LPG and damaged valves

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LPG and damaged valves

Post by bushwhacker on Tue May 28, 2013 4:39 pm

One for HJ since he did play with an lpg van but also anyone else who may have ideas.

Does lpg cause burned or damaged valves?

The reason I ask is that I was told on Saturday of a case where a Porter 1.3 had damaged valves in no 3 cylinder which was ascribed to a known problem with running on lpg. The advice was that lpg engines should be run occasionally on petrol to stop this but I am not sure what that amounts to.(In any case most people run lpg for the cheap fuel so having to run it for a while on expensive fuel seems to rather defeat the object). I was also under the impression that any engine could run on lpg if it could run on unleaded (all cars these days).

The vehicle in question was converted at the same place mine was and has done about 55k miles since.

Has anyone looked at the valves on an lpg engine at similar mileage and were they ok?

In my case I do not do a high mileage so it will probably never affect me but I am having other problems and am getting rapidly fed up with the whole thing! (The vehicle is rapidly turning into a money pit!).
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Re: LPG and damaged valves

Post by HighlyJetted on Tue May 28, 2013 11:23 pm

I stripped the head on that LPG one with 80k and the valves were beautiful - how much LPG it had ran is something I will never know.

If you were to blame LPG which causes "valve seat recession" Read me LINK

then I would expect to see more that one valve in the head show the same issues - at a guess anyway as I'm no expert or even experienced in this field.

Lots of valves fail that run purely on petrol, they are mechanical components that work in the most extreme of enviroments - heat, pressure, cooling down and warming back up. They get a damn hard life.

Woody has ran his van(s?) on pretty much 100% lpg for a good while if I understand correct, and I don't think he has had any failures. Chip in!

El_venturo seems a bit paranoid of valve seat recession as I think in Italy they do alot of LPG, and they have poor quality cars like Fiats Wink and Opels Crying or Very sad , which are very prone to valve failure anyway in our country where they are ran 100% on petrol.

I can only guess many people blame valve failure on LPG, where many of the actual failures are just plain old valve failure.

I think the way to tell is strip it down and see what damage is done, then make an unbiased guess at the cause.
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Re: LPG and damaged valves

Post by Guest on Wed May 29, 2013 12:47 am

I certainly concur with you on that HJ.. In the time that I was working at Romahome we sold over 350 of them while I was there ( and they sold a lot more than that between 1989and 2004 when I delivered the very last one they built to the gorgeous THAI solicitor in Croydon or Merton to be precise.

I cant recall of ANY we had to recall or refer to a Daihatsu Dealer in the 2 years I was Service and Warranties there.

It seems to me that these Garages make up these stories to get business or " seem very knowledgeable when in fact they know sweet FA.

The "R" reg Silver 3 cylinder MPV I bought at the weekend had a rad weep

and the garage told him that the "Throttle Body" was knackered and needed a new one.

HJ and I were talking about it last night and its so sad that customers

get ripped off because the garages dont know what they are talking about.

I bet if HJ had a tenner for every time he has told people on here that it is

the warm up valve (cold start) under the the inlet manifold that gets an air

lock or no warm water to it he could have bought a brand new Piaggio

Porter by now. cheers

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Re: LPG and damaged valves

Post by Guest on Wed May 29, 2013 4:34 am

Oh hell it is 4am and I still cant sleep. Usually I put some of my favourite TRANCE music on--- I've got loads of Best Of Euphoria Trance CD's -- I just LOVE it.
Yes I know I am wierd liking that at my age. I have now got Trance FM on on the Internet Radio and my favourite Station is ENTRANCED FM. I love being different to all the rest of all the other Old Farts my age

At least my Grandchildren think I am COOL liking THEIR music. Crikey, I was listening to it before they were born !!!


Anyway back on the previous Garage rip-off subject the one that makes MY blood boil ( you have got to be on my wavelength to see where I am going with this line of thinking )

Your Hi-Jet is overheating or any car( thats watercooled ) --- I know of at least one certain comedian up there in Kilmarnock who would suggest that a V-Dub Beetle wouldnt ).

The usual Con man Back street garage comes out with " oh yeah your water pumps gone mate. you need a new one ".

