Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: royhall on January 15, 2015, 04:08:08 PM
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Hi me again, sorry to be a pain. This F2 of mine doesn't want to be finished so it's putting up a fight.
Sorted my other carb problem with some scrounged bits (thanks for the comments).
Now I find the carb rubbers are so hard I cannot get the carbs on. Pushed and wriggled them so hard that at one point I actually lifted the bike off its centre stand, good job I had the front brake taped on. Anyways, before I order an unbelievably expensive new set, is there an easy way of softening them. I know Ash has a method using unobtainable noxious chemicals, but was hoping for an easier technique.
So far I have tried oiling the carbs and rubbers, heating rubbers with the wife's hair dryer (sschh), and brute force, sometimes rubber mallet assisted.
Any help or ideas would be greatly appreciated.
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It's not that it's particularly noxious but only available for Industrial use I thin in largish quantities.
You can also use Wintergreen essential oil mix as per SOHC4 site but can't vouch for it.
Depends how much of a rush you are for them but you could always send me them to soften but I'm really chocker with work at the 'mo so turnaround would be about a week.
Ash
Will have to work on the firm I get the Refos stuff from ...see if they will sell me a load ... but no promises.
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Thanks Ash, time isn't really an issue. To be honest don't really need the bike before the Classic TT. If I could take you up on your kind offer, I shall parcel them up and get them off to you. Could you PM me your address, and let me know the costs so I can reimburse you. Nice one. Cheers.
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Thanks Ash, time isn't really an issue. To be honest don't really need the bike before the Classic TT. If I could take you up on your kind offer, I shall parcel them up and get them off to you. Could you PM me your address, and let me know the costs so I can reimburse you. Nice one. Cheers.
Will PM address .. don't want anything for doing them, I will just bung them in with some I am doing.
Ash
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PM sent
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Cheers Ash got the PM. The job has reduced by 25% as I found a crack in one whilst packing them up. The others look okay so will whizz them off to you in the morning. No rush for them back, whenever you can fit them in. Many thanks.
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Hi Roy,
Received carb rubbers safely yesterday ...so will have a go at them early next week.
Ash
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Ash let me know if you ever manage to get anymore of the solution
pete
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Pete .. I am working on it .. I also need to find all of the rare 'O' rings I bought in bulk for sealing K0 heads/Large oil pump one etc but found the others for oil pump.
I did give some of the softening stuff to ChrisR yonks ago and he said it didn't work but you have to leave it soaking for quite a long time at around 70 °C and it definitely does work. Think Chris said he only tried it in his shed at a fairly low temperature.
Ash
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Thanks Ash. No rush with it.
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http://www.ebay.co.uk/itm/Honda-CB750-K7-intake-rubber-number-2-new-and-unused-/251805836887?pt=UK_Motorcycle_Parts_13&hash=item3aa0cc2657
Also I found one of the larger of the two types myself. Which one is split of the four you sent me...cant see it.
Ash
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I should have made a note of this at my age with my memory lapses. It was definitely the right side of the bike, I think No.3. Its a small split at the top edge, on the engine side. Thanks Ash.
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Had a go at Roy's rubbers tonight ;D Bunged them in a glass dish containing the Reofos 50 for about 5 hours, maintained at 75 deg C in a water bath. Used an old slow cooker to maintain the heat (don't ever accept any invitations down to our place for a casserole! ). Last night "Off down to the pub dear don't turn off anything in the garage" Then she spots where her slow cooker disappeared to .... well I found it in the loft ...unloved for about 15 years !
Because they are relatively rare parts and not mine I don't want to 'overcook' them. Does anyone have a NOS 750K7/F2 one I can compare the hardness with? They are definitely a lot softer now but not sure how far to go . I do have a K7 carb body so I could push them onto that. Is the stub on the F2/K7 head the same as the K0-> K6?
I was going to try to get a bulk amount of the Reofos 50, via my industrial contact and offer it to members here but seems I told you porkies about the toxicity so I have chickened out. Don't want to be responsible for anyone becoming one of Nurse Julies patients !! Magic stuff though.
Link to supplier/safety data sheet .
http://www.greatlakes.com/Industries_We_Serve/Building_and_Construction/Other_Building_Materials/Reofos_50
It states 'Restricted to professional users'.... in the Safety Data Sheet. It's not a known carcinogen or anything like that but still nasty.
