Why don't 2-stroke pipes bolt on?

[wilkin250r]

Why don't 2-stroke pipes bolt on the same way 4-stroke pipes do? I can't imagine that the difference in thermal expansion between 2-strokes and 4-strokes is all that much? Why deal with the gaskets and rings of the exhaust flange, why not just bolt it on?

[Pvt. Maggot]

i dunno...but i wish 4 stroke pipes did the same thing cuz they sure are alot harder to change. just taking off a spring or 2 is way easier then unbolting and stuff. good question

[wilkin250r]

I can understand why 4-stroke pipes bolt on, I think the pressure is much higher than a 2-stroke.

[Pvt. Maggot]

from what i know...i don't know if this is 100% right but...the expansion chamber sucks the exuast out? and the 4-stroke blows it out...so it needs bolted down...-shrugs-

[hondafox440]

I think it has something to do with the design of the 2 stroke cylinder, and how ports in the cylinder affect the spots that you can bolt into? Maybe it is because the size of the pipe, it is more affected by wind resistance and the terrain?

[Jeffksf]

I would think vibration might have something to do with it.

[440exnacsracer]

yes...vibration is everything...if the pipe on a two stroke were bolted to the head, the vibration would shake the whole pipe, eventually breaking the mounting tabs/brackets.

[skemp]

Originally posted by 440exnacsracer
yes...vibration is everything...if the pipe on a two stroke were bolted to the head, the vibration would shake the whole pipe, eventually breaking the mounting tabs/brackets.

DING DING DING :)

[wilkin250r]

Originally posted by hondafox440
I think it has something to do with the design of the 2 stroke cylinder, and how ports in the cylinder affect the spots that you can bolt into?

No, because the exhaust flange bolts on, and then the pipe fits over it. You could just as easily bolt up the pipe directly to the same spot.


Originally posted by 440exnacsracer
yes...vibration is everything...if the pipe on a two stroke were bolted to the head, the vibration would shake the whole pipe, eventually breaking the mounting tabs/brackets.

So does that mean that 4-strokes don't vibrate? Granted, the Quadzilla and many two-stroke dirtbike engines vibrate like crazy, but the Blaster, Banshee, and 250r all have very little vibration. I know my girlfriends 400EX vibrates more than my 250r.

I'm not saying you're completely wrong, but do you KNOW this, or are you guessing?

[hondafox440]

I asked this on another forum, and got a few ideas. The back pressure of a 4 stroke is greater than the 2 stroke, thus it requires bolts instead of springs. Another idea was that since the 2 stroke pipe is much larger and hangs out farther (on dirtbikes), mounting it via springs instead of bolts allows some play in case of a crash that lands on the pipe. The other idea was simply ease of disassembly, since 2 strokes require top ends more frequently than 4 strokes.

[wilkin250r]

I was dealing with new springs this weekend, and they took a lot longer than a few simple bolts would have taken.

As for backpressure, yes. 4-strokes may NEED to be bolted on, but why couldn't you also bolt on a 2-stroke pipe anyways? Just because it has less back pressure, why dink around with exhaust flanges, rings, springs, leaking and the whole mess?

[Jeffksf]

Originally posted by skemp
DING DING DING :)

Thats what I was thinking, 4 strokes vibrate to?

[hondafox440]

Originally posted by wilkin250r
I was dealing with new springs this weekend, and they took a lot longer than a few simple bolts would have taken.


You suck then :D j/k

I find springs much easier. Takes me a few seconds to take the springs off with needle nose pliers, and the same time to put them back on.

I just thought of something. Maybe the goal is for the pipe to leak? If it didn't leak at all, all that gunk would be inside the pipe and you would have to clean it much more often, as compared to spraying some degreaser on the engine and hosing it off? But a leaking pipe goes against everything I know about how the negative pressure waves function in a 2 stroke so I highly doubt thats the reason behind it.

[AndrewRRR]

Originally posted by wilkin250r
I was dealing with new springs this weekend, and they took a lot longer than a few simple bolts would have taken.

As for backpressure, yes. 4-strokes may NEED to be bolted on, but why couldn't you also bolt on a 2-stroke pipe anyways? Just because it has less back pressure, why dink around with exhaust flanges, rings, springs, leaking and the whole mess?

Two strokes do have big honkin pipes hanging off that one flange at the cylinder. I imagine with vibration (not just from the engine but terrain and jumping too) and the thinness of 2 stroke pipe steel and the weight of the pipe, thats a lot of leverage on that one joint. I would think they would crack often if they were bolted. I agree though, it's a PITA messing with springs and RTV.
http://pictureposter.allbrand.nu/pictures/AndrewRRR/MyR13.JPG

[wilkin250r]

Originally posted by hondafox440
You suck then :D j/k

I find springs much easier. Takes me a few seconds to take the springs off with needle nose pliers, and the same time to put them back on.

Well, maybe you just have pansy wimpy springs :blah:

I bought new springs, and I couldn't even use needle nose pliers, I had to use big channel lock pliers to get enough grip on them. I had to pull on them with both hands, they were MUCH stiffer than the old springs I pulled off.

[wilkin250r]

Originally posted by AndrewRRR
Two strokes do have big honkin pipes hanging off that one flange at the cylinder. I imagine with vibration (not just from the engine but terrain and jumping too) and the thinness of 2 stroke pipe steel and the weight of the pipe, thats a lot of leverage on that one joint. I would think they would crack often if they were bolted. I agree though, it's a PITA messing with springs and RTV.


