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Author Topic: Oil pump oil leak  (Read 4113 times)

Offline Dolomite_

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Oil pump oil leak
« on: March 29, 2026, 12:14:42 PM »
What I thought might be a leak from the oil pan turned out to be from the oil pump. I've not had a chance to start it up with the chain/sidecover off to see where the leak is coming from but I suspect its from the oil pressure switch. When I stripped it I used Julie's O-ring kit and replaced them all.

Whats the best way to way to help prevent oil seeping up the thread of the oil pressure switch? Would PTFE tape be fine?

If its not the oil pressure switch what would be best to add some more seal protection to the surfaces of the oil pump?
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Offline McCabe-Thiele (Ted)

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Re: Oil pump oil leak
« Reply #1 on: March 29, 2026, 12:20:23 PM »
Did you clean the oil relief valve & check it operation?
Unless it's a new switch it might be leaking at the terminal & oil seeping down, never needed PTFE tape on the threads.
« Last Edit: March 29, 2026, 03:10:36 PM by McCabe-Thiele (Ted) »
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Offline Bryanj

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Re: Oil pump oil leak
« Reply #2 on: March 29, 2026, 02:08:36 PM »
More common is the gearchange shaft seal under the same cover, you can use ptfe tape but it is a tapered thread and should not need it BE CAREFULL as it is tapered doing it too tight can crack the housing of oil pump
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Offline Dolomite_

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Re: Oil pump oil leak
« Reply #3 on: March 29, 2026, 08:34:11 PM »
I rebuilt the engine just under 2 years ago so all the seals are pretty much new.

Ted
Is the oil relief valve in the oil pressure switch?
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Offline Bryanj

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Re: Oil pump oil leak
« Reply #4 on: March 29, 2026, 08:35:54 PM »
Wouldnt be the first new seal i had leak!
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Offline McCabe-Thiele (Ted)

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Re: Oil pump oil leak
« Reply #5 on: March 30, 2026, 08:01:05 AM »
Quote from: Dolomite_ on March 29, 2026, 08:34:11 PM
I rebuilt the engine just under 2 years ago so all the seals are pretty much new.

Ted
Is the oil relief valve in the oil pressure switch?

Iirc it's built into side of the  oil pump, I could be confused with the 500 oil pump.
« Last Edit: March 30, 2026, 08:20:53 AM by McCabe-Thiele (Ted) »
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Honda CB400NA Superdream (current money puddle)
Honda CB500 K1 (second money pit)
https://www.sohc.co.uk/index.php/topic,28541.0.html
Honda CB400 four super sport (first money pit)
Link to my full restoration http://www.sohc.co.uk/index.php/topic,23291.0.html
This is a neat 500 restoration in the USA.
http://forums.sohc4.net/index.php/topic,151576.msg1731556.html#msg1731556

Offline Nurse Julie

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Re: Oil pump oil leak
« Reply #6 on: March 30, 2026, 08:44:48 AM »
The pressure relief valve is in the pump as Ted says.
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Offline Dolomite_

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Re: Oil pump oil leak
« Reply #7 on: April 06, 2026, 09:15:18 PM »
I cleaned the oil from the pump, checked the bolt toque and seals. It all appears fine.

I went out for a ride today and checked when I got back, it's coming from the oil pressure switch. I'm going to check the oil pressure switch is torqued correctly later this week.

Are there any other measures I can take? Or is it a case of replacing the switch and testing it?
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Offline Bryanj

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Re: Oil pump oil leak
« Reply #8 on: April 06, 2026, 09:57:14 PM »
Torque on that part wont work as it is a tapered thread, new switch with a small amout of liquid ptfe or tape and not super tight or you can crack the casing
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