Carb rubbers

[AshimotoK0]

 Quote "Forgive me if I am out of order and missed the point but I would buy new rubbers if I were you.😉
  Nige. Ps, and good luck"

Beginning to think you are right Nige .. The other thing is the fragility of the alloy carb mounting plate on the K0   (don't ask me how I know this ask the welder I know    )  I would still like to know if the softening process made them go porous though or the other path of the leakage.

Ash

[UK Pete]

Surely they would never be porus enough to let that much air through, the correct f2 clamp is crucial to correct sealing in my opinion
pete

[Lobo]

I'd have to agree with you here Pete; the airflow volume would barely be dented by a little porosity?
Poor clamps / new splits .... more believable.

Any mileage Roy, in pressurising the Airbox (Hoover outlet) and then painting a soapy solution abouts the rubbers to look for leaks?

Simon

[AshimotoK0]

I'd have to agree with you here Pete; the airflow volume would barely be dented by a little porosity?
Poor clamps / new splits .... more believable.

Any mileage Roy, in pressurising the Airbox (Hoover outlet) and then painting a soapy solution abouts the rubbers to look for leaks?

Simon

When I get back to work Simon I will do some testing and plot the air decay after pressurising. There is a rubber property in the 'Industry'  called compression set (CS) . I suspect it may be that the softened nitrile may not have the same CS properties, although the recovery when compressed looked OK to me. Once I have done some tests and consulted the 'oracle' guy, who has worked in the rubber processing industry for almost 40 years, I will post on the US site because they have done loads of softening with essential oils, and we can compare notes.

http://en.wikipedia.org/wiki/Compression_set

One thing I did notice with Roy's parts was that initially there were a few fine threads of rubber came off,  which I assumed was moulding 'flash' but perhaps if the rubbers are removed when cold from the bike, then tearing of the surface layer could occur. I never noticed this on the K0 I softened in 2010.

I will also ask DS if he has any technical info on the pattern ones he sells. I suppose it's guys like Roy who have the biggest problem because the ones for the F2/K7 are mega expensive.

[royhall]

Thanks for all your interest guys, was beginning to get demotivated with this.

Am off work today so going to take the carbs off yet again and have a really close (magnifying glass) look at this. Am wondering if the rubbers were just too hard before they were softened up. Have got a used set on the way from DK for £26 so I have a comparison. I did notice before fitting the rubbers that the engine side is about 50% thicker than the carb side, and was a fair bit harder. Maybe due to the extra thickness they haven't softened as much on that side. Will know better this afternoon after I pull them again. Will report back.

On another note. My other F2 is fitted with replica rubbers from the USA that are also leaking now. Looking online a great many people are having problems with these, most with air leaks they cannot get rid of.  They look okay, but they are very soft and have a shiny finish. Don't think they are made from the correct material. There are some reports that at about a thousand miles these rubbers go rock hard, and one guy reports having a carb actually detach (snapped off rubber) whilst riding. Got these from Vintage CB750, so if anyones tempted to order these DONT. £136 wasted me thinks.

Further thrilling instalments to come. Watch this space.

[AshimotoK0]

Know what you mean Roy about getting despondent but we need to get all of our facts. I can easily get the polymer type of anything done at Hull Uni. All I would need is a sliver of the polymer from the aftermarket ones, from a non critical area and he could tell us if the material is fit for purpose or not. Then we can join forces with the USA guys and complain as a united force. If DS cannot tell me that the pattern ones he is selling are  correct with data from the supplier to back it up , I am going to suggest he donates one for me to test out. He should be agreeable as he has a  degree in Chemistry, I think, so he should appreciate our concerns.

I have another friend who runs a rubber moulding company in Hull (and a keen biker) who could mould parts in the correct material (i.e. nitrile Rubber) but, as always, it's the tooling costs that kills it. He worked with myself (and the Chemist) at Fenner PLC in Hull yonks ago and they made parts for Jaguar /Rover/Delphi and Mitsubishi/Volvo plus others, so he knows what he is talking about.
I am no expert on Rubber but as I remember the Key properties are:-  1) Correct Polymer type (including any fillers , 2) IRHD Harness,  3) Solvent / chemical resistance 4) Compression Set, 5) Resistance to ozone cracking 9hence black colour) ,  6) Temperature resistance.

The most highly specced polymer parts I have found in Honda's are the little D shaped things that cushion the bottom of the cam chain tensioner on the CB250/350 K's. They are a dark blue colour which probably means they are made of a fluorocarbon material (like Viton). They are quite soft but never seen one that's hardened up.

Ash

[royhall]

Should be able to scalpel off a tiny slither of rubber for you Ash if that's all you need, will have a go tomorrow.

Progress with the F2, it appears its leaking at the head side of the rubbers only. Carb side seems good. Have re-tightened the clamps as much as they would go then ran the engine until it was all as hot as possible. And Bingo, got another turn on the screws. Repeated this a couple of times during the afternoon and have now got it 99% or so leak free. When I test it with WD40 the engine does not react, but I get a slight reaction with carb cleaner as its more volatile. Bike is running okay though and ticks over okay but at 1200 rpm not 950.

Going to leave it at that now and commission it for the road and use it for a while. Never know I may get a bit more on the clamps yet that may get it leak free.

