Ball bearing clearance specification normal or C3

I would contact a bearing supplier for more specifics, but in my experience the clearance in a ball or roller bearing should be zero, or at least relatively. In fact in taper roller bearings like you have in differential carrier side bearings, pinion gear taper roller bearings, and most taper roller wheel bearings for front wheels of rear drive cars, trailers etc., they actually have a preload on them. In assembly they are brought up to zero clearance, and then tightened further to put a specific rated drag on the bearings. In other cases, a steel tube placed between the outer bearing and the nut, and is crushed to a predetermined load.

 

Don't claim to be an expert, but have a fair amount of familiarity with your question and SKF's website/catalog/use. Matching up the basic size is the easy part -- figuring out and understanding the correct batch of alphabet soup suffixes is the hard part -- and saying "go check the www.SKF.com website" is like saying "go read the internet" -- way too much information

There will be no single answer to your question, because it depends on how the bearing is mounted and used. For example, if you're talking about the unpreloaded, deep-groove bearing #30 in this jpeg (that is only supporting a radial load), using the C3 vs a CN would maybe (needlessly) add a small additional amount of possible radial runout to the drive sprocket's position (which isn't a plus), but in the total scheme of runout tolerances, it isn't a big deal, and I doubt that you'd ever see a significant difference in performance/life for C3 vs CN. The internal clearance values are shown of page 4 of this brochure:

http://www.skf.com/files/059324.pdf

(and the tech information at the start of the angular contact bearing product chapter is a good general read too)

In a preloaded mounting, the C3 internal clearance would give a deep groove bearing a bigger contact angle and would help increase the axial load capacity and maybe help prevent ball skiding in a high RPM situation, but IIRC the gearbox and diff don't have any single-row ball bearings.

With regard to the cages, it's a speed vs noise vs lube compatibilty vs cost trade-off -- see the SKF website.
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Are you sure that #5 is a deep groove ball bearing? Can anyone confirm/deny? It might be an angular contact ball bearing with a very large contact angle (like 25~40 deg), because the helical gear will put a fairly high axial load in that direction, and a preloaded single-row angular contact ball bearing really doesn't have a radial clearance when in operation. If it is a (preloaded) deep groove bearing, the C3 internal clearance would probably be preferred to increase the contact angle from a few degrees to maybe 5~7 deg to better deal with the axial load.

With regard to the transmission shaft bearing, can you give a part number and/or item number from the SPC illustration?

 

I dug through one of my boxes of used parts and came across a set of bearings which I believe are the #30 ones. Unfortunately, not like the others I have, I did not write down where these came from on the engine, but they have the same ID/OD as the seal #29 (which I labelled) and were right beside them in the box. In any case, those bearings are SKF 6203/C4QE6. I'll have to dig through one of the other boxes and try to find the #5 ones for the SKF number.

 

I'm busy with a rather extended rebuild of my 2V 308 and am having the same issue .I don't have the bearings that came out in front of me so I don't have the exact numbers ,but I am sure mine are C4 .I don't have much history of my car so no idea if they are correct or not .I got hold of the SKF tech rep in SA and his response was that the bearing I had were discontinued . My numbers are different at the end (QE6) I've got alot more the rep said that was the lubricant used and he had requested an alternative from the factory .As soon as I know more I will post such .

 

I should retract my earlier statement -- perhaps they knew that the machining/tolerances for bearing #5 relative to bearing #30 wasn't so great so had to accept a "sloppy" bearing #30 to minimize binding on those when the tolerances all combined in one direction -- my bad for speaking too quickly without enough study.

The "QE6" = special electric motor quality (no longer used)

and all the "Q" specs seem related to "optimized internal geometry" without much real explanation. They don't stock (or even make) every possible bearing combination, so even if Ferrari wanted some more today, they might have to make a substitution from their original desire.

Dave -- Your 1980 alphabet soup is different because circa ~1978 they changed the design and switched the positions of the outer bearing and the lip seal. Yours uses a sealed, grease-lubricated deep groove for bearing #30 -- please post any SKF numbering/letters that you have for it.

Craig -- What's the background? If it's easy enough for these guys to just read it off the bearing why couldn't you? Did you already know yours were non-OEM? Did you buy some from a supplier and the SKF PNs didn't match-up exactly?