WHAT ?? Where's it gone ? It' still there and going round so how the hell can it have "GONE" ?

The only two things that can go wrong are the bearings wear and /or cause a leak/ or the water seal leaks and you loose your water that way.
If it isn't leaking then it CANT cause the engine to overheat.

What a lot of cobblers!! How many of you have fallen for that old trick ?

IN all my years working on cars I have only ever seen ONE impellor come off -- on an Anglia.

Dont get caught out by that old load of Cobblers again -- PLEASE.



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Re: LPG and damaged valves

Post by HighlyJetted on Wed May 29, 2013 11:03 am

I've seen a couple of water pumps that have been full of rust/radweld buildups and instant gasket - one on a landrover non the less!
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Re: LPG and damaged valves

Post by Guest on Wed May 29, 2013 6:10 pm

H.J. You and Logi told me not to use the L.R. swearword on this site . Very Happy Utterly Disgraceful !!! Youth of today. There's no hope.

Yes I have seen them gunged up with rust on the old cast iron impellors but most are stainless today --or even on poor quality imports -- Aluminium.
But they have still been swilling the coolant round though.

When I found that Anglia pump with the impellor rusted right off I could'nt believe it --- or stop laughing.

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Re: LPG and damaged valves

Post by 8bit-ash on Wed May 29, 2013 7:58 pm

When I did my HG I changed some valves as they where worn. under 40k miles. Whether the two are linked who knows but the guy that skimmed my head said a local taxi firm bought a load of LPG cars, alot had valve wear issues after not that many miles.
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Re: LPG and damaged valves

Post by HighlyJetted on Wed May 29, 2013 8:09 pm

I wonder how well most after market LPG installations are tuned?

Reading about El_venturo misfiring issues, and then the improvement after he has tuned his setup is just the tip of the iceburg.

Car manufactures spend a lot of money and time developing the engine management system for a particular engine, with hundred of hours of rolling road time plus test track time and data logging.

LPG kit installers seem to be able to tune them in a couple of hours - seams a bit odd to me does that.
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Re: LPG and damaged valves

Post by 8bit-ash on Wed May 29, 2013 8:18 pm

I've always assumed its because of the clean burning and lack of additives.
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Re: LPG and damaged valves

Post by rich the mechanic on Wed May 29, 2013 8:49 pm

8bit-ash wrote:I've always assumed its because of the clean burning and lack of additives.

Form what I have read up on the subject it is that and that LPG is harder to ignite so it puts a lot of load on the ignition system so in my mind if not for real it will make the engine work harder also it is supposed to create less power which also backs my theory up at least to me anyway.

As for rip off garages I have worked in the trade long enough to be very untrusting and nobody except the MOT man touches my cars/bikes if I can help it and I chose them very carefully and I need some tyres so I stopped off at tyre place to see if they had some and the guy just wanted to sell me tyres from a Mini.
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Re: LPG and damaged valves

Post by HighlyJetted on Wed May 29, 2013 9:01 pm

Being interested in alternative fuels and niche subjects I have done some reading into LPG tuning in the past.

LPG burns at a different rate with a different resistance to detonation. Doing a little digging the ignition timing curve looks different for LPG to Petrol, due to the burn rate differences in the fuels:-



The LPG hijet setup I've messed with (prins) uses the same ignition map for both LPG and petrol as the ignition timing is controlled by the daihatsu petrol ECU.

Looking at that graph, when burning LPG on a petrol ignition curve, below 2500rpm the timing is way too late so the burn will still be occurring during the exhaust stroke causing valve seat burn damage.

To add to Rich's statement - the mixture of air and LPG gas does not conduct electricity as well as it is "dryer", so the plugs should be gapped smaller, and if possible a higher spark voltage coil used.

On the average LPG conversion, non of these factors are really addressed.

