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Author Topic: She's leakin oil in the alternator compartment.  (Read 1077 times)

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vtx4me

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She's leakin oil in the alternator compartment.
« on: July 23, 2009, 10:35:24 am »
I noticed a small leak under the "dynamo" cover on my 1977 CB750F. I pulled the cover off to address a charging problem and noticed a coating of oil throughout the compartment and a small pool of oil at the bottom of the cover. The oil could be leaking past a seal in back of the rotor...which I don't have a removal tool for yet.

Any ideas where this oil could be coming from?
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Offline Duke McDukiedook

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Re: She's leakin oil in the alternator compartment.
« Reply #1 on: July 23, 2009, 10:39:28 am »
The seal in the back of the rotor. I don't think there a lot of seals in that compartment.

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Offline MCRider

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Re: She's leakin oil in the alternator compartment.
« Reply #2 on: July 23, 2009, 10:43:15 am »
Quote from: vtx4me on July 23, 2009, 10:35:24 am
I noticed a small leak under the "dynamo" cover on my 1977 CB750F. I pulled the cover off to address a charging problem and noticed a coating of oil throughout the compartment and a small pool of oil at the bottom of the cover. The oil could be leaking past a seal in back of the rotor...which I don't have a removal tool for yet.

Any ideas where this oil could be coming from?

The 750 naturally carries oil in the alternator. No problem there. If memory serves there is no crank seal on that side, I'll check a microfiche. PS: I checked, don't see a crank seal on the alternator side.

If by leak you mean its leaking on the floor, that's likely just the gasket between the dyno cover and the crankcase. Fairly common.

Put the bike on its centerstand. Prop a sliver of wood under the foorpedal of the centerstand to give it a bias lean away from you so oil drains back into the crankcase from the alternator. Remove the dyno cover and replace the gasket.

PS I just reread your post and see you already have the cover off. All's well to reinstall. Be sure that gasket is in good shape as it has a job to do.
« Last Edit: July 23, 2009, 10:47:49 am by MCRider »
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Ron
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vtx4me

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Re: She's leakin oil in the alternator compartment.
« Reply #3 on: July 23, 2009, 10:58:42 am »
Man, that was quick! Thanks for the help...and the quick response.
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Offline MCRider

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Re: She's leakin oil in the alternator compartment.
« Reply #4 on: July 23, 2009, 11:03:05 am »
Quote from: vtx4me on July 23, 2009, 10:58:42 am
Man, that was quick! Thanks for the help...and the quick response.
Sure.  As I'm thinking about it, the oil is likely there to lube the electric starter gear train and clutch. Other than that it doesn't need the oil. Most other bikes alternators probably run dry, but they don't have their electric starters in with them.

PS: But now I'm thinking of other electric starters that run dry, so I don't know why there is oil in there but there is.
« Last Edit: July 23, 2009, 11:05:22 am by MCRider »
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Offline Don R

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Re: She's leakin oil in the alternator compartment.
« Reply #5 on: July 23, 2009, 04:56:24 pm »
Really? Oil in the dynamo? that would be good news because mine is pouring oil from the cover and a cover seal would be easier to repair than a crank seal.
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Offline MCRider

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Re: She's leakin oil in the alternator compartment.
« Reply #6 on: July 23, 2009, 05:11:49 pm »
Yup that's right. Sometimes you can just tighten the cover and the gasket may seal up.

Otherwise, do the tilt away trick, put a catch pan under it, there won't be much to catch if its tilting away.

Its heavy with the dynamo bolted in, but you can get the old gasket off and new one on without disassembly of anything.

The pin the the starter idler gear spins on may fall off but its easy to slip back in.
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