1979 CB750 DOHC Monoshock Build

jpmobius said:
Usually I am on the other side of this conversation, but I doubt you will have any problems with the bars. That is indeed a mighty big hole, looks like it would have been better to make a slot with a die grinder - next time maybe. Great idea to smooth it out though. Street bike bars generally have a pretty easy life - stay off the moto X track and maybe a good idea to soft land those wheelies. Failure is very unlikely to be instantaneous, but if it does get a fatigue crack and you don't pay attention and notice it, it might seem that way if it does indeed start cracking - depends tremendously on the heat treating. Carefully cleaning up those holes will help a lot in preventing it. Try bending it now by hand - use enough force that you feel is within the range of likely use. If you can not damage it I'd run it and keep an eye on it. Do the bend test every so often. If it does start to crack you'll likely notice before it falls off in your hand. And if you are riding one day and you notice that grip starts vibrating differently - wake up!

Going to stay tuned for the turbo/hat challenge (dohc has a sense of humor after all!)
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Good call. I'll clean everything up and make sure to keep checking on it as part of my pre-ride inspection.

deviant said:
How wide is that switch? Most clutch perches are 1 - 1.25" from the end of the grip. Weakness of the bar aside, I wonder if you have too far a spread for the lever. You might need finger extensions. I thought about getting one of these switches too, and always wondered how big the switch body is. It's a shame how big it is. I also hope there's room for your connectors. Doesn't look like it from my seat.
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The switch is pretty tiny, just looks big all zoomed in. It's 41mm width, 18mm height, sticks out 8mm from the bars. (1.6" x 0.7" x 0.3" for you savages). There's an extra 4.75mm (0.19") inside the bars for the wiring loom. 5 wires total, two are grounds. I got a picture of the full setup for you. I didn't mock up at all so you freaked me out for a second there. It all fits!
VDtqTZB.jpg


xb33bsa said:
that blue switch housing plastic could have been trimmed down quite a bit as well, corners rounded and and overall cut back without ruining it ..plenty of meat there to gain the use of a smaller barhole,thats the way ide doit
like mjoboius was promoting it is not likely to break street riding ..;.but the alloy and treatment, makes them bars not like localized bending ,they do fine flexing a bit as a long spring, but the hole takes that longness away and any load will concentrate the flex in one really short zone,the one thing to avoid and also why the riser clamps should be radiused as well
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I just followed the install instructions that came with the thing. The risers were installed professionally by a machine shop.

jpmobius said:
Yes indeed!
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Will pull those off to check when everything is heading to paint.
 
;) this is a handy dang tool right here, debur , slight chamfer and even a small radius on hole entrance
works on long outside corner edges as well
ruko_deburring_tools_300.jpg


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What's that tool called? I was planning to just carefully chamfer using a dremel tool + sanding bit.
 
Typically, that switch would be on the other side of the clutch lever bracket. However, if you did place it on the other side then there would be a greater leverage upon the holes that you drilled. Why don't you contact the manufacturer of your handlebars and ask them about drilling holes in them. They should know what is best.

I am enjoying your build and also how you accept the criticism and your openess to learn. I wish you success in this build.

Brian
 
bananas said:
What's that tool called? I was planning to just carefully chamfer using a dremel tool + sanding bit.
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haha i ferget what they are called butthey are handy
the idea on the riser clamps is just an easing of the sharp edge where the bars enter the clamps lots of risers clamps are already done but you could do it with a pocket knife even aluminum carves like butter
 
CarbsAndCylinders said:
Typically, that switch would be on the other side of the clutch lever bracket. However, if you did place it on the other side then there would be a greater leverage upon the holes that you drilled. Why don't you contact the manufacturer of your handlebars and ask them about drilling holes in them. They should know what is best.

I am enjoying your build and also how you accept the criticism and your openess to learn. I wish you success in this build.

Brian
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Thank you sir. Unfortunately my small girly hands wouldn't be able to reach that far. The setup is quite comfortable this way -- feels exactly the same as my Duc.

xb33bsa said:
haha i ferget what they are called butthey are handy
the idea on the riser clamps is just an easing of the sharp edge where the bars enter the clamps lots of risers clamps are already done but you could do it with a pocket knife even aluminum carves like butter
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I'll look out for something like it next time I'm tool shopping -- can never have enough tools!
 
