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Start logic: (Read 207 times)

ohiomoto

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Re: Start logic:
Reply #15 - 11/20/16 at 20:38:21

Dave is correct, there will be extra drag when cold. Get a bike with a kick start and you'll see that there is extra drag.

When the bike is in gear you are turning the gears even if the clutch is disengaged. When the bike is in neutral, you're not trying to spin those gears. And as Dave pointed out, the oil is thick and sticky when cold thus requiring extra effort to spin those gears.

In all my years racing MX, I never wasted the effort trying to start my bikes in gear when cold. The risk of flooding it out wasn't worth it. Even with my later bikes that would start on the first kick, it wasn't worth it. Once warmed up, it was usually possible to get it started in gear but if the bike didn't light up after 2-3 kicks, I would always find neutral and it would start right up.

It's probably not a big deal with our bikes, but I'd rather not put that extra stress on my battery and starter.

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badwolf

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Re: Start logic:
Reply #16 - 11/20/16 at 21:37:01

In a constant mesh tranny when the input shaft is turning, ALL of the gears are turning. (hence the term constant mesh) When you hear grinding gears, it's not the teeth but the engagement cogs on their sides. The clunk you hear when putting the bike in gear is the cogs on the gear sides not the teeth. When in neutral, none of the side cogs on them are engaged, so they all turn easy. If the bike is in gear, and the clutch is pulled in, the clutch is forced to spin within itself so the input shaft won't spin, creating drag. Cold oil would create more drag than hot oil. But the extra drag is coming from within the clutch, not from spinning the gears.
In theory, a dry clutch would have less drag than a wet clutch.

But we live on earth, not in theory.

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Kris01 Serious Thumper Offline Eat, sleep, RIDE! Posts: 3767 Tennessee Gender:	Re: Start logic: Reply #17 - 11/20/16 at 21:43:36 I guess I'm confusing myself with the way a clutch works in a car vs a motorcycle. Push the clutch pedal down in a car and nothing behind the flywheel is attached to the engine. The starter only spins the engine. Apparently motorcycles are different animals. Thanks for the education!
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badwolf Serious Thumper Offline Ridin' my Lil' Bagger - 153k miles so far Posts: 801 Palm Beach County, FL Gender:	Re: Start logic: Reply #18 - 11/20/16 at 21:58:33 Kris, You are right, with a car there is much better disengagement tween the two. But they still have a safety switch on the clutch.
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Dave

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Re: Start logic:
Reply #19 - 11/21/16 at 02:31:11

Kris01 wrote on 11/20/16 at 21:43:36:

I guess I'm confusing myself with the way a clutch works in a car vs a motorcycle. Push the clutch pedal down in a car and nothing behind the flywheel is attached to the engine. The starter only spins the engine. Apparently motorcycles are different animals. Thanks for the education!

The car has a dry clutch, the motorcycle clutch is bathed in the engine oil. The clutch has several steel plates, and several fiber plates, and they alternate (same way you make Lasagna). When the clutch is released (clutch lever pulled in), the spring pressure is transferred to the cable, and the plates are not held together by spring pressure. The engine oil that is between the plates does cause drag between the plates when the engine oil is cold and thick, and this drag is reduced when the engine oil is warm and does not stick the plates together nearly as much. When you take a clutch apart it becomes it would be easy to understand, as the plates want to stick together from the surface tension of the oil between them.

Here is a video that shows how the clutch works, however the can make multi-plate clutches wet (runs in oil), or dry (Ducati). The dry clutches don't exhibit the same drag when the engine is cold.

https://www.youtube.com/watch?v=TcYsV063lk8

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