a couple of items that puzzled me

timcosby · 01-10-2017, 10:35 PM

item no. 1 greasing the front axle???? seems like it doesnt make sense since the bearing are what needs the grease but maybe im missing something.
item no. 2 enlarging the air box holes. seems there is more sqaure inches of opening on the airbox than the sq inches of the carb throat so i cant see where that would help if it aint restricted?

ben2go · 01-11-2017, 12:34 AM

The grease is to stop corrosion on the axle and it siezing in the bearings. I'm not sure on the airbox deal.

pete · 01-11-2017, 12:40 AM

grease stops the axle seizeing in the bearing inner race...

the motor creates a vacume on the motor side of the air filter
so you need enough air flow to recharge the space on the motor
side of the filter in the split second when the intake valve is closed...
some air boxes/filters are more restrictive than others....

..

Krasi_BG · 01-11-2017, 02:34 AM

If you ever have to take out a rusty and stuck axle using a big hammer, you'd be bathing it in grease before putting it back in.

As for the big holes in the air box - think of them as a "natural compressor"

Ariel Red Hunter · 01-11-2017, 05:37 AM

Quote:

Originally Posted by timcosby

item no. 1 greasing the front axle???? seems like it doesnt make sense since the bearing are what needs the grease but maybe im missing something.
item no. 2 enlarging the air box holes. seems there is more sqaure inches of opening on the airbox than the sq inches of the carb throat so i cant see where that would help if it aint restricted?

I'm only going to speak to the airbox issue. An air box can perform several functions on an off-road motorcycle. Originally they were to prevent water and mud from being ingested into the engine, and keeping the air filter dry. I built one for my AJS scrambler in the late fifties when I switched to a dry paper element air cleaner from the stock brillo pad type air cleaner that came with the bike. The original air cleaner was only good for preventing gravel and small, low flying birds from being injested into the engine. I had read about air boxes, and seen pictures of them in English motor cycle press articles. Motor Cycle, and Motor Cycling. Anyway, first race, went bombing down and across a pitiful excuse for a creek, got a hat full of water on to that paper element air filter, and I was done for the day. So I went home and made an air box out of a kid's school lunch box, put the air filter in there, latched the box shut, and taped the door seams. Air filter to the front, air inlet to the rear, and a drain hole at the bottom rear. Worked. Eventually, air boxes came with the bike from the factory. Over time the air boxes became more and more restrictive. The one on the Hawk is pretty restrictive, as it comes. An attempt to silence the air intake noise. Unfortunatly, it also restricts the air flow to the cylinder, and the faster you go, the more it restricts it. That is why people modify their air boxes - to get more air flow per nano-second. As Pete says, that vacuum created by the piston descending in the cylinder is only available for a very short period of time, so you got to get all of the air to the carburetor possible.

Emerikol · 01-11-2017, 05:40 AM

Tim, the other reason that you should grease the front axle is because there is room for you to install and remove the axle bolt without having to heat or cool various parts. From a maintenance perspective that's a good thing, however the dilemma with that is two fold: 1) enough room to easily put the bolt in means enough room for the bearings to spin on the axle, and not the races. Normally that's not the case, but when the suspension is ratcheting up and down, it happens often enough to be a concern. 2) If there's room around the bolt, that means there's not a seal there. Any water you come across (not even ride through, just riding in the rain or splashing along in puddles) will be drawn to the inside 'safe space' between the bearings. The axle bolt is designed to keep the front tire on the bike, not guard against corrosion. As a result, any water you get in there will do what water does and start breaking everything down to it's base elements. As for the airbox, there are very rapid pressure changes that occur inside when the bike is running. Think of it this way: The fuel/air mix from the carb wouldn't go anywhere if there wasn't a vacuum to draw it into the cylinder. That's why timing and valve adjustment are so important on an engine. When the air starts moving from the airbox into the carb, that would naturally create a low pressure zone in the airbox. Air is drawn in from outside to airbox to try and restore a pressure balance. If the engine can't breathe freely, you would be slowing that movement down, and thus reduce engine power. You had mentioned the carb throat being smaller per square in than the airbox openings. That smaller size is required to create the venturi that will draw the fuel up out of the float bowl (through the jets) and create the fuel air mix. So the short answer at the end of this very long response is this: It's not the size that matters, it's how you use it!

Hope this helps shed some light on the questions you presented.

'16 TT250 · 01-17-2017, 12:41 AM

I've seen a fair bit of airbox modifying/eliminating go badly. Any time you modify any part of the intake tract be prepared to possibly have to re-tune.

Just enlarging the air inlet hole on the box is unlikely to change the tuning since it's also unlikely to change air flow, it'll make it a little louder which many people equate to more power. If you decide to open it up do some before & after speed runs to see if it helped or not. My guess is it won't just like you're guessing based on the logic that the hole is already bigger than the carb inlet, but it would be interesting to find out.

