Lpg Conversion

[Bluesman]

mike,if you think about it running on petrol preduces carbon which protects the valves to a certain extent,lpg is hotter and remove carbon from your engine(valves)over time,hence the damage to some engines over a very long period,i've had two ls400's converted to lpg in the past and both required certificates for insurances purpose's, and a new certifacate had to be issued after so many years,but your right sbout about the ls400,it has hardend valves and dosnt require flashlube,i've been humming and harring about having my lexus gassed, think i might bite the bullet and go for it

Hi Jimmy,

LPG has only 85% of the calorific value of the same amount of petrol, so it is impossible for it to create more heat. It can only make 85% as much.

The causes of VSR Valve Seat Regression

There are at least 3 reasons why engine valve heads and stems recess into their seats;

1. Brinelling (flowing or change of shape of the metal that makes the valve heads and seats)

2. Erosion (through friction, resulting from the rotary motion of the valves when closing, caused by the helical valve spring(s)

3. Microwelding (ask your local Metallurgist or research on the 'net)

Note that these factors and their combined effects are present when an engine runs on ANY fuel.

A

breakdown of these effects;

Brinelling

(factor 1).

Brinelling

is well demonstrated by a Blacksmith who heats the metal he wants to re-shape in order to make it flow (Brinell) more easily under his Hammer. The metal being worked on is said to become 'softer' (more Ductile) when it is heated. The more the metal is heated (up to the point where it becomes molten or liquid), the softer it will become. The Blacksmith could re-shape the metal when it is cold although it would take him far longer. From this we can see that more heat can accelerate the rate of Brinnelling.

In addition, the rate of change in shape or flowing of the metal depends on its hardness and ductility at any given temperature. Lead, Copper or Gold would be easy to work when cold, whereas Tool Steel would have to be glowing bright yellow with heat before a heavy hammer could make any dent in it. Metal hardness is therefore a factor directly affecting the rate of Brinelling. In a Piston engine, the valve heads are taking the Blacksmith's place, hammering on the valve seats. The softer those valve seats are, the more they will change in shape as their metal flows. As in the Blacksmith's Forge, it is clear that the rate of Brinelling can be accelerated by more heating of the valve seat and the force exerted upon it by the valve steam /head. To carry the useful Blacksmith analogy a little further, the effect of Brinelling can be increased by using more force or a heavier hammer (which amounts to the same thing). Engine designers would like to make their valves as light as possible in order to reduce the force, although they have to be made of enough metal to do their job adequately. One way of reducing the force exerted on a valve seat by the valve head (the Hammer) is to use two valves to do the job of one. This will almost halve the weight of individual valve heads. This solution is demonstrated in engines having 3 or 4 valves per cylinder. Many think that 3 or 4 valves per cylinder are used to improve the 'breathing' or gas flow of an engine where, in fact, the method is used to reduce the weight of the valve heads and thus reduce the force exerted on their valve seats. If this design solution is used it will minimise the effect of Brinelling and retard the onset of VSR.

Erosion

(factor 2)

This effect cannot be avoided by using any pure fuel, it is purely a mechanical problem which can only be overcome by stopping the valve heads and stems rotating. When the heads rotate, they simply rub metal off both mating faces, and the softer of the two will suffer more erosion. Efforts to resolve this problem are made by engine designers, the most common solution is to use two springs with opposing helixes.

Because one spring must be smaller in diameter than the other (one spring must fit inside another in an axial fashion) then the turning forces cannot be totally balanced and valve head/stem rotation will still take place, although it will be reduced.

Another partial solution for Erosion is found in lubrication of the valve head and seat. If we apply lubrication to surfaces that are eroding each other then less molecules will be worn off each surface. Lead used to be added to petrol because it provided a form of lubrication for the valve head and seat sealing faces. Nowadays, Lead is not added to Petrol so that lubrication benefit is gone.

Microwelding

(factor 3)

Metallurgy shows us that any two similar metals that are truly clean (right down to a molecular level) will begin to stick back together if left touching for any length of time. The longer they are left this way (when the engine is not running), the more similar the metals are, and the cleaner their surfaces are, the more quickly they will begin to Microweld. When two Microwelded surfaces are pulled apart, molecules of metal are pulled from both, resulting in surface damage. After prolonged surface damage due to Microwelding the valve head and seat may not produce a gas tight seal any more. The simplest way to prevent or retard Microwelding is to add 'Dirt' to the surfaces of the two pieces of metal. That 'Dirt' could be the Oil we use to stop things siezing up, it could be Polish or Paint of some kind, it could also be the Soot produced by burning some fuels. It is convenient that Petrol combustion produces lots of carbon (Soot) whereas it is a little inconvenient that LPG burns much cleaner than Petrol and does not leave Carbon deposits. Thus, the cleaner combustion of LPG and other fuels (CNG for instance) can actually promote Microwelding.

Can an Engine with Hard Valve seats be damaged?

