95 replies to this topic

[tonyp]

As soon as the back of the car flexes at all the bushings bind unless the rear end is bulletproof. Bearings can still be misaligned and spin free.

[Cheater]

That just made me cringe, if I am thinking about that correctly, it would be pulling the oil away from the crank surface.

That's not my thinking. A sintered-metal oilite supplies oil via capillary action, but Steve Dieter's post above provides part of the answer: "oilite bronzes are excellent for light duty on low speed shafts where low friction and no maintenance is required." IMO we're not in the "light duty - low speed" realm with 1:1 cars or high-perf slot cars.

The reason oilites are completely inappropriate for crank bearings in an IC engine has to do with how plain bearings work: the spinning shaft interacts with the oil in the bearing clearance to form a hydrodynamic wedge that separates the parts and keeps the shaft from contacting the bearing the vast majority of the time. My opinion is that it would not be possible for a hydrodynamic wedge to form against a porous bearing, i.e. an oilite.

As I have posted before, I have a half dozen or so of the TiN-coated 3/32" axles Cahoza used to sell and the difference in the wear patterns in the gold-colored coating when they're run in oillites vs Slick 7 solid bronze bushings is very noticeable. And I'm sure many of you have noticed the same thing: axles run in oilites do wear pretty substantially over time. The wear I see in properly-aligned and well-lubricated Slick 7 bronze bushings isn't zero but it's pretty minimal. BUT the bushings have to be properly aligned, with the bores coaxial and parallel, and synthetic oil should be used (as that's what gives the lowest observed wear).

As soon as the back of the car flexes at all the bushings bind unless the rear end is bulletproof. Bearings can still be misaligned and spin free.

Sure, blame the bushings for the chassis's failings... LOL.

I believe one of the biggest issues in scratchbuilding is assuring adequate strength and stiffness in the rear cage/motor mount assembly. Especially with contrate gearing. Most racers don't realize the level of the forces involved in this area.

Tony, on occasion I have seen wear patterns in those TiN-coated axles that illustrated the rear cage was not sufficiently stiff. Instead of a broad stripe the width of the bushing there were two narrow stripes indicating the axle was running on the edges of the bushing.

Hard to prove one is better than the other... ya pays yer money and ya makes yer choice.

And that's the real bottom line.

If we all agreed on everything, there'd be nothing to settle through racing... LOL!

[Pappy]

If we all agreed on everything, there'd be nothing to settle through racing... LOL!

Do we all agree that this thread should be moved to a different forum for maximum exposure?

[Cheater]

Good point, Butch.

I'll move it to the Technical Info & Advice forum.

[Mopower71]

OK, now how about when you factor in cornering forces? A bushing may spin free in a static situation, but slot cars are hardly static when they are being raced.

Hard to prove one is better than the other... ya pays yer money and ya makes yer choice.

Wouldn't a tapered roller bearing work better in this situation?
The reason they use them in automotive applications is due to the cornering loads, correct?

On the two go karts I have, I have to frequently replace the wheel bearings. They are ball bearing, and with the side loads that my wife and kids inflict on these things, the ball bearings just don't survive. And it's not due to lack of lubrication, or poor adjustment. They just can't take the side loading with all the power sliding that goes on. I for one have had the kart on its side, sliding from the yard to the pavement. If I were able to find the proper size tapered roller bearings, they would probably never fail.

[Mopower71]

That's not my thinking. A sintered-metal oilite supplies oil via capillary action, but Steve Dieter's post above provides part of the answer: "oilite bronzes are excellent for light duty on low speed shafts where low friction and no maintenance is required." IMO we're not in the "light duty - low speed" realm with 1:1 cars or high-perf slot cars.

The reason oilites are completely inappropriate for crank bearings in an IC engine has to do with how plain bearings work: the spinning shaft interacts with the oil in the bearing clearance to form a hydrodynamic wedge that separates the parts and keeps the shaft from contacting the bearing the vast majority of the time. My opinion is that it would not be possible for a hydrodynamic wedge to form against a porous bearing, i.e. an oilite.

That's what I was getting at, being porous, any load put on a part of the bearing would tend to push the oil out, thus causing contact with the bearing surface. Would this not be the same effect you get with them on the axle when a load was applied?

[Hworth08]

Anyone know what automotive engine bearings are made of (without looking )? The materials are already used on slot cars.

Here's the answer, both old and new:

Engine Crankshaft Bearings

The serious slot racers might gain a bit of info from that site.

[Steve Deiters]

This comparison between between slot racing axles (a simple rotating shaft suspended between two points) and a crankshaft (an eccentric rotating shaft between multiple bearing support locations with pulsating, varying stresses on the eccentric shaft and bearings during each of the four cycles of each piston) is comparing apples and oranges.

