ceramic bearings

[Don Ferrette]

So we could keep steel and lighten the flywheel for the same advantage.

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Only thing you've got to watch out for with lightening the flywheel is if you go too far there won't be enough "stored energy" in the flywheel & your boat won't launch. :huh:

 

[TimD]

Yep - I'm with Don on this. I found prop selection and launching harder with the lighter flywheels on 21 engines when I tested them. I now use a STOCK N/R flywheel or a slightly heavier OS item. A light boat helps too

The performance aspect of the ceramics doesn't sound like it would equate to much - if anything in boating applications.

The longevity of them would be the key selling point by the sound of it.

 

[Don Ferrette]

The longevity of them would be the key selling point by the sound of it.

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And right now on what is CURRENTLY available longevity is the WEAK point. :blink:

 

[EatMyShortsRacing]

The longevity of them would be the key selling point by the sound of it.

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And right now on what is CURRENTLY available longevity is the WEAK point. :blink:

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The longevity in ceramics may look bad due to some experiments with some brands / ball refits.

With the correct ceramics I can see that there "should" be an increase in longevity. What we need to know is which bearings to use and how to get that longevity out of those bearings.

I think most of the other advantages apart from the lower rotational load wont affect performance at all since the mass of the flywheel alone makes the mass of the balls insignificant.

 

[EatMyShortsRacing]

Yep - I'm with Don on this. I found prop selection and launching harder with the lighter flywheels on 21 engines when I tested them. I now use a STOCK N/R flywheel or a slightly heavier OS item. A light boat helps too 

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Ahh it also depends WHERE you remove the weight from the flywheel B)

 

[TimD]

True

Centrifugal force and all that stuff!

 

[izitbrokeyet?]

I guess nobody has tried an ACB (angular contact bearing) on the front with a standard flex system. I'll try it and report back....................... (maybe )

As a follow up to the speed secrets...I know some of the fastest Pylon racers(speed society winners) deepen the rear bearing pocket by about .010" so that the axial load is taken up by the front bearing only. The front bearing is better for taking up this load because of the smaller diameter, higher limit speed due to ball speed, slip etc.. There are some that deepen the pocket and insert a PTFE disk in there to take up some of the thrust load from the rear bearing inner race. The only point would be that there that knowing how the bearings work and their limitations may help to move this issue forward.

I agree about the decrease of torque available at the shaft due to flywheel and bearing weights being a non-issue if not a negative for performance.

I still think that there is some advantage in the top end (in the dremel range of rpm) that's added torque available at the shaft. after all....it is all the small things that add up to some significant value.

 

[TimD]

As a follow up to the speed secrets...I know some of the fastest Pylon racers(speed society winners)  deepen the rear bearing pocket by about .010" so that the axial load is taken up by the front bearing only.  The front bearing is better for taking up this load because of the smaller diameter, higher limit speed due to ball speed, slip etc..  There are some that deepen the pocket and insert a PTFE disk in there to take up some of the thrust load from the rear bearing inner race.  The only point would be that there that knowing how the bearings work and their limitations may help to move this issue forward.

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Yep - one of the Thunder Tiger 21 engines I had built by a pylon & C/L engine guru had this done. Big Job. Glad he did it and not me.

 

[Ian Inverarity]

KB,

What size is the front bearing? I have some listings of angular contact bearing sizes here that may be different to your listing.

Ian.

 

[izitbrokeyet?]

Thanks for looking Ian,

the .21 fronts are typically 607 size which is 7mm ID x 19mm OD x 6mm thick....the best ACB size we could find was a C3 fit 7mm x 19mm x 10mm (if memory servs) that would leave me with a big mod job for my NR case or having an additional 4mm of bearing to deal with (I think I choose the later) I was curious to know if any one had tried to get a flex collet to work with 4mm less shaft to grab on to.

in a perfect world there would be a bearing with the thickness less than 10mm to try in a c3 fit

 

[EatMyShortsRacing]

As a follow up to the speed secrets...I know some of the fastest Pylon racers(speed society winners)  deepen the rear bearing pocket by about .010" so that the axial load is taken up by the front bearing only.   The front bearing is better for taking up this load because of the smaller diameter, higher limit speed due to ball speed, slip etc..   There are some that deepen the pocket and insert a PTFE disk in there to take up some of the thrust load from the rear bearing inner race.  The only point would be that there that knowing how the bearings work and their limitations may help to move this issue forward.

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Yep - one of the Thunder Tiger 21 engines I had built by a pylon & C/L engine guru had this done. Big Job. Glad he did it and not me.

