Reversing crankshaft rotation?

xXNightRiderXx

Active Member
Jan 12, 2017
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Hey there folks, I was thinking, dangerously. I've looked at the internal mechanisms of the 79cc predator, and was thinking, would it be possible to reverse the shaft rotation if I converted the camshaft from meshed to chain driven? The camshaft rotates in the opposite direction of the crankshaft, which would make them both rotate in the same direction if they were reconnected with a timing chain. The only issue I see with doing this is maintaining rotation speeds of the camshaft in relation to the crank. It would take some experimentation, and a lot of time to figure this out. But if I'm going to motorize my marlin 5, it will be well worth it.
 

5-7HEAVEN

Well-Known Member
Aug 2, 2008
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Questions to ask yourself before starting any project:

How will I benefit from this?

Do I have a plan?

Do I have the know-how?

Do I have the skill?

Do I have the money to fund this project?

Do I have the time and space?

Do I have the discipline to see this project to fruition, throughout its trials and tribulations?

Will something else in my life hinder or obstruct my success in completing this project?

BTW, how far did you get on your V-twin project?

Did you get past the planning stage?
 

xXNightRiderXx

Active Member
Jan 12, 2017
415
62
28
Boise
Questions to ask yourself before starting any project:

How will I benefit from this?

Do I have a plan?

Do I have the know-how?

Do I have the skill?

Do I have the money to fund this project?

Do I have the time and space?

Do I have the discipline to see this project to fruition, throughout its trials and tribulations?

Will something else in my life hinder or obstruct my success in completing this project?

BTW, how far did you get on your V-twin project?

Did you get past the planning stage?
I benefit from this by reducing the amount of hardware required to put power into my gears.

I have no plan.

My father has the know how.

I have the skill.

It won't take much money for the hardware.

I have more time than I know what to do with, and plenty of space.

Maybe not the discipline, but certainly the will.

There will always be something in life that hinders progress.

I have not gotten past the planning stage, because I still need to get components, materials, and equipment. That in itself will take a while, so I put that on the back burner until I have the ability and contacts to have the tubing made and the components fabricated. The chain, derailleur, freewheels, chainrings, and cassette will be possibly the most expensive parts as they must be made by someone who fabricates them, such as shimano or SRAM. If I attempt to make these components myself, I will be looking at certain failure and injury. However, the frame will be made by me and stress tested to DOT standards. I plan on the frame being salvageable in any crash not involving intense heat, such as combusting fuel. Engines, forks, wheels, and other components can be replaced rather easily. Not so with a frame of this design, the tubes being three times larger and thicker than a standard motorcycle frame and being made of airframe aluminum.
 

5-7HEAVEN

Well-Known Member
Aug 2, 2008
2,527
140
63
Then you should ask your father.
He knows how to do it; he has the know-how..
You have the skill to do it.
Do you have access to a machine shop?
You have the money.
Just do it.
Please take lots of pictures.
I'm curious as to how reversing engine rotation will affect piston slap.
And don't forget about the oil dipper on the rod.
That'll now be a non-dipper.
And the ignition issues.
And the pull starter.
And the catches on the flywheel now face the wrong way.

All of this to reduce the amount of OEM-engineered components and not gain an iota of hp.

One thing that large manufacturers are good at is eliminating unnecessary components in their final product.

I think I've been trolled.....again.
 
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xseler

Well-Known Member
Apr 14, 2013
2,883
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OKC, OK
“Reality continues to ruin my life.”

“You know, Hobbes, some days even my lucky rocket ship underpants don't help.”

"We need more special effects and dance numbers."

"There's never enough time to do all the nothing you want."


Calvin says to Hobbes.........
 

xXNightRiderXx

Active Member
Jan 12, 2017
415
62
28
Boise
Then you should ask your father.
He knows how to do it; he has the know-how..
You have the skill to do it.
Do you have access to a machine shop?
You have the money.
Just do it.
Please take lots of pictures.
I'm curious as to how reversing engine rotation will affect piston slap.
And don't forget about the oil dipper on the rod.
That'll now be a non-dipper.
And the ignition issues.
And the pull starter.
And the catches on the flywheel now face the wrong way.

All of this to reduce the amount of OEM-engineered components and not gain an iota of hp.

One thing that large manufacturers are good at is eliminating unnecessary components in their final product.

I think I've been trolled.....again.
Two things that are easy to fix are the dipper on the rod and the pull starter. Just flip the rod, and reverse the recoil spring in the starter. Ignition and the flywheel catches aren't as easy. And please, explain to me what piston slap is, for I don't know. I don't have access to a machine shop, but I know someone who has at least a drill press. If I need a new flywheel made, I will gladly pay for a machinist to do it.

