britbrat

Relatively speaking it is, being part of the induction system --- and it actually is partially flooded during start-up. The crankcase of a 4-stroke does not see fuel in any significant quantity -- which is why sealed bearings are necessary -- there is no adequate source of lubrication, other than that encapsulated within the bearing.

canadagoose

My Feedback: (2)

Sealed bearings are not necessary in a 4 cycle. Lubrication to the lower end comes from blow by past the ring and it's end gap. All my 4 cycles have open bearings except the main bearing in my OS 91 Surpass II. These sealed bearings being put in 4 cycles is a fairly new practice.

Sport_Pilot

Sealed bearings have lip seals, else they are shielded. The grease turns to a liquid, about the same viscosity as the engine oil when cold. The four cycle engines have to hold up to a mixture of fuel and oil, that mix includes methanol and nitro.

RTD

Thank you all for your input. I've learned a good lesson about bearing preparation and installation. I'll install some new bearings and follow the advice given (oven heat the engine case, don't wash the bearings, and don't freeze the bearings). I did enjoy the banter WRT sealed / shielded / 2 cycle / 4 cycle applications. Thanks again

Flyboy Dave

My Feedback: (21)

The front bearing is never a problem, you can bump it in/out without heat
or freezing. If you freeze the rear bearing to make it easier to install
just remember to use some heat from the heat gun, or a hair dryer to
dry up any condensation on the bearing after it is installed. Blow in through
the rear of the engine with the back-plate still off, and dry-up the bearing
real good. Then apply some oil to the bearing....it's ready for action.

Most of the time, if the case was heated before the bearing was installed
the heat will transfer to the bearing and it will not make condensation.

However, you can't count on it (as you found out) so it's better to blow in
the hot air and make sure the bearing doesn't get corroded from water. []

FBD.

Flypaper 2

Bearings can be bought as double shield, single shield and no shield. Same with seals. No need to heat or cool anything to install. It's not done at the factory. No need to remove the grease. Haven't seen sealed brgs in either two stroke or four stroke. no need for them. Four strokes, as well as two strokes have positive crankcase pressure. It's used to pump oil through the rear brg, through the front case and through the front brg, and to oil the gear train on four strokes. Before installing the brgs., oil the case where the brgs fit. Any oil will do. Dry fit is harder on things. Use the crankshaft as a puller. Slide the rear brg. on the crank. Slide the crank into the case. Slide the front brg on the crank. Put a washer on the crank with a close fit . the outside dia. needs to be slightly smaller than the OD. of the brg. Put the propnut on and pull the brgs together as far as the thread allows. take the nut off ond put an oversize nut, or the prop on to act as a spacer and pull the brgs together till they hit bottom. Good to go.

Sport_Pilot

Flypaper,
It is easier on most people and less strain on the case to heat the case and cool or freeze the bearings and just place the cold bearing in the hot case. As far as four strokes having sealed bearings read the information from the OS web site.

http://www.osengines.com/engines/osmg0890.html

BarracudaHockey

My Feedback: (11)

Thats because its done with a perfectly aligned bearing press. For the rest of us, heating makes life easier.

Flyboy Dave

My Feedback: (21)

True....I like the easy way myself. Heat the case, chill the bearing, and push it home
by hand....no pulling or hammering required. Install the bearing dry. If you oil the
bearing or the case, the baked in oil can come back to haunt you the next time
to try to remove it. Notice the factory doesn't lube the bearing to install it....

....neither do I.

FBD.

Flypaper 2

Sport Pilot:
That's something new for OS, otherwise it wouldn't have been advertised as such.
Baracuda :
Can't get any better alignment than the crank pulling the bearing in.
Flyboy Dave:
No worse than having the aluminum corrode between the case and the brg
There are as many ways of doing things as there are people doing it. These are my ways of doing things after a number of yrs. of experience running a small engine shop for 35 yrs. plus many of the club engines.

Flyboy Dave

My Feedback: (21)

....fair enough Flypaper 2, you pull 'em....I'll push 'em.

FBD.

Flypaper 2

LOL Great stuff Dave

Sport_Pilot

<i>No worse than having the aluminum corrode between the case and the brg</i>

While there is a problem with aluminum corroding when in contact with dissimilar metals, the aluminums used for casting are assumed to be incontact with high quality steel and alloyed to resist corrosion when in contact with steel. Though there may be a few low quality brands or new manufactures who have not caught on to this.

NM2K

My Feedback: (14)

My old Enya four-strokes use open ball bearings. Those bearings last for years and years of flying.

