Ceramic Bearings

[djr]

like everything you will get lots of different opinions on this,
one advantage of plastic cages would be that if the cage did break you would only get pieces of plastic floating about which shouldn't do anymore damage, if a piece of steel cage broke off it could be a different story.
a bit like steel reed valves compared to fibre reed valves

[tony27]

My Sherco has the plastic caged bearings standard, no problems with them for me while running at 70+:1. When the factory changed to them the explanation was reduced noise

[Lozza]

Dynos and stop watches don't lie. Too much oil and balls will start to skid. Why run normal clearance bearings on the crank mains when C3 is no more expensive? On GP engines C4 is standard and old Formula A kart engines (100cc fixed gear rev to 22,000 rpm) C5 was needed

Too much oil certainly doesn't cause balls to skid. Gearbox bearings run in a bath of oil, crank bearings run on a drop of oil. Lack of lubrication can cause balls to skid, particularly in a differential load situation such as an engine.

Too much and the wrong type of oil will cause rolling elements or balls to skid, the balls have trouble pushing the oil out of the way and begin to skid. Gearboxes are doing roughly around 1/3 the rpm of the crankshaft are they not? Where crank mains are exposed to the gearbox oil they are not bathed at all for the reason the balls or rollers will skid.

How much REAL DIFFERENCE do any such mods make ON THE MX TRACK to the average VMX wobbler 

I wont argue for or against ceramic bearings or bigger oil galleries as I have NFI . I enjoy other peoples input though and learn a thing or two from these debates .

But at the end of the day I doubt very much that any such mod will make a difference to the average VMXers results even in a 125 .

How many of us can honestly say that we use all that even  a std 125 produces ? im not talking about holding it flat out down a straight ( you can teach a Chimp to do that ) this is MX not drag racing .

Better suspension ( put that power to the ground ) and brake .5 of a second later going into every corner and wind it on .5 of a second earlier coming out of every corner , 10 corners a lap = 10 seconds a lap improvement , 5 lap race and your nearly a minute in front of ole mate with his ceramic whatnots   

They do make a considerable difference Bill and they are in twisted racer logic great value, provided your bike fully is optimised. If someone else's bike is 3-5kmh on average faster you won't make that up going into or out of corners. You will just get tired quickly

like everything you will get lots of different opinions on this,
one advantage of plastic cages would be that if the cage did break you would only get pieces of plastic floating about which shouldn't do anymore damage, if a piece of steel cage broke off it could be a different story.
a bit like steel reed valves compared to fibre reed valves

Polymide cages actualy handle heat better, the steel cage wasn't the issue more the rivets holding it together. Funny thing is when the rivets and/or the cage goes on crank mains, a few times I haven't found many parts of the rivets or cage. Nor any witness marks on the piston/cylinder/head Considering where they sit and the tiny gap I think they must basically disintergrate insitu.

[MaxPower]

I have a 83 KX125 that I've spent have a total of maybe 6 to 7 hours on since rebuilding. When installing a new PVL I grabbed the stock rotor and gave it a shake. I was shocked to feel some movement. Not a lot. Hardly nothing. But it was defiantly something. I've never experienced this before on any bike. I know the bearing didn't spin in the case. Kawasaki has a nice steel sleeve in the aluminum case to accept the main bearing. I used Maxima 927 at 32 to 1. Nothing got past the air filter. I can only think it is the cheap shit Wiesco branded main bearing that I shouldn't have used that had something to do with it. I'm an old man riding a 125. I didn't use this bike anywhere to its limit to have a main bearing wear in 6 hours of use.
Anyway I'm going to change it and move on. I would rather be doing other things than taking my engine apart.Again. Thank you for the replies.

[sleepy]

I have a 83 KX125 that I've spent have a total of maybe 6 to 7 hours on since rebuilding. When installing a new PVL I grabbed the stock rotor and gave it a shake. I was shocked to feel some movement. Not a lot. Hardly nothing. But it was defiantly something. I've never experienced this before on any bike. I know the bearing didn't spin in the case. Kawasaki has a nice steel sleeve in the aluminum case to accept the main bearing. I used Maxima 927 at 32 to 1. Nothing got past the air filter. I can only think it is the cheap shit Wiesco branded main bearing that I shouldn't have used that had something to do with it. I'm an old man riding a 125. I didn't use this bike anywhere to its limit to have a main bearing wear in 6 hours of use.
Anyway I'm going to change it and move on. I would rather be doing other things than taking my engine apart.Again. Thank you for the replies.

