Lancia Montecarlo Unleaded Conversion

Throughout Europe it is now virtually impossible to obtain leaded petrol. There are a few places in the UK that are still permitted to sell it, but not many. There has been much talk about what owners of older Lancias should do for fuel. Three different proposals are being suggested by fellow owners:

• Do Nothing - Run your engine on unleaded and wait for it to fail, it could be some time away?
• Use Lead Replacement Petrol (LRP) - There appears to be mixed results with LRP, some people are complaining of running problems. Not all LRP is the same, try another.
• Fuel Additives - Add one of the many magic liquids to your tank when you fill up.
• Head Conversion - Make a permanent alteration to your cylinder head.

I elected to go down the proper unleaded conversion route.

The problem

We were left stranded by the side of the road in September 1998 when the cylinder head gasket failed. We were on our way to a Lancia Club Nederland gathering at Maastricht when the temperature gauge just went straight into the red. Plenty of fellow Lancistri stopped to offer us water and advice, but it was evident that the car was not going any further!

Back home we set about repairing the damage, essentially a major failure in the gasket. The cylinder head had to be removed and sent away to be skimmed, as the immense heat we generated could have warped it. I decided as the head was now off the car, to make the permanent conversion to Unleaded petrol.

Change the valves

Essentially the main area of concern is the exhaust valves on the older Beta engines. The valve seats need to be replaced with a hardened versions and the valves should be replaced to suit the new seats.

Additionally, the exhaust valve guides will need to be replaced with stronger bronze guides.

Pre-ignition

There is an additional problem of stopping the petrol pre-igniting (pinking) as unleaded fuel has a lower octane rating than leaded petrol. The higher octane ratio of leaded petrol causes it to burn more slowly, so the spark has to occur earlier, in order that the maximum pressure developed during combustion happens when the piston is in the right position for maximum push.

If the spark occurs to early, maximum pressure can happen before the piston has reached TDC with the result that there is a tendency for the piston to be knocked back.

In practice the piston will actually only be forced back when there is insufficient inertia such as during the starting process but the knocking sound that is characteristic of pinking is to be avoided at all costs otherwise serious damage will happen.

The pinking can be cured by adjusting the point where the spark comes in the combustion cycle. The standard timing advance curve is shown in the graphic, and the usual trick most garages do is to retard the whole ignition by a couple of degrees. This has a detrimental effect on the overall power of the engine and is not a nice solution.

I spoke to a number of people about the possibility of getting different strength springs to fit to the distributor. This would alter the rate the ignition advance took place and would reduce the overall amount of advancement. Unfortunately with everybody using electronic ignition systems it is virtually impossible to acquire a set of accurate springs to allow you to experiment in this way.

I sought the help of Barry Waterhouse of Evolution Engineering who told me that the problem was not the rate of advance, but the overall amount. The standard maximum advance is 14 degrees and this figure should be reduced. The amount of reduction is small, but it appears to stop the signs of pinking without affecting the overall performance of the engine.

Get the professionals in!

While Barry was doing his magic we set about dismantling the rest of the engine. Some water had been left sitting in one of the combustion chambers after the gasket failure. It was imperative to check that no corrosion had taken place or the ring was damaged. Barry also called me to report that signs of oil were found on cylinder 2, saying it might be the worn valve guides or a defective ring. Ultimately, all four pistons were removed and the crank checked for signs of wear. Fortunately the bottom half of the engine appeared fine and we were able to reassemble.

The result

The end result is better than I had expected. The head overhaul has resulted in a much smoother running engine, and no noticeable loss of power. The total cost was not cheap, and will probably never pay for itself. However at least I do not have to mess with smelly additives for my petrol!

Last updated: 2000-11-01