Adhesion to simple guidelines of squareness, perpendicularity, alignment, strength of supports, and most importantly, assembly will provide a superior minimal friction and virtually trouble-free environment for an axle to rotate it which should exceed the perceived advantages of ball bearings in this application.

[Cheater]

Don,

The earliest cars used cast in place "poured" bearings made from babbitt, a family of soft "white metal" alloys made mostly from tin, lead, and copper. They were a real pain (and still are for restorers). The bearing saddles had to be cleaned and tinned, and after pouring (using a casting fixture to form the bearings) the raw bearings had to be peened (to remove the slight shrinkage that occurred as the metal cooled) and then cut, grooved, and reamed to the proper size. (On the earliest Ford Model Ts and others, the final finish was produced by turning the cranks using large electric motors to "burn in" the bearings).

The first modern insert bearings came in the early '30s, though babbitt bearings continued to be used in large trucks and diesels for quite some time.

One of the big differences between crankshaft bearings in cars and axle bushings/bearings in slot cars is that the former have to deal with much more heat as well as a significant amount of particulate matter in the oil from other parts of the motor (the combustion process primarily). One very desirable characteristic in IC engine bearings is imbedibility; the bearing needs to be soft enough to allow particulates to imbed into the material itself, rather than to be trapped between the bearing and shaft to cause scoring of the journal.

The primary purpose of pressurized oil feed to the crank bearings is to remove heat. This is not something we have to deal with in slot cars.

Norman, the earliest Model T Fords used ball bearings for wheel bearings, but within a few years Ford changed them to roller bearings. While roller elements bearings do handle side loads better than ball bearings, I doubt that the forces involved in slot car racing would be beyond the capabilities of quality ball bearings in the sizes we use. It would seem to me that we dealing with no more than a few pounds of side load, at worst, whereas in a 1:1 cars the loadings would be far higher.

FWIW, ball and roller bearings were often used in high performance IC engines in the past, but AFAIK they're rarely utilized these days. Roller element bearings on crankshafts and rods require all kind of machinations: built-up cranks (Bugatti and Porsche/Hirth for example), split bearings, etc. One problem with roller element bearings on cranks and rods is that they don't handle shock loads very well and that's exactly what they get when cylinders fire. It is well known that lugging an old car engine with roller element crank bearings is a good way to damage them.

As a final comment in this long post, I find it amusing that so many seem to feel that ball axles bearings are superior, when someone like Ron Hershman (whose success in slot racing is unquestionable) says he doesn't use them because he can't see any difference between good bushings and bearings.

[Rick]

Steve,

You are correct that comparing a crankshaft to an axle oilite is apples and oranges. Cranks run in a pressurized system and run in a coating of oil and have almost zero friction loss because they never touch the bearings.

The question in slot cars is does a bearing make the car faster? We are looking for a tenth of a second. Will a bearing be faster than a well-aligned oilite? Try this sometime and see your results, drill a very small hole in oilite from the top to the ID and oil it there, the oil will have a quasi-reservoir, when you rev the motor up, you can watch the oil disappear from the hole and when you stop, the oil will chase back into the hole, for a little bit, anyway.

IMO the chief difference between the two in maintenance. Oilites need changing more frequently than bearings. As far as lap times, I don't think you will find an tenth of a second in BBs, but it makes you feel it's better. I would also state that the cheap axle bearing don't last very well, compared to the quality ones being sold. VBX bearings are almost as cheap as oilites but are rated Class 1, while GRW are rated Class 7, but they also cost about five times more?

Sure, the winners cars a lot of the time have BBs in them, but they also have a great car in every other respect, too. Perfect guide height, all hinges work as designed, etc., etc., etc. If anyone thinks the winners are winning because they use BBs, I would think they are grossly mistaken. The same drivers and cars would be winning and making the same lap times with bushings.

As Joel once stated, there is no lightning in a bottle. TonyP is very modest but I have raced with him and saw him perform. His cars are the best on the track, he never comes out of the slot, and is steady as they come. The same can be said for Hershman, Tom L, etc.

It's not their BBs that put them where they finish... It's the driver more than anything else.

[Cheater]

... drill a very small hole in oilite from the top to the ID and oil it there, the oil will have a quasi-reservoir, when you rev the motor up, you can watch the oil disappear from the hole and when you stop, the oil will chase back into the hole, for a little bit, anyway.

LOL!!! Years ago, Rick, I did exactly that, using a tiny hole to meter the oil into the bushing and then an enlarged hole above that to form a reservoir into which was inserted a bit of twisted cotton thread, like the cotton waste used in a plain-bearing railroad truck's bearing box.

Lots of fun to play with, but I quickly realized it made no difference whatsoever... especially considering that the volume of oil in the bearing matrix itself was probably larger than in my drilled reservoir.

