Fuel Economy Issue

[dom14]

If it blows a little blue smoke on startup it may be your valve stem seals are shot.
Question do you run an upper cyclinder lubricatant or Valve seat saver.
You could have valve recession, typically a head would only last about 200k before
requiring a head relacement with SS valves

I've been told these engine's built in late 80's onward don't need the upper lubricant protector or valve seat saver, 'cos the valve seats are already made to overcome the issue of excessive wear from unleaded or LPG or high octane petrol.

The head was done few years back by me(a partial rebuild) and I did the valve seats manually using grinding paste.
I took it to a head rebuilder to get the cracks welded and have it machined, the rest was done by me.
I focused mostly on exhaust valves and seats. I should've done the valve stem seals at the same time, but for some reason forgot about it or didn't have enough time or new seals ready. I did a partial rebuild 'cos I was bit paranoid about bottom end failing due extra compression from any new valve seats, valves & head machining.
I reckon valve stem seals are still ok though. No blue smoke per say, but just condensation on cold start, which used to take ages to go away, but since I installed the brand new thermostat, the condensation appeared to have disappeared for the most part.

[threedogs]

never heard that about petrol patrol heads, will ask around not that Im doubting you
Its a dying art hand lapping in valves a skil almost lost Me thinks lol

[dom14]

never heard that about petrol patrol heads, will ask around not that Im doubting you
Its a dying art hand lapping in valves a skil almost lost Me thinks lol

It wasn't that hard. I just used valve grinding paste and kept rolling the valve stem with my palms, back and forward.
Then I checked how go it is by filing up the valve seat with bit of water and see for leaks or blow bit of air from air gun to see if it bubbles up, while holding the valve. It's mostly the exhaust valves that tend to burn a bit(that if it happens). Mine wasn't that bad, but I did the valve seat grinding anyway. If I knew better, i would've used a rubber hose attached to the valve stem and other end of the rubber hose attached to a drill.
It was a good exercise.

Yes, definitely the cylinder heads from 90's onward were LPG ready.
I think the reasons for some of the LPG engine valve seat recession was due to bad tuning and cheap LPG installations. You still could've or can go for stainless steel sort of valves to lengthen the life of the valve seat, but the seats themselves were already LPG ready from what I've heard so far. I don't know if that's the case for all LPG converted engines, but I think it is for most engines. Most LPG issues were/are from bad installations and bad fine tuning of the ignition system, I think.

[mudnut]

Was talking to the dyno guy on Monday when I got the Falcon's gas system tuned. He said: "No matter how much work you put into the head and valves, LPG will cause valve recession because it is dry."

I asked him if I should fit a lube system, and he said: "That stuff does bugger all really as it sticks to everything and gums it up. It does however, work when running on petrol as it gets dissolved and flows to the valves where it should be."

[dom14]

Was talking to the dyno guy on Monday when I got the Falcon's gas system tuned. He said: "No matter how much work you put into the head and valves, LPG will cause valve recession because it is dry."

I asked him if I should fit a lube system, and he said: "That stuff does bugger all really as it sticks to everything and gums it up. It does however, work when running on petrol as it gets dissolved and flows to the valves where it should be."

To tell you the truth, mine didn't have much(or any) valve recession that I could easily detect.
I think it changes from engine to engine. The "dryness" of LPG is something I'm yet to understand in detail.
When compression stroke happens, ideally the valve seats should not be affected. Intake and exhaust strokes cause LPG gas & exhaust fumes to go pass the valves. If he is right about that, then the passing exhaust of LPG must have some properties the valve seats does not like.
Other explanation might be that since the timing needs bit of advancing the valves aren't properly seated when combustion starts?!
I prefer the first hypothesis, 'cos it's generally the exhaust valve seats that are more affected, but that's the case with other fuels too.

I believe(meaning along the lines of a hypothesis), not fine tuning the LPG ignition curve is the real reason.
Since LPG burns differently to petrol, the ignition curve adjustment need to be fine tuned with modifications to the ignition system, for example something like "dual curve ignition unit" that advances the timing a bit initially and retards is a bit later with warmed up or higher revs.
I'm sure that's the case with petrol as well, but the curve is different, which means the ignition fine tuning system has to be different to suit LPG.
For example, typical vacuum advance system in RB30 Patrols, etc are not designed for LPG, but for petrol combustion.

[mudnut]

Have a quick search for Valve recession online. I have found a few forums with threads that explain it.

Here's an Ad but it does explain it. https://www.youtube.com/watch?v=9VR_FE65zpo

[dom14]

Have a quick search for Valve recession online. I have found a few forums with threads that explain it.

Here's an Ad but it does explain it. https://www.youtube.com/watch?v=9VR_FE65zpo

It's actually marketing ad for their upper cylinder lubricant.

For example it doesn't explain why LPG is more "abrasive" as oppose to petrol, where the petrol get it's lubricant properties.
Petrol enters the combustion chamber as a fine mist of petrol fume, so I'm not sure. It may have some lubricant properties for a microsecond prior to combustion, but I'm not sure how that affect valve seats.

I still don't understand that "dryness" concept.

Petrol as a liquid in room temperature might have some lubricant properties by picturing pouring a bit of petrol on to a fine piece of metal and sliding another fine piece of metal on it. If LPG actually does cause excessive valve recession on average non LPG engines, then it's not yet fully explained. Having said that, I haven't googled the subject heavily yet.

I still believe LPG is a good choice of fuel for properly moded engine for LPG, and the engine can last longer than most other fuels.
I think we haven't quite fine tuned the LPG engine to make it commercially successful as a good choice for traditional petrol engines.
As for the LPG price wise at the bowser, it hasn't been worth a great deal for a quite a while now. I keep it going in mine, 'cos it runs better than
petrol(well, except the LPG guzzling atm ).

[Turtle_au]

never heard that about petrol patrol heads, will ask around not that Im doubting you
Its a dying art hand lapping in valves a skil almost lost Me thinks lol

I used to lap the valves on my mini's but I didn't think you could lap the modern engines due to the harder or coated seats and valves.

Sent from my SM-T355Y using Tapatalk

[Turtle_au]

It wasn't that hard. I just used valve grinding paste and kept rolling the valve stem with my palms, back and forward.
Then I checked how go it is by filing up the valve seat with bit of water and see for leaks or blow bit of air from air gun to see if it bubbles up, while holding the valve. It's mostly the exhaust valves that tend to burn a bit(that if it happens). Mine wasn't that bad, but I did the valve seat grinding anyway. If I knew better, i would've used a rubber hose attached to the valve stem and other end of the rubber hose attached to a drill.
It was a good exercise.

Yes, definitely the cylinder heads from 90's onward were LPG ready.
I think the reasons for some of the LPG engine valve seat recession was due to bad tuning and cheap LPG installations. You still could've or can go for stainless steel sort of valves to lengthen the life of the valve seat, but the seats themselves were already LPG ready from what I've heard so far. I don't know if that's the case for all LPG converted engines, but I think it is for most engines. Most LPG issues were/are from bad installations and bad fine tuning of the ignition system, I think.

I roll between palms for about 10-15 sec ( you feel the valve drag) lift and rotate about 90 degrees and repeat.
Every 4th or 5th time I hold the valve up and squirt a drop of oil on the valve stem.
NEVER use a drill. It only rotates one way and it will kill your valve guides. Valve guides are designed for up/down motion not high rotational motion.
It's one of those jobs that you can't rush if you want a good result.

Sent from my SM-T355Y using Tapatalk

[dom14]

I roll between palms for about 10-15 sec ( you feel the valve drag) lift and rotate about 90 degrees and repeat.
Every 4th or 5th time I hold the valve up and squirt a drop of oil on the valve stem.
NEVER use a drill. It only rotates one way and it will kill your valve guides. Valve guides are designed for up/down motion not high rotational motion.
It's one of those jobs that you can't rush if you want a good result.

I don't think there's huge difference between using a drill and manual tapping in this case.
It's not that different from using a hand drill and an electric one.

A drill can rotate both ways, so that shouldn't be a problem. You can momentarily switch the direction of rotation.
You don't need to use a high speed drill, just a power drill/driver unit can do the job without using high speed.

Manual hand tapping can be good, but time consuming when you have twelve valves in a six cylinder engine.
With proper care and handing of the power drill/driver, it should come as good.

Squirting a bit of oil into the valve stem is a good tip, 'cos the rotating motion is not good for valve guides as you explained.

But, in hindsight, I should have replaced the valve stem seals, 'cos rotating motion is not good for them either, be it using hand or power drill. Besides valve stem seals only cost few peanuts, or they always come with the gasket kit.