the only reason i can see to use the 6204 is price or if you have a 20000rpm rev monster or am i missing something ? dont say brain cells cos the 3 i have seem ok
using nu204 is wrong as it allows coaxial movements of the shaft and this is very dangerous! no wonder why Lauro uses 6204 c3, and believe me falc does not care about 5-10bucks difference in the bearings...
So why is that? Because the friction of the bearing is some 2% lower when compared to an ETS needle bearing? Mind you, 2 % difference in friction, not in power. What's that at the rearwheel? 0.00001BHP? I think both the ballbearing left and right version as well as the ETS type needle bearing all the latest 125 smallframes use have a track record to work just fine. At the end of the day it's very much a question of taste.
@johnyss: The NU204 means you are using a crank with a 19/20mm shaft. On a tuned engine these will shear of, with a heavy flywheel this may happen at a comparatively low state of tune already. So while this bearing in itself is ok, the crank you end up using may well cause problems. My 2 cent, of course.
Guys I am not sure if something is lost in translation here but if your solid type flywheel bearing is moving in and out in the casing when the engine gets warm that is not good. The motor case gets to around 80c (in my racer).. if at this temp the 6204 fly side brg is able to move then I would suggest looking at it as the casing may be worn. I am not sure if Mathius simply means that the bearing moves within its own tolerance or he means the casing itself tbh. If its the casing then this is not right.
Also..If you dont bolt up the crank to the primary side with the gear to correct torque to begin with when you build you run the risk of loading the 6204 on the other side and bearing failure will result. There is a little tolerance with c3 bearings but its very small really. If you dont have the lauro tool... then you can always fit the 6204 to the crank... heat the fly side and drop it on after you of course have bolted up the crank and fitted a gasket.. You then undo the primary-push the halves apart leaving the crank in the fly side..(this is 'kind' to the bearings).... then build up the rest of the motor and refit the half later. I personally would never fit the crank to the fly side first.
also---the reason for the two piece bearing in the vespa was for ease of manufacture. Remember the solid bearing although cheaper (good for piaggio) took more time to fit and if not fitted right could lead to failure and warranty claims. (not good for piaggio). So they went with a two piece in later vespa engines. Thats my thoughts and experience on this.
The bearing does move in the casing at 80°. Measure the bearing seat diameter, look up outside diameter of bearing in maker's spec sheet, take heat expansion rates of aluminium and of steel, and you'll see that this is a floating fit at 80° C. As I said, it needs to be. That's basic engineering. You're bearings would be ruined in no time if this wasn't the case just by different heat expansion rates of steel crank vs. aluminium casings. This is common practise in any application where a steel shaft runs in bearings in an aluminium casing. Older Vespa engines with ball bearing left and right even had bronce inserts on the flywheel side to allow replacement in case the bearing seat was worn out after a while. Quite usual in other engines too before market pressure lead to safing money in the production procedure by cutting corners.
Why then are ballbearings used in some race engines? Quite a few of the A-Kits for productions racers come with a needle bearing for the crank on the flywheelside btw.
If it isn't it will immediately kill your bearings once the engine heats up for the first time. Even a C4 bearing (or two of them) don't have enough side play to compensate for the difference in heat expansion rates of the shaft and the casing. And yes, the seat will wear out. That's why my point is that from an engineering point of view using a bearing like the ETS needle bearing is superior. The only drawback is that the needle bearing, as I have written above already, does not like squint. With the flexing of a crankshaft (inevitable and most pronounced at TDC) you have an angle error, that is squint, of the shaft realitve to the bearing. As this is not very big I personally think you are better served with a needle bearing on the floating side for this application than a ballbearing. As unreliablesc has already confirmed (I wrote the same further up) reality shows that both the needle bearing and the ballbearing do their job in a smallframe engine, and that the problem of wear on the flywheelside bearing seat is negligible in real live. Given the choice I'd go for the XL II engine any time though, simply because of the superiar shifting mechanism shaft design. Still there is a choice of using either ballbearing or needle even there.
so... if its a floating fit at 80c I should therefore be able to move this bearing? I am intrigued... and I will heat a casing to this temp to test. I understand the expansion rates and "basic engineering"...but I also feel the interference fit of the vespa fly side is too tight to allow this to happen. You have to heat this case way above 80c to get a cold bearing in let alone one that is in situ and getting heat transfer.. If the bearing can move in and out it will also spin. Sometimes you do see this if a casing is worn. You do not want the outer race spinning as this kind of defeats the object. But i will test on the next motor i build.
