Reply To: ETHANOL SHIELD, FUEL STABILISER

[David FaulknerParticipant]

Looks like I somehow managed to originally post this in the ‘Archive’ section so apologies for posting again.

I’m adding to this thread following recent issues with my Traction. Basically I had an exhaust valve on No3 cylinder burn out even though the head has hardened valve seats. The car has been run for around 12,000 miles on a mix of 95 ron unleaded and 98 Ron Premium unleaded and with a ‘Spitfire’ additive in the tank that others have used as well although I have not used an ‘Ethanol Stabiliser’ additive as all my fuel system has been replaced using ‘100% Ethanol safe’ items where possible having found that some flexible petrol pipining went ‘soft and spongy’ within a short period of time.

Reading back through floating power unleaded use has cropped up several times over the years and it is still relevant and it appears that professional advice was that using Premium grade fuel made no difference in a Traction. Now that advice came before Ethanol became a regular item in modern fuels though some sources claim that ‘Premium’ petrol has little or no Ethanol content, however is Ethanol in petrol as big a problem as no lead for running a Traction Avant?

Volume 14 1998 issue 01-2 June/July has an in depth article, part of which is worth repeating:

Fuel History: Before World War 2, leaded fuel was unknown. The maximum octane rating was about 92 but normal petrol had around 70. After the war, octane rating rose to 75 for normal petrol in 1956. At the end of the forties, lead was added.

Traction engine development: The first 70/s had a compression ratio of 5. 7:1. Later, with the increase of piston displacement, the compression ratio also rose to 5.9:1 and then to 6.2: 1. The first 11 OJ shad a compression ratio of 5.9: 1, increasing to 6.2:1 with the introduction of the ‘Perfo’ engines. From 1950 until May 1955 it was at 6.5: 1. The 11 D engine had, from 1955 to the end of production, a compression ratio of 6.8: 1. The 15/6 had a ratio of 6.2: 1 until 1949, and later 6.5:1 until the end of production.

Lead additives in petrol not only avoid ‘knocking’ but also decreases the valve seat wear. In addition, the lead helps to improve heat transfer. In the case of leaded petrol, the closing valves ‘beat’ onto a relatively soft, damping layer which is not built-up with un-leaded fuel.

The valve clearances thus decrease more rapidly, and burnt valves can be the consequence of neglecting regularly to check the valve clearances. Until the end of the forties, petrol was unleaded and cylinder head reconditioning was practised every 20,000 to 50,000 km and was considered to be a regular repair.

Volume 14 1998 issue 3 July has an item from FBHVC has a further item basically confirming the 1st article but leaning towards ‘additives’ available only being partially effective

Finally Volume 15 1999 issue 2 May has a further article that concludes that cast iron engines were more at risk from unleaded fuel and that whilst wear rates were unpredictable  and could vary widely in a 4 cylinder configuration No 3 cylinder frequently displayed the highest rate of exhaust valve seat recession which mirrors my personal experience.

The above are selected parts of the articles listed and it is worth reading them fully.

I’m personally guilty of not checking valve clearances since the engine rebuild in 2013 which has proved an expensive error and wish I had read those articles earlier, so will now make valve clearance checks part of my annual routine maintenance.