01-10-2017, 10:35 PM	#1
timcosby Join Date: Nov 2016 Location: robertsdale alabama usa Posts: 1,007	a couple of items that puzzled me item no. 1 greasing the front axle???? seems like it doesnt make sense since the bearing are what needs the grease but maybe im missing something. item no. 2 enlarging the air box holes. seems there is more sqaure inches of opening on the airbox than the sq inches of the carb throat so i cant see where that would help if it aint restricted?
	1

01-11-2017, 12:40 AM	#3
pete Join Date: Jan 2012 Location: ChCh , NZ Posts: 2,261	grease stops the axle seizeing in the bearing inner race... the motor creates a vacume on the motor side of the air filter so you need enough air flow to recharge the space on the motor side of the filter in the split second when the intake valve is closed... some air boxes/filters are more restrictive than others.... .. __________________ 09 XT660R ... 06 TTR250 ... 80 Montesa H6 125 Enduro... 77 Montesa Cota 348 MRR "Malcom Rathnell Replica"... Current resto projects.. 81 Honda CT110... 80 Kawasaki KL250A1... 11 Husaburg TE125 enduro... "sold" along with another 31... Lifan 125 Pitbike.. "stolen" ... KIWI BIKER FORUM...... http://www.kiwibiker.co.nz/forums/content.php All the best offroad rides in NZ... http://www.remotemoto.com/ E-mail... xtpete1@gmail.com
	1

01-11-2017, 05:40 AM	#6
Emerikol Join Date: Oct 2016 Location: Carrollton, GA Posts: 1,465	Tim, the other reason that you should grease the front axle is because there is room for you to install and remove the axle bolt without having to heat or cool various parts. From a maintenance perspective that's a good thing, however the dilemma with that is two fold: 1) enough room to easily put the bolt in means enough room for the bearings to spin on the axle, and not the races. Normally that's not the case, but when the suspension is ratcheting up and down, it happens often enough to be a concern. 2) If there's room around the bolt, that means there's not a seal there. Any water you come across (not even ride through, just riding in the rain or splashing along in puddles) will be drawn to the inside 'safe space' between the bearings. The axle bolt is designed to keep the front tire on the bike, not guard against corrosion. As a result, any water you get in there will do what water does and start breaking everything down to it's base elements. As for the airbox, there are very rapid pressure changes that occur inside when the bike is running. Think of it this way: The fuel/air mix from the carb wouldn't go anywhere if there wasn't a vacuum to draw it into the cylinder. That's why timing and valve adjustment are so important on an engine. When the air starts moving from the airbox into the carb, that would naturally create a low pressure zone in the airbox. Air is drawn in from outside to airbox to try and restore a pressure balance. If the engine can't breathe freely, you would be slowing that movement down, and thus reduce engine power. You had mentioned the carb throat being smaller per square in than the airbox openings. That smaller size is required to create the venturi that will draw the fuel up out of the float bowl (through the jets) and create the fuel air mix. So the short answer at the end of this very long response is this: It's not the size that matters, it's how you use it! Hope this helps shed some light on the questions you presented. __________________ First Rule of Aviation: -Never Pass Up The Opportunity to Pee I was struggling to get my wife's attention; I sat down on the couch and looked comfortable. That did the trick! My wife says I only have two faults. I don't listen and something else... If at first you don't succeed, try doing it the way I told you to... The Stable: 2005 Yamaha V-Star 650 - SOLD 2015 Suzuki DR 650 2015 RPS Hawk 250 - SOLD 2016 Ural Gear Up
	2

01-11-2017, 12:34 AM	#2
ben2go Join Date: Jun 2011 Posts: 1,335	The grease is to stop corrosion on the axle and it siezing in the bearings. I'm not sure on the airbox deal.
	0

01-11-2017, 02:34 AM	#4
Krasi_BG Join Date: Nov 2011 Location: Sofia, Bulgaria Posts: 436	If you ever have to take out a rusty and stuck axle using a big hammer, you'd be bathing it in grease before putting it back in. As for the big holes in the air box - think of them as a "natural compressor"
	1

01-17-2017, 12:41 AM	#7
'16 TT250 Join Date: May 2016 Location: Hacienda Heights, Ca Posts: 281	I've seen a fair bit of airbox modifying/eliminating go badly. Any time you modify any part of the intake tract be prepared to possibly have to re-tune. Just enlarging the air inlet hole on the box is unlikely to change the tuning since it's also unlikely to change air flow, it'll make it a little louder which many people equate to more power. If you decide to open it up do some before & after speed runs to see if it helped or not. My guess is it won't just like you're guessing based on the logic that the hole is already bigger than the carb inlet, but it would be interesting to find out.
	1