New Giant DH Team/Cromotor build thread

[Scott]

I don't have cranks or bottom bracket fitted to my DH Comp yet (but thankfully found a 150mm swing-arm in Perth). Do you happen to know what the maximum width of a battery box could be that wouldn't be hitting the crank arms?
Cheers

6.25 inches is about the max width from my crank to crank. I would keep it down to 6 inches to be safe. My battery box is 5.5 inches with 1/8th inch side panels for a total of 5.75 inches with plenty of clearance. Anything more that 5.5 inches would seem hard to pedal to me. I thought you decided to go with your Specialized Demo 9 instead?

 

[trevc2]

... I thought you decided to go with your Specialized Demo 9 instead?

Sure did. Riding that setup nearly every day.

This is for build #2, which is Cromotor V2, Max-E, 18650's, Holmes MMP rims + "Michelin Pilot Sporty" MC tires. Using the DH Comp since I wasn't able to sell it, and I got lucky in finding the 150mm swing-arm

 

[Obiwan007]

Where did you find that swing arm if you don't mind my asking? Any chance I could get you to go with a different frame? I know where you could unload your current one :wink:

 

[trevc2]

Where did you find that swing arm if you don't mind my asking? Any chance I could get you to go with a different frame? I know where you could unload your current one :wink:

Well, if a Phasor/Torque/Greyborg frame were to show up at my door, I'd be more than happy to. I'm not a huge fan of the Comp, but it has 2 big pluses: the open triangle and Kiwi adapters. Otherwise, it seems too small. Mine is an L and both the frame + swing-arms are shorter than my Demo9. I'm hoping it's not just a catapult with crappy handling when running the Cro.

I scored the 150mm arm from an ES member in Perth, Australia. Nothing but luck/timing. I'd been searching everywhere for several months prior and had given up. The Giant retail and company contacts in Australia can't get them either, claiming they're not being made and there's no longer existing stock (anywhere).

I suspect there's more swing-arms kicking around Australia, they're probably sitting on bikes in garages and not being used. I found a beat up 2002 DH Comp selling for $300 yesterday, trying to convince the guy to ship parts from it.

 

[Animalector]

Where did you get your 18650's? or where are you planning to get your 18650's. I'm already thinking about a light weight mid-drive, 750W with 18650's in the triangle.

 

[trevc2]

Where did you get your 18650's? or where are you planning to get your 18650's. I'm already thinking about a light weight mid-drive, 750W with 18650's in the triangle.

I'm still reading,reading, then more reading about batteries. No orders yet. I'm not in a huge rush.

We could try to pool our orders for any potential 18650 cell purchases, buying in bulk helps.

Apologies for hi-jacking the thread.

 

[Obiwan007]

Hey Scott, I have a question you may be able to answer. Here is a picture of the 150mm swingarm moonshine got new from Giant:


So I noticed that they chose to form an s-curve in the stays on the disk side instead of the straight outward bend that they used on the drive side. I surmise that the drive side is identical to the 135mm swingarm which makes sense. But why the s-curve on the disk side? I initially thought it may be a crank arm clearance issue but looking at my bike there is plenty of room to make it a straight outward bend. How close is the frame to your crank arms? Any thoughts on this issue? I'm suddenly interested in this since I am now contemplating a frame modification to widen mine. I wonder if they did it so they did not have to make new molds for the cast pieces in the front and their welding surfaces. For that matter the cast drop-outs and their welding surface angles would have needed to be changed too. What do you think, given that, unlike me, you actually have one of these to inspect Obiwan.

 

[Scott]

I initially thought it may be a crank arm clearance issue

I never realized it but mine is pretty close with about 2 cm of clearance from the swing arm and its hard to see in the picture but 1 cm of clearance from my phase wire bundle. What I did realize before is that it looks like the bend was made so a 203 mm disk can be used. The disk come pretty close the the "end" of the bend. And yes my tire has less than 1 mm of clearance to the swing arm on the right side (chain side).

 

[Obiwan007]

Hmmm...interesting. It's hard tell from the picture but, is your tire centered on the frame. What I mean is in the front of the swing arm is there an equal distance side-to-sid? The brake clearance won't be an issue for me with my recent modification of the disk adapter but I will need to pay close attention to the crank arm clearance.

