The effects of modern fuel on old engines. Many questions...

[JimK]

In the thread entitled "Long journey coming up" in General, ChickenJohn said:

If you drive an old A series with foot to the floor on modern petrol you are likely to burn out an exhaust valve.

My questions are:
What are the differences between fuel supplied now and fuel used when my A-series was built in '65? I realise that lead is no longer added, but what effect does that have? Is lead the only difference?

How does a different fuel cause exhaust valve burnout? Why do exhaust valves burn out at all? That sounds like a dreadful defect to me.

Is it possible to make changes to the engine or add something to the fuel to remove the problem, such that I can put the hammer down without causing such damage to the engine? I drove my Fiesta with enthusiasm for 120kmiles in 7 years, and the engine was still in rude health. What is it in the engine that has changed to adapt to the fuel?[1] Or is it the other way round? Are the valves made of different materials now?

In case it's relevant, I use Castrol Valvemaster additive (the one with the octane booster).

Now just in case ChickenJohn thinks I don't believe him: I've no doubt he knows what he's talking about, but I need hard facts and engineering so I can understand why he says what he says.
If you disagree with his statement, please keep quiet unless you can explain exactly why he's wrong.

[1] I know that modern computer-controlled engines have no fixed timing but adapt the timing every single time a cylinder fires, by advancing the timing as far as possible while detecting knocking using sensors. That system adapts to whatever fuel is currently being used, but I don't think it answers my question since it doesn't account for valves burnng out.

[ben739]

do you use the valve master in your engine even though it has unleaded head?

Ben

[alex_holden]

I think you can buy special "unleaded" exhaust valves that are presumably harder/more heat-tolerant than the originals, as well as obviously fitting hardened seats.

See http://morrisminorspares.co.uk/shop/pro ... ts_id=1434 and http://morrisminorspares.co.uk/shop/pro ... ucts_id=12

Perhaps people who have suffered more burnt valves with unleaded were still using the original valves?

[Willie]

Modern fuel burns hotter than the old type.

[JimK]

do you use the valve master in your engine even though it has unleaded head?

I'm pretty sure the engine is original and untouched, so I use the additive.

Alex, I've heard about the valve inserts, but I don't what it is about the fuel that makes them necessary. Why does the absence of lead require hardened valve seats? Why will the standard seats recede when there's no lead in teh fuel? I though the lead was a lubricant, not a valve seat temperature reducer. Or is it increased friction that makes the seats and valves heat up?

[ben739]

will it hurt the engine to use valvemaster if its an unleaded head?

[JimK]

Don't know. I don't think so, as the usual problem is additives with the catalyst, i.e. it kills them...

[Willie]

JIM, the lead is a lubricant and any lubricant reduces friction so if the lubricant is removed it is highly likely that greater friction temperatures
will be generated which with prolonged use will damage the exhaust
valves and seats. This manifests itself when the engine is used at above certain rev levels usually. The official tests on the A series type
engines found that prolonged high speed use was certain to produce exhaust valve/seat problems using unleaded fuel without an additive.

[rayofleamington]

What do modern cars have that means it doesn't happen to them?

They have hardened valve seats, better valve materials and better cooling of the valve itself.

Needed for reasons as explained by Willie.

[Packedup]

Every time the exhaust valve closes it sticks to the seat. When it opens again it pulls a very small amount of the seat with it, that can then be blasted off and out the back with the exhaust gasses. Over time this effect causes the seat to noticeably erode.

Cooler running fuel would help reduce this, as would a lubricant that helps prevent the stick (eg lead). My personal belief is higher octane fuel, with it's more controlled flame front, will be better for valve seats than lower octane, with it's rapid and hot flame front - Higher octane is less prone to detonation and so can be used with higher compression ratios and greater ign advance which is how it produces more power than lower octane hotter burning fuels. Though again, that's based on what little I've read and my own brand of flimsy science, so isn't to be taken as an ultimate motoring truth!

[chickenjohn]

Yes, basically I agree with all the above! Thats what I meant when I inadvertantly opened this can of worms

Stick to 60-65mph and don't hammer the car and it'll be fine. Maybe a high quality unleaded conversion will be more robust. But just drive it as it is for now.
As Onne said in the other thread listen to the car. The sound should tell you what speed the car is comfortable at. I'm not advocating completely pussy footing the car, just trying to suggest greater reliabillity can be had through a little mechanical sensitivity.