Check the fit of the bearing on the shaft. As little as .0005" wear will be noticable on the flywheel side. I have seen quite a lot of cases with steel sleeved main bearing mounts still spin bearings. Need to check the interference fit there as well.

[yamaico]

I have a 83 KX125 that I've spent have a total of maybe 6 to 7 hours on since rebuilding. When installing a new PVL I grabbed the stock rotor and gave it a shake. I was shocked to feel some movement. Not a lot. Hardly nothing. But it was defiantly something. I've never experienced this before on any bike. I know the bearing didn't spin in the case. Kawasaki has a nice steel sleeve in the aluminum case to accept the main bearing. I used Maxima 927 at 32 to 1. Nothing got past the air filter. I can only think it is the cheap shit Wiesco branded main bearing that I shouldn't have used that had something to do with it. I'm an old man riding a 125. I didn't use this bike anywhere to its limit to have a main bearing wear in 6 hours of use.
Anyway I'm going to change it and move on. I would rather be doing other things than taking my engine apart.Again. Thank you for the replies.

If you are using C3 bearings or greater they have movement when new. This is quite normal as they are a bearing with a higher internal radial clearance for high load/speed/temperature applications. I wouldn't be rushing to put a new set in, you may find exactly the same situation.

[MaxPower]

Is the grade of the bearing laserd on the outer race Yamico? So does that mean there should be no play when the engine is to operating temperature ?
What is interference fit Sleepy? Anything is possible because there is some kind of play, but I would be surprised if the bearing spun and had any wear on the crank as it was a pretty solid fit while reassembling
I appreciate both of your help

[yamaico]

It should have the grade inscribed as a suffix to the bearing identifier Max. You're correct, the clearance will decrease with temperature, which is also a function of speed and load. High clearance bearings are also used in low speed/temp applications with a high interference fit.
Many moons ago I was racing an AT3MX Yamaha on dirt track and was doing the ignition timing one night before a race meeting and experienced exactly the same problem as you described. I pulled the motor down that night, got new bearings the next day, fitted them up and had exactly the same amount of movement - lesson learnt.
Having said that I'm not saying 100% that yours are OK, it just seems unlikely that they are shot, particularly given the fact that everything was in good shape when you assembled it (I assume the crank was true), coupled with the quality oil and low amount of run time.

[sleepy]

What is interference fit Sleepy? Anything is possible because there is some kind of play, but I would be surprised if the bearing spun and had any wear on the crank as it was a pretty solid fit while reassembling
I appreciate both of your help

Interference fit is the difference in size between the bearing and the hole it goes in. The bearing will be spot on a MM size like 62mm and the case should measure less than that to be interference, probably 61.97. I have seen just recently a 1989 YZ125 that had both mains loss in the cases after only an hour or 2 of running and the engine builder was sure the bearings were tight on assembly.
In your case it still maybe that the play you are feeling is as others have said is that your bearings have C3 clearance. A C3 bearing of main bearing size would have between .013 and .028mm of movement, this is reduced with interference fit.
If you had a dial indicator mounted as to measure the up and down play it would be possible to work out if you had to much play or find a friendly engine shop near you to feel the play and give an opinion before stripping it down

[Oldfart]

Good advise ..

[Nathan S]

In addition to all of the above:
If the main bearings are buggered, they often sound like they are growling.

[80-85 husky]

except ktm needle roller mains...they sound like a plane load of poms has just landed....the engines are off ..........and whats that whining noise?

[tymes]

except ktm needle roller mains...they sound like a plane load of poms has just landed....the engines are off ..........and whats that whining noise?

bahahaha 

[MaxPower]

I'll bet you all are right. It is such a small amount that it's hardly noticeable. I'll get the engine hot and check to see if it goes way which it probably will. In all my years of riding this is the first I've heard of such a thing. It makes sense to me. Everything expands and contracts with temperatures. If indeed it is the issue I'm so grateful for the help. When I was 14 years old, I split cases because I had all the time in the world. Now I have to work on my bike at 11pm when I should be 2 hours asleep for work the next day.