Bending bicycle engine exhaust

happycheapskate · Dec 1, 2009

****, thats some redneck ingenuity right there. I think I'll try that or something like it. I got the motor where I like it and the danged muffler won't mate to the motor because of the Down Tube. I need to bend it or add some kind of bendable extension.

If you're drinkin' though, remember to USE HEAVY GLOVES!

oylavabeer said:
First BBQ your exhaust then jam it between a fork in a tree, shove a big screwdriver in the end of the exhaust and leaver to your own desire

happycheapskate · Dec 1, 2009

mine came with the throwaway black exhaust can anyway.

If you burned the looks off yours, get some Barbeque Grill paint and renew it.

I've got an idea. I wonder if the muffler off some type of lawnmower or heavy duty brush weeder can fit on the face of the grubee motor. Why the heck do they have to have this big ugly pipe anyway.

happycheapskate · Dec 1, 2009

If you try bending a 1 piece crank, you'll weaken it, plus the pedals won't be level.

You might find some wide 1 piece crank somehow, but I don't think you can just bend it.

If you have 3 piece cranks, why not try loctiting the parts and see if that helps.

Cabinfever1977 said:
i wonder if i could bend my 1 piece crank 1 1/2" so it would clear my wide engine? i know its solid steel,cause my power saw wont cut threw it.
right now im using a 3 piece crank,its falling apart,want to go back to 1 piece.

happycheapskate · Dec 1, 2009

fd107

From another forum, someone suggested silicone flex exhaust tubing. $20 for a bunch of it.

EDIT: I cannot find this in a thick enough Inside Diameter to go over the cut grubee pipe. I ended up making this (lawn mower muffler on grubee)
looking for box muffler for 48cc Grubee, lawnmower style - Page 2 - MotoredBikes.com: Motorized Bicycle Forum

I used a propane gas torch and managed to finally bend my pipe, but it distorted a little, and the gasket flange cracked at the weld. I'm saving it for a future repair/mod.

bairdco · Dec 1, 2009

i bent my exhaust about 45 degrees. it was the black one, and since the paint's gonna burn off anyways, i chemically stripped it all off first.

i wedged a spud wrench in a gap on my roomates boat trailer, stuck the spud end into the exhaust pipe, heated it with a Bernzomatic Map gas torch, and pulled down on the thing till it was where i wanted it.

i needed to bend my crank out about a 1/4" to clear the engine, so i pretty much did the same thing.

first, i outlined the crank on a piece of cardboard so i could line it up to see if it was bending, then jammed the crank into the boat trailer gap, heated it, and used a pipe over the crank arm to pull down. worked no problem, and i don't think it's gonna sacrifice any strength at all. plus, i ain't gonna be doing any backflip super jumps on it, so i ain't worried...

Scout Black · Dec 3, 2009

Re: Bending exaust

paul said:
i personally could not bend it at all so opted to bend the crank out a little to clear the exaust which was a hole lot easier

How do you go about bending the crank. I need to bend mine to clear a pull start and the pipe, but I have limited tools.

Scout Black · Dec 3, 2009

bairdco said:
i bent my exhaust about 45 degrees. it was the black one, and since the paint's gonna burn off anyways, i chemically stripped it all off first.

i wedged a spud wrench in a gap on my roomates boat trailer, stuck the spud end into the exhaust pipe, heated it with a Bernzomatic Map gas torch, and pulled down on the thing till it was where i wanted it.

i needed to bend my crank out about a 1/4" to clear the engine, so i pretty much did the same thing.

first, i outlined the crank on a piece of cardboard so i could line it up to see if it was bending, then jammed the crank into the boat trailer gap, heated it, and used a pipe over the crank arm to pull down. worked no problem, and i don't think it's gonna sacrifice any strength at all. plus, i ain't gonna be doing any backflip super jumps on it, so i ain't worried...

I like your bike in the picture, did you just turn the head around to point the exsausht to the rear? Any more mods to make that work?

bairdco · Dec 4, 2009

flip the head, jug, and piston. grind the transfer ports in the case to match.

at least, that's what i figure. the bike's not done, and i haven't fired it up yet. it's been done before, and supposedly it works.

it sure looks pretty, hunh?

there's more details in the "rustoration" thread.

happycheapskate · Dec 5, 2009

Re: Bending exaust

It would be a lot easier and safer to buy a wider crank. Lowrider bike parts supplier (hate those things, but some parts are useful!) might have it, or a major mo-bike vendor.

