Fuel cap problems RGS

Garry

Garry

Junior member
Location
Eelde, Netherlands
Hello, I have a question about the fuel cap on my RGS.

Now that I’ve got the RGS roadworthy again and I want to fit the fuel tank, a lot of petrol is leaking past the fuel cap when I try to refit it. I’m also expecting petrol to spray out of the cap during hard braking.

I think the small rubber ring just below the black plastic where the lock is has dried out.

Does anyone know a solution to make the fuel cap leak-proof again?
 

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The RGS fuel cap was made for a Fiat car and was never designed to have fuel sloshing against it which happens every time you brake hard.

In the many years I have owned my RGS I have replaced the fuel cap two times with new ones bought off Ebay from Italy. Even the news ones leak but not as bad. And a few years later they are leaking just as bad as the old ones. I have a new one on now I just bought last year. Even it leaks a little.

I have thought of replacing the thin rubber gasket with a fuel resistant piece of foam rubber as that is where it leaks.
 
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In the past I had Viton seals made to replace the original, that worked well.
Here’s an aftermarket filler cap, it’s a UK stockist but you should be able to source the same locally.

FIAT 127 CL (1977 to 1981) Locking Fuel Cap , In Stock £18.99

Free Lifetime Replacement Guarantee with this FIAT 127 CL (1977 to 1981) Locking Fuel Cap . Price includes UK Shipping. Track 24 and international shipping available.
www.petrolcaps.co.uk www.petrolcaps.co.uk
 
The fault obviously lies in the sealing ring, the cap itself is non-vented (sez so underneath).

I've replaced mine a couple of times, I've now learnt to live with it. Don't fill to the brim... that'll bite you anyway, on a hot day the expansion tank will be overflowing with the hot engine additionally heating the fuel from below by the time you return from the cashier or the dunny.

I fill to the point where I can just spot the fuel level through the snout, all good. Full enough to make the feeling of top heaviness complete again. :rolleyes:

The 1980's Fiat Uno had a very similar sealing/retention system, the cap can probably be made to fit. The car item has a large deco ring that needs to be removed. Fiat Ritmo et al probably had similar.

piet
 
Lemons Sprint suffered from fuel expansion leak past the cap…… Scrumpy and I had to move away to have a quiet smoke while it was being rectified on the footpath in front of a village shop 😬

I still question how much fuel can be removed by using a water bottle cap numerous times 🤣 but it was the morning after a very big night.
 
andre g said:
My RGS fuel cup looks diffent to the one of Garry.
I know, it is a Fiat item, but do not know which model. It is tight - almost, Andre
View attachment 104304View attachment 104305
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I still have a spare tank that had a fuel cap on it but no key... I drilled the lock out today and managed to remove it. So it’s exactly the same as the one in your photo. This rubber has also gone hard. I’ve now soaked the rubber in engine oil to soften it up a bit. I got this tip from an old Laverda dealer.☺️
 
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I’ve sorted it out for now with a extra spare O-ring. It’s sealed for the moment... I’ve ordered a couple of spare Viton O-rings in size 44x2 and 3 mm thick. Let’s see if that works as well.

By the way, does anyone know where or which cylinder lock fits into the cap, as shown in Andre's photo?
I’ve drilled out the cylinder and am looking for a suitable cylinder lock for this.
 
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I fill mine up at the start of my ride giving it little time for expansion from the heat. That's when it leaks the most...regardless of the expansion tank which is probably useless under pressure given the leaking cap. Never found a full proof method to seal it up but dont think mine leaks too much just from sloshing. Often thought of cutting off the lip of the filler neck and welding a different one on that had a better cap design.

Wolfgang Haerter adopted SFC 1000 style filler caps to his RGS. Good solution if you need a paint job anyway.

Or you can just live with a bit of leaked gas as it's so cheap these days who cares!
 
henrywillms said:
Or you can just live with a bit of leaked gas as it's so cheap these days who cares!
Click to expand...

I say, fill up while it’s so cheap, two days fuel (1000lt) at $3:10 per litre is about the cost of 2 months insurance.

At one outlet I get a free coffee at no charge for buying over 500lt 🥳🥳, that’s a small coffee…. not the whole coffee machine!

Back to the topic, with fuel being so costly (here we go again) save a few bucks and leave more room.
 
I fill my tank until I can see fuel just making the see through pipe I have got on the breather - anymore and it will be pissing out of the overflow with the heat -I regularly spray lithium grease on the cap mechanism so it isn’t a hard turn for the key which has a cable tie so it doesn’t get lost - no one is going in there so it’s pretty safe and I never have to search for the key - the washer has been replaced a couple of times
 
Sir Sidney Ruffdiamond said:
I fill my tank until I can see fuel just making the see through pipe I have got on the breather - anymore and it will be pissing out of the overflow with the heat -I regularly spray lithium grease on the cap mechanism so it isn’t a hard turn for the key which has a cable tie so it doesn’t get lost - no one is going in there so it’s pretty safe and I never have to search for the key - the washer has been replaced a couple of times
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That's nice to know where I can siphon a bit of fuel the next time I get a bit low.... ;) :)
 
