Carb rubbers

[AshimotoK0]

Got this back from DS:-

Hi Ash,

A question was raised from a customer some time ago as to whether our aftermarket inlet rubbers were resistant modern fuel. There has been reports that the additives attack rubber components and is generally far more corrosive than the old type leaded petrol. We investigated this matter at the time and was given assurance that the inlet rubber components were made to resist modern fuel. It will be difficult to obtain the precise chemical composition because this is commercially sensitive information, however if anyone does have an issue with a particular inlet set that we supplied, we would send it back for testing. We have to date sold around 600 sets of CB750K0-6 inlet rubbers over a period of 3 years and I am not aware of any complaints.

We have used several sets of aftermarket inlet rubbers on our own CB400F's without any issues.

We use 2-3 different suppliers for tensioner guides and inlet rubbers who mostly manufacturer the same type of components as original equipment for the major brands and are specialists in their fields.

I will be at Stafford-look forward to seeing you there.

Best Regards

David

David Silver Spares LTD
www.davidsilverspares.co.uk

[royhall]

Got my spare set of genuine (used) rubbers from DK today. They are going right back. They are so hard I'm sure they would shatter if I hit then with a hammer. They have gone so hard I cannot squeeze them at all even on the thin end. Incredible!!!

[AshimotoK0]

BTW Roy ...  my 'man' is on with analyzing the rubber from the aftermarket F2 carb rubbers and says he will have an answer tomorrow for us, after I chased him up on it.

also he says it may be beneficial to post cure the 'Reofos 508'  softened ones in  an oven at the maximum temperature they would see in service? Can anyone suggest a temperature or in a position to measure it on a hot engine? I have a digital temperature meter but no running bike to try it on.

Ash

[paul G]

I have had two sets from DSS for the 550 K3 both crap.
Neither fitted correctly when I spoke to them about the first set they said I had ordered the wrong ones so would only sell me the correct ones !! guess what yep they did not fir either ended up with a set off fleabay, guess what they FITTED 

[AshimotoK0]

I have had two sets from DSS for the 550 K3 both crap.
Neither fitted correctly when I spoke to them about the first set they said I had ordered the wrong ones so would only sell me the correct ones !! guess what yep they did not fir either ended up with a set off fleabay, guess what they FITTED 

We need to get evidence from other members that the DS ones are crap as he reckons they are fine (see earlier in this post)  and wasn't prepared to let me have one to analyse to see if the rubber type is up to specification.
So anyone else had problems? they should be made from Nitrile rubber.

Ash

[paul G]

They can have both my sets back for cost price, ever since this I try to get parts from other suppliers and only use them as a last resort.
When I spoke to them re both sets they were not interested so guess what I'm not interested in them.
My I add, I have spent an absolute fortune with them restoring the 400 4 and the 550 K3
Rant nearly over.

[Trigger]

BTW Roy ...  my 'man' is on with analyzing the rubber from the aftermarket F2 carb rubbers and says he will have an answer tomorrow for us, after I chased him up on it.

also he says it may be beneficial to post cure the 'Reofos 508'  softened ones in  an oven at the maximum temperature they would see in service? Can anyone suggest a temperature or in a position to measure it on a hot engine? I have a digital temperature meter but no running bike to try it on.

Ash

The rubbers don't get that hot Ash. I always drop them in boiling water, makes fitting them a lot easier 

[AshimotoK0]

Still waiting on rubber analysis ..it's going to be Tuesday now ..sorry Roy 

[royhall]

Cheers Ash. This should be interesting. Don't forget mine are not DSS items, they don't do 750F2 rubbers. They came from Vintage CB750 in the States.

[UK Pete]

DS does sell aftermarket rubbers for the F2 about 110 a set
pete

[royhall]

Well I never, so he does. When I rang him just before Christmas they said they didn't stock them. The little tinkers.

[AshimotoK0]

Got this back from my mate who analyzed a sliver of the rubber from Roy's Aftermarket F2 carb 'rubbers' sourced in the US. I have asked him if he can explain now why the aftermarket parts leaked in service (possibly inferior compression set properties). The CB750K0 OEM inlet 'rubber' he tested for me in 2010 was also found to be  nitrile rubber.

Roy has the rubbers fitted to his bike now that I softener for him. We have both come to the conclusion that you need to soften in the fluid and THEN  post cure them in an oven afterwards.

"Ashley, your small  black rubber sample is a good quality NBR containing a process oil, nitrile rubber and carbon black with  no extending inorganic fillers. 

I don’t have micro IRHD (micro-hardness meter) but looking at its overall composition, in particular that it has about 150pphR of carbon black, it will be around 80 IRHD. It still has about 40 pphR of plasticizer in it so wouldn’t have thought it had lost much.

So it is a good quality hard NBR   (Nitrile) "

[royhall]

Ash. Is Nitrile rubber good for these parts. Aren't they supposed to be Viton? The ones you softened for me are working pretty good, but cant seam to get rid of the last tiny leak on No.2. Cheers.

[AshimotoK0]

Ash. Is Nitrile rubber good for these parts. Aren't they supposed to be Viton? The ones you softened for me are working pretty good, but cant seam to get rid of the last tiny leak on No.2. Cheers.

Got this back from the guru  Roy. I don't think Viton was ever used...too expensive for such a large part:

"It depends how hot, this bit was NBR, the original may have been HNBR which has higher temperature capability. Also with standard NBR for hot oil a high acrylonitrile polymer is likely to have been chosen, however on balance if this part failed and the OEM was OK then I would guess the OEM was HNBR as oppose the standard NBR"

I replied  ....It would probably see about 150 degrees at the clamping point interface  on its outlet side  and has fuel/air  vapour passing though it , no significant contact with oil..

REPLY:-
150 is far too hot service temp for NBR

IS MY ESTIMATE OF 150 deg C realistic ? ? ? ? ?

[royhall]

What's the outcome then Ash? Are these expensive new rubbers any good. Sounds like they may be made from the wrong rubber. If they are this NBR type, what's the likely outcome from prolonged use. Cheers Roy.