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Ummm guys you dont see a problem with this statement????? That would work on pylon engines because the prop is pulling the crank towards the front bearing. In a boat the crank is being pushed in the opposite direction so all the axial load IS on the front bearing only. (unless the crank connects to something else past the rod then there is potential to transfer the thrust to other areas)

 

[Ian Inverarity]

KB,

No joy, the listing I have shows 6 ID x 19 OD x 6 W, then 8 ID x 22 OD x 7 W. The later is about $100 US as well!!

I think the collet would still work 4mm shorter, but you would probably have to make it fairly tight.

Personally I use square drives, 1/4" for my 90's. The struts I make myself and have needle roller bearings and ball thrust bearings, the strut has an oil line which runs from my muffler. I make my own ferrules, and my own prop shafts from ejector pins. The system is pretty reliable, I have had very few failures in years of use. The thrust bearings last about a season. I like to test other people's drives for how easy they are to turn over, so far I havent found anyone with a free-er system than mine! B)

TimD has seen my system.

Ian.

 

[TimD]

Yep - Ian's drive's are the smoothest I've ever seen.

Craig,

I would have thought you of all people would have figured that one out! Mine was for a gear drive set up Thrust direction - whats that :lol: :lol: :lol:

KB,

what about some sort of captive mechanical drive joint that removes the thrust from the crankshaft end but still utilises a welded stub type flex cable. More rotational mass and a potential failure point, but is it worth looking into?

 

[EatMyShortsRacing]

Craig,I would have thought you of all people would have figured that one out! Mine was for a gear drive set up  Thrust direction - whats that  :lol:   :lol:   :lol:

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exactly.... no axial thrust whatsoever..... so why do that mod at all for a gear drive engine?

 

[TimD]

Craig,I would have thought you of all people would have figured that one out! Mine was for a gear drive set up  Thrust direction - whats that  :lol:   :lol:   :lol:

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exactly.... no axial thrust whatsoever..... so why do that mod at all for a gear drive engine?

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Why, because when a guy who has built multiple world championship winning engines, (and not just in 1 form of racing) and also has my absolute respect in regards to anything mechanical he put's his mind and hands to suggests that he will do it to gain a few more rpm at peak - I don't doubt him. I don't know the theoretical reason for it, I don't do it to my own engines or for engines I've done for others.

A shame an exploding bearing killed that motor - it SCREAMED on the gear drive! It would make your one sound sick.

You seem to be quoting me all the time - stop it or I might develop a complex!!!!!

 

[EatMyShortsRacing]

Why, because when a guy who has built multiple world championship winning engines, (and not just in 1 form of racing)  and also has my absolute respect in regards to anything mechanical he put's his mind and hands to suggests that he will do it to gain a few more rpm at peak - I don't doubt him.  I don't know the theoretical reason for it, I don't do it to my own engines or for engines I've done for others.A shame an exploding bearing killed that motor - it SCREAMED on the gear drive! It would make your one sound sick.

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I dont doubt him... again though sometimes the habbit of modifying engines relative to your own strain of the hobby can be a hard habbit to break - although if by locking the crank to the front bearing and the tolerances were too tight and the crank was pulled into the main bearing then that modification would make sense.

You seem to be quoting me all the time - stop it or I might develop a complex!!!!!

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Think of it this way..... I see your comments worth quoting

Now is that good or bad????

 

[TimD]

I gotta dig out that gear drive again! The reactions I got from people when I ran it was awesome.

Back to the thrust thing now please!

 

[EatMyShortsRacing]

..as I build a new boat for the Nova or CMB gear drive.....

thats gotta work.....

And I didnt quote you so you didnt end up with (another) complex Tim!!! :lol:

 

[Propjockey]

As TimD already stated, some FAI pylon racing engine manufacturers use ceramic ball bearings. For instance the dominating F3D pylon engine - the Dutch MB .40 - is a true masterpiece featuring lots of refinements making this engine apparently unbeatable.
It is a very nice example of the "reduce moving & non-moving parts approach".

It handles rpms up to 35K without probs - and this is a 6.5 cc engine! Keeping in mind those engines run only full throttle ceramics seem to be a good choice in this particular rpm regime and application.

http://home.kabelfoon.nl/~fiorimet/Index.htm

View chapter "Crankcase"

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This isn't about bearings...but did anyone go to this link and look at the pics of the engine?

Check out the PORTS!! :blink:

 

[Preston_Hall]

I guess when I suggested lightening the flywheel I thought it would be obviously clear that you would lighten it only by the weight you would loose by going to ceramics. GEEEZ!

But as far as the flywheel weight needed for launch, I think mostly BS. Peeps thought that back when there where big brass flywheels. If weight was good we would still be running brass flywheels. Also, your engine is not really turning any RPM at launch so again the weight of the flywheel is questionable to me.