I agree, two-stroke pipes are thinner. If they were as thick as 4-stroke pipes, they would weigh 30 lbs. However, is seems that the strength issue could be solved with an extra rubber mount on the neck right about where the pipe makes the 180 degree bend. Or, make the neck a thicker wall.

the best way to instal those springs is with another spring and pliers so the pliers dont get in the way of hooking onto the pipe.

otherwise go buy a motion pro spring puller..

also, a opn end wrench works too, you put the closed part on the spring and pull...

[hondafox440]

I just take needle nose pliers and grab the hook as soon as the spring straightens out, stretch it to the little tab on the pipe, and once the hook is over, I let it go.

http://www.quadstop.com/images/spring.jpg

Grab it there.

[Rocketman250r]

I asked this question in another forum, this is the best answere I've seen for the question.

I don't have enough time to go into complete two stroke exhaust theroy but, basically two stroke exaust gases are sent into the expasion chamber creating a soundwave type of effect this is how they build there power. that is why they are shaped differantly each shape has a differant power characteristic. now what dose this have to do with the springs? because of these waves the pipe needs to be "suspended" from the frame and motor. this also why they have rubber mounts on the silencer. for if it was solid mounted, the pipe & silencer would pick up the vibrations transmitted through the frame and motor. this would cause disturbace to the waves inside the chamber as they flow out the pipe. at the very least your not getting full power out of your bike at the worst it could actually reverberate a wave back to the cylinder and cause engine failure due too the disterbance in the flow. however this is a rare extreme. this is why the two stroke exhaust system seems to vibrate/float by it self because it needs to be its own semi seperate system. i hope this clears some things up and helps

[hondafox440]

Rubber mounting a silencer has nothing to do with negative pressure waves. These pressure waves do not exit the "fat part" of the pipe - they hit that and reflect back towards the engine, pushing the fresh gas mixture back into the engine.

[wilkin250r]

Yeah, that's where I tried to grab the springs, but I couldn't squeeze the pliers hard enough to hold on to the spring.

[wilkin250r]

Originally posted by Rocketman250r
I asked this question in another forum, this is the best answere I've seen for the question.

I don't have enough time to go into complete two stroke exhaust theroy but, basically two stroke exaust gases are sent into the expasion chamber creating a soundwave type of effect this is how they build there power. that is why they are shaped differantly each shape has a differant power characteristic. now what dose this have to do with the springs? because of these waves the pipe needs to be "suspended" from the frame and motor. this also why they have rubber mounts on the silencer. for if it was solid mounted, the pipe & silencer would pick up the vibrations transmitted through the frame and motor. this would cause disturbace to the waves inside the chamber as they flow out the pipe. at the very least your not getting full power out of your bike at the worst it could actually reverberate a wave back to the cylinder and cause engine failure due too the disterbance in the flow. however this is a rare extreme. this is why the two stroke exhaust system seems to vibrate/float by it self because it needs to be its own semi seperate system. i hope this clears some things up and helps

Ok, I understand the theory, but I'm not sure I completely believe it. The amplitude of the pressure wave inside the pipe has got to be 5 or 6 orders of magnitude greater than the amplitude of the vibrations coming through the motor. I can't imagine that the disturbances caused by vibration would affect it much.

It's like a cricket rubbing it's wings next to a foghorn. If they are both going at the same time, the cricket doesn't have much of an effect on the overall sound wave.

[bigbadbrad]

yeah but on weadwackers and chainsaws and smaller 2 strokes like that the expansion chamber is bolted on.

[Rocketman250r]

I don't think they are as worried about performance on your weed wacker...

[bigbadbrad]

on my old skidoo it is bolted on too

[GoLikeHell]

I think the real thing everyone is missing about two strokes is the exhaust temp varies alot. Since the pipe temperature will change very rapid, it will expand faster then the engine. And will also cool faster then the engine. This is why you have a sealing ring that keeps internal pressure on the exhaust pipe. If the pipe was hard mounted, it would crack after a short period of time.

4 strokes exhaust do vary in temperature, but nothing like a 2 stroke.

Mark

[Pappy]

why does the sun set?

why do tree's grow

why does a rainbow only have 3 colors?


sorry ...i watched joe dirt last night:D

[wilkin250r]

Originally posted by Pappy
sorry ...i watched joe dirt last night:D


Pappy, it's not a documentary about you, just in case anybody else hasn't told you yet... :blah:

[Pappy]

Originally posted by wilkin250r
Pappy, it's not a documentary about you, just in case anybody else hasn't told you yet... :blah:

lmao...i was in tears:D

[bigbadbrad]

i asked that to my automotives teacher and he said that it is because of how the 2 stroke works, how the pipe sucks out the gases and he also said it has to do with the sond waves

[hondafox440]

Actually, I read an interesting response on this.. (popsted by Spanks on dirtbike.com)



I think you may be looking at it backwards. Four-stroke pipes aren't held on with springs because they can't be. The much stronger exhaust pulses will simnply blow the pipe out. If the manufacturers could use the simpler and lighter two-stroke method of a couple of springs, I'm sure they would.

[F-16Guy]

I was thinking vibration, too. I agree that both motors produce vibrations, but a two stroke produces much stronger, higher frequency vibrations because of their higher rpm operation and firing every stroke. I would think that this would lead to fatigue cracks more often on a two stroke, making it sensible to insulate the pipe from the engine to reduce the amount of vibration that is transmitted to the mounts. Four strokes aren't exempt from fatigue cracks either, just ask someone with a White Brothers E-Series. :eek: