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Old 05-16-2014, 04:44 AM
Vic_LeChic Vic_LeChic is offline
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Location: Spain
 
Join Date: Jan 2013
Posts: 25
Mein Auto: E92 330i Coupe N52B30
LPG conversion: valve damage?

Hi everyone

Whilst reading avout LPG conversion I came across an article about valve damage. Has anyone experienced this problem?

http://www.amrautos.co.uk/index.php/lpg-systems

quote

Due to the ever increasing cost of LPG and the unsuitability of most modern petrol engines from around 2006 onwards most now suffer from severe exhaust valve and valve seat recession when converted to run on LPG. This is caused by cheap and poor quality materials being used in the manufacture of the exhaust valves and seats, and also the discontinuation of Manually Adjustable Tappets, Self Adjusting Hydraulic Tappets and engines with VVT Variable Valve Timing.

In most modern multi-valve engines in a bid to reduce prices and ease of manufacture, the makers have opted for fixed clearance or solid tappets which cannot be adjusted without extensive work and often the removal of the cylinder head. These components and materials are fine when running on petrol only, I will explain in more detail below.

This is where the problems with valve seat recession starts, LPG once vaporised is a pure vapour and has no lubricating properties at all, this then passes through the inlet valves and into the cylinder where it is ignited by the spark plugs, combustion takes place and the hot spent gasses exit through the exhaust valves.

Because these gasses are very hot and contain no lubricants or additives they very slowly start to burn the valve face and valve seat of the exhaust valve away, this process (called recession) over time eventually causes the valve to recede in to its seat eventually reducing the valve or tappet clearance to zero. Once this has happened it is only a matter of a few miles before the valve head starts to disintegrate causing loss of compression and misfire. This will also lead to catalytic converter failure if the vehicle continues to be driven with misfires by way off unburnt fuel passing through the exhaust system to the catalytic convertor.


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Montego blue - beige leather - piano black - M3 18" rims- Aero M sport front bumper - M3 rear spoiler - Sport seats

- SEAT Leon Cupra R mk1 (210 bhp) 2003
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Last edited by Vic_LeChic; 05-16-2014 at 04:46 AM.
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