Motorboy

Sealed against corrocion, but "prevent" to be lubricated of oil from fuel and after-run oil can not keep sealed bearing free for corrosion if the inside of bearing are allready rusted.. bad idea

Jens Eirik

Jackster00

Flypaper: When you use the crank to press in the bearing, you're putting all the pressure on the INNER race with the crankshaft flange, thru the balls to the OUTER race with the interference fit of the crankcase, as the crank bears only on that inner race. I agree that the crank is a good guide, but by using the balls on the races to do the job of pressing is not recommended by any bearing manufacturer.
As far as the heat and cold trick, that's a great idea, as long as you get that bearing into the case FAST and started STRAIGHT. You still need a good guide to do this, as many-a-bearing's gotten cocked in the bore about halfway down and stuck there. Then, you've got some REAL troubles!
Jackster

canadagoose

My Feedback: (2)

I am all for sealed bearings as long as the seal will actually provide a good seal for a long time. My Ford F250 has sealed u-joints on the driveshaft that have never been changed from new and have over 300,000 km on them, so i know sealed bearings can last an awfully long time. Sealed bearings i believe will last longer overall than open bearings for the majority of people. I think manufacturers are trying to make their engines more fool or fuel proof by using these bearings.

Motorboy

Ballbearing in the driveshaft and ballbearing in the engine are in difference environment and are not in same time in wear and tear of chemicals, dust, oil, grease, temperature, pressure, vacuum etc, etc...

Jens Eirik

Jackster00

You will find NEEDLE BEARINGS in the U-Joints (driveshaft). They just move a little bit to make up for any mis-alignment between the transmission and the differential, and should last for a very long time.

canadagoose

My Feedback: (2)

That is why i said as long as the seal provides a good seal (meaning from it's environment) And a driveshaft u-joint here lives in a harsh environment with the salt and the sand and dirt they throw on the roads 6-7 months out of the year and temperatures from 100+ degrees to -40.

canadagoose

My Feedback: (2)

Yes they do move less and at a much slower speed than what the balls would in an RC engine, but there is quite a big misalignment in my truck between the tranny and diff so they would be constantly moving back and forth fairly quickly over a short distance. Lets face it though that bearings in vehicles would not stand a chance if not sealed, why shouldn't a sealed bearing in much less harsh environment be any good then? as some are suggesting.

Motorboy

Sometime you find ballbearing in U-joints to example in Mercedes, Toyota, Nissan and mis-alignment in moving forward and backward are taken up of splines at shaft inside the gearbox, sealed bearing are in the house of rubber against vibration and mis-alignment in all ways. I am car mechanic..
Slower speed and low load = long life.

In model engines and other engines with needle- or ballbearing are difference from drive shaft in speed and influence of load of combustion pressure...


Jens Eirik

canadagoose

My Feedback: (2)

This should be good for some opinions.

I think i figured why they don't use sealed bearings in 2 strokes.

1st thing is front bearings don't usually corrode anywhere near as much as rear bearings.

2nd, a 2 stroke would have to have 2 sealed bearings unless only the front bearing is sealed. You wouldn't be able to just use a rear sealed bearing because oil has to be able to go through the rear bearing to lubricate the front one and a passage can't be machined through the crank like a 4 stroke otherwise the crankcase seal would be lost and therefore little or no pumping action of the mixture through the crankcase.

3rd two sealed greased bearings probably would have quite a bit more drag than open bearings running in oil.

4th any dirt injested through the carb and found it's way between the crank and crankshaft housing between the two bearings would stay there because there would be no flushing action as oil made it's way to the front bearing. There's usually always a little oil and fuel that gets flung out of the nose bearing.

Sport_Pilot

In two strokes the fuel goes right into the front bearing between the crankshaft and housing, in fact many engines has a groove which pumps fuel away from the front bearing to prevent too much fuel, which causes fuel to spit out the front. So only a rear bearing is feasible. This method would work to get rid of dust as well. Sealed bearings do have noticeable drag from the seal when new, but becomes negligible after a few hours of use.

I can only think of three reasons not to use them in two strokes, and I don't know if they are valid.

1. The seals may not take the higher revs of a two stroke.

2. The seals will have to be in contact with methanol and nitro on one side and petroleum grease on the other. I don't know it silicon seals would hold up to petroleum grease, but I suspect it will, or a more compatible grease could be used.

3. Cost. Many two stroke customers are more conscious of cost, so this would hurt