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Engine basics => Engine set up tips => Topic started by: frank mccune on January 29, 2016, 08:11:56 AM
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Hi All:
I bought a set of bearings for my engine yesterday that were shielded. The original bearings were the open type and the chap at the bearing supply house told me that the shielded bearings were lubricated with grease for life. He suggested that if I did not like the shields, I could pry them off and run the bearings as a standard bearing.
What should I do: Run the bearings as shielded or remove the shields. Oh yes, all that he had in that size were stainless steel.
How is the best way to remove the shields?
Tia,
Frank McCune
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I've pryed metal and plastic shields off before and they don't impress me that grease will stay contained in the long term on a 12k rpm glow engine...but I've never run full shields on glow engines either. It reminds me of the sealed bearing (intermediate shaft bearing) problem on the Porsche Boxsters...the grease works its way out and trashes the engine.
One of my engines (RJL K61) has the front bearing shielded but only on one side (the prop side) to keep dirt out and open on the back for lube. I saw no difference between that one and my others with non shielded bearings. If memory is right, Boca had instructions that say to take the shields out on a some rc engines but I haven't looked lately to see if that is still the case.
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Bearings with grease are sealed bearings and I believe there's at least one 4 stroke that uses them for the main bearing. Sheilded bearings usually have a metal shield on both sides but there's a small gap near the inner race where oil can flow through. IOW they're not sealed. Some engines use a shielded front bearing but others use an unshielded bearing, kind of depends on whether the prop driver wraps around the front of the crankcase like the ST does to help keep out dirt. I've used a sealed bearing as a front bearing to cure a massive fuel leak but removed one rubber seal and washed out all the grease first.
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One of my engines (RJL K61) has the front bearing shielded but only on one side (the prop side) to keep dirt out and open on the back for lube. I saw no difference between that one and my others with non shielded bearings. If memory is right, Boca had instructions that say to take the shields out on a some rc engines but I haven't looked lately to see if that is still the case.
That's the way I run them too. Boca still says the same for most types of their bearings. I recommend reading up on their tips. Here's a link:
http://www.bocabearings.com/bearing-tips-advice.aspx
I think their least expensive bearings are better than the OEM parts. They have great customer service too.
Rusty
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I would say that there are three basic options: Open bearings, shielded bearings and sealed bearings. I would prefer shielded (that usually means on one side only), but have used a sealed bearing with one seal removed. I'd only use an "open" bearing for the main bearing, and a shielded or (one side) sealed bearing for the front. I can't recall if I hosed out the grease when I used the sealed bearing or not. It would probably be a good idea to remove it. A good blasting of WD-40 or carby cleaner should do the job. y1 Steve
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Good point on the sealed vs shielded. The RJL K61 I mentioned above actually had a rubber seal, not a metal shield. This engine is a replica of the Kraft 61, which also had the one sided seal on the front bearing. I still have a hard time believing grease will stay contained long term under high rpms and constant fuel flushing. Unfortunately the Kraft version died from the rear bearing exploding.
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The OS Max-H 40 I changed bearings on recently had the front bearing installed with the shield on the aft side and the front open! That bearing was actually OK when it was cleaned up. The rear bearing, unshielded, wasn't in very good shape though.
I followed Bocas instructions as the front bearing they supplied was shielded on both sides.
The only sealed bearings I see in the aviation industry are used in applications undergoing very limited rotation, like flight control rod ends.
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I have used a #11 blade to get under the lip and raise the shield enough to get a small pick under it. Be very careful and pay close attention to your knife blade tip as you don't want to break it off. It can easily get lodged in the groove where the shield locks into. Look closely at your knife after the shield is removed to verify it's still there. Ken
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The only sealed bearings I see in the aviation industry are used in applications undergoing very limited rotation, like flight control rod ends.
I'm pretty sure that at the speeds we run things you want continuous fresh oil on the bearings.
'lectric motors may be a different story -- but I claim no expertise there.