Britbike forum Forums British motorcycles in general Bsa gold star forum Loose timing side main bearing

The issue with finding a substitute metric bearing that could be made to work in the cases is that Imperial and metric bearing designers seem to have used the same guiding principles. As a result, the OD of the outer race is related to the ID for the shaft in approximately the same way for both Imperial and metric bearings of comparable sizes.

If a metric roller bearing had an ID larger than ⅞" (22.23 mm) it could be sleaved for the shaft, but it simultaneously would have to have an OD less than 2¼" (57.15 mm) so it could be sleaved to fit in the 2¼" bearing cavity. Unfortunately, metric designers liked 5 mm increments (20 mm, 25 mm, 30 mm ...) for the IDs, and they also liked 62 mm (2.44") for the OD of a 25 mm ID roller bearing.

Lighter-duty metric roller bearings with the necessary 25 mm ID are made with ODs of 47 mm and 55 mm, so they could be sleeved to fit, but the ones I found have load ratings less than 50% of that of the stock bearing. However, that doesn't mean that someone more motivated than I am to search might not find a suitable, heavier-duty metric bearing in one of the many catalogs.

Another possibility would be to modify a bearing with 20 mm ID by increasing its bore by the necessary 0.088". I did that for my Ariel's metric drive-side bearing, but in that case only needed to increase the bore of a 25 mm ID bearing by ~0.014" to convert it to fit the nominal 1"-diameter shaft. Still, increasing the bore of a bearing by 0.088" isn't unreasonable to consider.

I do like a flurry of activity!
As Magnetoman's bearing spec' search found similar close comparison between the 2.25" & the 2" versions as my search turned up & having mulled it over some more, I am pretty sure I'm going to go for the 2" "cure".
I think the minor trade off on specs is as MM say's, probably irrelevant in all but the most extreme uses. As much as I knock around pretty quickly, I will not be doing 4 laps flat out at the Classic TT, plus multiple practice laps, plus many short circuit races to qualify!


The engineer will have no problem making a correct adaptor sleeve for the housing & I have left the cases with him to check the housing for truth, until I confirm the go ahead for sleeving (& get a bearing). I would dearly love to be able to do this stuff myself & whilst I do occasionally machine simple odds n sods", my skills & machinery are not up to this task.

I am looking into using one of the now much discussed SKF sleeves, (other sleeves are available) for the loose rear wheel bearing housing of another bike. If the housing isn't true I will no-doubt have to completely dismantle the wheel to enable machining, which doesn't exactly fill me with glee... Fortunately I was given an old wheel building frame years ago, which makes life a little easier for that job.

No need for that, remove the tyre and it would fit my lathe with its gap bed.

To put your mind further at ease, the SKF bearing that BSA specified for the DBD was a CRM7, whereas the specs I quoted in a previous post were from a 1968 SKF catalog for the 'A'-suffix versions which were "a new design having increased capacity." In light of this, it certainly could be that the improved 2" CRL7A doesn't have 4% less capacity than the old 2¼" CRM7. You might not be giving up even 4% in using this later version of the smaller bearing.

Thanks for looking through your catalogues MM, I only have the online search option for them & some aren't very user friendly. The differences are sufficiently minor for me not to be overly concerned; & knowing that the newer specs are better anyway is all to the good.

Kommando, I take it that was not an offer to take on the task! note you are in Scotland & I bet, closer to John o' Groats than Gretna Green. Even G-G is quite a drive for me!
I don't think my local engineers has a gap bed lathe but they have a lot of other mills & the like, I will see what their max capacity is.
It's a real shame my go-to guy retired & moved away as he was able to do an amazing number of things & knew his bikes.

Several years ago I tracked down contemporary catalogs for all brands and types of bearing used by BSA. It was time well spent since the engineering information different companies included often is complementary. I also have maybe a half-dozen modern catalogs as well. Interestingly, the old FAG catalog is 300 pages, but the modern one is over 1600. Even where information is on the web I find paper catalogs easier and faster to use, and more convenient for determining possible substitutions.

Hi All,
Another bearing that might be worth considering as it is 17mm wide so nearer the width of the original is an RMC22L 50x 22 x 17
The Id would need enlarging 0.225mm to match the crank . Ok its a bit expensive at £72 from Veteran Triumph ??

John

Thanks for the info Chater' I might well have had a look at that if I hadn't already ordered the LRJxxx. Worth bearing in mind tho'