This is all because I don't have enough space between my rear wheel and the seat tube for a jackshaft, so I need to mount the engine backwards. I am not reducing the amount of hardware inside the engine. I'm not looking at increasing HP until I can get the cylinder bored.
 
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5-7HEAVEN

Well-Known Member
Aug 2, 2008
2,527
140
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"I benefit from this by reducing the amount of hardware required to put power into my gears."

So you're doing this major engine reconstruction because you don't have room for a jackshaft?

O.....M.....G.

So there's no reason for me to explain why it's so difficult to reverse engine rotation, for want of a jackshaft.

Do you actually have the engine mounted in the bicycle frame?

Simple and not so simple ways of mounting a jackshaft with a 79cc engine?.

Someone has probably done a 79cc shift kit install.

But not a 79cc engine reverse-rotation.

Do your research on the MB forums
 

xXNightRiderXx

Active Member
Jan 12, 2017
415
62
28
Boise
"I benefit from this by reducing the amount of hardware required to put power into my gears."

So you're doing this major engine reconstruction because you don't have room for a jackshaft?

O.....M.....G.

So there's no reason for me to explain why it's so difficult to reverse engine rotation, for want of a jackshaft.

Do you actually have the engine mounted in the bicycle frame?

Simple and not so simple ways of mounting a jackshaft with a 79cc engine?.

Someone has probably done a 79cc shift kit install.

But not a 79cc engine reverse-rotation.

Do your research on the MB forums
I do not have the engine yet. I'm trying to gather as much info as possible before attempting this. I know timing will be affected, and will have the proper tools to accomplish this task. The reason nobody has dared attempt rotation reversal is because of the amount of time, money, and tools it requires. Not to mention how difficult it would be to match up the timing. The only way I can think of is reducing the size of each gear enough to maintain ratio while allowing a chain to drive the cam.
 

5-7HEAVEN

Well-Known Member
Aug 2, 2008
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The reason no one has dared attempt engine rotation might be because the end result does not justify the time, $ & effort involved.
Even extending the bike a few inches behind the seat tube would be less drastic than an engine reversal.

Do your research.
 

xXNightRiderXx

Active Member
Jan 12, 2017
415
62
28
Boise
The reason no one has dared attempt engine rotation might be because the end result does not justify the time, $ & effort involved.
Even extending the bike a few inches behind the seat tube would be less drastic than an engine reversal.

Do your research.
When your frame is aluminum, it takes very expensive equipment to extend it. An engine reversal is cheaper and less drastic than extending alumimum.
 

5-7HEAVEN

Well-Known Member
Aug 2, 2008
2,527
140
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So you have the aluminum frame and no engine?

1)Make a plan.
2)Take measurements of bicycle mid frame.
3)Find measurement specs of the engine online.
4)Buy the engine if it fits into the bicycle specs.
4)Take measurements of engine in the bike frame.
5)If the engine doesn't fit, find a steel bicycle frame.
6) Repeat steps 2 & 4.
 

5-7HEAVEN

Well-Known Member
Aug 2, 2008
2,527
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When your frame is aluminum, it takes very expensive equipment to extend it. An engine reversal is cheaper and less drastic than extending alumimum.
I cannot think of anything MORE drastic than engine rotation reversal.
JMO, It does not take very expensive equipment to extend a frame.

Let me see.....
1)Build a jig.
2)Cut the seat stays and chain stays.
3)Measure carefully.
4)Add x inches.
5)Have a professional do the welding.
6)Orrr, have a pro do the entire job.

It might be cheaper to research which frame a member used to fit the 79cc shift kit.....
then buy that frame.
 

xXNightRiderXx

Active Member
Jan 12, 2017
415
62
28
Boise
So this Trek Marlin 5 is the bike you intend to fit a 79cc engine into the frame:

https://www.trekbikes.com/us/en_US/...ountain-bikes/marlin/marlin-5/p/2014600-2017/

O.....M.....G.....

I'm wasting my time here.
This is my last post.
I won't be using the stock air filter or tank or even the stock exhaust. The frame is large enough to fit not more than the block. To me, if the equipment will cost me over 200 bucks, its very expensive. I'm also using this bike because its what I have and because its the bike I want to use for major offroading. Besides, i would rather not modify my frame in any way because it will affect the performance of the entire bike. To make sure i have enough room for the engine, I will use a plate of my own making to mount the engine. Two seat post mounting points rising from the plate, and two down tube mounting points also rising from the plate, essentially forming a cradle. I will have the shift kit crank assembly however, and will have it directly connected to the clutch.