RR 3.5 V8 LPG question

[Nightbar]

A colleague of mine is running mid 80s 2 door RR 3.5 with an LPG conversion but has hit a few problems. He has asked on one or 2 French LPG blogs and the advice thew have given him is at odds with what our local mechanic says (and no there are no LPG experts in our area). I thought I would ask here to see if anyone could shed some light on the matter. So here goes:

The engine began to cough/splutter is if there was a fuel line blockage/blocked filter. The garage said that there was a lack of compression on 3 cylinders and that the LPG was to dry which had damaged the valves. The garage also said that the rings and block was also damaged. The French blog confirmed that too dry LPG could damage the valves and advised changing them about every 4 years. They did not believe that the rings/block should have been damaged.

I think there is a lot of conflicting information in the above statements and wondered what you thought.

Many thanks in advance for your help/guidance/thoughts.

[Rossko]

A few engines are prone to accelerated valve recession when run on LPG. Typically what were then "high tec" designs that rely on sooperdooper petrol additives; certain japanese engines. RR V8 not known to be among them though!! After all the mechanicals in these engines were originally intended for agricultural conditions/fuel.

I have no idea what "dry" autogas might be. In the UK its nearly 100% Propane, with traces of butane etc from the refinery. Plus some teeny amounts of waxy additives. Those are intended as valve lubricants (because liquid propane has zilch natural lubrication properties) ... but thats nothing to do with the valves in engines, its to stop the brass valves on storage tanks squeaking and sticking!

In mediterranean countries I understand Autogas may contain rather more Butane (cos its cheaper) which doesn't happen here (cos it doesnt evaporate on frosty days) but I can't see how thats relevant either.

I wonder if "dry fuel" is a transalation failure from the French, and what they mean is "it has been running lean" ??? Thats more likely, as most folk ignore LPG servicing until it packs up ; its not at all impossible for a fault to make it run lean enough to wreck an angine eventually.

cheers, Ross K

[webber1982]

lpg by nature is dry ie a gaseouse vapour going into the engine not like petrol which is a wet atomised spray the petrol being wet helps lubricate moving parts ie valves and reduce combustion temperature lpg does not do this. the rover v8 is not a problem engine as long as it was designed to run on unleaded. i have never seen a rover v8 recess the valves due to lpg use. the waxy substance in the lpg is called heavy ends and is a result of the stenching agent in the gas this is known to cause loads of problems in a lpg system ie sticking solenoid valves on cold mornings. the most probable cause of ur friends problem is due to the lpg system running weak the increase in combustion temperature within the engine will cause the valves to burn out or not seat properly. there are loads of reasons why a system would run weak depending upon what type of system is fitted. the most common reason is lack pf proper lpg system maintance.

[Sooty Zooki]

I have read that SU carb's need a mod to run on LPG. This is because the gas has no lube properties like unleaded and the needle in the carb wears out quickly due to friction (it normally floats on a jet of liquid petrol). A solenoid is required to lift the needle to prevent wear when running on gas. Some RR 3.5's run twin SU HIF44's - its worth checking out if your mate's has this carb set-up. Would be unrelated to any valve problems but could also explain a splutter (I would double check local garage compression diagnosis as a French mechanic will not be able to help himself from ripping off a customer if they detect a wiff of English accent - I presume he is not French himself, LOL!).

[pope]

It doesn't matter if the needles are completely worn out when running SU's on gas, the fuel is mixed straight into the airflow, either before or after the carb, the needles do nothing, I have read that you can remove the carb pistons altogether and get a much freer flow of fuel mix though I haven't tried this as you cannot then run on petrol.
I've wondered about valve lube too, I run some chainsaw 2 stroke mix petrol through it now and again (just because I have it left over from work)for piece of mind but don't know if this is really necessary.
I doubt if it's a worn engine causing your running problems, V8's are usually quite happy to run even if they are totally worn out, more likely just some fuelling hassles. Fit a new in line gas filter to start with. A lot of gas is quite dirty, there's a small filter housing fitted beneath your fuel solenoid under the bonnet, you have to turn off your gas supply from your tanks first, there'll probably be manual screws tap on top of your tank, some are just electric and will be shut when the ignition is off. You'll lose a bit of gas out of the pipes when you take them off.
LPG is quite fussy, make sure plugs, leads, cap etc are all perfect and check all your relays and solenoid wiring on the LPG system, i've had a lot of entertainment from dirty contacts on relays.

[Sooty Zooki]