As I mentioned, I no longer use oilites but here's a little trick for those of you who do. The quality of the oil used to "fill" oilites at time of manufacture is usually not very high. You can replace it with good synthetic oil a couple of ways. Soak your oilites in lacquer thinner to remove the old oil then heat them for a few seconds on the tip of a clean soldering iron before dropping them into a small container of good oil. You can skip the soaking if you want and just boil the "bad" oil out on the iron tip if you want, but I preferred to soak first when I was using this technique.

[Prof. Fate]

Hi,

Grin. I love it when we talk dirty like this!

I use Mobil 1 zero weight.

Back to retro. Tubing was not universal in the '66-68 period. The Russkit bracket was designed for it. And the thing was popular in SoCal mostly. Personally, I used this AND the Du-Bro bracket. The first time I saw the tubing idea was from Jim Russell directly. In '63 in correspondence, he said "just try it, you will be amazed at how well it works. It works, he said, because the extra surface area spreads the drag around".

And it does work, but pretty much, you replace it every race. Well, at least I do. Side bar, Duffy, Rick and I often get obsessive about tolerances in these things, and tubing has tolerance issues.

In wire Jail Door frames where you have multiple rods soldered to the tube it gets tedious to replace the tube regularly.

Most of my surviving period chassis use bushings or bearings because, surviving means I have kept running them, and it takes moments to pull a bushing, and bearings don't usually wear out any time if maintained.

To ME, I have one other thesis.

1) rules are written out of fear

2) rules often ban bearings to hold costs down.
a) because everyone will use bearings if allowed raising costs.

3) THEREFORE, bearings are better; if not, no one would bother and cost would not be the issue!

Fate

[Steve Deiters]

...because the extra surface area spreads the drag around.

In a bushing set-up, whether it is tubing or oilites, you want to strive to minimize the amount of area to reduce the parasitic friction loss to the lowest point possible. Might explain one of the reason tubing bushings weren't around for long back in the bad old days. Not sure what Jim was thinking of on that one.

[tonyp]

Remember this is the era where they thought tubing gave better brakes and Gene Hustings in one of the R&C reports suggested running the Cox gears set tight if you wanted more brakes.

It was an innocent era. All was new... They were inventing the technology as they went along...

[Zippity]

To ME, I have one other thesis.

1) rules are written out of fear

2) rules often ban bearings to hold costs down.
a) because everyone will use bearings if allowed raising costs.

3) THEREFORE, bearings are better; if not, no one would bother and cost would not be the issue!

That was exactly the point I was making in Post #23.

[Nick D]

I would tend to go with BBs generally. BBs have some give which does come in handy when an excessive hit tweaks the rear bracket. Oilites/bushings can seize up, but BBs will keep you running.

Enough said.

[Pablo]

I'm a bushing guy, but only Slick 7s... NOT cheap oilites.
I spend time ensuring the bushings are aligned precisely and installed securely, then face them with a diamond tool.
The axle will drop right through vertically, and balance itself with a gear on it.

I've used BBs in my retros, but have stopped.
I have yet to wear out a pair of S7 bushings.
I don't use any secret oil, just Liquid Bearings or Trinity Purple. Sometimes I'm lazy and only oil twice in a race.
I've never stripped a gear, either.

I agree with the theory that a BB will take a hit and keep on turning better than a bushing, but that's why I build a well-braced rear end.
I have never seen a S7 bind up.

Oilites are for rental cars.

[Cheater]

You tell 'em, Pablo! LOL!!!!

[The Bugman]

So whats the difference about Slick 7 bushings and brand-x oilites?

[Cheater]

Oscar,

Oilites are made from compressed bronze powder mixed with a plastic powder (18% of the latter IIRC) and once the powder mixture is formed into a solid under heat and pressure, the oilite is baked to evaporate the plastic powder from the solid. This leaves voids in the metal matrix and oil is then "pushed" into these voids using vacuum.

The Slick 7 bushings are machined from a particular grade of "bearing" bronze that works really well as a bushing. The Slick 7 axle bushings are IMO made to a much more accurate tolerance and are extremely consistent in dimensions, unlike most of the oilites I've used in the past.

Get your hands on a sample of each type and inspect them under magnification. You'll see the difference.

[idare2bdul]

I've bound up a Slick7 bushing but it was from stupidity, they were new and I forgot to oil them. Other than that, no problems. I use the Slick7 oil, it works fine.

[68Caddy]

As you know or some of you, I got into the C4C program so I have a new car, I will take it in and ask them to replace all the ball bearings to bushings,
what do you think?
It took me along time to figure this one out but I did it finally.
Choices are so hard for me.


Nesta

[Mopower71]

Nesta,
Just give me your new vehicle.
I'll take care of the bearings for you.

Better than what the dealer did to your old vehicle.

[Mopower71]

What did that have to do about ball bearings or bushings in a slot car?

[Zippity]

Absolutely freakin' nothing - but that is par for the course