Valve damage can occur when running on any fuel. If the valves are made to run too hot due to incorrect fuel/air mixtures this may make Brinelling and resulting VSR much more likely. Incorrect fuel/air mixture, especially if too weak, can overheat the valves, resulting in accelerated Brinelling. It is important for the correct mixture to be supplied to the engine whether it is being run on Petrol, LPG or any other fuel.

In Conclusion

It would be incorrect to heap all if the blame for VSR on LPG.

If an engine's valves are truly fit to run on modern unleaded petrol (for any reasonable length of time) they are good enough to run on LPG with no additional problems, and it must be remembered that all of the effects described above still occur when running an engine on Unleaded Petrol, especially if the valves have been 'engineered down to a price'.

The plain fact is that ALL engine valves will reach the end of their useful life at some point.

Nothing lasts forever, although valves with harder seats made out of quite different material to the head and stem assembly will definately last longer when running on any fuel, as will desmodromic valve arrangements.

Finally, note that most modern LPG systems depend on the car's original [petrol] fuelling system to deliver the correct mixture at all times, e.g. if the petrol system delivers weak mixtures that is a problem in itself, and will be translated directly into weak mixtures when running the engine on LPG simply because the LPG system is doing what it is told to do by the petrol system. In a case like that, the LPG system and the installer cannot be held responsible - it is an ordinarily (as if it were unconverted) car maintenance issue, not an LPG issue

Certificates for insurance companies. This is just a requirement that some insurance companies request, there is no legal requirement for the insurance company to ask. The request from some insurance companies who request further certificates X years later is not a request which backed or needed by law its just something some insurance companies request. I have never in 16 + years of LPG motoring ever been asked for further LPG safety certificates further on down the line.

Hopefully this will give you the confidence to convert your LS to LPG and sleep peaceably knowing your bank balance doesn't go down as quick, as LPG is half the price of petrol. Your doing your bit to help the green brigade and your engine will last even longer because you don't have the pollutants that petrol has.

Make sure you research carefully whoever it is you choose to install your system. All info with thanks to Steven P. Sparrow BSc (Hons) Good luck with it Mike.

[Mybikes a cx500]

Facinating stuff Bluesman, but the desmodronic aspect of valves refers to the way they close:- Desmodromic valve - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Desmodromic_valve

A desmodromic valve is a reciprocating engine valve that is positively closed by a cam and leverage system, rather than by a more conventional spring

[Bluesman]

Facinating stuff Bluesman, but the desmodronic aspect of valves refers to the way they close:-

Desmodromic valve - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Desmodromic_valve

A desmodromic valve is a reciprocating engine valve that is positively closed by a cam and leverage system, rather than by a more conventional spring

Hi Ian. Many thanks for pointing that out. You wouldn't believe I proof read that a dozen times and never picked it up. I will point it out to Steven P. Sparrow BSc (Hons) from who I got most of the facts and figures. Regards Mike

[jimmy-g]

cheers for all the info mike,already got a few people in mind if i go for lpg, tubbs in ludlow or profess gas,jimmy

[7149capricorn]

Glad to have engendered so much comment. Bluesman, you really should attribute your quotes, especially if you are going to copy out so much material from the internet. And other readers may be interested to learn about the credentials of Steven P Sparrow - try this link:

http://www.lpginfo.co.uk/whoisgolpg.html

Information I have got from a number of LPG fitters suggests that up to the Mk4 LS400 valve seats were sufficiently hardened; with the 430, emission controls meant that modifications to the seats were made resulting in them being more prone to wear. I don't know how much truth there is in this, but it fits with my experience. The bottom line is, if you are thinking of going the LPG route, find out as many facts as you can and don't be swayed by anecdotal evidence.

[Bluesman]

Glad to have engendered so much comment. Bluesman, you really should attribute your quotes, especially if you are going to copy out so much material from the internet. And other readers may be interested to learn about the credentials of Steven P Sparrow - try this link:

http://www.lpginfo.co.uk/whoisgolpg.html

Information I have got from a number of LPG fitters suggests that up to the Mk4 LS400 valve seats were sufficiently hardened; with the 430, emission controls meant that modifications to the seats were made resulting in them being more prone to wear. I don't know how much truth there is in this, but it fits with my experience. The bottom line is, if you are thinking of going the LPG route, find out as many facts as you can and don't be swayed by anecdotal evidence.

I did. See post #78, I had forgotten to attribute it in post #76. I have now done the attribution for Steven P. Sparrow BSc (Hons) on post #76 I have still yet to hear from any LS430 owners of VSR which has firmly been attributable to LPG. The more likely hood is that the engine set up had been wrong. The 460 cannot at this time be converted because of direct injection and engine management issues which cant be overcome. Give it time and they will. Mike.

[Chris Skelton]

That's 'likelihood' Steve! (-:

The other type is US slang for bonnet!-of car.