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augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

okay, let me start by saying I'm was way overdue for an oil change.
I just got my timing just right with more vacuum holding at 16 .
Oil pressure has been jumping around and the wires to the sender are dry and cracked.
I have a new(used sender but have not got around to puting in yet.
Today on the way home it was warm out and the car was running well.
So-
I really winded it out on route 280 heading for the turnpike.
Running 3rd at 4500 to 5000rpm for a mile or 2.
This was a first for me for I never run it this hard.
I've had bad deposits that have been clearing away in the past on my valves.
When I slowed down at the toll booth and started up again I heard a pinging sound.
The sound was only on acceleration at about 3200 rpm to 4000 then it would blend away. Oil pressure stuck at 2 bar lower at idle.
When I got home I changed the oil and did not hear it the sound but I did not warm it up.
No metal in the oil ,just dirty
Oil pressure normal on startup.
What do you think?
I'm worried I threw something in the lower engine or caused some sort of damage .
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Smoothie · Posted: Wed Apr 20, 2005 11:01 am Post subject:

From connecting rod bearing failures I've had in other cars - it sounds like someone's in your engine hammering away. It hammers right from startup and at idle as well as when you rev it up, obviously changing speed with the rpms. -So with your description of it happening only on accelleration and at 3-4k, I'd say it's more likely knock (pinging) than a bearing problem.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Paul · Posted: Wed Apr 20, 2005 12:12 pm Post subject:

No metal in the oil?

Relax, a failing rod bearing will always dump metal into the oil.

That said, a healthy 924 will usually have about 4 to 5 bar of oil pressure above 3000 rpm and 1.5 to 2 bar at 1000 rpm.

Was your oil diluted with gasoline?

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Wow -I feel better Thanks
F-ing timing. It did sound like pinging.
Why all of a sudden after a hard run?

I'll see how it run after its' warmed up Tomorrow.
Thanks
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Paul · Posted: Wed Apr 20, 2005 12:39 pm Post subject:

Could be caused by deposits on the head, a cylinder running lean, or badly controlled timing among other things.

Is your vacuum advance connected and working? It actually retards the timing under acceleration to prevent pinging.

Smoothie · Posted: Wed Apr 20, 2005 12:51 pm Post subject:

Joes924Racer · Posted: Wed Apr 20, 2005 2:20 pm Post subject:

and maybe some bad gas thatll do it. Though youve
talked your out of it. I quote augi

'I've had bad deposits that have been clearing away in the past on my valves.
When I slowed down at the toll booth and started up again I heard a pinging sound.
The sound was only on acceleration at about 3200 rpm to 4000 then it would blend away. Oil pressure stuck at 2 bar lower at idle.'

The oil was dirty, probly a little heat build up. timing a little to advanced
and last but not least you were in the wrong gear werent you i rarely
do that like that in 3rd with the revs that high.... You must have a 4 spd.
plus you would see metal. Last rod bearing i spun just melted the shiny stuff the bearing and locked up the motor it spun at idle in a corner and just quite running. I had to pry the stuck bearing shell from the crank
all the metal melted in to a oil hole on a crank journal & the other time
which was the first time the bearing spun so badly... the rodrode the crank
cause there was only halfl a chewed up bearing left the other was chalk.
the motor would start that time though it clanked badly..then there was
the time with the amc concorde i had ( very similiar engines) and I was on my way to drill for the army reserves and I actually put a rod through the block to get there on time. So end of it is youd see metal in the oil as a giveway. Its good to be able to talk your way out of a problem
like that on the board.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

924RACR · Posted: Wed Apr 20, 2005 10:23 pm Post subject:

2 bar is not a great number at the high revs, but it won't do the engine in. My real-loose race motor, really only turns about 4 bar max at 5k+, but lives. As noted, it's kind of a hammering sound when the bearing spins/dies - though it's always been hard for me to note, due to a very loud car.

I'd agree it's likely a combination of deposits, bad fuel, retained heat, etc. Drive a little more gently and pay real close attention, especially to your oil pressure. And fix that sender!!! You deserve to lose the engine if you don't fix your pressure readings!

For the best confidence in your bearings, nothing will beat a tear-down - meaning drop the oil pan (requires removal of the LH engine mount, so you'll want a 4x4 to support the engine with a chain) and pull all the bearing caps one at a time. Don't do this without a torque wrench to re-torque them properly. Doesn't take that long. You could even just save yourself trouble and put a new set or rod bearings in anyway, for security - only about $60 for the bearing set, plus maybe $20 for the pan gasket. Certainly cheaper than a full rebuild with maybe crank and rod replacement, not to mention quicker!!!
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

924RACR · Posted: Wed Apr 20, 2005 10:24 pm Post subject:

Nearly forgot - you may want to look into the cooling system as well, see if that allowed it to get hotter than it should have. Also check the oil pressure relief valve/piston, make sure something didn't get shook loose to jam it.

Good luck!

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Joes924Racer · Posted: Thu Apr 21, 2005 11:26 am Post subject:

you can remove the bearing rod ends and check each bearing
[theres no shavings in the oil so why bothe]
coming up short of punching out the pistons to check the rings.
Ive broken rings also.
though it really sounds like a fuel ping & you seem not to be
able to get rid of it.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

924RACR · Posted: Thu Apr 21, 2005 10:45 pm Post subject:

Yeah, throw some octane boost or high-octane fuel in there, see what happens. Quite possible this distributor has a stuck advance mechanism - try pulling the cap and checking it.

To hold the engine, you cut a 4x4 to fit just between the fenders, on the rails where the fender bolts are. The chain is wrapped around the beam, and tied to the block anywhere that's convenient; I usually use a bolt into the AC bracket on the LH side of the block.

But I agree that would be more of a comfort thing, it's more important to look at your combination of octane and timing right now (before you do hole a piston).
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype