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Open or shielded bearings for a DA 85???

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Open or shielded bearings for a DA 85???

Old 02-02-2009, 05:16 PM
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asmund
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Default Open or shielded bearings for a DA 85???

Hello, I have a friend who has dismantled his DA 85 to change the bearings. Both stock bearings are grease packed and has two sided RS (rubber) shields. I wonder if the grease packed bearings are really neccessarry or it it would be ok to remove the inner shield of the front bearing and leave the back bearing completely open? This way the gas/oil mix will wash/lubricate both bearings and it will give less resistance than bearings packed with grease. This is the most common way of istalling bearings in glow engines and I can`t see that it should be any different in this gas engine, I might be wrong though.
The owner told me that there was alot of grease coming out of the front bearing and making a mess around the hub, this is why he is going to change the bearings.

Any comments are appreciated[8D]
Old 02-02-2009, 07:45 PM
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liquid_TR
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Default RE: Open or shielded bearings for a DA 85???

Im running my 160FX engines on gasoline, and they have their rear bearings open. - but still, in theory a closed bearing with its own grease will usually last alot longer than an open bearing.
Old 02-02-2009, 08:15 PM
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Default RE: Open or shielded bearings for a DA 85???

Leave them sealed. If a lot of grease/oil is coming out of the front bearing the seals are not holding and the bearing needs to be replaced.
Old 02-02-2009, 08:20 PM
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jack1933
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Default RE: Open or shielded bearings for a DA 85???


ORIGINAL: liquid_TR

Im running my 160FX engines on gasoline, and they have their rear bearings open. - but still, in theory a closed bearing with its own grease will usually last alot longer than an open bearing.
Where did you come up with this theory? It is absolutely FALSE. my goodness, where do some of you fellows get these ideas?
Old 02-02-2009, 08:25 PM
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AirWizard
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Default RE: Open or shielded bearings for a DA 85???

Why would you take a chance of destroying a good engine ......This engine should be under warranty and DA has the best customer service of any engine manufacture.
Old 02-02-2009, 08:31 PM
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Default RE: Open or shielded bearings for a DA 85???

He lives in Norway, not worth shipping it back for a simple bearing replacement. A good bearing will "usually" last as long as the rest of the engine.
Old 02-02-2009, 08:55 PM
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jack1933
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Default RE: Open or shielded bearings for a DA 85???


ORIGINAL: AirWizard

Why would you take a chance of destroying a good engine ......This engine should be under warranty and DA has the best customer service of any engine manufacture.
Was not aware I was going to destroy an engine. How did you get this from my post? Fact is, the statement he made about a sealed bearing outlasting a open bearing, just struck me as absurd.
Old 02-02-2009, 09:03 PM
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Default RE: Open or shielded bearings for a DA 85???

You definitely want to use sealed bearings (2RS) in your engine.

They have to hold crankcase pressure otherwise you will get a decrease in performance. For the front bearing, try to get an NTN with the orange seals for the front bearing. The orange seal is a full contact seal and withstands pressures better. The rear bearing has to be a factory bearing as it has a special radius on the inner race. Try and contact a DA dealer in Europe.

Cheers
Alan
Old 02-02-2009, 09:58 PM
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Default RE: Open or shielded bearings for a DA 85???


ORIGINAL: jack1933


ORIGINAL: liquid_TR

Im running my 160FX engines on gasoline, and they have their rear bearings open. - but still, in theory a closed bearing with its own grease will usually last alot longer than an open bearing.
Where did you come up with this theory? It is absolutely FALSE. my goodness, where do some of you fellows get these ideas?
Jack,

I think you rushed through reading the first post. Asmund was simply looking for an opinion on the bearings as to whether the seals were necessary. I think you over reacted as if he was making a statement. I believe his statement about the sealed bearings being better than unsealed was really a veiled question. Can't tell now though because I think he edited his original post.
Old 02-03-2009, 03:32 AM
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asmund
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Default RE: Open or shielded bearings for a DA 85???

Yes, I edited my original post because I was informed that also the rear bearing was sealed at both sides, I overlooked this in my first post. I`m not making any statements here, just asking for opinions regarding what to use for replacement. As always opinions wary some
Regarding the destroying of the engine, I don`t know if this engine is still under warranty or not, what I do know is that it is extremely expensive to ship the engine all the way over to the US to get a simple bearing change. To change the bearings really is a quite simple task so don`t worry about that poor engine beeing destroyed, it will be fine

I just don`t understand why this engine needs both bearings to be stuffed full of grease and sealed when none of my tuned twostroke scooters, mopeds or none of all my glow engines has this kind of bearings.

Well, maybe the safest bet is to just order 2RS bearings and not worry about the extra drag they produce?
Old 02-03-2009, 01:52 PM
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Default RE: Open or shielded bearings for a DA 85???

Couldn't you just order two stock bearings from DA for a direct replacement? Or are you looking for a better bearing?
Old 02-03-2009, 05:41 PM
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Default RE: Open or shielded bearings for a DA 85???

I believe that all roller, ball and needle bearings in an engine should be unsealed and unshielded. The only bearings that should be SEALED are those exposed to the elements. Take a look at an automobile automatic transmission or manual transmission. Caged bearings require minimal lubrication and are happy with the fuel/oil mix. The constant cycling of fresh and used lubricants in and out of caged bearing is a healthy thing. We are only inclined to run 20 - 25% lube in our fuel to accomodate plain bearings and the piston and ring.

Bill

Old 02-03-2009, 06:10 PM
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Default RE: Open or shielded bearings for a DA 85???

There are sealed ball bearing in every alternator in a our cars, they last for a very very long time. Ya gotta at least use good sealed bearing on the output shafts to seal crank case pressure pulses or the engine will not run properly and will spew everywhere.
Old 02-03-2009, 06:22 PM
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Ram Jet
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Default RE: Open or shielded bearings for a DA 85???

Alternator bearings, wheel bearings, and universal joint needle bearings do not have the luxury of fresh and replenished oil/lubricant supply. Your point is wll taken in the case of my new Enya SS.40BB 2 cycle with merely a shielded front main bearing. It's hard for me to understand why there isn't crankcase leakage. I'll know more when I diasseble it. It will not see a drop of fuel until the front main bearing is replaced with a sealed bearing. It will run with an air filter also.

Bill
Old 02-03-2009, 06:48 PM
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Default RE: Open or shielded bearings for a DA 85???


ORIGINAL: Ram Jet

Your point is wll taken in the case of my new Enya SS.40BB 2 cycle with merely a shielded front main bearing. It's hard for me to understand why there isn't crankcase leakage. I'll know more when I diasseble it.
Bill
2 stroke Glo engines get by with only shielded front bearings because of very tight clearances between the crankshaft and the front crankcase. Some of lesser quality do leak from the front bearing area causing a constant fuel spray and idle problems due to leakage. Its more common than you might think. Gassers are larger engines and depend more on the bearing seals to prevent crankcase leakage. Many gassers do not have a tight crankshaft to crankcase fit so the only seal can come from the bearing or external seal. I have never measured it but I would guess that larger engines have greater intermal pressures making seals even more important. Other than the front seal, I really have no opinion regarding completely sealed bearings in gassers. Seems like more are being used these days though. MVVS / Evolution even has a grease zert near the front bearing on a few of their newer engines.
Old 02-03-2009, 06:54 PM
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Default RE: Open or shielded bearings for a DA 85???

Does the DA rely on bearing seals for sealing the crankcase? I'm pretty sure it uses a crankcase seal.
Old 02-03-2009, 06:56 PM
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Default RE: Open or shielded bearings for a DA 85???

To answer the question in post one, Yes you can use a open bearing on the inside and a one sided sealed bearing on the outside but you will lose performance.

The only reason most high performance RC engines have two sided sealed bearing is to help stuff the crankcase.

Fox Gas engines still use open bearings on the inside and one sided sealed bearing on the outside and most Sack's Dolmar type engines also.

Milton
Old 02-03-2009, 08:21 PM
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Default RE: Open or shielded bearings for a DA 85???

Why was the question not put to DA? They are very good at taking care of their customers and typically respond quickly to e-mails.
Old 02-03-2009, 08:39 PM
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Default RE: Open or shielded bearings for a DA 85???

And miss out reading all this........no way
Old 02-03-2009, 08:55 PM
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Default RE: Open or shielded bearings for a DA 85???

just a thought. It seems that a two sided sealed bearing lubed with (viscous grease?) at manufacture would be a greater perfomance compromise than a one sided sealed bearing running on thinned crankcase fuel/oil.

Bill
Old 02-03-2009, 08:59 PM
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Default RE: Open or shielded bearings for a DA 85???

A seal or sealed bearing accomplish the same thing.

Bill
Old 02-03-2009, 09:02 PM
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Default RE: Open or shielded bearings for a DA 85???

That's interesting stuff and makes sense. Thank you.

Bill
Old 02-03-2009, 09:29 PM
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Default RE: Open or shielded bearings for a DA 85???


ORIGINAL: Ram Jet

A seal or sealed bearing accomplish the same thing.

Bill
Do you have an engineering reference for this? I've never seen it done that way. When you need to keep oil in, or a crankcase pressurized, you use a shaft seal. A sealed bearing will not hold pressure.
Old 02-03-2009, 09:47 PM
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Default RE: Open or shielded bearings for a DA 85???

I may have to stand corrected here. I have worked on many different two cycle engines. One I know of relied upon the oil on it's plain main bearings for a seal, another relied upon a separate seal over the caged needle bearing main bearings. I have to concede that I am not sure if the seal on a sealed bearings races would be an effective crankcase seal on a two cycle engine. The seal on a bearing my just protect the bearing from contamination but may not be an effective pressure seal. You know what they say about the word assume.

Bill
Old 02-03-2009, 10:38 PM
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Default RE: Open or shielded bearings for a DA 85???

No engineering data for the hard core number types. I wouldn't bother to look it all up and post it anyway. Just pull the sealed bearing out of the front of your engines and run an open one and get back to us. You won't like what you get in several ways.

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