Drilled through enginge mount disasters?

M

mekano

Member
Many people claims that a drilled hole in the frame to mount the china engine will cause a cracked frame. I have not drilled a frame myself but wonders if anyone have had a bad experience, such as a cracked frame?
Thanks!

/Mekano
 
I've done it on many dozens of builds that I sold to others with no problems. However, nowadays I use aftermarket mounts for oversize frames and the use of shifter kits requires a mobile mount to adjust the chains.
 
i've heard of a few frames breaking, but never saw one.

personally, i would never do it, and i would never advise anyone else to do it.

the downtube of a bike is a structural member of the frame. normally, if they crack, it's where the downtube meets the headtube. but if you drill a hole in it, you just made an even weaker link.

if you want to visualize a worst case scenario, picture your average rider on an average bike. now, think about the downward pressure the rider puts on the bars, the seat, and the cranks. now think of the upward force from hitting bumps or something.

now imagine having a big weakspot, almost in the center of the bike, at the bottom.

i can picture the bike buckling in half as that downtube breaks.

i don't wanna picture what happens to the rider at 30-40mph.

in the last year or so, upgrades and solutions to the various problems the chinese didn't care about have come up. there's so many better ways to mount a motor than drilling a hole, in my opinion, the only people who would still do it are the people with no mechanical ability and are out to make a quick buck and don't care what happens to the actual rider.

they can always claim, "but that's how the instructions said to do it..." if someone gets hurt.
 
bairdco said:
i've heard of a few frames breaking, but never saw one.

personally, i would never do it, and i would never advise anyone else to do it.

the downtube of a bike is a structural member of the frame. normally, if they crack, it's where the downtube meets the headtube. but if you drill a hole in it, you just made an even weaker link.

if you want to visualize a worst case scenario, picture your average rider on an average bike. now, think about the downward pressure the rider puts on the bars, the seat, and the cranks. now think of the upward force from hitting bumps or something.

now imagine having a big weakspot, almost in the center of the bike, at the bottom.

i can picture the bike buckling in half as that downtube breaks.

i don't wanna picture what happens to the rider at 30-40mph.

in the last year or so, upgrades and solutions to the various problems the chinese didn't care about have come up. there's so many better ways to mount a motor than drilling a hole, in my opinion, the only people who would still do it are the people with no mechanical ability and are out to make a quick buck and don't care what happens to the actual rider.

they can always claim, "but that's how the instructions said to do it..." if someone gets hurt.
Click to expand...

I can see it now. Me skiding down the street on my butt with my pants ripped at 30 mph.
 
I drilled my Jamis Explorer 1.0. I used a steel sleave to carry the crush force though. Ive seen airframe mechanics drill a hole at the end of a crack to prevent it from spreading. Also, there are several holes drilled in the down tube for the accessory mounts.
I'm not arguing that drilling holes makes your frame any stronger, but i bet if someone out of the 23000 registered users here had a frame fail from a drilled hole we would hear about it here.
 
I should add that i'm 6-2 300Lbs as well. I'm not the sharpest tool in the shed, but i'm not a total idiot:) If i go over the handlebars at 24mph (300Lbs LOL) from a cracked frame, pride wont stop me from giving y'all a full report.......After my broken fingers heal.
 
PatTheThird said:
I drilled my Jamis Explorer 1.0. I used a steel sleave to carry the crush force though. Ive seen airframe mechanics drill a hole at the end of a crack to prevent it from spreading. Also, there are several holes drilled in the down tube for the accessory mounts.
I'm not arguing that drilling holes makes your frame any stronger, but i bet if someone out of the 23000 registered users here had a frame fail from a drilled hole we would hear about it here.
Click to expand...

Well here is one for ya...

P1110096.jpg
 
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Thanks Al! That looked like a steel frame as well. I could only see the first link you put up. The discription says he was drilling holes to run the wires to the CDI. I was concerned when i drilled mine out. I spoke with a friend who works with metal a lot. His opinion was that drilling the hole wasnt as much af a concern as putting any crushing force on the tube at all. The hardened steel sleave was his idea, and very smart in my opinion. This allowed me to torque the mount very tight to prevent movement. While on the subject of mounting, like a lot of people the seat tube wasnt exactly the same size as the mount. A friend of mine broke his like a wishbone. I shaped mine with a file to mesh not only the diameter but the angle as well.
 
I would imagine a failure at the mount point wouldnt cause the bike to snap in half. More likely you would feel it go and have at least half a chance to stop before eating it. What do you think?
 
CrackFrame2.jpg


The check is inserted through the frame.

This was before I repaired the frame. I took a copper coupling, moved the frame apart, and slid the coupling over damaged area and braised.
 
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Al.Fisherman said:
CrackFrame2.jpg


The check is inserted through the frame.

This was before I repaired the frame. I took a copper coupling, moved the frame apart, and slid the coupling over damaged area and braised.
Click to expand...

Lol I wouldn't trust some copper . but that's just me

I would have taken it to a muffler shop and get them to weld it...
 
PatTheThird said:
I would imagine a failure at the mount point wouldnt cause the bike to snap in half. More likely you would feel it go and have at least half a chance to stop before eating it. What do you think?
Click to expand...

yeah, you might feel it going soft, instead of it failing suddenly.

but is that doesn't mean it's a good thing. either way, your bike's busted in half.
 
i've done it a few times for locals who wanted help putting there bikes together on the cheap, what i do is drill the hole over size, then insert a piece of tubing with 3/8 ID through the hole you drill, weld it in place and then put a 3/8 bolt through to the adaptor that come in the kit. the through tubing welded in stops from crushing the frame. i don't do it for myself but haven't had a problem with the ones i've done for others.
 
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