BTW There is a guy selling Cyanide copper plating solution in the UK on his website to Joe Public... Scary !! Think he was on Dragon's Den ! http://www.ebay.co.uk/itm/250ml-Copper-Strike-Plating-Silution-/301242031103?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item46236c9bff
Ash
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Ash I have a now set
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Ash I have a now set
Cheers Pete ... OK so I will try to get a method we can both use to compare the deflection at a given compression .. did you mean NOS?
Ash
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Yes nos I have predictave text on
I will be home next week so can sort out then
pete
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Success !!
https://www.youtube.com/watch?v=Y1kVSlLnR8k&feature=youtu.be
Bits of alumium in pics are to raise level of softener ! Old plate is to stop water condensing into the softener bath. Glass vessel in water bath.
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Whats for pudding Ash ;D
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Probably the pudding on the next hospital visit after they have pumped your stomach out.
This is a true story... my mate drank a bottle of the 'Rose wine ' coloured diluted antifree he had left stored in a wine bottle under the kitchen sink. He was gardening and it was hot outside, his wife found it and asked him what it was so he drank a glass of it then realised ! After they pumped him out they gave him whisky as it evidently combines with the the ethylene glycol in the anti-freeze..
He's got a 250 Superdream so you can imagine the type!
Ash
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Having read this post I was dreading trying to put on the carb rubbers today on my rebuild. The rubbers were supplied by David silver and went on with a hard push and wiggle so a very happy chappy now.
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Having read this post I was dreading trying to put on the carb rubbers today on my rebuild. The rubbers were supplied by David silver and went on with a hard push and wiggle so a very happy chappy now.
You won't have any problem with new ones or possibly a bike unused for yonks with low miles. It's the one's like my 750K0 that did 40k miles with all of that heat and fuel exposure that harden up ( cause of many a broken alloy carb. link plate :( ). Evidently, Vic World the sandcast resto guru in California checks the hardness of the airbox-to-carb 'rubbers' on any sandcast/K0 bike he looks at to buy, in order to gauge if the mileage is authentic.
One thing I am experimenting with as we speak in the CB250k ( and 400/4 as I remember) softening, as they have rubber to metal bonds which don't want to be weakened by the softening process. I have painted the interface of metal/rubber with industrial epoxy so that it stops ingress of the softener into the bonding, during the long softening process.
There are a lot of doubters on the other bike forums about my method but all I can say is I softened a rock hard '69K0 inlet rubber 5 years ago and it is still soft but never run yet on the bike. I have a video of before and after will have to put on Youtube. I am also trying to soften the little cover on the CB750 that covers the oil pressure switch. On other forums they bang on about using essential oils and glycerine, which may work too for all I know. However, I tackled the problem scientifically and asked someone who is a qualified industrial chemist and worked in the rubber processing industry for 20+ years and now operates from a university giving advice to industrialists, which he has done for about 18 years ( one of his main areas of work is looking at the crabby materials used in the caravan industry.. anyone who owns a caravan will know the havoc ingress of water into the structure has). We tried several methods whilst I was at his lab doing some other work in 2010 and we came up with the Refos stuff as the best method of softening nitrile rubber.
Having said all of this since 2010 you can now get brand new pattern rubber parts for some bikes at reasonable cost but on the F2/K7 750's you are still talking a lot of money for Honda replacements. Plus some parts like the oil pressure switch on the 750 are rare or unobtanium.
I wouldn't try the softener out on cam chain/primary chain rollers or other internal parts though ( e.g. primary drive cush rubbers).
I have also got some other stuff I want to try for treating the finish on other rubber components ( grommets, fork ear isolators etc) which are still soft but have had ozone exposure and develop a hard surface layer. I have some stuff I resurrected a colour laser printer with by removing the surface layer on it's paper feed rollers with 'rubber roller rejuvenator', so this is what I will try out.
Ash
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Hi All. The carb rubbers shown being softened in Ashley's witches brew pot are off my 750F2. When I sent them to him they were as hard as Bakelite and no way would the carbs go on. As I said earlier in the thread, I actually lifted the bike nearly off its stand trying to get the carbs on without success (didn't do much for my back either).
When they arrived back I gave them a good look over. They are now way softer than they were, and no visible cracks, splits, or surface bubbles nor any other form of reaction damage. They fitted easily one at a time onto the head, then with an almighty heave the carbs popped on (not forgetting to tape the front brakes on first). Not started the engine yet as I'm still waiting and waiting for Lancaster Bronze to send back my rechromed hose clips, but it all looks promising.