It will not spin because the friction of the ballbearing between inner and outer race is much lower than the friction between the outer race and the casing. If the bearing for some reason seizes this changes and the bearing starts spinning in the casings, which will then be rendered useless. Whether you will be able to move the bearing by hand at 80° C depends on your personal strenght. Whether the expanding case will be able to move the bearing is a different story altogether. For the user it is not necessary to understand how things work as long as they work. They do work in a smallframe engine regardless of what bearing you use. If you are interested in mechanical design I can check and recommend a book in English. I think quite a bit of Piaggio's engineering is not appreciated duly. Quite a lot of details are surprisingly clever.
FUCK OFF the pair of ya, we all no on this forum you 2 are proberly the best, most cleverist cunts on here dont be so fucking proud............we are just smallframe humble people who love our smallframes and look at people like you 2 for advise and information because we trust you because you 2 are the best ,................dont keep on and on and on and ect ,ect trying to out do each other with BORING knollage that most of us dont even understand a fucking word of it anyway............ ;D ;D amazombie, and tony are whot make this the best feckin forum for smallframe riders...............sorry juan, and the mods but after a few stellas i can see this isnt ever going to go away unless a daft old cunt like me says something............ still love you all........... .......abit drunk russ .....sorry.
Point taken. It's just that I had the same debate some years ago when I was involved in the design and construction of an engine. My position back then was the same as Tony's now. I found the information, after the guys' had explained the technical situation and I had understood it, very interesting. As I said I understand that it probably isn't interesting at all for the majority of people. I also think it is a piece of information which may be of interest to Tony. Hence I thought it worthwhile to explain something I find exceedingly complicated to explain in a language I nowadays speak but once or twice a year. Sorry if that clumsy explaining of something rather dry and of little importance in real life bored you guys to death. Since you managed to type a response it hopefully didn't go as far as that and it will not leave any lasting effects. As far as I'm concerned there's not need to apologise, neither for calling me a twat, nor for drinking a few pints. Does it have to be Stella though?
yes ive had a love affair with stella for some years now ;D my point is / was why cant we have BOTH of you opinions were no where near you 2 for knollage and we thank you both for sharing it with us mere mortals........... one life people ...............................one life.....
Post by scooteristforever on Apr 3, 2011 10:07:49 GMT
people will always have different views and opions on engine builds....
im always keen to pick up tips from those that do it properly, but alas sometimes a lot of the techy stuff goes over my head.....
the lads that build and ride fast reliable road and track scooters are the people to listen too ( IMO )
what is it the racers say " when the flag drops the bullshit stops" not sure if this means it sorts out the good riders from the not so good.... or if it means the big power claims will be proven OR NOT as often is the case...............!!!!!!
the scooter world seems to have gone a little DYNO crazy nowadays,, i fully understand how essential it is to have a tuned (expensive) motor set up properly on a dyno...... but the clowns that just want to spout big BHP numbers in the pub AMUSE the fuck out of me, especialy when many of these scooters are tuned beyond practicality, and arnt used for sporting purpose...
people like Scuari and Mr Falc that build tune and sprint missile like Vespa`s are hero`s in my little world.......
people like Norrie Kerr, Terry Frankland & Tony O`B, that build tune and race missile like Vespa`s are even better in my little world, because they`re from the UK............. ;D ;D
@ Mathias, back on the bearing topic abit, when you say its basic engineering...? i had two years working in a machine shop, working on a lathe a milling machine a surface grinder and also a bit on a capsten lathe... ( all on a very semi skilled nature) IE.. i can turn something to within say a couple of thou and mill something at very least square..... this isnt anywhere near your engineering league/level mate.... but is however BASIC Engineering.......... so come on old boy your a VERY VERY clever fella, but dont insult our inteligence with your "GRASP IT" its basic stuff......... are you coming to England anytime soon.... always good to put faces to names, and gain a bit of knowledge of course.... cheers Col
Last Edit: Apr 3, 2011 10:10:06 GMT by scooteristforever