 

I redid my timing drive bearings back in '02. The OEM outer timing drive bearings I removed were C4 clearance:
Remove front bearing on timing belt drive pulleys
http://www.ferrarichat.com/discus/messages/256120/21198.html

Robertgarvin was doing his bearings at the same time & also found his OEM ones were C4s:
Timing Gear Bearings
http://www.ferrarichat.com/discus/messages/256120/74985.html

Here are the 2 industry std p/ns off of the OEM timing drive bearings:

Inner SKF 6201-J
outer SKF 6203-2RS1/C4HT51

IMHO, the extra clearance on the outer bearings is to allow for expansion due to the elevated temperature enviornment + additional temp rise due to high speed. Also, the outer bearings are indeed subject to axial load due to the helical cam drive gears. Under load the gears will press outwards.

IIRC, somewhare in the marathon JWise timing drive service post Phil Hughes(rifledriver) factory trained tech said that C3s could be used, but didn't last as long as C4s.

 

Craig, yes, I went through my receipts and those are indeed the bearings and the new ones I bought were also the same (6203/C4QE6). I purchased these through Dennis McCann about seven years ago...

I can't find anything in my boxes and in my receipts on the inner bearings and I seem to remember now that because of that, it was that I didn't replace those. I only did these outer bearings as they truly did show their age (rough, grinding feel as I spun the gear/shaft in my hand) and at the time, I seem to remember alot of discussion on this forum, maybe on the ferrarilist.com or possibly on expensivecar.com's old forum(!) that these were prone to failure at an early age/mileage due to a lack of proper lubrication (splash only) and that it was prudent to replace them. The inner bearings felt good as I spun them and they have a dedicated, pressurised oil supply, so I made the decision it wasn't necessary to replace those.

 

No. I was puzzled at the time I encountered it, & spent over a day researching it. I recall coming across bearing application design guideline info on either the SKF or NSK web site that made it clear that Ferrari definitely knew what they were doing. However, that was 5 years ago & I haven't needed the info since.

IIRC, it was a formula that had to do with the bearing inner races being mounted on a steel shaft, while the outer races were mounted in Al. I vaguely remember it as only one of a shaft's bearings had to have a relaxed fit to deal with differences in thermal expansion. Other parts of the internal clearance calculation were operating speed, temperature range, & class of fit on the shaft. I'm an engineer & was satisfied I understood it at the time.

 

Hello from Germany,

having all the SKF stuff always at hand, I just did a thorough search. But I cannot find any lifetime calculation examples which involve the bearings internal clearances ( C1 to C5 ).
They just state, that CN relates to usual recommended tolerances and normal conditions and if there are higher temperatures, press fit on both shaft AND housing you have to check the remaining bearings play after installation.
Due to my personal experiences there is a lot of trial and error during the design stage.

Best Regards

Martin

 

Verell, I have to challenge you on these statements. The jpeg shows the forces acting on the Driven Gears -- can you dispute? It would be a very poor design that would put an axial load on a bearing only supported by a snap-ring IMO.
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why ? on the rear wheel bearings we have the same situation. Inner bearing takes the axial load and is just supported by a snap-ring in one direction and a cover in the other direction. Outer bearing only takes radial load and this is why the inner one gives up first.

Best Regards from Germany

Martin

 

Actually, the axial force direction varies depending on whether the crankshaft is accelerating or decelerating the cams. But you're correct that the majority of the time the axial force is inwards. As I said, I haven't thought about this in several years & miss-remembered the normal case.

I'm not going to comment on the desirability of only using a clip ring to resist a secondary axial load, but I've certainly seen it done in the past on other cars, motorcycles, etc. At least we concurr that there are axial loads on the timing drive shafts. Last time I recall this coming up was in the 408 thread where roller bearings were proposed for the bearings.

Martin, I took a quick look & haven't been able to find the design info I was referring to, SKF's site seems to have changed a lot. It may not have been NSK. Could have been one of the other major bearing mfgs sites that I was looking at. IIRC, it wasn't a lifetime calculation, but rathar formulas/questions to help the designer determine if additional clearance might be indicated.

 

No argument -- didn't say that it wasn't done, but why not take advantage of the better precision in the machined seat for the #5 bearing? (and I'd put Martin's example is a different category -- larger and much lower speed).

Does a lot of slack appear in the long driven timing belt runs when you rapidly close the throttle from rational RPM?

 

Ok You asked that I post the bearings that came out of my 1980 308 GTB carb/drysump
outer bearing SKF 6203 - 2RS1/C4VG154
Now the local SKF rep said the VG154 was the type of lubricant used and was trying to get a spec on it to supply an equivalent
inner bearing can't read anything ,I would like to know the details .
I don't have much history on the car but I can assume that if the motor had been rebuild it would have been done by the local agents ,not to my private shops around here that would have tackled that job !