Your switch is in the same place as where a normal switch block would sit, so it's "right" as it where.


It would be pretty funny asking a handlebar manufacturer if it would be OK to drill their bars - as if they would say anything other than "no fucking way".... ;D
 
hillsy said:
.
It would be pretty funny asking a handlebar manufacturer if it would be OK to drill their bars - as if they would say anything other than "no fucking way".... ;D
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Yep.

Chamfer all you want. It's not going the give the bar its strength back.

The bars are ruined you should change them. This is not a small issue, it'll kill you.
 
DohcBikes said:
Yep.

Chamfer all you want. It's not going the give the bar its strength back.

The bars are ruined you should change them. This is not a small issue, it'll kill you.
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I refuse to die at least until I watch you eat that hat. I'll test these out around the block once this thing is running. If they're really that janky I'll swap to LSL Stainless bars. If I don't make it I'll have my brother update the thread to let you all know aluminum bars + big holes are not the way to go. ;)
 
Xb's tool is a de-burring tool. I have one - use it all the time. That little blade is on a swivel and works like a caster to aim the cutting edge at the right angle - very clever gadget. Super handy especially on just drilled holes - just swish that thing around once and it makes a perfect little chamfer all the way around. The best thing is you can do the side opposite the tool if your hole is in a sheet or thin as your handlebar. Your risers only need a very tiny relief at the edge - just knock off the sharp corner where the edges wrap around the bar with a fine round needle file or a chain saw sharpening file - should only take a couple of minutes.
 
Sorry, that was an embarrassing brain fart regarding the switch position . I guess the size of the switch threw me off.

Nothing wrong with contacting the manufacturer though.

The concerns expressed warrant looking into this issue further before you start riding this beast, I believe.
 
Alright, so I'm pretty flattered by everyone's concerns for my safety. For anyone looking to install the Posh Switch on a Renthal bar it seems like this is not recommended and done at your own risk. I'm going to keep these on the build to mock-up only. They'll be swapped with heavier LSL stainless bars of the same design. Last season I fractured my clavicle and two other ribs after a highside during a high-speed canyon run. Still have a bit of random sharp pain in bad weather. I learned a lot. Not something that I want to experience again.
 
Sweet build!
I wonder if any of the chopper guys have ever managed to fail a bar after installing one of these?
After all, Harley's shake like a sh!tting dog, that may be enough to start a stress riser crack!
 
Alex jb said:
Sweet build!
I wonder if any of the chopper guys have ever managed to fail a bar after installing one of these?
After all, Harley's shake like a sh!tting dog, that may be enough to start a stress riser crack!
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Harley bars are larger in diameter and made of steel.
 
first off i aint judging just sayin....
that switch was designed by stupid fuckers,that have no clue how fucking stupid they are selling it
it is a fucking stupid thing to use and buy
ooo ooo it looks cool !! give me a break ::) if those,closet midget pimp,tranny fashion fag motherfuckers :mad: :mad:had any design savvyy at all it would not need a gaping hole ...they should have both hands chopped off for designing,and selling garbage like that to poor saps like you
..butteye dyegress... :mad:


put a large enough hole in a tube it weakens the structure no matter steel or aluminum alloy
a piece of chromo used as part of a clipon is not very likely in a heat treated state probably more towards annealed in its most soft and ductile state
it will just bend and you arernt weakening it enogh to bend very easilly in that use it would take forever to finally break....
there are all kinds of fancy engineering terms modulus's of elasticities and whatnot's
but heat treated aluminum alloys used structurally must be kept to a tiny minimum angle of deflection of repeated flexing in short zones they have to be made stiff
thats why jeremy mcgrath said fuck you honda when they came out with the aluminum, framed cr250 and told him to race it
it was so stiff (it had to be)that it didnt handle as good as the flexible steel frame and he jumped ship to suzuki
the renthall bars are springy but only can be becasuse they are carefully engineered to flex in a long gentle zone ,after the drilled holewill not bend like a gumby toy
you wont notice it being droopy and go whoa that shit aint right
it will just fucking snap, with zero warning, after drilling the hole because the alloy has a very short fatigue life and its been concentrated to a short area
but steel if fine
on stainless steel i am not familiar or educated in stainless steel alloys i have no input on those but do not assume ss is going to act like steel
 
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