Reenforcing down tube?

Discussion in 'Painting, Welding, Bending and Gas Tanks' started by Trokair36, Oct 4, 2011.

  1. Trokair36

    Trokair36 New Member

    I hope this is the right place for this and if this has been talked about before just send me in the right direction. Thanks

    I was just wondering if it would be possible to reenforce the down tube so that it won't crack after a hole has been drilled in it. I did this to mount my HT engine and I would like to ride it to school but I'm a little worried that it will break while I'm on the road. The frame is from a Raleigh m20 mountain bike and it's made from alluminum idk if it's strong enough for the stress of daily rides with that hole in it. Any thought would be greatly appreciated.

  2. DougC

    DougC New Member

    Ride it carefully until you can find a steel frame.

    The problem with trying to reinforce the aluminum frame is that you would likely need to weld (or have welding done) on it. Aluminum softens a lot from welding, and must be re-heat-treated to restore its original stiffness.

    A steel frame on the other hand can be welded on, and won't require re-heat-treating afterward.

    Also--steel tends to bend quite a bit before cracking--unlike aluminum, which tends to be much stiffer but cracks much easier as well.
  3. Al.Fisherman

    Al.Fisherman Active Member

    First for all that read this, I don't recommend a hole drilled in any tubes, especially for mounting a engine. Why...this was a steel tube.

    A very small hole was drilled (where a water bottle attaches), to run wires through it. I only drilled out the anchor for the screw.

    The bike can be repaired, but at what cost? I repaired the crack in mine but I chose to use a different frame. Me the cost was none as I have the equipment, but safety was the reason.
  4. get a magnet

    The monocoque frame appears to have lasted a single year (1996) and is gone. The aluminum frames continue on with the M800, M600, M400 and M200. Steel bikes are the M80, M60, M3000 (cheap full suspension), M55, M50, M40, M30 and M20.

    You have a steel frame. should be fine...
  5. Al.Fisherman

    Al.Fisherman Active Member

    Just to make sure..test it with a magnet. A refrigerator magnet will do.
  6. oneninesixnine

    oneninesixnine New Member

    Be a man of your word.

    Do right by me, FarRider.
  7. retromike3

    retromike3 Member

    don't drill you will be sorry

    On my bike I drilled the seat tube and It looked like somebody had cut it with a hacksaw. The vibrations coupled with the stress risers inherent in that type of mounting will go though steel quick. Sick Bike Parts make a frame mount that really worked for me when I had the tubes to large on my seat tube.

    Its gone OK for me for half a year, but I did have a bolt get loose after a while because I intentionally did not put a double bolt on one of the mounts gust to see if they would rattle loose. It did but in a strange way, it only exhibited problems in a certain RPM range. So when I got home I checked it out and sure enough I had two blots that needed tightening.

    So I double bolted them (with a little blue lock-tight thrown in for good measure) and it been going grate since then.

    Those guys really know there stuff. I am thinking of getting a shift kit but I think I will have to build a new frame and maybe get a morri engine for that project.

  8. jeffuehrer

    jeffuehrer Member

    Crack in my tube!

    I recently spotted a very fine crack in my down tube originating from what appears to be the stock water bottle cage threaded hole. The frame is Atomic 13 Aluminum (whatever that means) - (if interested you can see the full specs here "". Anyway, I was wondering if it is still safe to ride? I cruise at 20mph-22mph (90% of the time) and burst no more than 30mph (10% of the time). Also, would I be able to repair this type of problem on my balcony? I've included pics for more accurate assessments. Thanks team! :grin5:

    "If it ain't broke yet, keep on ridin' that thang!"

    Attached Files:

  9. keep riding , but

    I would buy some alumaweld or similar rod and eventually grind off the paint and fill that crack line in. Just so that crack does not expand. You will have to move or remove the motor , but I can get one off in 15 minutes. A $15 4 inch grinder and metal wheel from harbor freight should take off the paint and feather the crack line in a couple minutes. If i am looking at the bike corectly you should turn it upside down and use mapp gas or propane torch to melt the rod in.
  10. BigBlue

    BigBlue Active Member

    Is it still safe to ride? I would probably say not. Why take a chance of injury. At minimum, I would recommend having it welded. Best bet would be to switch to a steel frame. Others on this forum can attest to the durability of aluminum frames. If possible, look on Craigslist for a mobile welder and/or a steel frame.

    Good Luck,

    AKA: BigBlue
  11. jeffuehrer

    jeffuehrer Member

    I was looking at some JB weld epoxy kits that looked interesting but I don't know if they would work. I've been researching repairing the frame and the majority of findings have been to scrap the aluminum frame. Regardless I will continue to ride it (10 or so miles with my fingers crossed) until my new bicycle comes. It is the same frame (almost) and brand (Raleigh Venture 3.0 only this time it's a steel frame - if you're interested you can see it here ""). I like the comfort design because of the spring loaded seat post and large comfortable seat and frame design however it appears as though the angle (pic attached) looks less favorable but I'll see if I can make it work. I'll have rear brakes and gears again too.

