Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: JohnN on December 22, 2009, 10:39:16 AM
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Here's another reason that needle bearings are not so good for motocross bikes....
(http://i100.photobucket.com/albums/m26/YZ_John/NeedleBearings.jpg)
Out of curiosity, how often do you perform major maintenance on your bike/bikes?? Grease steering bearings, swingarm bearings? How about cleaning your air filter?
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I will confess, I have owned my current ride a 2000 KTM 300 EXC for 3 years. During the time I've owned the bike, I've done the top end (piston, rings, needle bearing, replaced clutch plates, wheel bearings (front and rear) and replaced the juice in the hydro clutch, and replaced the fluid in the brakes front and rear, and replaced the brake pads.
All of the above was done during the off season, all I consider normal maintenance. I've yet to pull the swingarm, although its on my list for the off-season. KTM does not have linkage suspension; they use an F-bushing. Plans are to pull the swingarm, replace bearings as needed, check F-bushing, replace if needed, and grease everything. I'm not sure if I'll get to the steering stem.
During the season I replace the gear fluid 2 times, and clean the filter after every 6th ride.
I need to get the above done, as I need to do the top end on my son's quad. Yes, not only is he a quad turd, but he rides a 4 stroke... (Honda 400EX). When we purchased the quad used, (two years ago), knowing it needed new rings, and valve seals. So its time to tear it down, and replace the top end.
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In all fairness, if you skip regular maintainence on a bushing, it will hate you the same. BUT, (I've had to do this more than once) if you leave the bearing in there, the outer shell will attach itself to the swingarm bore sooooo tight, you need to grind it out. Then it tears up the bore among other things. I have a bearing out of my Maico right now. I am in the process of making bushings for it. I hate needle bearings on a reciprocating shaft.
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I'm not a big fan either but that pic shows a desperate lack of maintenance.I swear by Maxima waterproof for grease-the best I've found to date anyway.As for the KTM heim joint setup,I'm not a big fan of that either.I found mine never lasted that long before you'd start getting a little up and down play when it was on the stand.The KTM units aren't supposed to be greased as they have a teflon coating that the grease will destroy(supposedly anyway).On the other hand,left dry the teflon wears off in short order.I put pivot works in mine.Probably not quite the quality but when greased they lasted well.As for the needle bearing discussion, the same could be said for steering head bearings as they aren't designed for that type of force either but I'm not sure what a better setup would be.
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Re-greasing the needle bearing will help, certainly that photo on top shows an extreme lack of maintenance. Although it's not as unusual as you would think!
As for the steering head bearing they are much bigger and sturdier.... as long as they are kept greased and adjusted properly they should last quite some time....
(http://www.maxmx.co.uk/upload/products/1157458630UBG0178.jpg)
The swing-arm bearing are subjected to much more intense conditions, plus almost everyone cleans their bikes with power-washers now which degrades the grease and allows water to penetrate the seals and sit inside the bearings... not conducive to keeping things working smoothly.
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Steering head bearings are tapered, and they are preloaded. This keeps an even, constant pressure on the bearing. It keeps the bearings "rolling" rather than "rocking" in place like a needle bearing does.
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True,but by nature they aren't designed for a side force,they are meant to roll.In the case of any sort of impact,you get a metal to metal to metal force over a very small area due to the fact the part of the roller that contacts the race is very small,which is why after a fairly short time you will feel a "catch" in the straight ahead position.If you figure the actual contact area given that the stem isn't straight up and down the majority of the force is on the front few rollers of the lower and the rear rollers of the top which being rounded have a very small amount of contact area on the races.It works,just not ideal.When I come up with a better idea I'll let you know.Working on it....... :)