Bearing grades

[mick25]

Going back some years , I remember someone asking what’s the best option for bottom end bearings from bearing shops was it C2 ,C3 or C4 ?

[fred99999au]

Yamaha specify C3 for mains, at least in my bikes.

[Tomas]

would say that 0.01mm extra clearance does not make much of a difference but I guess it may help. When motor heats up everything expands not just inner or outer bearing race. Pulled apart some Jawa and CZ motors and only had standard bearings. Also got some genuine Suzuki crank bearings but no c3 stamped on them just part number. And also got some genuine Koyo bearings. C3 printed on sealed box and after unpacking and checking whats stamped on bearing, there was no c3 just bearing size and made in japan. Suzuki owners manual recommends replacing all bearings with genuine Suzuki ones

[80-85 husky]

Husky bearings are C3, pretty important they are at least this grade

[sleepy]

The clearance depends on a few factors. What size motor is it and what RPM it is going to do and also what is the fit of the bearing in the case. The tighter the fit the more the bearing is squeezed reducing it's clearance. The higher the RPM the higher the clearance needs to be.
C2 is a bearing with less internal clearance than standard and C3 has more clearance the standard and C4 is bigger again.
Most manufactures call for C3 but standard bearings would generally work if C3 is not available although a screaming 125 may work better with a C4.

[Wasp]

The engines I built (EML Jumbo 820 ) I used C4 . Actually I bought the much cheaper standard version from SKF  to begin with  and then ground them to C4  clearance .

[mick25]

Thanks for all the info guys , it’s a XL500 bottom end and some of the oem bearings are no longer available. Sounds like C3 grade is my best way to go .

[Dungar Pilot]

Hi All,

The engines I built (EML Jumbo 820 ) I used C4 . Actually I bought the much cheaper standard version from SKF  to begin with  and then ground them to C4  clearance .

That is interesting and makes me wonder if I was thinking about it the right way, I thought the extra clearance was between the balls and inner/outer races? Do you mean the clearance is between the shaft and inner race, outer race and casing or what did you grind?

[Tomas]

in most of cases discussed here (shaft diameter let say between 10 to 40mm)difference between standard and c3 bearing would be somewhere around 0.01mm. for example standard  bearing xxxx has a clearance 0.005mm than same size bearing xxxc3 has a clearance around 0.015mm. Not a lot but as mentioned earlier it may help when things are pressed together and heat up. It would be quite hard to remove 0.005 from inner and outer bearing race to increase clearance by 0.01 to convert standard bearing to c3,c4 bearing. would have to split cage etc.

[Wasp]

Hi All,

The engines I built (EML Jumbo 820 ) I used C4 . Actually I bought the much cheaper standard version from SKF  to begin with  and then ground them to C4  clearance .

That is interesting and makes me wonder if I was thinking about it the right way, I thought the extra clearance was between the balls and inner/outer races? Do you mean the clearance is between the shaft and inner race, outer race and casing or what did you grind?

Just checked my data . It started life  as a NJ206ET . Then grind the inner ring on OD  for relieve till you get to C4 .I remember those bearings cost about $100 each then , compared to $400 in the C4 version. So when you multiplied for 2 bearings , it was a big saving .

[sleepy]

Thanks for all the info guys , it’s a XL500 bottom end and some of the oem bearings are no longer available. Sounds like C3 grade is my best way to go .

You could bolt together the cases and measure the inside dia of the cases to check on the fit, but I would think that C3 would do the job. Your biggest problem is more likely the positioning holes in the bearing outers, bearings and not to easy to drill.

[mick25]

While I’m at it , I’ve ordered a Carrillo rod , pin , thrust washers and bearing From the states but it’s a two mth wait , these XL500 have the tin cover set up on the crank half’s do you do these sleepy ?
I want it balanced etc .
One of the oem gear box bearings has a groove machined in it for a steel ring to go around it to lock it
in the cases but this bearing is no longer available, I’ve heard someone buy the same size bearing and machine the groove into this one .

[sleepy]

I thought it was only the 2 stroke Hondas that had those stupid tin covers but anything is possible with Honda. Can't understand why they would fit them onto 4 stroke as the Crankcase volume isn't important. I have a jig for the 2 stroke ones but I'm not sure if the XL500 would fit. What are the main shaft diameters. 

The gearbox bearing with a groove may just be the same as aftermarket bearing that comes with a circlip.
Dimensions of a 6205NR will give you an idea.https://www.bearing-king.co.uk/data/images/45278.jpg
If the bearing has just a shoulder on one side it can be machined into a normal bearing but ceramic tooling is required.
 

[Momus]

The 4 stroke Honda cranks have the crank shaft drilling organised so that the oil is centrifuged and sludge trapped in the cavity the metal plate forms before it goes into the crank pin and rod bearing.

[mick25]

I thought it was only the 2 stroke Hondas that had those stupid tin covers but anything is possible with Honda. Can't understand why they would fit them onto 4 stroke as the Crankcase volume isn't important. I have a jig for the 2 stroke ones but I'm not sure if the XL500 would fit. What are the main shaft diameters. 

The gearbox bearing with a groove may just be the same as aftermarket bearing that comes with a circlip.
Dimensions of a 6205NR will give you an idea.https://www.bearing-king.co.uk/data/images/45278.jpg
If the bearing has just a shoulder on one side it can be machined into a normal bearing but ceramic tooling is required.


I will have to measure the crank shaft later today
Thanks for the tips on the bearing I will chase something up and see how I go .
I have seen the tin covers left off the XL500 cranks ? Not sure if this is wise or not ?