ESE's works engine tuner

[JdG]

Just a brain fart…

Has anyone ever tried ceramic needles or ceramic bearings? My knowledge on the subject is limited. I’ve been told by people that claim to be more knowledgeable, that ceramic bearings in general can survive almost anything, as long as they don’t overheat. Lubrication isn’t overly important because of the hardness of the bearing materials.

Overheating is the issue here and I don’t know what temperatures are lethal for the ceramic bearings.

I also don’t know if the load cases are even suitable for ceramic materials.

Just wondering.


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[pete376403]

Are the bearing races also ceramic? If the balls are super hard does that make the races wear faster?

[Frits Overmars]

Has anyone ever tried ceramic needles or ceramic bearings? My knowledge on the subject is limited. I’ve been told by people that claim to be more knowledgeable, that ceramic bearings in general can survive almost anything, as long as they don’t overheat. Lubrication isn’t overly important because of the hardness of the bearing materials. Overheating is the issue here and I don’t know what temperatures are lethal for the ceramic bearings.
I also don’t know if the load cases are even suitable for ceramic materials.

We've been using homemade hybrid crankshaft bearings (ceramic balls between steel inner and outer races) in 35.000 rpm model engines for about 30 years now; they have proven to be bulletproof.
I'd love to use ceramic rollers in big end bearings too, where their much lower specific mass would be very welcome for the constantly accelerating/decelerating masses within each crankshaft revolution, but the ceramics experts are still reluctant to let me apply them.

The main problem with ceramic bearings is not overheating (ceramic parts couldn't care less) but the fact that their elastic deformation under load is about zero. In English: they're as hard as a rock .
The outer race of a bearing exhibits a curvature in the same direction as the balls or rollers in contact with it, but the curvature of the inner race bends away from that of the roller bodies, causing the contact area to become so small and the contact pressure so high that the inner race fails. The ceramic roller bodies themselves almost never fail.

[Niels Abildgaard]

We've been using homemade hybrid crankshaft bearings (ceramic balls between steel inner and outer races) in 35.000 rpm model engines for about 30 years now; they have proven to be bulletproof.
I'd love to use ceramic rollers in big end bearings too, where their much lower specific mass would be very welcome for the constantly accelerating/decelerating masses within each crankshaft revolution, but the ceramics experts are still reluctant to let me apply them.

The main problem with ceramic bearings is not overheating (ceramic parts couldn't care less) but the fact that their elastic deformation under load is about zero. In English: they're as hard as a rock .
The outer race of a bearing exhibits a curvature in the same direction as the balls or rollers in contact with it, but the curvature of the inner race bends away from that of the roller bodies, causing the contact area to become so small and the contact pressure so high that the inner race fails. The ceramic roller bodies themselves almost never fail.

I seem to remember that You showed us a crossection view of one of these phenomenal 2.5ccm engines.

Have it been tried to make a crankshaft where the inner races have been made from ceramic,stellite or carbide material and brazed with cupper or nickel?

Are there a newer version?
https://itat.bmfa.uk/08-03-2022

[Wos]

I wrote the original Freetech50 rulebook so yes, injection and a lot of other things are free in Freetech50 (what's in a name )

About part throttle deto: it was a major problem at Aprilia. The RSA and RSW bikes were just about bulletproof regarding WOT deto, but they would detonate terribly at part throttle + high revs conditions. For that reason celebratory burnouts were strictly forbidden.
I figured out that the cause was actually quite simple: part throttle means low crankcase pressure and although there was ample blowdown time.area at WOT, the cylinder pressure drop before transfer opening was not deep enough for this part-throttle crankcase pressure, so exhaust gases entered the transfer ducts, heating up the fresh mixture.

Frits!

Ktm had massiv problems with there first Injektion in motocross bikes

Now they changed to throttle BODY Injektion to solve lubrication problems of Injektion into transfers...hard way of learning for ktm

Do you know if Injektion is used or was testet in freetech50 ?


Thanks!

Wolfgang

[Frits Overmars]

I seem to remember that You showed us a crossection view of one of these phenomenal 2.5ccm engines.
Have it been tried to make a crankshaft where the inner races have been made from ceramic,stellite or carbide material and brazed with cupper or nickel?
Are there a newer version?
https://itat.bmfa.uk/08-03-2022

Hej Niels, it’s much simpler than that.
As you know, the MB40 model engines (6,5cc, not 2,5cc) have a rotary intake system in which the inhaled mixture flows through the hollow crankshaft.
For good power, that channel – and therefore the crankshaft journal – needs to have a decent diameter. But that diameter also determines the size of the crankshaft bearing, and that bearing in turn determines the maximum safe rpm.

The solution: take a standard steel ball bearing, keep the outer ring and the synthetic cage, and discard the steel balls and the inner ring.
The steel balls are replaced with ceramic balls and the inner raceway for the balls is ground directly onto the crankshaft itself, so that we achieve a combination of a substantial diameter for the intake channel and a relatively small diameter for the inner race.
So this inner race is simply the steel of the crankshaft. Nothing special, no ceramic, stellite or carbide material and no copper or nickel brazing.