[JimK]

So the Valvemaster Plus I use is helping to preserve both valves and seats by lubricating and making the fuel burn cooler? And that should preserve both?

[bmcecosse]

Moderate driving will see the valve seats last very well indeed - even with unleaded fuel and original cylinder head. The tetra-ethyl lead used to form a protective film on the exhaust valve seat - and matching valve face. No lead - no protection. Modern cars have much harder seats and much tougher valves - all designed to be run without the protection of lead. Usually if you run without lead in an original head - the exhaust valves will 'recess' slightly - sinking into the head - until the valve clearance closes up. this then causes hot gases to roar through the tiny gap - and swiftly errode the valve and seat. So - if you keep an eye on the exhaust valve clearances (and I suggest 15 thou as a starting point) - then if you see the gap closing up you will know a little recession has taken place - and you can consider whether to add some chemicals (Tetraboost is the only one with lead tetra-ethyl) - or to invest in an 'unleaded' head. I suspect some unleaded heads are being run with standard exhaust valves - and so while the seats are hard - the valves are not - and recently there have been some cases of 'unleaded' heads on here - with burned out exhaust valves. If you do big mileage and drive the car hard - I suggest Tetraboost additive. Otherwise - just run on unleaded fuel, and keep an eye on the valve clearances - that's what I do!

[JimK]

I do about 150 miles a week, so not too many miles. I'm an enthusiatic driver, though mechanically sympathetic in the way I drive.

I've been using Castrol Valvemaster Plus so far. I'll look up the additive you mention, and look for some reports about it.

[chrisd87]

The thing to remember is that if you're running a standard 12G202 head they only cost about a tenner and are very easy to change over so it really isn't the end of the world if you wreck the odd one.

The previous owner of my car ran it on pure unleaded for (I assume) about 5 years and I continued to do this, using the car everyday. I do tend to hammer it a bit, using full throttle to accelerate a lot of the time. Eventually the exhaust valves and seats burned out on 2 cylinders, so I just stuck a spare head on. I now use valvemaster though.

[minor_hickup]

JimK, I recently burnt out an exhaust valve on an unleaded head, see my thread here http://www.morrisminoroc.co.uk/index.ph ... ic&t=13775.

I do between 10 and 15k a year, most of it rural NSL and fair bit dual carriage way and fast roads. I drive fairly sympathetically, ie. i take time changing gear, let the car warm up gently but it also gets run hard on long trips often loaded up.

I suspect as with many minor bits, these hardened valves are not designed for my sort of everday use but the 2k a year on the show circuit people assume of an old car. Funnily enough I seem to get 2k from brake light switches before I take it back to the supplier and they declare "Not another bl**** one!"

[rayofleamington]

Funnily enough I seem to get 2k from brake light switches before I take it back to the supplier and they declare

You could try getting an original one from a scrap Minor. That could possibly outlast the next 10 brake light switches you get from this supplier.

[bmcecosse]

Chris - if you had checked the exhaust valve clearances - you would have caught the problem before it got so bad. And I will take all the 202 heads I can find at £10 each!!!

[rayofleamington]

I suspect as with many minor bits, these hardened valves are not designed for my sort of everday use

On a high mileage A-series, things like a failed valve are a pain in the rear but just part of the 'character'. Valves used to fail in the 70's when we had good old leaded fuel - long hard runs are a major factor to cause this.
Despite an uprated unleaded head the risk of failure is never reduced to zero (although it is reduced significantly) and also the materials used in new spare parts are not always as good as they could be.

Unleaded Minor cylinder heads are usually done to a cost - to compete against other suppliers. It's possible to get extremely good valves (the kind of stuff used in highly tuned engines) but few people would interested in the difference and even fewer would want to pay what they cost.

[Dominic]

and recently there have been some cases of 'unleaded' heads on here - with burned out exhaust valves.

In my case, it wasn't the valves or head at fault, but "over-lubrication" from a scored cylinder, allowing about 1 pint of oil per 100 miles to be consumed, by that 1 cylinder!
Soon to be fixed however