 

[Scott]

What I mean is in the front of the swing arm is there an equal distance side-to-sid?

Nope! There is 1 mm between the tire and the swingarm on the right (chain side) and 2.2 cm on the left (disk side). My camera ran out of battery power so ill post a picture in a few hours when the batteries charge.

 

[Obiwan007]

OK thanks Scott. Are you running much dish in your wheel? Did you lace it yourself? I'm pretty sure I'm going to lace mine but I can't do anything until I know if I'm going to be going with a widened swing arm or sticking with the 135mm because the wheel will have to be laced with quite different spoke lengths depending. I want to try to run the widest tires I can get in there...3" should fit OK if I can get my hands on some decent ones; Nokians or something. I have been looking at these:
http://www.unicycle.com/unicycle-ha...36-inch-tires/duro-wildlife-leopard-tire.html

 

[Scott]

3 in would definitely fit in a 150mm swing arm. 3.5 inch might be possible but it would be very close. 3.5 in would not work in the 135 mm swing arm I have. my tires are 2.7 in. I don't know too much about off road tires I just searched for the best street tire (because all I wanted to do was go fast) and found the Maxxis Hookworms. It looks like Zombiess' Shinko 2.75 x 19 MC tires worked out pretty well here. I personally absolutely loved Moonshines blue MC rims which are 19x1.85" blue prowheel rims with 12ga spokes with a DMR revolver hub. He put shinko 241 tiers on it. I have heard that off road bike tires wear out really fast.

I bought my Cromotor from Zombiess already laced into a 26in rim. I don't really want to do any dishing but If my spokes come loose I will. I laced a wheel for my old nine content hub motor and it was not to hard it just took a lot of time.

It was not possible to capture a personal view of the clearance in one photo so I took two shots of it. It may be hard to see but the weld on the lower swing arm is the widest part of the swing arm closest to the tire. The lighting in my garage is pretty bad and its dark out side already.

 

[trevc2]

I think you can fit up to a 4" tyre in the 150mm arm if the wheel is dished towards the disc side, so it's properly centered:

 

[Scott]

I think you can fit up to a 4" tyre in the 150mm arm if the wheel is dished towards the disc side, so it's properly centered

That must be a 20 inch wheel or something because my 26 inch wheel comes to the welds at the very left edge of the picture where the swing arm gets a lot smaller.

 

[Obiwan007]

So good news, I just got off the phone with the guy who is going to re-work my swing arm. He has gone over the pictures I sent him (lots of different angles of both my 135mm swing arm and of the 150mm ones that I had pictures for. So his assessment is that he can do it, no problem. He assured me that he is well aware of the heat treating issues and uses techniques that either maintain or restore it. He talked about several similar projects that he has worked on for professional bike racers. All ini all I was impressed. He could not give me a cost until he can inspect the swing arm first hand and we made arrangements to do this on Monday. If the price turns out to be right I'm going to have it done and can then report on the quality afterward. I did ask him if he would be willing to do the same modification for other who may want to ship to him and he said he would be willing if this one goes like he thinks it will.

 

[trevc2]

If he's doing that sort of custom work, is he able length it at the same time? Might help keep the front wheel down a bit.

So good news, I just got off the phone with the guy who is going to re-work my swing arm. He has gone over the pictures I sent him (lots of different angles of both my 135mm swing arm and of the 150mm ones that I had pictures for. So his assessment is that he can do it, no problem. He assured me that he is well aware of the heat treating issues and uses techniques that either maintain or restore it. He talked about several similar projects that he has worked on for professional bike racers. All ini all I was impressed. He could not give me a cost until he can inspect the swing arm first hand and we made arrangements to do this on Monday. If the price turns out to be right I'm going to have it done and can then report on the quality afterward. I did ask him if he would be willing to do the same modification for other who may want to ship to him and he said he would be willing if this one goes like he thinks it will.

 

[Scott]

Thats really good news! I thought I said it before but I guess I didn't, I would have him stretch it to 155mm or 160mm because I still had to stretch mine some since the Kiwi drop out adaptors take up space.

