Sounds good
I will be doing a long stroke conversion to my M20 shortly ( been saying that for 10 years ) and then I still have a spare big piston from Ian to fit so I will keep your bearing in mind.
Down here it was only the army B40's that sufferred this problem & I have , rightly or wrongly attributed this to labouring the engine in top
When I did mine I used a spare original I had on hand , then over geared the final drive so it became a 3 speed with expressway only overdive and in that form it gave me 12 years of good service till some one decided they needed it more than me .
On a high reving engine , no problems because the inertia is just not there .
After that it was turn down the journals to take the 1/4 x 1/4 .
I did hear of a person who found an off the shelf replacement with the same outer diameter & smaller inner so you had to nmacine down the journal
The complete bearing did not have an oil hole
On the first he drilled one through with a Dremel tool
On the second, he cut a groove around the outside of the outer race then cross drilled the conrod as per the A10/A65 to throw oil up the bore but no direct supply to the big end , just splash.
Apparently both worked when newly done but no idea about how they have lasted as we have lost contact .

I've owned multiple BSA heavyweight singles continuously for around forty years and also had a few examples before that...For much of that time I ran standard big ends but started to fit needle roller big ends when they became available from a contact who made them (sadly now retired)...These were particularly good for the tuned engines as the 'skidding' of the rollers that is inherent in a roller bearing design is reduced by the use of much smaller rollers and helps reliability at higher revs.....

BSA engines of this era don't suffer at all from oiling related problems in my experience and I've built them standard, slightly tuned and very tuned, nearly doubling the power output of the B33 for example...Engines I've built have been raced, sprinted, ridden to work and used for touring by myself and various owners...All apart from one had standard specification oil pumps...

To date, over hundreds of thousands of miles, I have never experienced a big end failure in a properly rebuilt and maintained engine...I've had many through my hands that have had big end problems but honestly, I'd say poor maintenance combined with overly hard use has been the probable cause of that problem...Most engines showed the signs of exactly that...

Personally, I'd certainly be inclined to try Marks big ends for both tuned and standard applications, particularly as original big ends are generally no longer available....Ian

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

The Royal Enfield idea of running caged rollers directly onto the main shafts leaves a bit to be desired in my opinion. I've just rebuilt this 1938 500cc engine where the main shafts were badly marked. Darren supplied me with needle rollers and hard sleeves for the shafts and my mate John turned up the OD sleeves for the crankcases.

Jan gave me a specially made big end pin which again Darren provided the needle roller for.

I have also recently noticed that Hitchcocks are now offering needle roller main bearing conversions for C and CO engines.....Sounds like the way to go. Ron

email (option): ronpier@talk21.com

A PES Big End Liner pressed into a M20 Conrod.
The liner has been honed to suit the pin.
Also shown is the silver-plated hardened cage roller bearing and thrust washers.

https://pesltd.uk/?product=66-0483A



Mark

email (option): pes.sales@btconnect.com