Rear Wheel Bearings

[Roland]

I recently took a decision to change out the original rear hub shafts on my Elan Sprint for some new solid billet shafts. This obviously resulted in a rear wheel bearing change which went well after following the extensive advice previously posted on this site.

The thing that surprised me was that after I disconnected the driveshafts I discovered some radial play in both inner bearings (2 thou on near side, 3-4 on offside). This was a little surprising since the previous owner had only done the rear wheel bearings about 2500 miles ago. The outer bearings were fine no play at all, at least not that I can feel or measure.

Is this kind of play common on bearings with so few miles? The bearings are SKF and are of Malaysian manufacture, fairly typical I imagine. The bearings were supplied and fitted by a reputable Company (by the PO).The play is definitely within the bearings, bearing to hub shaft fit was fine and bearing to strut housing fit fine.

Am I being unreasonable on the amount of play, I would expect on bearings of this design and age to 'feel' no play at all.

On the new bearings I have fitted I have no discernable play as expected.

Rgds

[RichardHawkins]

Roland,

I have always found SKF technical help very useful. It is more than a few years since I have used this service and it may have migrated on line and away from a telephone conversation.

I still have an old paper SKF catalogue, but sadly my brain is not what it used to be. On page 88 SKF state that the radial clearance should should be virtually zero, on page 181 for a bearing of this size the clearance is in the range of 5 to 20 microns. There are of course several caveats i.e. that the fit of the bearing in the housing and on the shaft are correct. Bearings also come in a range of clearances, but I do not expect this to be relevant to our application.

I suggest you ask to speak to an application engineer, he will have had real world field experience and will know what is acceptable even if not correct, he might even be an old car enthusiast.

My last phone conversation was with SKF Luton 01582490049.

I hope SKF are still there and that I have been some help,

Richard Hawkins

[StressCraxx]

The inner bearings may be "C3" internal clearance. Some of the internal clearance is taken up when the bearing is pressed on the shaft for a slight interference fit.

Most bearing houses sell these bearings for industrial electric motors and other machinery. The "C3" internal clearance is preferred because they run cooler and more quiet than standard clearance (C2) bearings.

I don't think the additional inner bearing clearance will cause any harm or issue at all.

-Dan (former SKF employee)

[Roland]

Gents, thanks for the replies. I will try the Luton SKF number and see if I can understand this in more detail just for my own interest really.

As mentioned I removed the bearings because I was changing the hub shafts. The bearings hadn't failed an MOT and there were no issues on driving. However on the offside with the wheel on the play was noticeable with the wheel jacked up and rocking by hand.

I can't feel any play at all in the new bearings I have fitted. I did perhaps wonder if the old inner bearings had picked up some damage on installation.

[miked]

For my two pennies worth, they can easily pick up some play by side loading on installation. Even with great care they can develop some play after the first few miles of driving if some side load is present by slight over pressing or pushing when fitting.
I have had this drive me nuts. However, it does not seem to go any worse with large mileage. I kept checking and it was the same.
I have no background in bearings but have changed quite a lot.
There is a lot of discussion on here about fitting techniques. I favour pushing in the inside bearing on its outer race using the cut away pipe method. I have a guide dolly in the outer part of the case whilst doing this to keep the drive shaft central not picking up on the bearing on the case.
Then I carefully tap the outer bearing in with a parallel dolly (working around the dolly edge) using a very small hammer. Again, no pick up. This is similar to doing motorcycle alloy hub bearings.
Arrangement sat on my knee so no weight on the drive shaft.
Heat if the case is a good fit. Generally not, so Loctite. I don't like a press involved with the outer bearing. Not wishing for an arguement with those that do. Each to their own.

[2cams70]

Deep groove radial ball bearings (as rear wheel bearings generally are) are just that. They are designed to withstand radial loadings more so than axial ones. If for some reason your rear drive shafts are putting a significant axial load on the bearings through binding, etc. you will get an increased wear rate.
Having said that it is quite normal for this type of bearing to have an amount of perceptible axial play.

Taper roller bearings are different - they can withstand a significant amount of both axial and radial load.

[Billmack]

The stresscrax guy has the answer. In a bearing manufacturers part number the "c" number at the end is the amount of play in the bearing. Bigger number equals more play. Often if the shaft is highly stressed a larger amount of play is called for so there is not a stress riser on the shaft as it bends under load.I have seen c4 bearings called out on crankshafts of high revving kart engines and people come to grief using the tighter ones. Some motorcycles actually use bearings with bean shaped rollers to alleviate this trouble

[69S4]

My two stroke motorcycle engines use C3 spec bearings in their crankshafts and normal ones elsewhere. As I understand it the C3 requirement is because of the raised crankshaft temperature when the bike is running normally. I've replaced quite a few of them, both normal and C3 spec, over the last year or so and had to search out the C3 spec bearings from my suppliers. If you just gave the bearing number you'd get a normal spec bearing. I suppose it's not impossible that you could fit C3 bearings by accident into the rear hub as they would go in just as normal but I'd be surprised if you got those by mistake from a reputable supplier.

[Roland]

I have had a chance now to look at the old bearings more closely:

Outer Bearings - SKF bearing of Malaysian manufacture, stamped 6206 2RS1. There are no suffix's for clearance . Both these outer bearings are in perfect condition, no axial or radial play. This is what you would perhaps expect of a bearing with 2500 miles on it.

Inner Bearings - I can't find any number or manufacturer on these bearings and they both have axial and radial play. The axial play was not apparent on the car probably because the outer bearing was still good.

So either the inner bearings were defective (from manufacture), C3 clearance (?) or they were damaged during fitting. However if I wasn't changing hub shafts I probably would have run them longer. As mentioned the bearings were supplied and fitted from a reputable Company as far as I can tell from the PO records.

The new bearings I have put in came from TTR. I was super careful during fitting and actually did not use my press. I made up the tools detailed on this site and used heat/cold to open up clearances as best I could. I fitted them using relatively small 'taps' so hopefully I have put minimal stress on the bearings.

I don't think I will investigate this one further, just monitor the new bearings and hopefully they will be fine. Just one thing I did find was my hub to shaft fit was not great on both sides, I doubt the taper was lapped and the key was forcing the hub off centre very slightly. Obviously the newly lapped in TTR hub shafts have sorted this.

[RichardHawkins]

Roland,

Thanks for the update and I hope everything works correctly now. I never cease to be amazed at the small savings people will make by fitting an unbranded bearing. The amount of work put in to dismantle and reassemble dwarfs the cost of the bearing, and then it all has to be done again.

Richard Hawkins

[rgh0]

If the inner bearings had no identifiable number or manufacturer on them then they were probably cheap no name bearings with excessive play from the start

cheers
Rohan

[Roland]

Rohan,

Yes very likely they had excessive play from the start. Anyway it’s all fixed and replaced with components from TTR. I seem to be using them more these days and have some confidence in what they do.

Roland