Knocking/tapping sound in VS ecotech 3.8L gets louder with RPM

[norlesh]

Hi all, first post so be gentle. Had an LPG backfire in the VS 3.8L while on the freeway (blew the clips off the air filter box) and now the engine is making a very distinct knocking/tapping sound that gets louder with revs. Prior to this there was a different tapping that went away with revs on LPG and wasn't there when on petrol - I don't think it's related since the sound was different and the new noise is in both LPG and petrol - really hoping its something that doesn't require the engine out! Any thoughts / suggestions much appreciated.

Update: Just noticed in the shed that there is coolant leaking from the engine somewhere which is a new thing also

Made a recording of the sound if that would help anyone with diagnoses - [video=youtube_share;pQxu3G_XFkU]http://youtu.be/pQxu3G_XFkU[/video]

 

[PlenumBiscuit]

wow thats definitely a knocking & not a tapping

the boys helped me recently with a tapping so maybe unrelated but i got this kinda advice.....


check spark plugs are in properly and not broken
are spark leads on too
check oil level is full, use 20-50 mineral oil
i had to change a PCV valve on inside the manifold
my intake manifold bolts were all loose

a few checks to check but your sound seems a heavier knock unless its spark related

 

[HICOMPVN]

I wouldn't be running that engine at all, ne more and your doing damage, to me it sounds like something has worn away, and you have a lot of play on engine internals, crank to connecting rod bearings, conrod to piston, gudgeon pin worn, or you could have even done a cam lobe, it sounds tooo metal on metal sound, like cast iron on cast iron. if I was you I would be pulling engine out and opening it up..!!!

 

[Wozza]

Hmmm thats pretty nasty...check the harmonic balancer hasnt spat the dummy...the rubber brakes down and the outer shell can spin independently of the center hub causing a very loud noise like that.
remove the belt and see if you can move the outer shell without he motor turning over it will only move about a inch or so back and forth and will need a fair bit of force (you can also try running the car without the serpentine belt for a few seconds, with no load on the balance the noise should stop or be very minor)
if its fine..run the car and pull CAREFULLY one spark plug lead at a time, if the noise go's away or gets less then a big end or little end has gone on the cylinder of the lead you pulled....

 

[norlesh]

just took the belt off and tried it and noise is just as bad

 

[Wozza]

just took the belt off and tried it and noise is just as bad

ok try removing the spark leads one at a time, use a rubber glove and a pair of pliers..if the noise gets less or go's then maybe an internal bearing gone, if not then you may have dropped a valve..
Im thinking a little ends gone, the noise before may have been the little end rattling... then when it backfired it put to much stress on it and it gave away....cant really think of anything else soz

 

[IBLOWN]

Replace motor. Shes dead. Bottom end fo sho.

 

[norlesh]

ok try removing the spark leads one at a time, use a rubber glove and a pair of pliers..if the noise gets less or go's then maybe an internal bearing gone, if not then you may have dropped a valve..
Im thinking a little ends gone, the noise before may have been the little end rattling... then when it backfired it put to much stress on it and it gave away....cant really think of anything else soz

Couldn't tell any big variation after removing each spark lead - my left arm can attest that sparks are being delivered

 

[Wozza]

The test is definitive, I suppose if the little end has broken apart and dropped down into the sump its still going to be noisy, but with out the bang on top should quieten down a bit....
If its just a valve thats dropped then your only looking at removing the heads to fix, that said your not going to get much change from 1K unless you can do yourself, even then its prob going to cost as much as a 2nd hander....

 

[norlesh]

The test is definitive, I suppose if the little end has broken apart and dropped down into the sump its still going to be noisy, but with out the bang on top should quieten down a bit....
If its just a valve thats dropped then your only looking at removing the heads to fix, that said your not going to get much change from 1K unless you can do yourself, even then its prob going to cost as much as a 2nd hander....

Well since its sounding f'd might have a poke around inside the engine to do some lernin before I decide whats to be done with the carcas. Are there any good videos or sites that give a birds eye of the inner workings of similar engines? I have the Ellerys book but that's about as clear as sump oil in places.