I recently had a front bearing replaced in an Enya 45BB and was surprised when the service tech asked if I wanted to upgrade from a shielded bearing to a sealed bearing. I always thought the front bearings were sealed but found out they are only shielded. My question is - Would an upgrade to a sealed bearing be more advantageous than a shielded bearing for use in the front of our engines?

But if you take away the sealing on the inside and keep it on the outside it must be quite good? No leakage in the front?

Ok, thanks for that clearification! I learn lot here on stunthanger 

I did as Brian on a used K&B .40 I was fixing & reworking for a FF friend. The sealed bearing was the only one I had that fit, and it worked just fine, and probably still is. Since it was flown at the dusty field at Taft, California, I figured it might just be a good thing. I'd probably do it for combat, too.  Steve

I did as Brian on a used K&B .40 I was fixing & reworking for a FF friend. The sealed bearing was the only one I had that fit, and it worked just fine, and probably still is. Since it was flown at the dusty field at Taft, California, I figured it might just be a good thing. I'd probably do it for combat, too.  Steve

I sincerly believe that a shielded bearing with only a shield on the outside would probably be the best configuration for a stunt engine.
Our stunt engines run larger props and are subjected to higher rapid changing loads on the bearings than racing or speed engines and typically run for longer periods of time.  They also decellerate and accellerate much more often.

This scenerio probably requires much better lubrication than a racing engine, and is likely better insurance against wear.
It also insures that lubricant flow will flush out any micro particles that might be a product of wear!

This is just an opinion based on engineering experience with bearings and familiarity with the operating environment we fly in.
There are a lot of things to consider in bearing selection and lubrication and our environment is not a friendly one in any case!

Randy Cuberly

If my memory serves me correctly all you need is the one seal. I think the bearing will have a z after the part number, if it has front and rear seals it will say zz. The seals are easy to remove. Bill

Quick question here, would not a ball race with a true 'seal'  have significant drag?

I have tried a sealed grease free bearing in a rebuilt engine and the crank would not spin freely at all whereas a shielded bearing had almost zero drag and spun up nicely.

Is a sealed bearing OK because the seal frees up rapidly - but if it does then it no longer is a true 'seal.'

The FMV article pertains to Team Race diesels that use a very dry fuel mix and a low percentage of oil on top of that so most things in that engine are just air cooled. Plus the fact that diesels run with a hotter crankcase by virtue of no latent heat of evaporation help from methanol and distortion is a very real problem.
Its hard to say if a stunter treats its front race any worse than a Team race engine but consider that with the very rapid onset ignition found in a model diesel engine the acceleration/deceleration issue is with every power stroke and not just with sporadic manoeuvres.
The savageness of the diesel pulse has made many a glow engines crankshaft suffer from spiral fractures and cranks and bearings must be of a larger size to survive.

Anyway, does a seal have significant drag?

Thanks.

It is certain that life of a stunt bearing is like holiday compared to life of it's team-race cousin.
 Most usual bearing failure in stunt is due to neglected care, nearly allways the failure starts from some sort of corrosion, either corrosion caused by fuel chemistry or fretting corrosion caused by some dried up oil or other foreign particles that cause balls to slide rather than roll. Also the quality of bearings in mass produced engines isn't often ideal. Longevity comes from quality, fits & plays and care. I'd say that stress loads play very little role.
Racing engines break because they are used so close to their limits (except combat engines, they are run also underground). And racing people in general take better care of their engines, dismantling and cleaning them all the time.
So if your bearings keep breaking, usually it's the guy in the mirror to blame.
The engine in picture has over 1500 flights with high stress loads (big 14" prop) and and best fuel economy in universe (75..80ml/6,5min flight), yet zero mechanical problems. Even piston ring is still getting better and better.
Maybe it's because there is a team-race guy behind this consept and its bearing design, mr. M from FMV.

L

It is certain that life of a stunt bearing is like holiday compared to life of it's team-race cousin.
 Most usual bearing failure in stunt is due to neglected care, nearly allways the failure starts from some sort of corrosion, either corrosion caused by fuel chemistry or fretting corrosion caused by some dried up oil or other foreign particles that cause balls to slide rather than roll. Also the quality of bearings in mass produced engines isn't often ideal. Longevity comes from quality, fits & plays and care. I'd say that stress loads play very little role.
Racing engines break because they are used so close to their limits (except combat engines, they are run also underground). And racing people in general take better care of their engines, dismantling and cleaning them all the time.
So if your bearings keep breaking, usually it's the guy in the mirror to blame.
The engine in picture has over 1500 flights with high stress loads (big 14" prop) and and best fuel economy in universe (75..80ml/6,5min flight), yet zero mechanical problems. Even piston ring is still getting better and better.
Maybe it's because there is a team-race guy behind this consept and its bearing design, mr. M from FMV.

