Author Topic: Master cylinder cap seal  (Read 884 times)

Offline fogrider

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Master cylinder cap seal
« on: May 13, 2021, 05:11:32 PM »
Now I'm fully on the road, batting around has created small water splashes on the newly painted fuel tank. Thought nothing of it, wiped it off, it happened again even on these  dry days. Suspected fuel cap leak but it did'nt flash off like petrol. Finally realised it was brake fluid that has marked the new paint.
The nylon seal in the cap is breaking up with old age. Just tried CSML, 4  euro for the seal, 23.40 final price delivered !
Bo***ocks to that !
Are they available in the UK anyone ?,  not shown on David Silvers, just a new cap with no seal.
Regards, Terry.

Offline Bryanj

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Re: Master cylinder cap seal
« Reply #1 on: May 13, 2021, 05:56:45 PM »
Take the part number toany honda dealer and see if its available

Offline Seabeowner

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Re: Master cylinder cap seal
« Reply #2 on: May 13, 2021, 07:02:22 PM »
Phil
1971  CB500K0  Candy Jade Green or Candy Gold
1973  CB500K1  Candy Ruby Red
1975  CB550F1   Shiny Orange
1978  CB550K     Excel Black

Offline Bryanj

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Re: Master cylinder cap seal
« Reply #3 on: May 13, 2021, 07:17:49 PM »
As its a superceeded number almost certain to be available fro local dealer with no post cost

Offline fogrider

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Re: Master cylinder cap seal
« Reply #4 on: May 14, 2021, 09:47:09 AM »
Took the advice and tried our local Honda main agent in Hull. One on its' way for just over a fiver including vat.  Why did'nt I think of that ?
Too used to hearing  " obsolete, no longer listed etc. "

I looked at Silvers and other places that had repro caps for sale but they did'nt appear to have the seal in them.
Sorted.

Regards all, Terry.

Offline Bryanj

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Re: Master cylinder cap seal
« Reply #5 on: May 14, 2021, 06:16:50 PM »
Can i say told you so, as long as you give partnumbers and dont tell them how old the bike is most dealers will order parts

Offline fogrider

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Re: Master cylinder cap seal
« Reply #6 on: May 24, 2021, 03:04:44 PM »
The new seal was in a Honda packet , from a Honda main dealer. It does'nt appear to be the right one and is a poor fit. One way up it leaks, the other it does'nt fit properly. The original was a two sided soft lip seal, the shallow lip sealing in the centre of the recess in the cap. The new seal is a hard seal, lip one side only. It is too small in diameter too . As it has the correct part number, I'm wondering if the master cylinder is a wrong look-alike ?

The reservoir is 43mm inside diameter, can someone check the int dia on their their 550f please ?

Regards, Terry.

Offline Seabeowner

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Re: Master cylinder cap seal
« Reply #7 on: May 24, 2021, 07:15:26 PM »
Just measured a couple 43.3 and 43.5.
You do have the diaphragm do you, I think that does most of the sealing?
https://www.cmsnl.com/honda-cb550k-1978-usa_model7222/diaphragm-non-oe-alternative_45520300000p/
Phil
1971  CB500K0  Candy Jade Green or Candy Gold
1973  CB500K1  Candy Ruby Red
1975  CB550F1   Shiny Orange
1978  CB550K     Excel Black

Offline fogrider

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Re: Master cylinder cap seal
« Reply #8 on: May 24, 2021, 08:16:07 PM »
Many thanks for the measurement, looking good there, and yes, the diaphragm is missing !.  It's how it was when I bought it, I assumed it was original and realised it was missing when I had a better study of the parts diagram this afternoon.

That explains  everything. Back to the main agent.....

Regards all, Terry.


Offline kent400

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Re: Master cylinder cap seal
« Reply #9 on: May 25, 2021, 09:43:43 AM »
By some coincidence I had to replace the master cylinder diaphragm on my 400 four early this week as the original had rotted and almost falling apart. I'm assuming that the master cylinder is the same as fitted to the 500 four.

I ordered the genuine diaphragm part number 45521MJ6006 and plate 45520300000, the plate is nothing more than a large plastic washer. The purpose of the washer is to secure the diaphragm in the master cylinder cap as it fits above the threaded portion of the cap.

I'm absolutely sure that the master cylinder and cap are original but the retaining washer although genuine is too small so it won't retain the diaphragm in cap above the threaded part. The original washer can't be used because the lip on the new diaphragm is smaller.

This means that when the cap is removed it leaves diaphragm in the cylinder. I don't think it's important but if it is the only remedy is to make a plastic washer using the old one as a pattern with a smaller hole for the new diaphragm

   

   

Offline fogrider

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Re: Master cylinder cap seal
« Reply #10 on: May 25, 2021, 12:10:28 PM »
Same problem I expect when I receive the new diaphragm in a couple of days. Strange thing is, the original two sided lip seal fitted perfect and there were no leaks, no diaphragm, just that nylon seal. There must have been some sort of revision sometime.
The seal CMSL list looks like my original but shipping etc costs are a no no.
We'll see.
Regards, Terry.

Offline Bryanj

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Re: Master cylinder cap seal
« Reply #11 on: May 25, 2021, 04:23:55 PM »
Diaphragm is supposed to stay in master not cap,plastic washer is so you dont distort the rubber and get a leak

Offline fogrider

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Re: Master cylinder cap seal
« Reply #12 on: May 25, 2021, 07:57:01 PM »
Got it.

 

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