LPG - valve issues

 
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lowcatjo
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PostPosted: Mon Sep 18, 2017 7:58 am    Post subject: LPG - valve issues Reply with quote
I have lived with LPG since 1999 and it has been OK. Power is slightly reduced, but costs make a big difference.

I am worried however about possible valve issues.

I have had at least 4 cracked valves since then (2001 (catastrophic engine failure), ~2006 ~2014) and one in the middle. The middle one I had put down to parts quality. But this has got me to thinking.

Every time a valve goes, it leads to it being a new head, because of some form of collateral damage - be that valve seats or valve guides.

Following on from my last posting about the rattle. Having checked I am compression 1:160 2:150 3:160 4:160. Exactly the pattern last time I had no 3 valve split. So I'm worried no2 may have gone again.

Cost vs benefit. Any thoughts, because if it is another one, and looks that the gas it at fault, I am contemplating taking the whole darn system out...

Anyone any experience with LPG and thoughts about my rate of attrition with valves at all?

I know that Leics had gas powered ambulances 1970s / 80s and had massive problems with valves.
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Last edited by lowcatjo on Wed Sep 20, 2017 6:32 pm; edited 1 time in total
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Alan Drover
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PostPosted: Mon Sep 18, 2017 12:51 pm    Post subject: Reply with quote
Afternoon lowcatjo
I wonder whether LPG burns at a higher temperature than petrol but I have never heard of that happening. Of course the cylinder head needs to be converted to unleaded for LPG but I would have thought that would cause valve failure. Might be worth getting the system checked professionally as there might be a problem in the system itself.
. Alan Drover
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Geoff2
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PostPosted: Tue Sep 19, 2017 11:39 am    Post subject: Reply with quote
I took one of my vehicles into the garage today for its MOT and I mentioned this issue to the mechanic whilst chatting. He said the timing really needed to be set differently depending on whether the engine is using lpg or petrol and that there is a device that can be fitted to electronic ignitions in the distributor which will change the timing as you switch between the two. I know nothing about this myself as I've never considered an lpg conversion but wonder if you've considered the issue at all.
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lowcatjo
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PostPosted: Wed Sep 20, 2017 6:31 pm    Post subject: Reply with quote
Hi.

Was that Chris you chatted to by any chance, Geoff?

The system was professionally fitted and is annually maintained by a competent engineer, so should be ok. I have the timing set for LPG, and that side is fine.

I guess it's one to see if it is another cracked valve and go from there.

Head is unleaded Turners. Supplied Recon exchange on last failure. Just frustrating...
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"I may be old, I may be slow,
but I get to places you'll never go"
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Alan Drover
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PostPosted: Wed Sep 20, 2017 7:04 pm    Post subject: Reply with quote
Evening lowcatjo.
My knowledge of LPG systems is non existent but one thought. What about the spark plugs? Are they the right temperature range?
. Alan Drover
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Geoff2
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PostPosted: Wed Sep 20, 2017 8:09 pm    Post subject: Reply with quote
Quote:
Was that Chris you chatted to by any chance, Geoff?


Yep
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Dave88
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PostPosted: Thu Sep 21, 2017 9:04 pm    Post subject: Reply with quote
I ran a Disco V8 with LPG for 80,000 miles with no major issues - in fact I never needed to take the heads off.
I remember a few things unique to LPG.
LPG has different timing requirements - in fact not only does it typically need more advance at say 3000rpm to get the best from it, but the "advance curve" is different to that of petrol. Ideally you need a distributor that's set up with weights/springs to give an LPG shape advance curve.
I tinkered with my ignition timing to get a good compromise but stuck with the petrol curve (i.e. standard distributor), with a few degrees more advance than normal at idle IIRC and always used 97 octane petrol for starting.
Also, LPG does not make the same "pinking" noise as petrol, so you can have detonation without realising.
And if you don't have a feedback loop (i.e. oxygen sensors and an ECU) the mixture then needs to be set manually and professionally. And if the timing is not optimal that will be hard to get right.
Some people recommend a "bigger spark" coil set up as it's harder for the spark to jump across with LPG, but I ran standard plugs with the gap about 0.1mm smaller than usual with no issues, other than when I tried a cheap rotor arm and got lots of mis-firing!
You do need top quality plugs, rotor arm and cap as you've probably found.
I do miss paying 60p a litre. Smile
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lowcatjo
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PostPosted: Mon Sep 25, 2017 4:47 pm    Post subject: Reply with quote
So the latest update.

Gas system is annually checked and serviced by an approved engineer (has to be for insurance) it is due December.

Looked inside No 2 with an endoscope and there is what appears to be a burn hole on the inlet valve. Head will come down at the weekend.

I also checked dates and the last wasn't very recent, it was actually 2011.

The one before that was down to poor quality parts and the one before that was interesting. So conclusion, the Turner's head was good (one on order now).

I will then be keeping a Turners head in stock for when this one maybe needs a swap.
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but I get to places you'll never go"
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