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I'm amazed at the thin oils used in such old, high mileage engines.
Comeon buggers, think of when you're old and your cartilidge wears out between yr bones - the aches and pains - makes you wish you had "THICKER" cartiledge.
We all know that older engines no longer have the same tight clearances as new engines - that's why some guys experience oil consumption with thin synthetics - clearly the oil does not provide adequate protection and lubrication at cold start-up.

Don't get me wrong, I'm all for synthetics, but only from 20W - 50W to 20W-60W.
I use Castrol 20-50 (non-synthetic as we don't get synthetics that thick) and my engines run super-smooth - without taps and knocks, leaks - and zero oil consumption - and the oil remains superclean.
What more could one want?

An older engine in good condition that is using oil is running on too thin an oil for cold start-ups.
An older, higher mileage engine, in my opinion, is not suited for such thin synthetics.

"clearly the oil does not provide adequate protection and lubrication at cold start-up."

And cold start-up is critical as most engine wear occurs when the engine is cold - why then run it on such thin oil (in places like RSA and OZ) which will just accelerate engine wear ??

I use Castrol GTX (original formula) 20-50 in my 450 and my 6.9 has Redline synthetic 20-50.

I have no problems with either except the cost of redline is now $135 per 3.6 litres and at 12 litres for a 6.9 it's a bit of a knee trembler but there is zero consumption and zero problems.

I have used Castrol synthetic 10-60 in the past with no problems.

Bill

Check the leads are connected to the right plugs.  I'm probably wrong but I've had this before.  When hoplessly mistimed and misfiring after putting the distributor back in and some injectors not working I've noticed a "donk" as the engine wallowed on a few cylinders then failed.  It was some time ago but never thought much about the source.  It sounded like that wooden mallet sound TJ spoke of, not just a single knock but it would just happen before the engine stalled.  I timed the engine at idle and the stalling stopped but I couldn't get rid of the misfire and an occasional knock but not pinging.  Two ignition leads were on the wrong plugs   Who knows what damage I've done trying to rev that misfire out.  But it was 3+years ago, it's still a better beast now than it was when I got it.

The thing is, I haven't noticed it again, even though now my plugs seem to foul easily over this winter and there's at least two cylinders misfiring during a cold start.  Still no knocks during a misfire and when running warm, all is well.  Anyway, if the leads are fine, I'd visit the LPG place if it only started occuring after the LPG install.  Get their thoughts on what's going on.

Re: the oil, (pompy will be shaking his head in disappointment)  but not for long  .  Early last year I started on full synths, Mobil  5w-50 and this year to Castrol 10w-60.  I'm really not sure what to think.  I am blowing smoke on a cold engine during acceleration that clears when it's warmed.  I have relatively new valve seals and no smoke on the overrun, so this stuff is going past the rings.  I would go thicker synth but it's hard to get hold of in my town.  I agree with the notion of thicker oil regardless what you use.  Higher tolerances, worn surfaces and bigger gaps need thicker oil.  All depends on how worn the engine is I suppose.  My 350's done over 400,000km and was abused by the previous owner so far as oil wasn't changed very often, just topped up.  The thinner synths - I've changed the synth oil three times in the last 15 months with only 5000km approx travelled and have noticed the oil not only comes out black, but stinking of fuel as though you could set it alight.   It's done a lot of cleaning I'd imagine and although I've heard that black is nothing to be worried about,  to my mind it means impurities and the oil loosing its characteristics.  The blow by gasses and other crud is turning this thin oil into water.  Well, sort of.   Next change, if I can't find a thicker synth, I'm going back to thick mineral. 

When my 6.9 is on the road, I'm sticking with GTX 20W-50 with 5,000km changes.

Tim

Hah!  (tosses his cape of crepulence over his well-engineered shoulder)

I stand affirmed.

Begone with your unhappy knocks and watery oil-like substances.

Petroleum - the thicker the better!

Hey guys finally got around to taking a video of my engine and the noise it seems to make. It doesnt seem to make it when its completely cold,and the car idles fine when cold.  After it warms up a little and the idle drops, and the car is sitting around the 80 degree mark, thats when it seems to get really loud. The car also struggles to idle when in drive at this time.

After the car is completely warmed up (around 85-90 degrees) the car runs great and the noise seems to get quieter.

Anyways check this out -
http://hk.youtube.com/watch?v=nnU6lZjqxIM

That's very noisy, there's something wrong there.

If the oil pressure is acceptable, I would think it might be detonation of sorts. You should check the ignition timing, mixture and spark plugs ASAP. I would not be driving the car until it is fixed... engines do not enjoy making sounds like that.

Tim

It would also be a good idea to pull the oil filler cap off and have a really good look at the camshaft/oiler pipe and ensure it isn't loose. The top end also sounds noisy, although perhaps the tappets just need adjusting.

Tim

the frequency of the noise is 360bpm, which is exactly half of the idle revolution speed.

it could still be the bottom end, making the noise on the power stroke of one cylinder (every second rotation), OR every rotation of a camshaft.

Sounds worrying regardless.

Sounds like a diesel. 

Good pick up Pat on the frequency.  I was reluctant to say it's just tappets because whilst some of it sounds valve related, it still sounds like something else is going on.

First step Ryan, have to take both rocker covers off and inspect the cams, oil pipes, valves, rockers and cam bearings.   Check that all rocker retaining springs are intact and look for dry components.

Whitey did the same thing on Saturday, 360bpm loud-as-all-getout knock until it'd warmed up and I'd given it a few revs.

Curious because it has sat since the sandown race day where it has been revved regularly to over 5000.  The knock sounds like from the front of the engine, at the top, like the tensioner isn't pressurising... Also as I've stated many times before, whitey has the lowest oel pressure of any M117 but still hangs in there...

What I would do Ryan is go to a you-pull-it type wrecker which has a D-jet 350SE or 450SE and remove and buy the chain tensioner, for testing purposes, and see if the tone of the knocking changes/goes away.  If so, renew your cam oiler junctions on both cams and install a new chain tensioner.

I'm going to check the cam oilers on whitey this weekend.

Ian.

Thanks for all your help guys. It seems to have only been doing it since its been converted to LPG. Do you think it could be running too lean ? Or perhaps the installer didnt adjust the ignition timing correctly?

Oil pressure is at the top of the guage (3 bar) so that seems ok, although i guess i could try a thicker oil.

I hope its not the chain tensioner because that sounds like a big job.

I was under the impression that if it was bottom end it wouldnt get quieter as the engine reaches operating temp?

Chain tensioner is real easy its just two bolts and the unit sticks out the side of the engine behind the alternator.

Remove the battery and battery tray and you'll have plenty of access to the tensioner.

Ian.

Just on this point, the indicated pressure is measured from the left hand bank, the hose is connected to the block or head (can't remember exactly) facing the firewall.  Just because it shows 3bar doesn't mean the rest of the oil circuit is getting enough oil, there could be a blockage above the cams or elsewhere like the tensioner that 13B mentions.

It seems too coincidental that the knock occured after the LPG install.  No idea what they could've done to cause it though.