front bearing, zz or rs shield??

front bearing, zz or rs shield??
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front bearing, zz or rs shield?? - 3/17/2006 8:37:53 PM

asmund

Posts: 1909
Joined: 11/20/2005
From: Floroe, NORWAY
Status: offline

Hi I have to replace the bearings in my beloved asp 52 xls. Can I use a frontbearing with zz shield (metal) or must it have rs (rubber) shield. I will keep it open on the inward side of course so it gets lube. A rubber shield will not leak air as easily as a metal one, but metalshield is easier to get here and they give less resistance too.But will the metal provide enough tightness? The stock bearing had rubbershield that had a missing piece of the rubber so an airleak arised and made the engine run like cr.p what do you think guys??

Post #: 1

RE: front bearing, zz or rs shield?? - 3/17/2006 9:12:04 PM

Kweasel

Posts: 1087
Joined: 1/7/2004
From: fort worth, TX, USA
Status: offline

All types have been used by manufacturers. I prefer some kind of shield or seal but I have ran many Webras and old Supertigres with open front bearings and never noticed any tuning or idling difficulties.

(in reply to asmund)

Post #: 2

RE: front bearing, zz or rs shield?? - 3/18/2006 1:33:36 AM

loughbd

Posts: 2111
Joined: 11/29/2003
From: Bremerton, WA, USA
Status: offline

First off, the rubber seal isn't what makes the seal for the front end. It's the fit of the crankshaft in the crankcase. You can remove both shields in the average engine and not notice anything different. Most engines come with the R6Z with just the front shield. Second. Buy the R6ZZ and remove one shield. Be careful you don't screw up the balls or the retainer doing it. Yoou want a small amount of leakage past the front bearing. that's what lubricates it.

If your engines run poorly without the rubber seal, it has a lousy shaft to case fit. Common in inexpensive engines. Think about this. Non ball bearing engines have ZERO shields or seals and they run just fine.

(in reply to asmund)

Post #: 3

RE: front bearing, zz or rs shield?? - 3/18/2006 3:11:15 AM

RaceCity

Posts: 1842
Joined: 7/10/2002
From: NotUpNorth, USA
Status: offline

Kweasel is right, but it seems that ASP (Sanye?) decided it was easier to plug leaks with a sealed bearing rather than machine the crank journal to better tolerances to preclude drawing air through.

Based on what you say (the motor runs poorly without the seal intact) if you were to run a "shielded" (ZZ) bearing you would still draw air around the shield.

Probably best to stick with the RS (sealed) bearing for the replacement.

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Post #: 4

RE: front bearing, zz or rs shield?? - 3/18/2006 4:34:02 AM

Flyboy Dave

Posts: 13467
Joined: 3/20/2002
From: San Bernardino County, CA, USA
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The rubber shielded bearing is always superior to the metal shielded, or
the plain ball bearing. The two stroke engine is designed to have a
sealed crankcase. Normally, a cheap metal shielded bearing will do the
job when the clearances of the crankcase, and the crankshaft are perfect.

The problem arises when things "are not perfect".

This is when the rubber shield (sealed) bearing takes up the slack, and

(watch my lips)

Seals the air leak, and allows the engine to perform correctly.

There is an exception in racing engines, where the front bearing is permitted
to leak....to facilitate lubrication of the front bearing. The reason is....the racing
engines spin so fast....there has to be massive lubrication for the bearing to survive.

FBD.

_____________________________

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A mechanic says..."Oh yeah, watch this".
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Post #: 5

RE: front bearing, zz or rs shield?? - 3/18/2006 4:41:52 AM

Ed Cregger

Posts: 7746
Joined: 1/31/2002
From: Ringgold, GA, USA
Status: offline

quote:

ORIGINAL: asmund

Hi I have to replace the bearings in my beloved asp 52 xls. Can I use a frontbearing with zz shield (metal) or must it have rs (rubber) shield. I will keep it open on the inward side of course so it gets lube. A rubber shield will not leak air as easily as a metal one, but metalshield is easier to get here and they give less resistance too.But will the metal provide enough tightness? The stock bearing had rubbershield that had a missing piece of the rubber so an airleak arised and made the engine run like cr.p what do you think guys??

-------------------

The crankcase seal is achieved by the combination of crankcase bore diameter, crankshaft diameter and the oil in the fuel that actually forms the seal. Whether a bearing is shielded or not has nothing to do with how your engine tunes, IF the proper dimensions are established at the factory. I can't see how someone using CNC machinery to manufacture engines could not help but achieve the proper dimensions if they paid the least bit of attention to the machining process and programming.

You don't need sealed bearings of any kind. To me, using sealed bearings is why so many engines have bearing failures. When engines came with open front and rear bearings, you seldom had to replace them. Surely, not as frequently as they appear to need replacing today.

Additionally, open bearings usually give you a sign when something is going wrong and seldom fail catastrophically. On the other hand, sealed bearings are forever losing pieces of their shield that muck up the internals of an engine with no warning. I'd rather use open bearings and have a chance of saving my entire engine, thank you. This sealed bearing things is a fad that should quickly disappear. At least with two-stroke engines.

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"Flying models since the Fifties - I'll get the hang of this yet!!!"

(in reply to asmund)

Post #: 6

RE: front bearing, zz or rs shield?? - 3/18/2006 4:48:59 AM

loughbd

Posts: 2111
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From: Bremerton, WA, USA
Status: offline

Funny, ball bearing engines worked perfectly fine for 50 years WITHOUT sealed bearings. ALL engine not just racing engines have to leak a bit for front end lubrication. That from master engine designer and writer Clarence Lee. My old Johnsons, Foxes and Super Tigers had no shields at all and they worked fine with no excessive leaks. Another litle item. The net pressure in a two cycle crankcase is positive so the ONLY draw back to an excessive leaking front end is fuel waste.

