Author Topic: CB400F Oil pressure switch slow leak  (Read 323 times)

Offline Alexrayz

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CB400F Oil pressure switch slow leak
« on: April 11, 2024, 06:56:30 AM »
Hello ladies and gents!

A year ago I had a slow oil leak at the oil pressure switch thread.
When running at temp I would lose a drop or two every five to ten minutes.
A degreased the oil pump housing, switch and the threads before putting
yellow loctite (577) on said threads.
It worked for 300km and started leaking again.
So I got a new switch. Turns out the OG one has replacements currently manufactured
and fitted on modern japanese cars. So yeah no need to spend 60€ for a used one on
Ebay as I previously thought.
Fitted said new switch without loctite (Wasnt mentioned in the holy book)
Then I tightened it as much as I could, that is until I got scared to strip something.
The bible does give a torque setting but impossible to fit a torque wrench in there.

3 months have passed with small rides, I washed it thoroughly for the first spring ride.
Still leaking a drop or two.  >:(

Have you fine people run into similar issues?
I would like to read your thoughts and opinions on the matter, maybe make this topic a compendium of OPS issues and fixes, who knows!

Cheers from across the channel! 8)
If it aint broken don't fix it

Offline ka-ja

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Re: CB400F Oil pressure switch slow leak
« Reply #1 on: April 11, 2024, 09:58:30 AM »
strip, clean and try again with a decent sealer, say Hylomar? rolls royce compound.
nice bike,nothing in the bank

Offline Laverda Dave

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Re: CB400F Oil pressure switch slow leak
« Reply #2 on: April 11, 2024, 11:15:11 AM »
Or maybe a couple of turns of the white PTFE tape on the thread (just make sure it is only on the thread and not protruding on the end in case it blocks the oilway to the switch).
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Mikep328

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Re: CB400F Oil pressure switch slow leak
« Reply #3 on: April 11, 2024, 12:25:23 PM »
Is it possible that the pipe thread on the "modern" sender you purchased and the pipe thread on the moto do not match?  There are three or four different specs for "pipe threads."  I have no idea what Honda used in the '70's vs what they may be using now.  But if they don't match that could be a reason for the seep.

Offline McCabe-Thiele (Ted)

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Re: CB400F Oil pressure switch slow leak
« Reply #4 on: April 11, 2024, 12:32:40 PM »
It's been a while since I fitted mine FWIW I assumed they are a taper thread - if it is I would use some yellow grade PTFE tape making sure as has been said that you keep it off the end of the unit as Dave mentions.

White PTFE tap might be okay I have Yellow for when I used to do gas pipe fittings I believe it is more resistant to chemical attack.

When I fitted mine I just made sure the threads were clean and greased then just nipped them up - no tape used. Thinking about it Yellow tape might be too thick.
« Last Edit: April 11, 2024, 01:10:16 PM by McCabe-Thiele (Ted) »
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Online Athame57

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Re: CB400F Oil pressure switch slow leak
« Reply #5 on: April 11, 2024, 12:46:14 PM »
Are you sure the source of this leak isn't actually the seal for the oil pump housing? I'm about to have mine replaced also, it was missing from the seal kit I got for a recent rebuild. Maybe it is a semi-orphaned thing?  ;D
I brake for animals!
1978 CB400F2 called Elen.

Online Bryanj

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Re: CB400F Oil pressure switch slow leak
« Reply #6 on: April 11, 2024, 01:59:58 PM »
Its possible the housing has a small crack due to overtightening the taper thread or it could be the cover plate leaking, nurse julie does O ring kits for the pump

Offline Alexrayz

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Re: CB400F Oil pressure switch slow leak
« Reply #7 on: April 20, 2024, 04:06:56 PM »
Hey everyone,

I haven't taken a look yet, I have been mainly investigating on the web. Will keep you updated

Cheers
If it aint broken don't fix it

 

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