LPG actually has the potential to make more power than petrol if correctly tuned due to it having a RON of 106. So you could increase the compression ratio considerably and thus make more power. It does contain alot less energy than petrol per KG, and you get less KG per litre as well - but you make up for this by burning more of it at a time, just like methanol etc. Diesel contains the most energy per Litre, to quote some wikipedia:-


Diesel 38.7MJ per litre
Gasoline 34.6MJ per litre
Bio-Diesel 30.5MJ per litre
LPG 22.2MJ per liter
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Re: LPG and damaged valves

Post by Guest on Wed May 29, 2013 11:39 pm

I AM AFRAID THAT SOME OF YOUR FACTS AND FIGURES ARE AT THE MOMENT A LITTLE OVER MY HEAD.
I DO FIND THAT IN MY O3 PLATE MPV THAT IT DEFINITELY PREFORMS FASTER ON LPG THAN ON PETROL WHEREAS ON ALL THE OTHERS IT WOULD BE DIFFICULT TO SAY IF THERE WAS A DIFFERENCE ON ACCELERATION.
THEY DO USE MORE LITRES OF GAS THAN PETROL BUT AT ALMOST HALF THE PRICE IT IS A GOOD BIT CHEAPER THAN PETROL TO RUN.

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Re: LPG and damaged valves

Post by bushwhacker on Thu May 30, 2013 2:28 pm

Thank you for the link HJ. My vehicle more or less runs on lpg all of the time and has done for about 3 years but doesn't do a high mileage. LPG does make it run quieter which of itself may make it seem to accelerate better but I think it probably actually does.

From the link:

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.

His Piaggio Porter is actually a 2007 model whereas mine is in fact a 1996 so I would guess from the above that I will probably be ok.

(Like you, I would also have thought that all cylinders would be affected.)


Last edited by bushwhacker on Sat Jun 01, 2013 12:22 pm; edited 1 time in total (Reason for editing : Correct Porter year.)
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Re: LPG and damaged valves

Post by El_Ventu on Tue Sep 24, 2013 12:50 pm

HighlyJetted wrote:
El_venturo seems a bit paranoid of valve seat recession as I think in Italy they do alot of LPG, and they have poor quality cars like Fiats  Wink  and Opels  Crying or Very sad , which are very prone to valve failure anyway in our country where they are ran 100% on petrol.
I'm not paranoid No , the fact is that I live between mountains, small engines were overloaded driving on mountain roads.

Fiat engines aren't of poor quality, even as car bodies were rusty already in the catalogs...Laughing 
Fiat is the only one make in the world that have a huge know-how on LPG and CNG factory fitted since the early '90...

And fiat engines runs perfectly on LPG and CNG from decades.

The same thing I've seen on older opels, I've seen and driven a Kadett Club 1.4 8valve that runs only on lpg for over 300'000km.

At that km engine were worn out, but it is still running.

On some japanese engines, instead of using the hardest materials for valve and seats surfaces, they use hard valves on "not so hard" seats, to improve sealing thanks to a better self adjustment between valve and seat in break-in period.

But a "soft" valve seat wants slightly higher lubrication to run properly, lubrication given by the ridiculous amount of soot in the exhaust gases, and soot pratically disappears from exhaust gases of engines running on LPG, or in a worst case, running on CNG, that have also a noticeably longer combustion angle, with higher exhaust gases temperature.

However it seems that our engine, both the 1.0 and the 1.3, have no or little problems with valve seat recession.

In any case, running on an injected system, I set a certain amount of petrol injection on medium to high engine load.


This cost me about a half gasoline tank every 16 to 20 LPG tanks refill...

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Re: LPG and damaged valves

Post by El_Ventu on Tue Mar 18, 2014 10:13 am

Er...
It seems that all my misfiring issue comes from an wrong play setting.
I think that the mechanic that changed the engine head gasket before I bought my van has to repair shoes instead of engines.
Now my engine runs perfectly...

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Re: LPG and damaged valves

Post by HighlyJetted on Tue Mar 18, 2014 10:22 am

Here is a 1970's article from practical motorist regarding converting your car to LPG.

http://www.gaspoweruk.co.uk/history/images/petrolvspropane.pdf

My grandad has a Morris 1000 or something back in the 60's on LPG
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Re: LPG and damaged valves

Post by El_Ventu on Sat Mar 22, 2014 2:49 pm

"The equipment [...] is made by Landi den hartog".

Like mine, Landi

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