 

[Obiwan007]

Ya, I used a Shinko 244 2.75" tire on my first build and it was ultimately wider than 2.75, almost 3" and I had to grind off some of the edge tread. But this swing arm is considerably wider. I think I will go with 3" bicycle tires to start and see how I like them (those shinkos with moto rims are HEAVY). If I ultimately don't like them as well I'll convert over to the moto rims and I think I will also go with the 241 Shinko this time too. It seems like a little better design for dual sport.

 

[Obiwan007]

Yep, I have been keeping that in mind Scott and I will be talking it over with him and have the motor on hand when we decide just how to move forward. I think I will shoot for 155mm if it can be accomplished without any other issues like crank clearance. I think that I will be less likely to need more clearance than that however after doing the profile lowering steps on the drive side and also eliminating the disk bolts on the the other side. I'm excited to see how it turns out and to finally be able to look forward to getting back to the build that has been stalled out because of this problem.

 

[Obiwan007]

Went to have my swing arm modified today and got to take some pictures of the process. The technicians are a pair of guys, one of which is a heliarc fabrication specialist and the other is a metallurgist. They are both are bicycle enthusiasts and have built and modified many frames for various projects including IC bike conversions. The technique they are using involves a custom made jig to keep everything true and square. It engages the the center hole in the front cross member, and then the drop outs to produce a center-line reference:


Once the jig was prepared, they ground down all the pertinent welds that would provide relief to the outward movement of the stays:



With the relief cuts done, the swing arm will be clamped to the bench and, with the application of heat,
Moved out the 20mm we determined would be our target. The jig will reference this distance and also allow the maintenance of the perfect alignment of the drop-outs to each other. Then the whole thing will be immediately quenched. All the relief cuts will then be re-welded. Finally, if necessary, the same process will be done on the drop-out end to make the drop-out face parallel to the center line. We took some careful measurements and it looks like the stays can remain straight with no problem (crank clearance) rather than the s-curve used on the stock 150mm drop outs. Alas, he could not finish it in one day and I won't be able to pick it up for several days. I'll report more later. After we see how this one turns out he will come up with a regular process price for anyone who wants to have this done on a shipped basis in the future. But the preliminary estimate is that he can do these for less than Giant was charging for new one (I think I recall moonshine saying that he paid $240.00). It will be interesting to see how the brakes line up when it is finished. I have a plan for moving the disk either direction though so it should be OK. Obiwan

 

[dan974]

personnally I won't do it, search on welding DH cracked frame and Al, if you don't get the same alliage, won't wedl well and after the initial welding the frame was heat treated...when you weld again you break the heat treatment around the aera of the new weld and so shoul heat treated the whole piece again...doen @ your own risk hope you won't jump 6" with it or apply 10Kw to wheelies :wink: maybe I'm pessimist,be aware and check for cracks on the first rides and as a regular checkup...

 

[Obiwan007]

Dan, I will definately be watching for problems and 6' drops were never in my future. I think I mentioned that one of the two guys doing this mod is a metallurgist and is making sure that compatible materials are used. What I failed to mention in my previous posts is that the quenching that they will do after movement of the components is to normalize the affected areas. When the whole thing is done they WILL be re-tempering the swing arm. In addition, since this is 6XXX series aluminum it falls into the category of alloys that will precipitation harden or age harden. According to my reading the majority of the hardening process would occurr naturally at room temperature in the first few days and continue slowly after that. Here is a link to the best article (by far) that I have found on the subject:
http://www.bikepro.com/products/metals/alum.html
I, for one, found it very informative. In the end it turns out that it is my ONLY option since I have been searching diligently for three months now internationally for a 150mm swing arm. Apparently these have become as rare as a lamb chop at a coyote picnic. Obiwan

 

[dan974]

Ok with heat treatment, I just wanted you to be aware after the process, I can't imagine breaking the rear arm @60kph in trafic @ a corner

 

[litespeed]

Sounds like you did your due diligence on this modification. Very impressive and looking forward to the results and the out the door pricing.

Tom

 

[Obiwan007]

You and me both Tom!