Anyone ever tried to improve the lubrication to the primary drive side crank bearing?

I've got 4 shot cranks here (3 NSR and one RS), every one has that same bearing gone and all my NSR cases show signs of that bearing having tried to spin. I think it's got to be a weak point as the other 2 are lubricated via little pools with holes down to the crank in the top cylinder transfer ports.
The same system is used on the primary drive side one but rather than it being a pool the holds oil that then drips down to the bearing it's a slightly uphill path (or at best flat) with no effective pool at all (as ithe "pool" is past vertical) so the only chance it gets to pull any oil though is going to be when (if?) air and hopefully some oil get pulled through the "wrong way".

I was thinking I could probably make some effort to re-engineer the pool to make it able to hold something and make the lubrication path slightly downhill?
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I would think that you may be thinking about this "problem" too much?
I could be wrong but, I would think that the evidence of trying to spin might just be from when the bearing was failing, extra drag causing the outer race to be being pulled on.
I would also think that this bearing would be carrying the most load/torque as it is right next to the primary drive gear.
As for lubrication, when running, the primary compression should be forcing mixture through the bearing.
Only problem I could see is maybe after a long lay-up the bearing could drain down and be compromised at early start up, maybe? Even this is a long shot, as all of the engine internals could be at the same risk?
I would think that the cranks you have got were just at the end of their service life.
Racing puts a lot more stress through a whole bike, let alone just the engine.
Racing and race tracks are pretty extreme places for an engine/bike.

Chester362 wrote:
As for lubrication, when running, the primary compression should be forcing mixture through the bearing.

If that's the case then why do the other 2 bearings have lubrication from the top cylinder transfers? Even on the RS when it's got to cost power to mess the base of the transfers up and cost money to machine the oil ways. Matt suggsted long ago if power was all you were after you should fill them in.

And why did the mc28 add a drip feed from the oil pump to that bearing?
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fontyyy wrote:

Chester362 wrote:
As for lubrication, when running, the primary compression should be forcing mixture through the bearing.

If that's the case then why do the other 2 bearings have lubrication from the top cylinder transfers? Even on the RS when it's got to cost power to mess the base of the transfers up and cost money to machine the oil ways. Matt suggsted long ago if power was all you were after you should fill them in.

And why did the mc28 add a drip feed from the oil pump to that bearing?

Obviously the oilways are there to aid longevity of the bearings. If they weren't there, the engine would still work.
Maybe the loss of power due to turbulence is offset by the reduced drag of better lubrication and better reliability?
Yeah, the late MC21 and '28 engines have the oil pump feed down the crankcase bolt hole. Good idea on a road bike. I would think it means that the right side bearing is under more load and benefits from the additional feed, rather than an inherent design fault.
Sticking to maintenance schedules would ensure failures are non-existant or due to other reasons, eg, poor maintenance or unusual failures of components, etc.....

I too have had an engine that seemed perfectly fine with just the RH main bearing worn out. Possibly due to poor oil feed from front cylinder? Possibly not.
I have thought about this issue before and do wonder if the front cylinder bearing lube "pool" being slightly past vertical renders it basically useless.
I was tempted to fill it in with DevCon and re-drill the 2 holes as there is no point having a pool that has gravity working against it I guess.
I don't have the bike in a 70 degree wheel stand all that much.
There is a 3 part photo here which shows what we are talking about (sort of).
The rear cylinder transfer port areas lube the centre and left hand main bearings. The front cylinder right hand transfer port area lubes the RH main bearing.

Of course, you have to agree with the reasonably obvious points made by Chester, but Fontyyy does make a good follow up argument, thats for sure.
I do not have any engine cases that are apart at the moment, so can't really have a look to see if it might be possible to machine an oil lube pool/path that would work better with gravity for the front RH cylinder.

It is an interesting point, but a new bearing probably lasts a pretty long time anyway?
The cost/effort of re-machining the cases, and/or adding a extra line from the oil pump, probably outweighs the cost/effort of replacing a main bearing every 20,000 km/miles??

Why did Honda bother to create a lube pool at all for the front cylinder, if it doesn't work?
Maybe there is more to this than just gravity? Or maybe it was just done for symmetry?
Most of the time when running, it will be so turbulent that the "pools" probably make little difference.
Keep thinking Fontyyy.
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When building my race engine, I gave some thought to the route of the air/fuel/oil mix from carb to cylinder head. The front cylinder is a nice straight run, but the rear required the air/fuel/oil to go round a 90 degree bend. I assumed this was why there was double the lube pools and two oilways vs only one at the front, as it affects the speed of the gases and what oil they 'dump' on the journey. I filled the pools on my race bike and with 'scheduled maintenance' as Chester Roy says, I've never had a problem with crank mains failing.
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geckoracing1 wrote:I assumed this was why there was double the lube pools and two oilways vs only one at the front, as it affects the speed of the gases and what oil they 'dump' on the journey.

Hmmmm....I assumed the top pools were there to lube the flywheel side/centre mains and the oilways (I won't say pool as it's past vertical, nothing will ever pool in there) in the outside front tranfer port were to lube the remaining bearing. Obviously the centre and flywheel side mains are going to get better lube as oil will collect in the little pool and drop down to the bearing so only a crazy man would oil the center main from the front transfer. The center bearing even has holes in that line up with the holes in the cases.

