A word from the Automobile Association...
I thought the following details released by the AA may be of interest to other Capri owners (written circa 1999 but the information is up to date as of 2013):-
LEADED FOUR -
by The AA Technical Information Centre.
So leaded petrol is a thing of the past. Most people agree that on balance, this is for the general good, but what are the possible problems?
It was in the 1920's that a lateral thinking named Midgley discovered the benefits of lead compounds as fuel additive. Engine efficiency was severely limited by the fuels then available as they tended to burn too rapidly in the cylinder. The treatment allowed the development of higher 'octane number' fuel, up from 60 to perhaps 110 in the end. At the time, there was no consideration given to the affect of the lead compounds on the engine valve seats, it was only found later that lead had the property of protecting them.
There are therefore two possible problems with pre-
Firstly, there will be a loss of about two 'octane numbers' from Four-
Secondly, in the case of an engine with the valve seats cut directly in a cast iron cylinder block (as used to be the normal practice), the loss of the protective affect of the lead compounds means that under conditions of hard, high speed use, erosion of the seats can lead to valve seat recession. If the seats recede by more than pre-
The use of 'Super Unleaded' petrol can overcome problems due to the reduced octane value of Premium Unleaded, in the case of those cars that cannot easily be re-
(a) Dosing the fuel with proprietary branded additive, or
(b) Seeing what happens on unleaded.
Of those options, (a) is probably the favourite. It is really not possible to say that valve seat recession cannot happen with these additives, the problem being that there's an enormous range of engines out there, and they can be in any condition from pristine to near collapse. However, the use of fuels with the additive blended by the fuel supplier is probably more reliable than adding it yourself, as mixing and dose rates can be quite difficult to get right in small amounts. Option (b) is not completely daft, in that driven gently for limited mileage, the valve clearances will not be taken up between services, so with reasonable care no harm should result provided you know what to look for. If compression is lost on a cylinder, or the valve clearances disappear, then something will have to be done.
These comments will cover probably 95% of the older cars on (or temporarily off) the roads in the UK. There are unfortunately going to be some exceptions though, which may need special thought. For a start there are some specialist high performance cars that need high octane fuel. These vehicles were made in the days of 100 octane pump fuels, but are getting by at present on 97 octane leaded. Going to 95 octane unleaded just could cause trouble, even with the ignition retarded. In such cases, the long term option is to lower the compression ratio, at some power loss, but with benefit to engine life. Usually a new set of pistons can achieve this, again, engine specialists can advise. There are some proprietary 'octane boosting' fuel additives, but the affect of these on different fuels can be unpredictable.
Some engines will present particular problems in fitting hardened valve seat inserts, either because the seats are very close together. If inserts cannot be installed, you are back to option (a) or (b) above.
There are advertised fuel-
LEAD SUBSTITUTES FOR PETROL
At present we are aware of a couple of possible sources of proprietary lead-
1) Castrol Valvemaster additive: this has been used by several Capri owners who report that it works extremely well. (price per litre of fuel treated approx 17p). Note that there are two types: Valvemaster & Valvemaster Plus. The later provides an octane boost to unleaded petrol to counter pinking and knocking
2) Millers VSP Fuel Treatment. Treats 40 litres of fuel at a cost of 6p per litre
3) Redex 4-
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