L

Yes the compression load on a diesel is much higher than on a glow engine.  However most of that load is carried in the rear bearing (depending on the shaft length it could be as much as 90%).  We were discussing front bearings (read the original message) where prop and accelleration loads are significant on a large propped stunter and lubrication is very little in most circumstances.  
You are of course correct that fit and tolerances of the bearing is very important and I seriously doubt (in fact I know they don't) that most engine manufacturers use high grade bearings, they're simply too expensive.
Stunters are also often flown in far dirtier environments than FAI Team racers.  Stunt engines are often flown on grass circles where dirt and grass particles are ingested...this is one of the most likely threats to the bearings especially the front and is why I mentioned that a lubricant flow through the front bearing and a shield (not a seal) there is desirable.
Also as you mentioned the bearings in Team Race diesels are significantly larger for the engine size than the bearings (especially the front) in most 65+ size stunt engines.  There in spite of the higher pressures the actual loads on the balls and races of the engines are lower.  Also the smaller the balls are, the more likely they are to slide than roll on accelleration...deadly for bearings as you mentioned!

So, basically I do not agree with your premise that a stunt engines bearings have such an easier life than a team race engines bearings, for the reasons mentioned.

Lubrication is even more important in a dirty environment and the difference in bearing sizes defy direct comparison with diesels!

As you obviously know, a typical ball bearing that is twice as large will carry loads more than 6 times greater all other things equal!

Randy Cuberly

Randy and Laurie, this is an apples vs oranges debate.
The only way to determine bearing  life is through failure and determining what is a pass or fail between disciplines varies, as much as the type of usage.

I have a truly radical idea. Your engine is being worked on by a tech. That means a professional. And he specifically referred to one bearing style over another as an upgrade. You might want to acknowledge the obvious and simply go with the suggestion of a fellow who works on engines for a living.

Dan

How about another radical Idea Dan...It's what he had on hand... .

I'm sure either is OK!  Personally I don't like sealed bearings.  And I'm very much a technical person also when it comes to bearings.

I said earlier that I was giving an opinion and that's all it is.  It is however a highly educated opinion!

As a mechanical engineer you get used to being ignored on technical issues! 

Randy Cuberly

On one side the bearing is flush against the round counterbalance end, while on the other side the bearing is flush against the crankcase.

No. On one side, the inner race of baering is flush with the round counterbalance end, while on the other side, the outer race of bearing is flush against the crankcase. So, no problem.

Aki

Yes Aki, I understand and considered the races to be part of the bearings, a matter of definition I guess 

Thank you, Lauri, for the reply. I know you are right about pressure finding its way. Still, it is somewhat difficult for me to see how a rear bearing on a round counterweight crankshaft will run as cool as one on a "normal" counterweight crankshaft. By its very design the roundie restricts the free flow of fuel/oil. For what it's worth, the only rear bearings I had that failed were on ST G21 .35s and Fox CS with roundies, although I'll admit the shape may have had nothing to do with those failures (was running higher rpm on higher nitro, etc.). Best, Chad

well, for what it is worth
here is my 2 cents worth  LOL

When I started to race model boats, I had to change bearings at least 2 -3 times a season due to the type of cages
that were then available. (metal ones)
Then when the new composite caged bearings came to be, started to use those and never looked back.
I asked a friend of mine in Germany that worked at Fafnir bearings about the failures and bearing seals/shields and he said that alot of the failures are due to the harmonic vibrations of the cage material itself as well as a lack of a good oiling of the motor after the last fight for the day.
He also flew FAI pylon and told me that the sealed bearing with the one seal removed on the intake side
of the bearing is the way to go. It receives lube from the incoming fuel mix and does not (if the seal is a good one)
leak out the front end of the motor.
All my CMB marine motors as well as my control line motors )ST, K&B, ASP, ect.) that use bearings all have the composite cages and ALL my
bearing equiped motors have the sealed front bearings in them.
One of the main reasons for the bearing failures on our CL motors that I have seen and have told people about is the LACK of an after run
oil used at the end of the day. Some listen and others I just shake my head at.
When I used to ply FAI patter back in the 90's, I used to used Stainless steel caged bearings and also used a good after run oil every time I flew.
no bearing failures, but on all my motors that are in use, I change bearings out yearly anyways. An ounce of prevention, is worth, well. you know........

I know the above is a bit off topic but if does hit the subject of the front bearing eventually.  LOL