If you look the oilways themselves in the front transfer are inclined a bit but there's no way they're going to work like the other two do.

It looks to me like the NXA has one across from the inlet side (which has got to work well) as well as one (without a pool) from the transfer;


Looking at the NSR it may be possible to do something similar though the case bolt near the oil pump is in the way to replicate the exact path.
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Considering the pressures and turbulence which will be present in the cases, its unlikely gravity has any effect at all I would think.

Imagine the certifugal (centripetal if you prefer) forces when the bearings are spinning at 12,000 rpm. Is it likely that any oil dripped 'onto' the bearing will do anything but be flung straight off? Much like a drive chain and sproket...

One can only assume Honda knew what they were doing, but it is interesting to work out what that was!

Again, thinking in straight lines and 90 degree bends etc is probably pointless once the engine is spinning, as all those nice easy paths will be meaningless.

I'm not a fluid dynamics expert, but I do know enough about aerodynamics and jet engines to know it isn't as simple as it looks!
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Dave Ett wrote:Considering the pressures and turbulence which will be present in the cases, its unlikely gravity has any effect at all I would think.

What about when the bike is sat there, warm after a race and the transfers are coated in a film of oil at and the oil suspended in the chamber at the time the motor stops? Do you think a drip or two might make it's way down into the pool then? Even if it's just one tiny droplet every now and then?

The point is Honda went to all the trouble of machining the cases with these oilways (and on the NSR/NF5 RS specing a special centre bearing) and they carried on doing it in the RS right up to the NXA. So it's a fair but they do something.
And they went to further trouble on the '28 to improve the situation on the one oiled from the front transfer.
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Hmmm, they might yeah. What good they'd do for a motor that wasn't running, I don't know.

Absolutely Honda knew what they were doing and those shapes must do something - swirl chambers perhaps? Pressure traps? Joke machining to confuse owners 20 years after manufacture?
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Dave Ett wrote:? Joke machining to confuse owners 20 years after manufacture?

I think the pool is just that, a pool, they changed it's shape but retained the idea, this is an A-Kit RS250 NXA motor;


There's lots of odd shapes in the NSR (and even the NF5 RS) cases. There are far fewer in the later models.
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They may actually be for pressure relief - to draw oil through the bearing as the case is pressurized, like the venturi in a carb.

Maybe.
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I like to fill in the 'pools' with epoxy and then redrill the holes. I've done this since I started racing the MC28 in '94.

When I went to Harc-Pro in Japan for spares, they were doing exactly the same. They were even filling the 'pools' completely and just relying on the oil mist within the intake mixture to do all the lubrication.

The only real problem I see with no 'pools' or even holes at all is during cold startup, when there's a possibility that the bearings are dry. As Fontyyy and others have said, the oil film will dribble down and the 'pools' will guide the oil into the bearings.

NSR's have big pools because the idea is to ride them, park them, ride them etc etc. So the gathering of much oil is a good thing. A racer is pulled apart so development over time has seen the pools and channels change, as it's supposed to be overhauled time and time again.

Anyway, back to the main story, which is trying to improve the longevoty of the bearings. Have you considered that the cases may have gone soggy? We were advised to change the cases after half a season so as to avoid spun bearings and crank misalignment. And as we were running pre-mix there was no talk about bearing additional lubrication.

Also, force feeding oil to the bearing would cause immense drag, and if the spindle on my CNC machine is anything to go by, excess oil causes it to run hotter, not cooler, as it can't disperse the oil quick enough to carry away the heat so the temperature rises. My spindle runs a positive pressure with very fine oil mist. I don't know if the bearing on a crank would be the same, but I would say that the oil carried in the intake mixture does a pretty fine job of lubricating and removing heat.

Seeing as Steve probably has nothing to do, and seeing as he no longer has to spend hours every day licking his RC45. Why don't you ask him nicely if he'll assemble the bare cases and measure the main bearing housings to see if they're out of round, or oversize. That might give a small idea as to what's going on.

The condition of the crank cases is very important to crank life I think. Quite often you can see damage to the bore face of the main bearings. The bore dia does tend to open up allowing the main to move. Once the main bearings start to give up the balls tends to skid in the race rather than roll forcing the outer race to move in the crank cases. This is where the damage to the locating pins happen.

We also forget that the helical primary gear on an NSR tries to force the crank left all the time. Not good for the crank or cases.

As with piston rings I'm anal about cranks, my F3's gets rebuilt every 1500miles keeping it in tip top condition. My reward is not one single failure and a very smooth non crank cases eating engine.

As far as I can see even before main bearing play can be felt the bearing is toast. It only takes one ball to skid once to cause damage to the race and that bearing is on a one way slope.
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Matt@TYGA wrote:
Also, force feeding oil to the bearing would cause immense drag, and if the spindle on my CNC machine is anything to go by, excess oil causes it to run hotter, not cooler, as it can't disperse the oil quick enough to carry away the heat so the temperature rises. My spindle runs a positive pressure with very fine oil mist. I don't know if the bearing on a crank would be the same, but I would say that the oil carried in the intake mixture does a pretty fine job of lubricating and removing heat.

That's an interesting insight. As usual!
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