Whilst pulling my M20 engine apart I thought, I wonder if anyone knows about our uprated BSA M20/21 and many others Big End Bearing kits?
These kits use a silver plated steel caged bearing. (std.shown) These give a superior service life over the pairs of rollers in a aluminium cage. The kits are £150.00 each plus VAT if it applies to you. Better than that we do a fitting service of the big end ring to the conrod. So when ordering a kit, if you send the conrod to us we can fit and finish it for you. Remember big end rings are supplied semi-finished to allow for honing.
As with most PES parts they are made in house. Only the caged roller bearing we have made.
Are they the same sized needle rollers as the B 50 bearings ?
I ask this because I have a box full of deceased B40GA conrods
The Aust army for some idiot reason specified their B40's with the same high speed rollers as the B50
This would be fine but they also fitted them with a rather strange box, being the C15 trials first second & third with a std top
This means you just about have to valve bounce in 3rd before changing to top
And changing down is even worse as I regulaly locked up the rear wheel if I accidentially changed down at any speed higher than 20 mph which was way too slow ( revs wise ) for top .
The logic behind this was 3 speeds for field use and the normal top for escort duties on the road.
The actual result was the riders would lug at low speeds in top gear rather than change down
because the cage on the needle rollers runs very close to the outer race, with a little wear the cage scuffs on the outer race till it wears through so you end up with a crowded race with 1/2 the required rollers
However when fitted with the std B 40 big end which uses the 1/4 x 1/4 rollers, this does not happen.
I have done this to at least a dozen of them in the late 80's because the army sold the remaining 300 of the 495 in 2 auctions in 1982 & 1984.
Lots of people bought them them thinking they got a bargan as most had less then 5000 miles on the clock only to find the bottom ends fall apart in a year or so of regular riding .
Now M20's will be reving a lot slower than B40's, even with the armys low compression of 6.5:1 and the long stroke will be giving the big ends a pounding.
I usually run mine under 3000 as max torque seems to be around there .
I would hate the think you & Anita have done all this work to make aproduct that fails prematurely in service.
Yes Trevor I know about the problems with the cages, this is why I had uprated cages made for the bearing. They were also used in the CCM trials bike with the B40 hybrid engine. I've been running them for a very long time without problems in B50's and a modified version for B44's. There's a few M20/21's running them without any issues too.
I've seen more big end failures with aluminium cages BTW, than with hardened steel and plated cages.
For big end use you must use a KZK style cage and they do appear to run close to the outer ring. The biggest mistake is over oiling the bearing. Roller bearings don't like a lot of oil. Trouble is if you reduce the supply to the big end, the piston and bore run dry.
I have a solution to this, but I'll experiment on my own first. I have been using a partial version on race B50's for over ten years without issue, but it requires to many changes for a road bike.
As with all PES replacement parts they are made to outlast any others in normal use. So if you have a problem we'd like to know. Then we can make it better.
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
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
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.