Saturday, October 11, 2014

A Shot of Lead in the Head!

In the previous post (Replaced the Head) I successfully managed to change the cylinder head on the Mini, and pretty chuffed I was with myself too as it was quite a big job. Anyway, now I have the old head off and in the shed I can start to strip it down and see what's what.

The head that went on was one I'd done quite a lot of work on (here) and is fitted with hardened exhaust valve seats. Because of this and also the fact the car was manufactured in the late 80's, I simply assumed that the head that came off would also be fitted with the same hardened seats. Turns out I was wrong, which is a bit of a shame as I really wanted to keep the head as a spare.

The original cylinder head
So why lead?
It seems that history has largely forgotten the name Thomas Midgley, which is unusual given his massive impact on the world. Back in the early 20th century while working for a subsidiary of General Motors, Midgely discovered that adding lead in the form of Tetraethyllead (TEL) to petrol (or gasoline if you prefer) worked really well as an antiknock agent and also prevented valve seat damage, in fact the lead accumulated around the valve seats and just made them work better. 

This discovery would have been brilliant had it not been for the disturbing fact that lead, as we all know is exceptionally toxic to almost everything that draws breath. Indeed Midgely himself and many of the workers at the time had to be treated for lead poisoning and a few even died from the condition.

So despite the deaths and obvious risk to public health, TEL was signed off as a 'safe' fuel additive and consequently used on a global scale for the rest of the 20th century. I'm sure the fact that oil companies and automotive manufacturers, being the owners of the various patents for the manufacture of TEL had absolutely nothing to do with that decision. Cynical! Well maybe just a little.

It seems crazy to think that at the time Midgely was actually awarded a prize for his discovery. As if being credited as the guy who introduced lead to petrol wasn't bad enough, Midgely went on to add the development of CFC's to his legacy also! It has been suggested that Migdely has had more impact on the atmosphere than any other single organism in Earth's history. Wow, I have to remember that next time I mess up!

As the 20th century rolled on, various environmental and health concerns were being raised about air pollution and the levels of lead found in soil and other weird and wonderful places. Fingers were pointed, arguments were had and opinions were formed, but there was no mistaking the source of the offending pollutant. So slowly and I have to say thankfully leaded petrol was phased out and eventually banned in most countries.

Unleaded fuel
Here in the UK unleaded petrol was introduced around 1986 to help the Government meet its objective of reducing the amount of lead emissions into the environment. With the levels of lead permissible in 4 Star being continually lowered, it was only a matter of time before leaded petrol was to become as extinct as the dinosaurs it was made from. By the time it was finally announced in 1998 most if not all of the new cars of the day were already able to run on unleaded.

So when were Minis equipped to cope with the dreaded unleaded? Reading through this excellent article here by Mini Mania it seems to be about 1990ish. However, at the time it looks like Rover had no hard and fast rules regarding the change over from leaded to unleaded heads making it very difficult to know for certain which type you have.

Valve Seat Damage
So where does that leave me and my little cylinder head? When I first examined the head, the combustion chambers looked exactly as I expected them to look.

Crusty, Dirty, and Black

It's only as the cleanup begins and the valves are stripped out that a real assessment can be made. The inlet seats looked near perfect, but as there was a lack of hardened valve seats on the exhaust ports and a lack of lead in the petrol, they had not fared as well.

Some worse than others!

Mmmm, not great!

Miles to Damage Ratio
In terms of trying to get a 'miles to damage' ratio I can only use numbers I have accumulated myself as I don't know what the previous owners did.

When I got the car the mileage was 72116 and when I replaced the head it was at 78321. Meaning that I know for certain that since owning the car I have driven 6205 miles on a diet of unleaded petrol with a head that was designed for 4 Star. As I assumed (stupidly) that the head was unleaded, I never used any additive in with the fuel.

Incidentally over that time I have averaged about 41 mpg, so that means I have chomped through 151 UK gallons which equates to about 688 litres of fuel! To get that into something I can understand, it's about the size of an IBC Bulk Container.

Considering all that unleaded fuel being burnt and looking at the extent of the damage, I'm actually surprised it's not worse. It just goes to show what sturdy little engines Mini's have. Who knows how many more miles I could have done before it conked out!

So what to do now? 
I really wanted to restore this head and keep it as a spare. I thought it was going to be simply a job of re-lapping the valves, putting some new seals in and make it look nice. But the discovery of the knackered valve seats has somewhat thrown a spanner in the works. Having thought about this for a while I considered my options.

  • Do nothing and don't have a spare - Why not, the head that I put on is happy to munch unleaded petrol, I didn't have a spare before, so why worry. Means I don't have to waste my time and it's the cheapest option,
  • Explore how much it would cost to have the head converted to run on unleaded and also put new valve guides in while I'm at it. It would be expensive but once done I would swap the heads back over and have the peace of mind that the job has been done properly. I would also have a good spare.
  • Try to lap the valves back in and get a good seal myself and still use the head as a spare with some lead replacement additive in with the fuel. It might be a waste of time trying to fix the damaged seats, but it will be free. 
  • Bide my time and try to buy another unleaded head from somewhere. This may be risky as there is no guarantee of quality with second hand goods and I may end up buying a dud.

As I want a spare, the first option is out, but I see no reason why I couldn't pursue all three of the other options. So my plan of action is to have a shop around and get some quotes to have the head converted. In the mean time, I'll get busy myself to see if a DIY fix is possible and also keep my ear to the ground and one eye on eBay (I appreciate that would look strange) as you never know what might come up!

Whatever the outcome, there will be fun to be had and something to blog about!

Oh and don't even get me started on E10!

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