Honda-SOHC

SOHC.co.uk Forums => CB500/550 => Topic started by: florence on March 25, 2020, 05:35:29 PM

Title: Petrol Tank
Post by: florence on March 25, 2020, 05:35:29 PM
Very shocked to find that after 46 year's service the petrol tank has developed a rust hole behind the Honda badge.  I thought I would get the bike going after a winter rest, and given that we can't go anywhere seemed like a good way to spend time.  Does anyone know where I might find a reasonable/useable replacement that won't cost silly money, assuming people are allowed to sell such things at the moment with this crisis and all that.  I have thought about patching but always found this to be unreliable in the long term.

I suspect that alcohol in the fuel might be to blame, does tend to attract water.
Title: Re: Petrol Tank
Post by: Erny on March 25, 2020, 05:39:59 PM
This back luck. if that hole is just tiny maybe proper liner applicaton can fill that hope safe?
Title: Re: Petrol Tank
Post by: Johnwebley on March 25, 2020, 05:48:24 PM
Can you solder a small patch



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Title: Re: Petrol Tank
Post by: Moorey on March 25, 2020, 06:03:04 PM
Solder it. if its done properly you will have no problems. Tanks were been soldered long before they were been welded.  ;)
Title: Re: Petrol Tank
Post by: florence on March 25, 2020, 06:15:11 PM
Soldering, now that is a good idea.  I've soldered land rover radiators but that is easy because they are made of brass.  Will I need a special flux being steel or will Bakers no.3 be OK?
Title: Re: Petrol Tank
Post by: royhall on March 25, 2020, 06:20:25 PM
I wouldn't solder it the ethanol likes to eat solder. Will only hold for a short while.  I can say from bitter experience it needs to be brazed. Trigger will probably back me up on that.

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Title: Re: Petrol Tank
Post by: florence on March 25, 2020, 07:19:32 PM
is that modern low lead solder that is the problem?  I have some old lead/tin solder, will that be OK?

If not what about epoxy resin?
Title: Re: Petrol Tank
Post by: Bryanj on March 25, 2020, 07:30:46 PM
If ethanol attacks fibreglass tanks i dont hold up much hope for epoxy. Not sure if i still got the tank from my burnt No 36, if so you may have to take an "essential" drive to Gloucester!!
Title: Re: Petrol Tank
Post by: Moorey on March 25, 2020, 07:51:12 PM
Its now going up to 5 years since i soldered the bottom of my tank and it is still good so are others i have done. It may well be possible to do a repair at the back of the badge without destroying the paintwork not so with brazing or silver solder. Soldering will certainly be your cheapest option. I use a coroline paste flux as it is easier to keep it exactly where you want it to work. The bakers 3 been a liquid acid could possibly damage your paint if not very careful but as a flux would be ok. I have soldered stainless using Bakers 3 and many think you cant solder stainless steel.
I think Ethanol to be far more problematic with rubber parts rather than the metals. After all Ethanol also corrodes brass and copper, but hay ho.

Remember cleanliness is next to godliness as far as soldering is concerned. If its not clean it will fail.
Title: Re: Petrol Tank
Post by: Moorey on March 25, 2020, 07:55:45 PM
is that modern low lead solder that is the problem?  I have some old lead/tin solder, will that be OK?

If not what about epoxy resin?

