Author Topic: Oil pump oil leak  (Read 255 times)

Offline Dolomite_

  • SOHC Member
  • Posts: 143
    • View Profile
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?

Offline McCabe-Thiele (Ted)

  • Grogu
  • *
  • Posts: 8239
    • View Profile
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) »
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 Bryanj

  • Grogu
  • *
  • Posts: 12183
    • View Profile
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

Offline Dolomite_

  • SOHC Member
  • Posts: 143
    • View Profile
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?

Offline Bryanj

  • Grogu
  • *
  • Posts: 12183
    • View Profile
Re: Oil pump oil leak
« Reply #4 on: March 29, 2026, 08:35:54 PM »
Wouldnt be the first new seal i had leak!

Offline McCabe-Thiele (Ted)

  • Grogu
  • *
  • Posts: 8239
    • View Profile
Re: Oil pump oil leak
« Reply #5 on: March 30, 2026, 08:01:05 AM »
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) »
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

  • 1977 CB550/4 Mongrel Brat. 1974 UK 500/4 K1. Honda CD250u.
  • Grogu
  • *
  • Posts: 8659
    • View Profile
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.
LINK TO MY EBAY PAGE. As many of you know already, I give discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new