Help with CroMo Question!!!
 

Hello All,

I might be picking up a bike for my girlfriend tonight but the frame doesn't have drilling in the dropouts to accommodate a rack. This is a big factor because she'll be using it to commute and I want to put a nice Topeak rack on there with a basket. The frame is a 1990 Novara Team Novara bike. The steel is Tange CroMo. Would I be able to drill and tap a hole on either side to install a rack? I'm a mechanic at a LBS and my boss said that once CroMo is drilled through, it is made susceptible to internal rust and corrosion. The last thing I would want is the bike to fall apart while she was riding it! Any help would be greatly appreciated, we're going to look at the bike tonight. Thanks in advance.

NOVARA "TEAM NOVARA" 17 in. MTB - FULL SHIMANO XT GROUP

Drilling and tapping wouldn't be my choice. Can you use P-clamps?

P-clips on the seat stays will allow you to mount a rack with no issues. You could drill and tap the dropouts, just make sure to put a decent coating of grease on the mounting bolts- keeps moisture out of the threads so they can't rust.

How much stuff is she going to carry? Can you use a seat post monuted rack?
BTW, the frame is already rusting on the inside. The tubes aren't sealed, so moisture will find it's way inside them and oxidise the steel. Plus any sctatches in the paint will let rust gain a foot hold.
Rust never sleeps.

Thanks for the quick responses! Could someone explain what P-Clamps are? I've probably used them, just didn't know the technical name. Clamps would definitely be an option and a seatpost mounted rack with a side basket might work. She'll be carrying a back pack with books and maybe some art supplies. The only reason I wanted to drill it out is because I like how "clean" a rack with a basket on top looks, without having to use extra hardware.

Aren't all rack and fender holes drilled and tapped? What am I missing here.

Fender mounts aren't just drilled into the frame, they are tapped into braze-on's that are (I believe) welded on and reenforce the hole. Drilling a hole and tapping it without reenforcing it, is just asking for trouble imho.

1. I'd just use the p clamps. You won't even have to buy them because most racks come supplied with them in the mounting hardware.

2. Other than the dropouts themselves, that cro-mo tubing won't be thick enough to tap.

Please re-read the OP. He asked specifically about drilling the dropouts. No one ever said anything about drilling the tubes, and if you look at the photos on the CL ad, the brake bridge is already setup with a fender mount that can be used for the top end of a rack. I agree that p-clips would be the easy route, but the dropouts look pretty beefy and drilling and tapping them wouldn't make the frame asplode from rust.

Well that's the part I was talking about drilling and tapping. Right above the rear dropouts, where fender/rack holes would normally be on other bicycles. I'm assuming they're not drilled into this frame because it's a mountain bike and was never intended for fenders/racks. This is the rack I wanted to mount onto the bicycle:

Topeak® Cycling Accessories ? Products - Explorer Tubular Rack (w/o Spring)

Sorry, realize this is becoming not so much about mechanical issues.

These are factory drilled and tapped. Unoccupied and ungreased for nearly 20 years. No rust problems. The tp two aren't even ChroMo.

I'd bet that if the OP stayed away from where the stress occurs, he'd be OK.

Proceed with caution though.

http://www.pedalroom.com/p/khaki-klunker-18268_6.jpg
http://www.pedalroom.com/p/tomato-krate-18420_3.jpg
http://www.pedalroom.com/p/chartreus...st-18284_5.jpg

Missed that, thanks. I think the CrMO threw me off.

answer is, IMO, drill and tapping cromo dropouts is no problem. i don't know what your boss is talking about. as far as attaching the rack to the seatstays. p-clamps aren't necessary, IME. here's a pic of a brake-hole mounting that has worked for me for many thousands of miles of touring.

http://bikeforums.net/attachment.php...hmentid=400347

http://www.thetouringstore.com/TUBUS/Fly/Fly-2.jpg

Well it seems like the overall verdict is that drilling/tapping the dropouts and using a good amount of grease shouldn't cause me any problems, but proceed with caution. Maybe the boss man was just trying to be a know it all about the rust/corrosion issue. In situations where there isn't drilling in the seat stays (but there is drilling already on the dropouts) for a rack and I don't feel like using clamps, I've had great luck attaching the two braces from the rack to both sides of the quick release.

A user explained that the tubes are already rusting/corroding inside because they're not sealed. Can someone briefly elaborate on that? Why isn't ChroMo sealed from the elements?

They could be rusting, but it's not certain. A good frame is treated internally after it's buit with a liquid like Framsaver that inhibits rust. That frame may be protected.

Got it. What about the actual process of drilling and tapping? Any special drill bit I need? I'm assuming I'd want to use some thread cutting oil to keep the bit cool, any other advice? If I don't feel like attempting to tap, I could always just use a nut on the other side. Thanks again for everyones input!

Yeah, just go for it. A regular bit designed for metal will work. If you have access to taps, do it. I always hear about rack bolts coming loose because they are so small. If it were me, I'd tap it and use a slightly too long bolt and put a nylon lock nut on the back as a redundant holder. IF there is room.

They wrap around the stays (upper or lower) in place of missing eyelets.

http://www.wallbike.com/sites/defaul.../pclampuse.jpg

so you really need to tap it? why not just a button head screw from the inside and a nut on the outside. not pretty, maybe not something i would do, but much simpler.

I've drilled & tapped dropouts before for racks on trail a bikes so you have a rack to carry stuff. Not a big deal. Personally I use loctite on rack bolts rather than grease as they can loosen up from the pounding they take. Just make sure of your location to clear the chain on the small cog etc before drilling. Center punch to start (or a very small drill for a pilot hole) correct bit size for the tap size, oil/cutting fluid, sharp bit helps too.

I dislike "p-clamps" and would vote for drilling and tapping if the op promises to practice on some scrap first.



Jon

Well, we bought the bike and it looks like the drilling will definitely be an option and I'm probably going for it! Unfortunately I don't have any bikes to practice on but I'm a pretty meticulous/neat guy anyway. There will be lots of measuring and double checking before any drilling happens, simply to make sure that the holes are in the same spot on both sides.

Purchase one of these to mark your holes: Center Punch - Automatic Center Punch with Brass Handle

Then drill a small pilot hole (3/32" or so), then 11/64" for the M5x0.8 tap. Harbor Freight taps are fine. Their drills leave a lot to be desired. Get your drills from McMaster or Fastenal or MSC or Grainger or similar Industrial Supply company.

After drilling, counter sink the holes slightly on both sides before tapping with a 1/4" drill bit by hand, not in a power tool. I have one of these: http://uytit.files.wordpress.com/201...rill-chuck.jpg that I use for holding drill bits for manual operations. Less than $10-

Use lots of oil both when you drill and when you tap. Any light oil is fine - I usually use TriFlow liquid - not spray.

Flush the oil out with Isopropyl Alcohol (from any pharmacy) just before you install the rack, and use blue or purple thread locker. That will protect the cro-mo and retain the screw, while still being removeable. DO NOT use red threadlocker - you will not be able to remove the screw.

as you noted where it is thick there can be holes threaded . but up on the top of the seat stay the tube wall is thin.
there you either braze in or onto the tube, a fitting to do the job , or do nothing to the frame and add the P clips.

I was referring to holes in the drop outs, since that's what the OP was referring to. ;)