on the side, or if I applied too much force, but the large sprocket is bent, but the smaller ones too. I can't really shift into the granny gear anymore.
I was towing a child trailer a bit, but really not that much. Maybe that screwed it up, or it was just cheap.

Now that I decided to keep this bike and upgrade (new brakes, cassette etc.) I wanted to take care of that too. and since I'm more on good paths with my 26" wheels, I would like a larger crank (48+ teeth). Currently I'm riding in the 27th gear often.

Edit: I just checked in my garage, what I sprayed in wasn't the normal WD40, it was a WD40 " penetrant rust release".
do you have a better product?

70sSanO

I assume your impact driver was electric and not pneumatic?

John