Author Topic: CB400F - Petrol Tap O ring - Found a Viton good fit  (Read 1043 times)

Offline 400 Cafe Racer

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CB400F - Petrol Tap O ring - Found a Viton good fit
« on: March 26, 2025, 09:05:31 PM »
Hi Guys,
 
I had a Kit from DS to overhaul the 50 year old petrol tap and also ordered their "O" rings for the seal between the tap body and the rotating handle. It was suggested that 2 would be necessary as 1 would not always seal !!

After carefully cleaning all parts before rebuilding I measured:-
1. the outer seal face of the rotating handle - then the inner seal face of the tap body.
2. the O/D and I/D and cross section of the OLD seal
3. the O/D and I/D and cross section of the NEW seal

Because the sealing faces are the inner and outer circumferences the cross section or thickness is vital to prevent leakage.

Measuring the DS seals they are undersize in thickness to make a seal and actually leave a clearance gap for petrol to leak through, so putting 2 in as was suggested is an incorrect solution.

Having spent a couple of hours on ebay I found a supplier of VITON O rings ( much better for unleaded) with a sizing very close to the original Honda size. Priced at £5.49 for 10) - great price.

Only a single O ring was used, assembled with a very thin smear general purpose grease to ease assembly when dry, and tested overnight with petrol in the tank, before refitting to the bike. It has now stood for 4 days with a 3/4 full tank and the sealing is bone dry.

I hope it may help others on the forum with same problem, I have posted below the name - details - and size Code BS018

This was purchased on their Ebay website

sealsuppliesUK

Imperial Viton Rubber FKM O Ring Seals 1.78mm Cross Section

BS018 - 18.77mm ID x 1.78mm C/S


Regards

Dennis
Retired Automotive Engineer   MIMI, MITRE, DMS, MCMI.

Latest     - 1989 CBR600F1 (FK) PC23
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              - 1939 Velocette GTP 250 twin port Two stroke

1988-91 - Lamborghini Countach QV replica design and
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In 1956 at 12yrs old and dirt tracking
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Online McCabe-Thiele (Ted)

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Re: CB400F - Petrol Tap O ring - Found a Viton good fit
« Reply #1 on: March 26, 2025, 09:09:32 PM »
Great tip I'll save that size for future reference.
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 neat street

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Re: CB400F - Petrol Tap O ring - Found a Viton good fit
« Reply #2 on: March 27, 2025, 07:41:30 AM »
thanks for sharing
CB500 1975
CB750F 1976
KLX250 1983
Lambretta SX200 1979
Mini Mayfair 1984

 

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