The engines have remained virtually unchanged for roughly 25 years, but they have racked up a handful of world titles since then and they are reliable, so why change anything? With a fuel consisting of 80% methanol, 20% oil and 0(!) % nitro, a well-tuned MB40 delivers 5 hp at the crankshaft and the competition still hasn’t caught up .

[Frits Overmars]

Frits! Ktm had massiv problems with there first Injektion in motocross bikes
Now they changed to throttle BODY Injektion to solve lubrication problems of Injektion into transfers...hard way of learning for ktm?

The reason for KTM to change back from TPI (Transfer Port Injection) to TBI (Throttle Body Injection) was not so much a lubrication problem but more a power problem.
KTM had patented a system of injecting fuel into the B-transfer ducts only, claiming that the content of the A-transfer ducts was more prone to short-circuit into the exhaust ports. But at full throttle the rich mixture from the B-ports and the air-only content from the A-ports had not enough time to properly mix and form a homogeneous combustible mixture, whereas injecting fuel into the throttle body meant the mixture was thoroughly stirred and homogenized in the crankcase before it entered the cylinder.

As I said, KTM had patented the TPI system. But New Zealand genius Neil Hintz could prove that he had a fully functioning TPI system before KTM applied for their TPI patent, so KTM had to withdraw it, with a painful loss of face.
Neil Hintz too had experienced the full-throttle problem but instead of switching back to TBI he fitted injectors on the A-transfers as well as on the B-transfers. The A-injectors are only activated when full power is demanded, engine power is perfectly controllable and fuel economy is a lot better than with TBI.

[F5 Dave]

His next move will probably leapfrog direct injection and inject at the expansion chamber

[Wos]

OK Frits

In many forums was discussed that Tpi was reason for failures caused by bad lubrication.

On the other hand...every carb can be tuned to lean...and it was told that Ktm with Tpi reached for harder emmission standards...

Think Ktm not only has to hide Patent Problems these days...what a pitty

[Frits Overmars]

In many forums was discussed that Tpi was reason for failures caused by bad lubrication.
On the other hand...every carb can be tuned to lean...and it was told that Ktm with Tpi reached for harder emmission standards.

As far as I know, the KTM oil pump that delivers oil to the intake manifold is identical in both the TPI and TBI versions. That pump can, of course, malfunction, but this is not specific to either the TPI or TBI systems.

Due to the increasingly stringent emission standards, internal combustion engines are being run leaner and leaner. If on top of that the fuel-air mixture is not homogeneous because the fuel is only injected in the B-transfers and not in the A-transfers, the engine may run too lean at full throttle and suffer from detonation.
Returning to Throttle Body Injection was the simple solution that KTM chose. They'd better have taken another look at Neil Hintz' TPI mk2 system.

[Wos]

Emission

Years ago thought about a pressure oil solution for 2strokes to lubricate every part that needs oil.

Minimum oil in combustion ...minimum oil wash wastet to ex - cleaner Emission ?

For sure very expensive to built ...
Dont know if this is the only way to really "clean" 2 stroke

Wolfgang

[Peter1962]

As far as I know, the KTM oil pump that delivers oil to the intake manifold is identical in both the TPI and TBI versions. That pump can, of course, malfunction, but this is not specific to either the TPI or TBI systems.

One of the members on the ktmtalk forum said that it is in fact an industrial pump, and has been tested for several thousand hours without failure. Good that ktm did not try to re-invent the wheel and uses what is available and reliable on the market.

Due to the increasingly stringent emission standards, internal combustion engines are being run leaner and leaner. If on top of that the fuel-air mixture is not homogeneous because the fuel is only injected in the B-transfers and not in the A-transfers, the engine may run too lean at full throttle and suffer from detonation.

There is also the problem that KTM is using a crappy connection of the CCP sensor, the standard one is prone to leak, giving an unreliable signal to the ECU and that of course gives problems for the mixture. Some do simply use some white silicone to try to avoid leaks, but the better solution is to use an aftermarket quality connection. https://www.pinitracing.com/videos

Returning to Throttle Body Injection was the simple solution that KTM chose. They'd better have taken another look at Neil Hintz' TPI mk2 system.

Its a shame they did not do that...

[lohring]

Thoughts on this opposed piston design starting at 14 minutes into the video? The interesting features are the large 30 degree exhaust crankshaft lead, the 45 degree up angle on the intake transfers with no swirl, and the annular, four plug combustion chamber with a central squish. I worry about scavenging the central core of the cylinder and the effect of the returning tuned pipe pressure wave with the transfers open. You would need a higher supercharge pressure for this to work. Would an annular combustion chamber with a central squish detonate?

Lohring Miller

[Vannik]

I worry about scavenging the central core of the cylinder. Lohring Miller

I agree, it will form an unscavenged core.

And the effect of the returning tuned pipe pressure wave with the transfers open. Lohring Miller

Towards the end he moved to megaphone only.

Would an annular combustion chamber with a central squish detonate? Lohring Miller

This is an interesting take on the comustion chamber issues of an opposed piston engine - and it will probably need the 4 plugs.

[Niels Abildgaard]

I agree, it will form an unscavenged core.



Towards the end he moved to megaphone only.



This is an interesting take on the comustion chamber issues of an opposed piston engine - and it will probably need the 4 plugs.

Or a central spark plug in piston