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SOHC.co.uk Forums => Anorak's Corner => Topic started by: AshimotoK0 on February 09, 2024, 09:30:21 AM

Title: CB400F airbox rubber sealant
Post by: AshimotoK0 on February 09, 2024, 09:30:21 AM
Any tips on the type of sealer/mastic to use between the the 400F plastic airbox and the rubber inlets/large oval rubber seal.

In the past I suspect I used this black coloured AS1701 silicone sealant. .. however the tube I have is very old and  has gone solid and it's now £50 a tube.

https://uk.farnell.com/acc-silicones/as1701-310ml/sealant-silicone-neutral-cure/dp/8497524

I found I do have some of this black polyurethane 2-part sealant (out of date but still usable) and I will use this unless anyone can suggest something more suitable.

https://uk.rs-online.com/web/p/potting-compounds/1608497


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Title: Re: CB400F airbox rubber sealant
Post by: McCabe-Thiele (Ted) on February 09, 2024, 09:37:36 AM
Would normal Black Silicone Bathroom Sealant do the trick or does it need to be none hardening?
Easy enough to remove last tube I bought was less than £5.00.
Title: CB400F airbox rubber sealant
Post by: magpie114 on February 09, 2024, 10:38:41 AM
Just done this myself using Threebond black RTV silicone sealant.


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Title: Re: CB400F airbox rubber sealant
Post by: Bryanj on February 09, 2024, 01:13:49 PM
Sikeflex, spelling could well be wrong mate
Title: Re: CB400F airbox rubber sealant
Post by: AshimotoK0 on February 09, 2024, 02:05:39 PM
I went with the polyurethane material in the end. Supposed to be pretty chemical resistant. The Threebond sounds OK though. It's probably close to the stuff I had in my 1st link.

I don't reckon that the original sealant was silicone ... possibly not in use so much then as an adhesive. From memory Hermetite orange RTV came out in the mid 70's ... you know the dreaded stuff that blocked tiny oil feed holes/ galleries when too much was used.
Title: Re: CB400F airbox rubber sealant
Post by: McCabe-Thiele (Ted) on February 09, 2024, 02:17:58 PM
Memories of Brown-Black Wellseal also spring to mind.
Local rumour was it was developed by RR Aero Division.
Title: Re: CB400F airbox rubber sealant
Post by: Moorey on February 09, 2024, 07:17:44 PM


     Black Sikaflex EBT

     Too late i guess.
Title: Re: CB400F airbox rubber sealant
Post by: AshimotoK0 on February 09, 2024, 10:27:38 PM


     Black Sikaflex EBT

     Too late i guess.

Seem that's polyurethane too but one part.
The stuff I used (2-part) seems to have worked really well anyway and is semi-flexible after curing.
Title: Re: CB400F airbox rubber sealant
Post by: Athame57 on February 09, 2024, 10:55:58 PM
I'm not sure I know what is going on here, I've never used a sealant before. Are they not airtight enough on their own or something?
Title: Re: CB400F airbox rubber sealant
Post by: Bryanj on February 10, 2024, 08:03:12 AM
They originaly have some sort of glue/sealant in the groove
Title: Re: CB400F airbox rubber sealant
Post by: Matt_Harrington on February 10, 2024, 08:28:49 AM
I'm not sure I know what is going on here, I've never used a sealant before. Are they not airtight enough on their own or something?

I'm with you on that one!
Title: Re: CB400F airbox rubber sealant
Post by: AshimotoK0 on February 10, 2024, 09:48:05 AM
Yes the original arrangement definitely had so kind of sealant on the rubbers and I don't think they would seal perfectly without it. The carb inlet ones also need to align with the raised dot on the airbox.
Title: Re: CB400F airbox rubber sealant
Post by: AshimotoK0 on February 10, 2024, 01:49:33 PM
Here it is after bonding with the 2-part Polyurethane

Had difficulty fitting the two centre rubbers to the carb intakes, despite  warming up the still fairly pliable rubbers. This is because the plastic collector box housing flexes ...... so came up with this 'tool'  to push from the inside of the air filter frame. Will see how it goes  :)

[attachimg=1]
Title: Re: CB400F airbox rubber sealant
Post by: AshimotoK0 on February 10, 2024, 11:06:54 PM
I'm not sure I know what is going on here, I've never used a sealant before. Are they not airtight enough on their own or something?

I'm with you on that one!

You can see sealant used on this picture of a NOS air-box assembly.


[attachimg=1]

Title: Re: CB400F airbox rubber sealant
Post by: Athame57 on April 04, 2024, 02:50:24 PM
Here it is after bonding with the 2-part Polyurethane

Had difficulty fitting the two centre rubbers to the carb intakes, despite  warming up the still fairly pliable rubbers. This is because the plastic collector box housing flexes ...... so came up with this 'tool'  to push from the inside of the air filter frame. Will see how it goes  :)
How did you get on with the tool you made? Would it make much difference if I invested in a new airbox manifold to replace my 46 year old one? I truly dread doing this job.  ::)
Title: Re: CB400F airbox rubber sealant
Post by: AshimotoK0 on April 04, 2024, 03:34:41 PM
Here it is after bonding with the 2-part Polyurethane

Had difficulty fitting the two centre rubbers to the carb intakes, despite  warming up the still fairly pliable rubbers. This is because the plastic collector box housing flexes ...... so came up with this 'tool'  to push from the inside of the air filter frame. Will see how it goes  :)
How did you get on with the tool you made? Would it make much difference if I invested in a new airbox manifold to replace my 46 year old one? I truly dread doing this job.  ::)

In the end i used a couple of pieces of wood ... plus the main thing is to heat up the rubbers as much as you can off the bike and before fitting ... I used an infra red heater.
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