    "Break it in to ride it and ride it 'til it's broken."

    Attached Files:

  12. Happy Valley

    Happy Valley Active Member

    Jeff, do yourself a favor, there is no "weld" in JB, it's just marketing for epoxy. Also, I'd be negligent if I didn't say after looking at the pics you posted on the cracked frame you're really pushing it. Not being snarky but that's serious and I wouldn't ride it. Be careful.

    I not sure what series alloy it is, some takes tig welding better than others, but as others have said upthread, aluminum needs re-heat treating after welding.

    On the original subject, I recommend to NEVER drill frames, regardless if they are steel or alloy.
  13. jeffuehrer

    jeffuehrer Member

    I originally had my first motor put on by someone else (1/2010) and he drilled holes in the top tube and where the chain tensioner attached. I will NOT be drilling any holes in my new steel frame and with my increased understanding with all the variables involved with these motors I imagine I should have greater success with my future builds. Thanks for the helpful advise to all of you guys.
  14. Al.Fisherman

    Al.Fisherman Active Member

    A custom mount will be needed. The ideal "V" is 75 degrees. You have a number of options.

    As far as JB Weld, it has VERY few applications on these bikes, the frame NOT being one. You might as well use tape.
    Last edited: Feb 19, 2012
  15. jeffuehrer

    jeffuehrer Member

    Crack and Mounting UPDATE!

    Hello fellow mtbers. Before my ride I took the bolt that goes into the threaded hole where the crack is and applied super glue to the threads and tightened it down (pic attached). That should help keep the two parts from cracking as fast. I made it five and a half miles with the crack in my frame before being brave (some may call stupid) and deciding to go 27mph after going the first five miles at 18mph. My left threaded rod snapped at the same place they always do right behind the front tube bracket. The mounting stud on the right is still going strong after 98 miles. Again, since I placed a nut close to the engine the bolt also snapped off inside the threads of the nut leaving enough exposed to just unscrew with some vise grips. I picked up a 6mm x 55mm (2.165") Grade 5 (8.8) bolt from the plACE. I didn't even have to take the motor off to replace the bolt. I slapped it back together and went home (six miles). I kept it at 18mph the entire ride. I plan on remounting the engine using two front mounts on either side of the crack so when it does finally give it will be held together by the mounts. I will be securing the rear mount first as suggested by everyone on this forum making sure that it is parallel to the seat tube. I will then adjust the angles of the u-bolts to accommodate the angle of the front engine mount. If all goes well than I should be able to get some more miles out of this frame until my new bicycle arrives. Wish me luck fellas!

    Attached Files:

  16. motorpsycho

    motorpsycho Active Member

  17. jeffuehrer

    jeffuehrer Member

  18. jeffuehrer

    jeffuehrer Member

    Mounting UPDATE!

    All of your well wishes have paid off immensely...Thank you, MBers. After setting a favorable position (7/16" top, 15/32" bottom from tube) for the rear mount I was able to finagle the two large (1 5/8" x 5/16) front mount brackets (sickbikepartsdotcom). As you can see from the photos the angle of the u-bolts had to be altered from a perpendicular (90° angle) to whatever angle they are in these pics in order to accommodate the rear mounting position. As with any remounting (unless you have welded mounts) the position throws off the entire chain length which in turn throws off the entire drive train. (a spring chain tensioner probably alleviates more readjustment then the stock tensioner). I also replaced all my tensioner bolts (4) with grade 8 (10.9) hex bolts and my tensioner wheel bolt with a 1/2" hex bolt so I can actually torque the wheel down properly (pic attached). I will now be riding blue lightning as blue flicker as her flame is almost out. The crack in the frame hasn't worsened so I can only hope (since it's worked so well for us) that my new mounting job will hold the frame together just a little bit longer. Let me know what you think fellow MBers.

    Attached Files:

    Last edited by a moderator: Dec 18, 2015
  19. jeffuehrer

    jeffuehrer Member

    Crack & Mounting UPDATE TOO

    Obviously not a whole lot of thinkers out there...just doers. :grin5: Anywho,

    I inspect the crack thoroughly before each ride and don't ride over six miles at a time.

    84 miles ridden with the crack (Max speed 29.4mph, Avg. speed 15.9 [computer readout]), (Cruising speed 18-20mph)

    62 of those miles are on the new mounting job.

    The new bicycle (18") didn't measure up so I left it at the store and ordered the 20". It looked like the tubes were a little smaller all around but that could just be the darker color giving it that appearance.

    Tip O' the Day - I used super glue to stop a seep in my gas tank. :D
    Last edited by a moderator: Dec 18, 2015
  20. jeffuehrer

    jeffuehrer Member

    150 miles with a crack in the tube. Chain tension is ready for no more tensioner. Just picked up the new bike also. Luck O' the Irish!

    Happy St. Patrick's Day!

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