(in reply to Flyboy Dave)

Post #: 7

RE: front bearing, zz or rs shield?? - 3/18/2006 5:15:12 AM

Flyboy Dave

Posts: 13467
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: offline

ED.... your statement would be true, if every engine had perfect clearances,
and no wear.

How many times has someone had trouble with an engine, only to find out
the engine has a severe air leak at the front bearing ?

Those who think that seals are unnecessary in two stroke engines don't
really have a grasp on two stroke engine theory.

Our aero-model engines have the luxury of an infinite amount of fuel that
can be dumped into the engine. This overcomes ALL SINS....including front
engine air leaks.

The fact of the matter is....in a sport engine....if there is a massive air
leak from the front bearing....the engine won't run worth a hoot....

....if it will run at all.

FBD.

_____________________________

An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
"Old Age, and Treachery will overcome youth and skill".
Revver Bro #4.

(in reply to Ed Cregger)

Post #: 8

RE: front bearing, zz or rs shield?? - 3/18/2006 5:33:53 AM

Ed Cregger

Posts: 7746
Joined: 1/31/2002
From: Ringgold, GA, USA
Status: offline

quote:

ORIGINAL: Flyboy Dave

ED.... your statement would be true, if every engine had perfect clearances,
and no wear.

How many times has someone had trouble with an engine, only to find out
the engine has a severe air leak at the front bearing ?

Those who think that seals are unnecessary in two stroke engines don't
really have a grasp on two stroke engine theory.

Our aero-model engines have the luxury of an infinite amount of fuel that
can be dumped into the engine. This overcomes ALL SINS....including front
engine air leaks.

The fact of the matter is....in a sport engine....if there is a massive air
leak from the front bearing....the engine won't run worth a hoot....

....if it will run at all.

FBD.

--------------

Model two-stroke glow engines have been produced for half a century without a shielded bearing in the crankcase. They have ran perfectly well, when the tolerance between the crankcase bore and the crankshaft outer diameter are maintained in a proper relationship.

If the engine has a leak at the front of the crankcase, the crankcase needs to be replaced or restored (plating or bushing). That is the correct way to solve the leakage problem. Using shielded bearings to solve such problems is bad engineering and is an attempt to cover up shoddy manufacturing by some manufacturers. shielded bearings can reduce their rejection rate of crankcases/front housings, at the expense of engine longevity when the shield fails and grenades the engine. I'm talking about two-stroke engines. The jury is out for me on four-strokes - for me - temporarily. <G>

Now, if someone was to tell me that their engine is no longer manufactured and there are no spare crankcases, I might be tempted to try a shielded bearing as a last resort.

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Artisan

"Flying models since the Fifties - I'll get the hang of this yet!!!"

(in reply to Flyboy Dave)

Post #: 9

RE: front bearing, zz or rs shield?? - 3/18/2006 8:27:29 AM

asmund

Posts: 1909
Joined: 11/20/2005
From: Floroe, NORWAY
Status: offline

thanks to all. I think you all are right about this. It`s just depends on the engine tolerances what bearings must be used. On my asp I`ll have to have a shielded airtight frontbearing(inside open of course) or my engine will not run. now with a missing piece in the rubbershield it starts and idles well but when I go wot the engine almost quits then full power then almost quits then full........ and so on. It`s just like I was rocking the trottle back and fourth all the time. On the other hand my os engines have metalshields(tighter tolerances in the crank?)

(in reply to Ed Cregger)

Post #: 10

RE: front bearing, zz or rs shield?? - 3/18/2006 12:43:49 PM

jaka

Posts: 4538
Joined: 12/11/2001
From: Upplands Vasby, SWEDEN
Status: offline

Hi!
Just forget about if the bearing has any shield or not ...its not important in a model airplane engine .
What you should be concerd about is bearing quality and play.
Most model engines are supplied with C3 or C4 bearings The C 3-4stands for how much play there is between the balls and the outer/inner bearing surface. C3 and C4 ballbearings have more play than standard ballberaings and as such is more suitable if you want low friction (which is good for our engines ).
The Swiss company WIB makes some very good quality steel ballbearings.
ie. all 40-46 engines on the market use the same rear ballbearing size, 28x15x7mm

Regards!
Jan K
Sweden

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(in reply to asmund)

Post #: 11

RE: front bearing, zz or rs shield?? - 3/18/2006 12:54:01 PM

asmund

Posts: 1909
Joined: 11/20/2005
From: Floroe, NORWAY
Status: offline

So you are saying that the missing piece in my rubber shield had nothing to do with my engine running inconsistable?? If that is the case I`ll have to check my engine for airleaks elswhere. I just assumed that the destroyed shield was the reason my engine suddenly became useless. I`ll check all seals in carb, needle and backplate when I reassemble it again

(in reply to jaka)

Post #: 12

RE: front bearing, zz or rs shield?? - 3/18/2006 12:58:44 PM

speedster 1919

Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline

Rebushing housing is cost prohibative. Magnum's originally had open bearings. Has you bearing been replaced before? Put in the ZZ and leave both shields on for best seal. They are packed with grease and will last a long time. Some lube will get into bearing around metal seal.

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Post #: 13

RE: front bearing, zz or rs shield?? - 3/18/2006 3:18:45 PM

britbrat

Posts: 3299
Joined: 6/15/2004
From: Deep River, ON, CANADA
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