main bearing seal ac generator side of engine - Honda Rebel Forum
 
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post #1 of 5 Old 08-18-2019, 06:16 AM Thread Starter
 
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main bearing seal ac generator side of engine

Has anyone ever seen the main bearing seal on the left side of the engine pop out? I started leaking oil from the gasket line on the left side engine cover, a huge leak. Hauled the bike home and tore it down thinking it was a gasket failure. Gaskets were fine, the vent at the bottom of the cover was where the oil was passing out of the case. The oil was coming from the large seal on the main engine bearing. When I pulled the AC rotor and the starter sprocket I found it loose from the engine case. It appeared unworn as well as the part of the sprocket it ride on. So I pushed it back which took some force so it didn't just fall out because of age.



Has anyone ever seen this happen before and find a good explanation for it?

1995 Honda Nighthawk 250
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post #2 of 5 Old 08-18-2019, 10:30 AM
 
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Yes..
there has been years of discussion as to the cause.. most noted supposition is overfilling oil.
No definitive cause had been nailed down.. Have you emptied the Puke tube in the past?
A restriction in crankcase breather could cause seal blowout as well..
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96 VS800 Intruder (sold 2018 ), 87 CMX250C Rebel,
79 CB400 Hawk (sold 93), 75 CB350 (sold 83), 71 CB350 (stolen 74)
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post #3 of 5 Old 08-18-2019, 12:30 PM Thread Starter
 
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Quote:
Originally Posted by SoakedKarma View Post
Yes..
there has been years of discussion as to the cause.. most noted supposition is overfilling oil.
No definitive cause had been nailed down.. Have you emptied the Puke tube in the past?
A restriction in crankcase breather could cause seal blowout as well..

I love this forum! Good to know I'm not the only one.



Luckily I had only run less than 2 mile when the leak appeared. Will blowing that seal drain the sump?


To your question about the puke tube I run a small filter on that vent, it was soiled with oil but I doubt it would have been sealed enough to pop that seal out. I had to work to get that seal back in.


I also wondered if I had overfilled or had a float bowl leak that filled the sump with gas. The oil did not smell like gas or have low viscosity so I doubt that was the culprit. If I overfilled it couldn't have been by much.


Has anyone established a mean time between failures so I can pop that cover from time to time and inspect? My engine is a 95 with 36,000 miles but I've only owned it since about 32,000 miles.

1995 Honda Nighthawk 250
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post #4 of 5 Old 08-18-2019, 01:20 PM
 
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Take note the crankcase vent has to suck in and exhale approx 250 cc of air for each revolution of crank as both pistons rise and fall together...
I would question any restriction of CC vent tube due to the volume of air that passes..

MTTF ?? many have never had the problem with many more miles..

96 VS800 Intruder (sold 2018 ), 87 CMX250C Rebel,
79 CB400 Hawk (sold 93), 75 CB350 (sold 83), 71 CB350 (stolen 74)
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post #5 of 5 Old 08-19-2019, 08:37 AM
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Over filling and clogged/restricted vent filters cause more seal failure than anything else.

Keepin' all the left over parts. Gonna use 'em to build another bike!

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