In case you’re interested in the story of the RGS fuel cap, which I’m guessing may not be widely known and is as told to me by the guy who was responsible…

Laverda was having problems with how to approach 1984 motorcycle evaporative emissions regulations coming into play in California and then eventually the US market generally. They contacted Alfa Romeo to see if they could help, and Alfa sent two guys to Breganze: Don Black (US director of Alfa engineering) and another engineer who was directly responsible for evaporative emissions compliance for US market cars. After looking at the issue, they came up with the idea of fitting Fiat car fuel components into the fairing. With this they could adapt a car evaporative emissions system, although I’m not sure if this actually happened. In return Alfa got free access to some patents that Laverda held related to valve actuation, and Don received an early RGS in the US as a gift from Laverda. Since he was a small in stature guy he gave the bike to the other engineer. Don told me the story in about 2011.

This was no doubt done in a hurry, during a short visit, and they probably didn’t consider the sloshing effect.
 
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Silvaire said:
In case you’re interested in the story of the RGS fuel cap, which I’m guessing may not be widely known and is as told to me by the guy who was responsible…

Laverda was having problems with how to approach 1984 motorcycle evaporative emissions regulations coming into play in California and then eventually the US market generally. They contacted Alfa Romeo to see if they could help, and Alfa sent two guys to Breganze: Don Black (US director of Alfa engineering) and another engineer who was directly responsible for evaporative emissions compliance for US market cars. After looking at the issue, they came up with the idea of fitting Fiat car fuel components into the fairing. With this they could adapt a car evaporative emissions system, although I’m not sure if this actually happened. In return Alfa got free access to some patents that Laverda held related to valve actuation, and Don received an early RGS in the US as a gift from Laverda. Since he was a small in stature guy he gave the bike to the other engineer. Don told me the story in about 2011.

This was no doubt done in a hurry, during a short visit, and they probably didn’t consider the sloshing effect.
Click to expand...

That explains the concept of the, somewhat goofy, fairing mounted filler …. I guess they got around the regulations and didn’t need to do it to the SFC though. 🤔
 
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The SFC 1000 was not sold in the US, and the lack of evaporative emission controls is one reason why. There were no similar rules for motorcycles elsewhere in the mid-80s. Later on the industry as a whole developed solutions. All the e.g. Ducatis of the 90s came with charcoal canisters and I really appreciated how they made the system so accessible and easy to remove
:)

(BTW in spite of the above I now have an ‘86 SFC in my US garage, and started it for the first time in my one week ownership today)
 
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Silvaire said:
In case you’re interested in the story of the RGS fuel cap, which I’m guessing may not be widely known and is as told to me by the guy who was responsible…

Laverda was having problems with how to approach 1984 motorcycle evaporative emissions regulations coming into play in California and then eventually the US market generally. They contacted Alfa Romeo to see if they could help, and Alfa sent two guys to Breganze: Don Black (US director of Alfa engineering) and another engineer who was directly responsible for evaporative emissions compliance for US market cars. After looking at the issue, they came up with the idea of fitting Fiat car fuel components into the fairing. With this they could adapt a car evaporative emissions system, although I’m not sure if this actually happened. In return Alfa got free access to some patents that Laverda held related to valve actuation, and Don received an early RGS in the US as a gift from Laverda. Since he was a small in stature guy he gave the bike to the other engineer. Don told me the story in about 2011.

This was no doubt done in a hurry, during a short visit, and they probably didn’t consider the sloshing effect.
Click to expand...

For the 1984 model year, the California Air Resources board was proposing rules that would require all motorcycles to adhere to the same evaporate emission rules as a car. This included all emissions such as fuel, paint fumes and plastic/rubber. So any aromatic hydrocarbons emitted by the bike was considered a bad thing. As California was Laverda's biggest market in the USA, they realized they had no choice and the RGS was the result. It too was supposed to have a charcoal canister and all carb breather lines were to go to it and the fuel tank. All the other motorcycles manufacturers fought the rule and as there was no way at the time to test the bike to see what chemicals it was emitting, the requirement was dropped. The use of Bayflex for the fairing was also a result of the rule as it would accept a very low VOC paint.

The RGS kept the filler neck and overflow tank but everything else that was needed to pass the emission test was removed.

I can't remember who told me this story but he was involved with trying to get the RGS legal in California. He went to the CARB meetings who he said had very little is any understanding about motorcycles.

So would the RGS have ever been made if not for California?
 
I gradually got used to this problem with my Corsa, but never fully cured it. Cap seal attention did help. Never fill up before you stop for a coffee/lunch/etc break, or even unless you're literally ready to ride off. I never got any sense of how much was in the tank when filling, just stop on the very first click of the bowser, never top it off. Still got used to the waft of fuel if braking hard soon after filling.

I did solve it 100% eventually though... sold it! :)
 
F**king about in the pits refuelling the Corsa through the front funnel, and getting the cap on and off was a right PITA at the TT in '85, and cost time......although not as much time as when it jumped out of gear shortly after leaving the pits and I thought the engine had blown!! :(
 
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