E: Engine Interesting big end...
- Thread starter GBewley
- Start date
The cages and long rollers remind me of two stroke main bearings. They had a long and happy life in my old racer.
The pin diameter looks far smaller as original,
I would place the item in its original conservative grease 'n wraping in a show case.
I would place the item in its original conservative grease 'n wraping in a show case.
In the new testament (Tuning for speed) our own PEI suggests slotting every other slot then turning the job round to do the others thus canceling any small deviance from true alignment good advice probably not applicable with latest modern equipment
The pin diameter looks far smaller as original,
I would place the item in its original conservative grease 'n wraping in a show case.
The pin diameter is HUGE. Most recent Alphas are 3/16ths, these are 1/4. The big end outer races end up being about 0.085” less than the nominal 1.875 of the most recent.
Sorry lost in translation.
Pin = big end bearing race diameter
Pin = big end bearing race diameter
Now that big end assembly is definitely olde style with them big 1/4" rollers in there. That was bad practise decades ago already when nobody had much of an idea what is going on in a big end with all that heavy weight in a very dynamic space. Do you realize that each of these overweight rollers have to be accelerated and shortly after decelerated in each single revolution of the crank ?? You will know the swivelling motion of the conrod when it goes past TDC and BDC pointing to the front of the bike and shortly after to the back of the bike. Means, the big end bearing accelerates a bit , then has to slow down a bit - each revolution of the crank. So there is a constant pushing and shoving within all components in the bearing and heavy items in there are quite simply "reeal baaad". In consequence there is a lot of slipping and friction between components to keep all parts in their places.
To add to the drama, the big end bearing does not rotate around its own centre but instead it is placed half of the crank stroke out from the centre of the crank main bearing so it gets the full force of the centrifugal effect at the crank pin radius onto all bearing components on top . So it is crucial to have light weight items in there and big rollers are just not what you´d want. You will not find these types of rollers any more in modern engines. INA have never had needle rollers bigger than 4 mm in their famous big end bearings, no two rollers in one steel cage slot, always full length. And they knew their job. BSAF in Netherlands get the 35-42-20mm needle bearings INA type for the new production Gold Stars, Manxes had the biggest INA type 40-48-20 mm needle bearing in last decades but both types are no longer available from INA for many years.
Anyway, no question for me to have the 40-48-20 mm bearing for the B-Rapides, pressed up crank with 40 mm pin, case hardened rods of my own design and manufacture. Big rollers make for a weak crank pin too, not great for long pins like in Vincents.
Vic
To add to the drama, the big end bearing does not rotate around its own centre but instead it is placed half of the crank stroke out from the centre of the crank main bearing so it gets the full force of the centrifugal effect at the crank pin radius onto all bearing components on top . So it is crucial to have light weight items in there and big rollers are just not what you´d want. You will not find these types of rollers any more in modern engines. INA have never had needle rollers bigger than 4 mm in their famous big end bearings, no two rollers in one steel cage slot, always full length. And they knew their job. BSAF in Netherlands get the 35-42-20mm needle bearings INA type for the new production Gold Stars, Manxes had the biggest INA type 40-48-20 mm needle bearing in last decades but both types are no longer available from INA for many years.
Anyway, no question for me to have the 40-48-20 mm bearing for the B-Rapides, pressed up crank with 40 mm pin, case hardened rods of my own design and manufacture. Big rollers make for a weak crank pin too, not great for long pins like in Vincents.
Vic
Ah, yes...it’s a touch under 1.3”! Ok...1.2906 and 1.2908. Quite small.
Nice looking rods Vic, do they have pressed in liners or are they one piece and honed to finish size. I have been playing around with some static balancing of the cranks I have here and come up with some interesting results. Cheers...............Greg.
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