Here, $30 from Wide Crank Pedal Kit - $29.99

You can install this yourself with a quality "crescent" wrench, a wide blade screwdriver, some fresh axle grease, and a little loctite (blue). (remember the nut on a 1 pc crank is righty LOOSEY!!! and one of the pedals too) Its just a cone, a keyed washer, and a nut to deal with. (need open end or pedal wrench)

Scout Black said:
How do you go about bending the crank. I need to bend mine to clear a pull start and the pipe, but I have limited tools.

bairdco · Dec 5, 2009

bending a crank is easy, peasy, made-in chinese-y.

just clamp it down, put a pipe over it, heat it up and crank it. unless you have some super-junk crank, it's not gonna break. especially with the minimal amount of pedaling forces we use as motorbikers.

seriously, you pedal, what, 10 feet? do you really think it'll break?

as far as the pedals not being level, so what? usually, you're not bending your crank more than a half inch. your feet will never know the difference.

happycheapskate · Dec 6, 2009

Mine would, but thats because I've been riding bicycles for 20 years and I can't stand any to be off level.

Your idea will work fine though for the casual guys.

I like to pedal mine a lot, to get out of the car parks without making a lot of noise right next to cops or pedestrians, and when I take off from stoplights.

I made the box muffler work!

looking for box muffler for 48cc Grubee, lawnmower style - Page 2 - MotoredBikes.com: Motorized Bicycle Forum

bairdco said:
bending a crank is easy, peasy, made-in chinese-y.

just clamp it down, put a pipe over it, heat it up and crank it. unless you have some super-junk crank, it's not gonna break. especially with the minimal amount of pedaling forces we use as motorbikers.

seriously, you pedal, what, 10 feet? do you really think it'll break?

as far as the pedals not being level, so what? usually, you're not bending your crank more than a half inch. your feet will never know the difference.

2door · Dec 7, 2009

When we're talking about bending cranks (lets not forget our newbie and non mechanical friends) that there are steel cranks and aluminum cranks. The steel, or forged steel, parts can be heated and bent without compromising the crank. This isn't so with aluminum cranks. They are made of a very tough aluminum alloy, something in the range of T6 or T8, that will not take kindly to heating or bending. Very small cold bends are one thing and you might get away with it but you still stand the chance of breaking an aluminum crank. Not sure which you have? Use a magnet. Aluminum is a non ferrous metal; a magnet will not stick to it. Steel will attract a magnet.

happycheapskate · Dec 10, 2009

Good tip, re aluminum. I agree. If you are not sure, you can buy a wide 1piece crank that will go right on a beach cruiser or common bike with a 1 piece crank.

If you have a "modern" bike with the thread in bottom bracket and square taper mating faces for the cranks, you can buy a new longer bottom bracket for about $20 and a tool to pull it out is probably $10 at nashbar.com. Use thread seal tape (1 wrap) or it may make creaking noises or freeze into the frame threads.

Good luck to all.

GrimBrothers · Dec 17, 2009

Thanks, this saved me like 60 dollars.
I bent my exhaust to fit my occ stingray so I didnt need to buy Barry's.

bairdco · Dec 17, 2009

i bent a one piece crank yesterday without heating it at all. found a spot on my roomate's boat trailer to wedge it into, then put a four foot long pipe over the crank arm and pushed down. super easy

and happy, what's with calling a one-piece cranked cruiser "common," and a bike with three piece cranks and an english bottom bracket "modern?"

if by "modern," you mean, "modern for the mid 1800's," or "modern compared to a swift walker (Bicycle,) then you're correct. check your history.

(just stickin' up for the cruisers. no offense meant...

)

xlite · Dec 18, 2009

Bending aluminum w/o heat is asking for trouble. Not so much with steel.

Dan · Dec 19, 2009

Just learned this the other day. Muffler was way out on a build. Christmas present so I was running out of time. Any way after kicking it, mallet methoding it, I put the flange in a vise so it was level and flat to the earth and just leaned on it. Worked great, left the chrome.

happycheapskate · Dec 20, 2009

Ok, Mr. Elite Member. I will refer to 1piece, 1900's- style cranks as Ancient, English threaded square taper bb'd cotterless cranks as Common, and FSA type standardized splined cartridge bottom bracket cranks and thru-axle Shimano dedicated hollow axle cranks as Modern.

PS I'm enjoying an Ancient style beach cruiser with the obsolete and antiquated 1" quill stem and threaded 1" steerer tube with <gasP> a coaster brake rear wheel! (the plunger brake just wasn't cutting it and the wooden wheels hurt my back.)
Spin Doctor Pro Bike Build - Schwinn Johnny Coasting Bike - Performance Exclusive

bairdco said:
check your history.

(just stickin' up for the cruisers. no offense meant...)

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