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Old 06-16-2009, 06:13 AM   #1
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Default Air leaks in front bearing, normal?

I am in need potentially for a front bearing for a Sportwerks V2 engine. Wanted to confirm it's a 7x19x6? After doing a test for leaks the front bearing shows air escaping. (engine has approximately 2 gallons on it. ) I have another V2 with less than half a gallon and there's quite a bit of moisture around the flywheel as well.

I performed this test on a Novarossi P5X with 3 gallons and a GRP .21 tuned (brand new, never run) and they both show air escaping also from the front bearing. Is this normal or acceptable if the engine runs ok? Or is it necessary to purchase one of the double sealed, ceramic bearings (boca, TKO etc) to prevent this?

Thanks as always.
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Old 06-16-2009, 06:18 AM   #2
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How are you testing these (GRP) if it was never run. Normally when you find theres a leak, Its from oil res coming out of the bearings not just air.
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Old 06-16-2009, 06:22 AM   #3
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I am sealing carb/exhaust with fingers, put soapy water around usual suspect areas that are prone to leak and blow into the fuel line. Air bubbles surface on the front bearing of all engines. The V2 with 1/2 gallon does have quite a bit of moisture around the flywheel/on the pipe however.

So I shouldn't worry about the air escaping, just fuel residue?

Thanks.
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Old 06-16-2009, 06:27 AM   #4
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When things heat up, they expand. Your test results would be a bit different in a running engine. When my front bearing went bad, there was fuel pouring out of it and it was impossible to tune. There was a puddle of fuel under the engine mounts after running it.
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Old 06-16-2009, 06:30 AM   #5
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The front bearings in RC engines are not airtight by design. The front seal on the bearing is more to keep dirt out of the bearing, not air and fuel in the engine. The seal between the crank and the crankcase is mostly accomplished by fuel providing a 'wet seal' between the crank surface and the crankcase itself behind the front bearing when the engine is running and tuned correctly. The fit at that point between the crank and the crankcase is very close and precise. If the tune is too rich, especially on the bottom end, fuel can push out thru the front bearing. If you are pressure testing the engine statically, the front bearing will very rarely show a seal, even in a perfect engine. Sometimes, if you are checking an engine that has been stored with after run in it, it might seal even without running - but not usually. The engine/carb pressure tester I sell has a silicone rubber gasket to seal off the front bearing so the rest of the engine can be checked statically for leaks.

Other 2 stroke engines, like motorcycle and kart engines, use a separate oil seal that are outside of the bearings, and that seal the crankcase directly to the crank surface. There isn't enough room on an RC engine to use this type of seal.
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Old 06-16-2009, 06:31 AM   #6
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Quote:
Originally Posted by Cannondale1974 View Post
I am sealing carb/exhaust with fingers, put soapy water around usual suspect areas that are prone to leak and blow into the fuel line. Air bubbles surface on the front bearing of all engines. The V2 with 1/2 gallon does have quite a bit of moisture around the flywheel/on the pipe however.

So I shouldn't worry about the air escaping, just fuel residue?

Thanks.
Make sure its the bearing and not the carb or a leaky fuel hose. take off the flywheel and see if there is oily dirt build up under, but i would not worry about air.
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Old 06-16-2009, 06:39 AM   #7
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Quote:
Originally Posted by Gary NJ View Post
The front bearings in RC engines are not airtight by design. The front seal on the bearing is more to keep dirt out of the bearing, not air and fuel in the engine. The seal between the crank and the crankcase is mostly accomplished by fuel providing a 'wet seal' between the crank surface and the crankcase itself behind the front bearing when the engine is running and tuned correctly. The fit at that point between the crank and the crankcase is very close and precise. If the tune is too rich, especially on the bottom end, fuel can push out thru the front bearing. If you are pressure testing the engine statically, the front bearing will very rarely show a seal, even in a perfect engine. Sometimes, if you are checking an engine that has been stored with after run in it, it might seal even without running - but not usually. The engine/carb pressure tester I sell has a silicone rubber gasket to seal off the front bearing so the rest of the engine can be checked statically for leaks.

Other 2 stroke engines, like motorcycle and kart engines, use a separate oil seal that are outside of the bearings, and that seal the crankcase directly to the crank surface. There isn't enough room on an RC engine to use this type of seal.
I don't see this engine/carb pressure tester you sell on your website. Kinda interested in it. PM me if you'd like. Thanks.
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