The lead free solder is more prone to cracking where vibrations come into play. Old solder is fine also.
Title: Re: Petrol Tank
Post by: florence on March 25, 2020, 08:45:48 PM
I'll give it a try, nothing to lose after all and the paint is not a problem, it is just Smoothrite black, hand painted.  Thanks for all the advice, I will drin it and give it a go tomorrow.  What's the best way to get rid of the petrol as I will be using a blow torch?  Just empty and leave it in the sun with the lid open?
Title: Re: Petrol Tank
Post by: Bryanj on March 25, 2020, 08:52:18 PM
Steam clean the inside and a good air flow through it
Title: Re: Petrol Tank
Post by: Moorey on March 25, 2020, 09:28:49 PM
I wouldn't use a blowtorch at all. A big copper iron. A soldering iron is quite capable of igniting petrol vapour never mind a blowtorch.
Title: Re: Petrol Tank
Post by: florence on March 25, 2020, 10:20:06 PM
I don't have a steam cleaner so will fill up with fairy liquid and hot water, give it a good wash then leave it in the sun for a couple of days, then see if I can get it to light!  ;D
Title: Re: Petrol Tank
Post by: matthewmosse on March 25, 2020, 10:31:53 PM
Hot soapy water and then braze weld worked with my landrover diesel tank. It was originally soldered at the joints and that was easy to re flood with solder when I found out about the soldered joints the hard way. Definitely have both cap, and tap off the tank, probably worth flushing with hot soapy water a few times, I'd not be that worried about drying it out before soldering, the heat from soldering should dry the relevant area, and the evaporating water from the rest might help reduce any fume build up from heat and fuel residue. I think there was a good 3 inches of water still in my landrover tank when I braze welded some pitting on it. It stood up to 6 or 7 years use before the weeping of fuel alerted me to the pitting probably having got deeper probably elsewhere - plenty of time to have sourced a spare tank, which as a bonus came half full of fuel.
Title: Re: Petrol Tank
Post by: MCTID on March 25, 2020, 10:43:35 PM
I have said this before......I worked with a Welder some years ago who did 'Foreigners' for some years then stopped. I asked him why and he told me that he'd been working on a car Petrol tank which 'unfortunately' caught fire whilst he was welding underneath.

The car was a total loss, as was the garage he was working in and it was touch and go whether he lost his house....and his life - although he didn't. His Insurance didn't cover any of this as he hadn't declared he did 'Foreigners' at his home premises.....and it took him a long time to recover financially from this near disaster.

DO NOT take any chances working with Fuel Tanks.....empty them, clean them out and let them ventilate properly until you are 100% sure there are no residues or vapours left.

I don't want to pontificate, but in my field of Health and Safety, never let a good accident be wasted ! As in my friends case, let's all learn from it.

Be safe out there........the Corona Virus isn't the only thing that can kill you.
Title: Re: Petrol Tank
Post by: K2-K6 on March 26, 2020, 08:34:42 AM
Old "out in field repair" trick to negate fuel tank volatility,  rubber pipe from car exhaust into tank for a few minutes after emptying to make it safe.

Replace fuel vapour with carbon monoxide.

Temporary,  get you home repair,  for a small hole,  used chewing gum is virtually impervious to fuel  :)
Title: Re: Petrol Tank
Post by: florence on March 26, 2020, 08:44:53 AM
Excellent, make do and mend.
Title: Re: Petrol Tank
Post by: taysidedragon on March 26, 2020, 11:33:48 AM
Plastic Padding car repair paste is petrol proof and can be used for small tank repairs.
Title: Re: Petrol Tank
Post by: florence on March 26, 2020, 08:33:44 PM
looking on the internet, I am amazed how few petrol tanks there are for sale and any I have found are so unbelievably expensive. 

I'm thinking of alternatives that will fit, 500t, 450t?, early 550.  Has anyone done this and are there any other models that will fit, or indeed from other manufacturers?
Title: Re: Petrol Tank
Post by: Bryanj on March 26, 2020, 09:01:53 PM
This has been a US thread for a while. Basicaly 500 and 550K 1971 to 1976 will fit but get the tap with it if its a later 550. 550 K3 but need sear as well plus seat hinge and lock mods.
Anything can be made to fit with time and patience but is it worth it
Title: Petrol Tank
Post by: SteveD CB500K0 on March 27, 2020, 06:23:39 AM
I had a 550K3 tank on my 500

The fittings all worked but there’s a gap to the seat.

So I fitted a 550K3 seat as well. The mounting points didn’t line up so a bit of hammering and bending was required.


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Title: Re: Petrol Tank
Post by: Tomb on March 27, 2020, 08:20:45 AM
I have a CB750K7 tank on my CB550F, not sure about seat fitting with it though as I have a CD175 seat on it too  ;D, they all kinda fit, just not perfectly.
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