Anyway thanks for that Professor Ash saved me a fortune (if there's no air leaks when the engine starts of course). By the way the replacement F2/K7 carb rubbers I bought for my other F2 came from the States but were not genuine Honda just reproductions. And with the cost, P&P, import duty and the Fedex charge they cost £136 and you don't even get new clamp bands with them. Next Honda will be a K series as F2's are just too expensive to restore (if you can get the bits at all).
Will report back when the engine starts. Cheers.
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Sorry for the delay in reporting back. Had to wait 7 weeks for Lancaster Bronze to replate my carb clamps (Jeez). Anyway, there back now and the carbs went onto the softened rubbers a treat. Engine started and no air leaks. Mr Ashley you are a weird and wonderful genius. Cheers all.
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Don't try softening the K0 airbox to carb 'rubbers' . Tried to soften 4 from a '69 K0 and they came out rock hard after a full night's immersion at >70 deg C. Think they are made of Polyurethane not rubber. Good news is that the funny grommet cover thing on 750 Oil pressure switch softens OK. I remember having chemical analysis of the polymer types on K0 carb "rubbers" done in 2010 and was told the K0 airbox 'rubbers' were PU then. Seems that the softener makes them harder !! K0 carb to head 'rubbers' are nitrile rubber, as are later K7/F2 versions, so they are fine.
Ash
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Sorry Ash its all gone pear shaped.
Put the carbs on Tuesday night and started it. Sprayed some carb cleaner around the rubbers and all was well. Not touched it again until today. Tried to balance the carbs with the vacuum gauges today and they were all over the place, couldn't get it to steady out. Tried the carb cleaner again and now got leaks on 1, 3, & 4. Have even tried clear silicone on the rubbers to stop the air leaks but barely helped at all.
Any chance the rubbers have gone porous.
Bit stuck for where to go with this now. May be the final push I need to bin the PD's and convert to F1 carbs.
Anybody any bright ideas to help out as I would like to use the bike sometime this summer ;D
Cheers all.
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Whoops doesn't sound good. I will do some tests on the one I softened in 2010 and report back but sounds like it may be a no no from what you are telling me. If you are having probs this early after fitting them it's going to be false economy in the long run. Did the clamps go slack at all?
Ash
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Cheers Ash.
Have fitted the clamps with cap head screws so I can get a better purchase on them with a long t-bar key. Think they have tightened up okay, but its hard to tell for sure.
Just retested my other F2 that has new pattern part rubbers from Vintage CB750 in the states (at huge cost) and that's leaking as well. So I guess I wont be going down that route again. These rubbers are slowly turning into a bit of a nightmare.
Going to stick with the originals for now, may try a bit of Hondabond. Cant make matters any worse at this point.
Cheers, Roy.
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Give me a bit of time to do some experiments Roy. I will clamp one like yours to a K7 carb body, pressurize it and put a pressure Tx in line and plot the pressure decay plus spray the lot will leak detector.
Anyone know what the DS pattern K0 ones are like or the Cruzinimage ones . Or are they the same?
Ash
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I had huge issues with my K0 carbs regarding air leaks on all four. I could balance all 4 for 10 mins and then they go all pear shaped again. I then ordered 4 new K0 rubbers from Silver and I have never looked back, not withstanding the fact the earlier the 750 carb the less likely it will stay balanced. Even out of balance the bike performs fine, just isn't as sweet. Round about 500 - 1000 miles to stay in balance. I spoke to my chap who does this for me and remembers working on the K0/1/2 carbs back in '69 and on and keeping them in balance after sale new was a nightmare! My carbs are from Mr 750 Carb and completely overhauled hanging part exchanged them. Even then they needed balancing. The 4 way splitter is a pain too, a poor design and Honda quickly changed improved/changed the system. I am envious of the K1 set up, a much better system but, heh, that's first 'edition' bikes for you!
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.
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i wonder if hi melting point grease would help seal them ?
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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
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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
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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
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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.
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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. ;D
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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
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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.
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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
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If you change your mind Pete, can I have first dibs?
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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..
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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.
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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
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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
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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
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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
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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!!!
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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
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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 :)
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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
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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. >:(
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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 ;D ;D
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Still waiting on rubber analysis ..it's going to be Tuesday now ..sorry Roy :-[
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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.
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DS does sell aftermarket rubbers for the F2 about 110 a set
pete
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Well I never, so he does. When I rang him just before Christmas they said they didn't stock them. The little tinkers. ;D ;D
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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) "
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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.
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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 ? ? ? ? ?
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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.
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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.
I will get the original Honda ones re-analysed and report back if they are HNBR or not.