Hi all,

I want to close an engine.
The bottom case is a NOS , complete with bearings.

It was all dipped in cosmoline, and looks great now, after washing,
But when I pulled the inner drive side roller, I see that there is
A slight discoloration on the race.
(Not rust, not pitted, smooth. only small "clouds" where the roller were touching the race.)

I am looking at replacing the bearings I can find new.
(Ian suggested to also replace the outer drive side with a closed type, so I already bought one)

Looking at the technical section, I can only find 3 bearings of of the 4..

So 2 questions, please...

1. Am I missing something, or there is a 4th bearing, which is not on the list?..
(Timing side) From the technical section/ "Bearings":

"Engine
Timing side lipped roller: MRJA7/8
Drive side lipped roller: MRJA25
Drive side ball: 6205C3
Engine main bearings should be a C3 class fit. Specify this when ordering."

2. The inner bearings, with the detachable race- They also C3, correct?
Cause few bearings dealers told me that there are no C3 for that kind of bearings,
But consulting with Darren Wrudd some time ago, he said that few MRJA7/8 I bought
ARE C3, ans it is marked by 3 circles on the race side..

Thanks !

Noam.

email (option): noam10@gmail.com

Hi Noam...The 'Tech Section' is incorrect in as much as one bearing is missing from the list...There is a 4th. bearing in the wartime and later engines..(in fact it was only in 1936/7 that the M20 didn't have four)

It is a ball bearing...RLS7....

All the main bearings should be a 'C3' fit, including the lipped rollers, but the Imperial ones (timing side) are getting expensive and harder to find in that classification..

The 'C3' classification does not affect the outside diameter or inside diameter of the bearing when compared to a 'standard' bearing, but refers to the slightly greater internal clearance in C3s...

This was to allow for the 'crush' exerted by the crankcase and the operating temperature...Ian

email (option): ian@wright52.plus.com

The 'Tech Section' is incorrect in as much as one bearing is missing from the list...There is a 4th.][/quote]

Solved.

email (option): ahum@quicknet.nl

For these bearings C3 are specified; however, I'm not sure if mine are C3. What are the consequences if you ride with non-C3

email (option): viaconsu [at] planet [dot] nl

THANKS IAN, HENK !!

Hans, in my bike I currently have an engine I rebuilt from scratch, (500cc)
And all of the bearings there are not of "C3" tolerance.

The engine only ran for about 2000Km, but all seems to be fine.

I remember I also asked Ian about it a long time ago (Or was it Henk?...)
And they replied that many, or maybe even most of the M20's
Rebuilds were not done with C3 class bearings, over the years,
And all seems to be fine.

After all, it is not an Italian 2 stroke 14K RPM engine,
(Which I overhauled many of them, some 25 years ago, few a day)
In which you "spilled" the bearing after a rather short while, (or at least made them sound really bad)
If you used the standard, non C3 bearings.

In the M20 they work rather slow, has a pretty good cool oil supply,
(Unlike 2 stroke, which only has fuel spray with some 2% oil mixture)
And can disperse the heat to the tick aluminum body, so I would not be too worried..

Noam.

email (option): noam10@gmail.com

I think many M20 crankcases have lost some 'fit' over the years as well, as the bearing housings acquire some wear with the removal and replacement of bearings...(though not your NOS ones Noam...or the NOS set I am fitting to my own bike!... )...Ian

email (option): ian@wright52.plus.com

Hi Guys
As Ian quite correctly pointed out, the C' ratings of bearings refers to the internal clearance of the balls/rollers, to the inner/outer races.

For example, if the gap for the rollers was 10mm, and the roller was 10mm, the bearing would not turn at all. There has to be a clearance to allow movement.

On these sizes of bearings, the range is near enough to generalise. So, a standard bearing, which is actually between C2 and C3, would have a clearance gap of 16 to 24 microns. A C3 version of this bearing, would have a clearance range of 20 to 26 microns.

So it basically just ensures that you get the top end of clearance should you be running under a particularly tight fit ( H6 ) which closes up the bearing slightly, coupled with high temperatures.

It would always be better, but not necessarily essential to run C3 bearings in these engines.

I hope that this helps
Darren.

email (option): dwrudd at lineone.net

Thanks for that Darren. I understood the theory but wasn't aware that the difference was so minute! As you explain it, a standard bearing could easily be within the C3 range? Ron

email (option): ronpier@talk21.com

It can Ron. But C3 guarantees the top end of clearance. So I don't worry too much about it in these applications.

email (option): dwrudd. at. lineone dot net

...So, a standard bearing, which is actually between C2 and C3, would have a clearance gap of 16 to 24 microns. A C3 version of this bearing, would have a clearance range of 20 to 26 microns.

So it basically just ensures that you get the top end of clearance should you be running under a particularly tight fit ( H6 ) which closes up the bearing slightly, coupled with high temperatures.

It would always be better, but not necessarily essential to run C3 bearings in these engines.

[/quote]

Hi,
I was starting to replace the drive side outer bearing (6205C3)
In a NOS cases, as Ian recommended to me, to a 2RS (Rubber sealed) ones.

The current bearing is an original one, for sure.
The internal bearing, the one close to the flywheel is marked "V3"
Which to my understanding, was the old making for the "C3",
But I noticed that the outer 6205 bearing is marked "V2" (C2)

So could it be that the outer bearings were "C2" and the inner ones "C3"?..
I did not check the timing side bearings yet..
I will try to do it later.
Here is a photo of the bearing.
It is new, only black from the cosmoline it was dipped in..

Noam.
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email (option): noam10@gmail.com

As far as I know Noam from looking at contemporary BSA Service Sheets, C3 were specified for Roller and C2 for Ball Bearings..

email (option): ian(at)integsci.com

Thanks Ian.

Interesting info..

So it is C3 afterall !

Noam.

email (option): noam10@gmail.com

Yes it is c3.
There is aways much confusion regarding the V3 V2 etc reference suffixes on older bearings. Largely caused by the 'modern' use of suffixes by SKF and others which refer to specific internal designs for use largely in the mining and paper industries. VLOC V210 etc are usually for high vibration industrial applications and don't have anything to do with the old references.

However. The old references which have largely changed to standards eg. Ref 125. = 6205. (Same thing) were often suffixed with V 2 or V 3. These did not refer to clearances, they were actually referring to generic drawings when bearing designs were sometimes altered to improve them. This was usually an edge radius change or another unconcequential dimension therefore one could say Version 2. Which is why you don't see V1. As these were the original drawings and thus no need to specify.

Clearance in the old references was designated by circles polished alongside the references. So actually a C3 would often be a 125 V3 OOO. Three circles=C3. The C rating was adopted by manufacturers over a period of about twenty years or so as more and more followed the trend and so by the late sixties more or less everyone used them.

So to surmise, don't worry about the V numbers, they don't matter, but technically the C3 should be used in these applications.

I hope that this helps.
Darren.

email (option): dwrudd. at. lineone dot net

Very interesting, Darren.

Thanks !

email (option): noam10@gmail.com