Will post some pictures when its all back together and the small teething troubles are ironed out.

Thanks all.

[UK Pete]

I have a Nos Honda set of rubbers which i was going to sell but reading through this thread i think i should keep them as i have 3 bikes with f2 engines
pete

[royhall]

If you change your mind Pete, can I have first dibs?

[Sparrow1]

I'm relieved we are looking more closely at air leaks.😳 although I could be wrong of course.
   Bear in mind that the hose clips supplied by Silver and others (from a realiable source) may a little too big and one shouldn't really be down to the last turn on those clips. You should have a least further 5/6 turns left. How do you know it's at the right tension when fully screwed in? I have learn't from this - air leaks are the scourge of a smooth running engine.
   I really hope you are now heading in the right direction. Good luck.

   Nige. Ps, as I said earlier, the Dave Silver rubbers (and airfbox ones) are working perfectly. If I have any rough running or incresing tick over or reluctant to return to tick over I immeadiatly focus my attention to those rubbers! I re tentision/tighten those clips backed up with carb cleaner leak testing, providing that doesn't damage the engine paint! Thread Locking those screws is not a bad idea..

[AshimotoK0]

Emailed this to DS:-

Hello David,

In 2010 I came up with a method of re-softening carb. inlet rubbers for the CB750K0 (no pattern parts were around then). This is a chemical used in the rubber processing industry and not the 'essential oil 'wintergreeen' treatment used by members of the USA SOHC forum.

To this day my sample retains its softness and compliance but has never been fitted to an engine. There was no significant swelling due to the treatment.

However, I softened a set of K7/F2 750 carb inlet ones for an SOHC.co.uk forum member and he is reporting inlet leaks so I am not sure on the 'Compression Set' properties on the treated rubber (the CB750K7/F2 ones are really expensive and as far as I know not reproduced as aftermarket parts).

However a few forum members have purchased aftermarket inlet rubbers and report similar leaks shortly after fitting, which worries us a little about fitting aftermarket parts. As I understand these aftermarket parts were sourced from the USA. I know you now sell aftermarket inlet rubbers for some models (including the CB750K0). Do you have any specification details of the rubber used in these please from your supplier ? I had a set of original '69 inlet rubbers analysed in 2010 and they were made of nitrile rubber. The airbox 'rubbers' were a form of polyurethane, borne out by the fact that, in the softening solution they actually hardened more ! If you don't have the technical spec. of the rubber used on the aftermarket parts, I could have these analysed FOC but I would need samples to try, which may be a destructive test, if I need to get a compression set value measured.

I am not a rubber expert but, as I remember,the Key properties physical & chemical properties are :-

1) Correct Polymer type (including any filler)
2) IRHD Harness
3) Solvent / chemical resistance
4) Compression Set
5) Resistance to ozone cracking (hence black colour)
6) Temperature resistance.
7) Swelling after immersion in petrol.

If a manufacturer cannot supply or understand these properties then I would question their integrity on the reproducing of these critical parts.

I am also interested in the type of rubber used on repro. cam chain tensioner parts. As far as I am aware, nobody reproduces primary chain tensioner polymer components for Honda's.

One member has fitted your pattern inlet rubbers ( I think to a 750K0), so that looks promising. What do you fit to your 400/4 resto's?

Hope to see you at Stafford.

Best regards,

Ash.

[Lobo]

Ash... speechless at your tech knowledge. School told me rubber came from trees in Malaysia & signed the topic off there... they woefully let me down!

A big thanks to this thread... my K2 was lately popping at idle... one of those jobs I kept forgetting. Anyways, took a mini socket to all 8 inlet clamps yesterday... every bloody one took a turn or more. Job done... fantastic.

Slight topic drift Ash... but you're the man... storage... better to spray WD40 over the metal parts... or silicon? My bro-in-law telling me WD40 overspray can degrade plastics / rubber, whereas silicone won't. Comments?

Ta,
Simon

[AshimotoK0]

Ash... speechless at your tech knowledge. School told me rubber came from trees in Malaysia & signed the topic off there... they woefully let me down!

A big thanks to this thread... my K2 was lately popping at idle... one of those jobs I kept forgetting. Anyways, took a mini socket to all 8 inlet clamps yesterday... every bloody one took a turn or more. Job done... fantastic.

Slight topic drift Ash... but you're the man... storage... better to spray WD40 over the metal parts... or silicon? My bro-in-law telling me WD40 overspray can degrade plastics / rubber, whereas silicone won't. Comments?

Ta,
Simon

I worked for a large company for yonks before I went self-employed about 18 years ago. After many rounds of re-organisation we were wittled down but we had ended up with a really a good technical  team of engineers / technologists. One was a chemist, myself electronics/physics, a rubber technologist, a mellalugist, an engineering plastics  expert and lots of mech. eng. experts. We have all gone our separate ways now but we still draw on each others specific areas of expertise. Sadly the metallugist is very poorly.
 
I will ask the chemist guy about affect of WD40 overspray on polymer parts.

Ash

[archmill]

Just done my carb rubbers with Wintergreen oil in the slow cooker, 1:50 mix oil and water and cooked them for a couple of hours ( hope she who must be obeyed is not reading this ). Worked a treat.

Archmill

[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