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Lead replacement petrol...

Chris

Enthusiast
Messages
33
#1
Hello there!!

I'm a Renault 4 fanatic having had two of them during a two-year stint teaching English in Slovenia, and I've been looking for one back here in the UK for ages.

I've found one, and I'm going to see it next weekend with a view to buying, but someone's pointed out to me today the issue of Lead Replacement Petrol. It's being phased out, and I can't find any information on the internet as to whether R4s can run on super unleaded or normal unleaded. Can you tell me if they can, or if they need to have any adjustments made to the engine??

As far as I know, the lead in petrol was for two things:

1) To protect the valve seats.
2) To increase the fuel's octane rating to make the engine
less prone to 'knocking' or 'pinking'.

Could anyone possibly tell me if Renault 4s can run on unleaded and, if not, what the best course of action is???

I hope you can help!!


Cheers,


Chris
 

malcolm

& Clementine the Cat
Staff member
Messages
4,133
Location
Bedford UK
#2
Hi Chris and welcome to the forum.

Two of my GTLs have suffered burnt exhaust valves after running on unleaded - one after 10,000 miles of my ownership and the other after 4000 miles. You can tell when they've burnt an exhaust valve as they idle on 3 cylinders, and the vibration causes the gearstick to knock. Bang bang bang.... The problem is the valve seat gets eroded, there is less contact between the valve and the seat, so the valve gets less cooling, overheats and burns away.

The valves are under most stress under sustained high speed running - such as motorway driving at 70-80mph. I'd recommend a lead additive such as Castrol Valvemaster for motorway use. You put a cap full of the stuff in with each tank of fuel. It's phosphorus based (the same stuff as they put into lead replacement petrol). Avoid the manganese Based additives (Millers and Carplan) if your car doesn't do many miles - manganese can turn to sludge in your tank. I'm pretty sure that unleaded plus the additive is cheaper than lead replacement petrol.

For running around town or cross country trips on A-roads I don't bother with the additive - there is much less thermal stress on the valves in these types of driving. It's probably safer going with the lead replacement additive all the time, but I like a risk

The other alternative is an unleaded conversion. This would require replacement of the exhaust valve seats and the exhaust valves with a harder material. The modifications to the cylinder head tend to cost about £200. Your local engine rebuilder / machine shop should be able to do the work and source the parts. It's not a DIY job.

An unleaded conversion would involve removing the cylinder head - something I try to avoid doing on the Renault 4 as it has wet liners. The cylinder liners are separate to the block, and are sealed at the bottom by neoprene seals. These seals harden after several years, and if disturbed will leak. I only have a 50% success rate on wet liner engines removing and replacing the cylinder heads without leaks.

The Renault 4 can be prone to pinking, although this is normally due to wear in the distributor rather than the octane level in the fuel. I ran my first R4 on 2 star without problems. If you do get pinking (a loud ticking sound (often like the sound of a triangle) on hard throttle at low revs, then it's worth retarding the ignition timing by a couple of degrees.

Let us know how you get on with the Renault 4 at the weekend. I'd guess it'll be older than those swish 1992 models they drive around in Slovenia.

:D
 

tasheido

Enthusiast
Messages
18
#3
What about the BP stuff

I normally use 98 octane with lead replacement wich is caled 'Super' here. Some companies still have it, others offer regular 98 and the lead replacement stuff on the side (but for free). but if the issue is just the octane rating what about the 100 octane BP offers ? i think is 100 octane gas. Should be something like avgas like the one they use in the aeroplanes. is it?.. i dunno what do you guys think?
 

malcolm

& Clementine the Cat
Staff member
Messages
4,133
Location
Bedford UK
#4
Avgas is wonderful stuff - it's 110 octane and so full of lead it's a wonder that aeroplanes can take off. Hardly any tax on it so it's really cheap. You need to have a good excuse to have it as it's illegal to use it in a road car (at least in the UK). Probably the customs guy wouldn't believe me if I told him I had a lathe in the garage powered by a Rolls Royce Merlin engine....

It's the lead (or lead substitute) that Renault 4s really need, although higher octane is useful for solving pinking problems without excessively retarding the ignition. The cars seem prone to pinking even though they are supposedly able to run on 92 octane. I use 95 without any problems.
 

tasheido

Enthusiast
Messages
18
#5
I thought it had more to do with te octane level than the lead. i read somewhere the lead's purpose was to increase octane level in a cheaper way. Higher compression, cooler burn and your valves would be safe. I dont know if it's illegal to buy avgas for a car here. but it usually only available near aerodromes. I have a friend who is a pilot i'll ask him if they pose any problems on selling avgas to regular folks. Is it safe to be used in a 4L ?(this is just curiosity.. ). Maybe the 1108 will think he is a merlin. hehe.. turning the babesmobile in to a Spitfire.
 
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