Giant DH Comp and E-13 Guide: bad chainline solution

sam_little · 05-25-2006, 12:29 PM

I sent the following note to the E-13 support folks. However, since I know quite a few people are still running this frame, I thought it might be worth posting this info. I can put up some pics if people are really interested, but they'll show my crappy workmanship.

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I have an E-13 SRS for my Giant DH Comp from 2003. I know that the guide fits by running the BB to ISCG conversion plate outboard, but this sends the chainline out of whack. Probably the biggest barrier to proper mounting is the little tab on the BB meant to secure the stock Giant guide to the bike. So, I took the following steps:

1. Dremmeled the tab off of my BB.
2. Reversed the ISCG conversion plate so that the bulbous portions faced forward, keeping them from interfering with the linkage and bearing cups. NOTE: This disallowed proper mounting to the boomerang, as the holes don't line up with the ISCG plate reversed (bulbous ends forward)
3. Drilled and dremmeled new beveled channels in the boomerang such that the boomerang would mount properly. NOTE: This probably compromises the strength of the boomerang significantly.
4. Mounted everything up, chainline is perfect, I'm happy.

So, why email you? I'm concerned that the strength of the boomerang has been compromised such that if I take a good hit to the boomeraing, I could shear the limited metal now holding it to the ISCG conversion plate. Though this won't likely have any earth shattering effects, it could easily ruin a riding day.

As this process was EXTREMELY easy, and as I am NOT AT ALL an engineer, I thought maybe you guys have produced a reversed-drilled boomerang to attach to the BB to ISCG plate when run inboard but with the bulbous ends forward. Any chance that this is the case? I know the bike is dated at this point, but maybe someone made a few of these a few years back?

Let me know if you get a chance. Thanks.
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sam_little · 05-25-2006, 01:01 PM

Quote:

Originally Posted by stoney98

I dremeled the tab off, and put it on as flush as possible. If your boomerang is up the the Chainstay, your should be fine hit wise.

I'm confused, you did something similar? Did you mount the BB to ISCG conversion plate inbound or outbound? If you ran it inbound, were you able to place it in the standard position (bulbous ends to rear of bike)? If so, how were you able to avoid the bulbous ends from hitting the bearing cups?

I forgot to mention above, I did have to dremmel away a small chunk of boomerang where it meets the chainstay, maybe 3-4 mm. Like you said, Stoney, I think I'll be fine as long as I don't land on a tall, skinny rock or tree stob that makes direct contact with the boomerang. I'm more interested in a cleaner version of what I've done for security.

dw · 05-25-2006, 02:06 PM

Dremeling off the tabs on that bike could always help. Keep in mind, those bikes were designed with, and came from the factory with a 135 rear end, and a 145mm BB spindle. The chainline pretty much blows no matter what you do, so your solution to get it inboard is a good one in my opinion. Those frames also had their "own" mounting standard for the guide that came with it, it wasn't an accepted or shared standard. The tabs were basically useless unless you used the guide that came with the bike. That being said, the ISCG mount plate is the same front or back. Its been a few years since I wrenched on those bikes, but Heikki is the one who originally set the guides up and wrote the instructions for the Giant, so he has as much info on this as anyone. I jsut cant remember exactly what it all looks like, but flipping the ISCG mount shoudl not require any mods unless the frame forces it. Maybe an ISCG05 adapter plate could help even more? Just brainstorming a little.

Dave

vitox · 05-25-2006, 02:37 PM

hey i once installed a SRS boomerang on the inside of the ISCG adapter, and from what i can remember (hotel room quickie fix before race) you dont need anything special apart from a thick washer to put between the bolt and boomerang, of course you cant use the original countersunk bolts when mounting the boomerang like this but they arent needed as you wont be hitting the chainring with them anyway.

a few years ago i installed a few SRS`s to dh comp`s and i can recall that those original mount tabs have to go. i also think what i did was to file down the iscg adapter to make it clear the linkage. this was the 02, white dh comp in case that matters.