knock knock knock knock...

[PDX-944]

So this last weekend, I spent a bunch of money and stress on my first hillclimb event. I planned to race my autocross 944.
Friday night my friend and I drive down to camp out with a bunch of other racers (trailering 944x). Upon waking up Saturday, our neighbor says "Hey your tire is blistered." F$#@!
So I send jim (who isn't racing) to drive an hour and a half back to get our other tires put on the front wheels.
He gets back JUST in time. I throw them on, test drive down the street, all good.
I pull into grid and EEEEEEEEEEEEE. Rock stuck against my rotor.
I jump out of line, take the wheel off, dig out the rock, and jump back in line.
So my heart is racing (no pun) because it's my first hillclimb, and I've been running around trying to prepare.
As I launch and go about 1/4 mile I hear a new exhaust leak over the road noise and through my helmet. Wtf. Oh well.
2.5 miles of almost redline in 2nd gear/low 3rd, I cross the finish, slow down and hear knock knock knock... That wasn't an exhaust leak...

I stop and shut off the car (I also heard some squeaking noises from the engine). A few minutes later it won't even crank. Seized? A few minutes later yet, it fires right up. Oil pressure is good, oil is full, only knocks when revved.

I'm not sure what went. I thought I saw a metal flake in the oil at first, but it's not very obvious if its there.
Ill cut open the filter soon.

Thoughts?

I ended up racing my 911 the next day. The 944 is better

[CHICKS]

Cut open the filter and take pics. I bet you spun #2.

[Lapkritis]

If not #2 then perhaps an overheat and piston/cylinder damage. Rap is probably rod bearing or piston slap. After shutdown, temps can spike which would explain the seize. Hill climbs can be rough on engines with no cool down. If you shutdown after a hard run then ideally let it sit for ~30mins minimum before attempted startup again. This allows temperatures of the engine components to equalize and dissipate.

If you are equipped with an after-run auxiliary pump then these instructions don't apply. For a racer with frequent shutdowns throughout the day when hot, such a pump might make sense as a retrofit. Most OEMs run the auxiliary pump to off the head into the heater core... Useful for cabin heat in the winter without the engine running as well.

I'm just rambling now...need coffee.

[PDX-944]

My friend suspected piston collapsed. I guess I'll have to wait and see what I find.
But I will say it's still running very well even with the knock, so anything involving major loss of compression isn't the case I don't believe.
Unfortunately on hillclimbs you race to the top then sit in line for about 5-20 min, then drive back down. So cool down time is based on whee you are in line, and 2.5 to 3 miles of twisties is a long way to coast down with the engine off!
I don't have an aux pump, the only racing I've done until this is autocross and I just let it idle between runs

[ckelly78z]

It sounds like you may have spun a rod bearing, so check the oil pan for a golden sheen (rod bearing material). I had a bearing spin on my Datsun 240Z, and while it ran fine at a set RPM, any time I accelerated or let off, I heard the knocking (not ticking).

[PDX-944]

Ah so even with a spun rod bearing it could still be quiet at low revvs?
Its not until probably 3k that it starts knocking.

[DannoXYZ]

Easy enough to pull the oil pan and check the #2 rod-bearing to be sure. Could also be collapsed valve-lifter.

[guru944]

Pdx-944;
How was your oil pressure before at idle at 3k and once it started knocking? What kind of oil and weight are you utilizing. I pray you are running 10w-30 as factory specified (OEM). What motor oil filter is also incorporated? Look for the weakest link... keep us posted.
Later....

[PDX-944]

Originally Posted by guru944

Pdx-944;
How was your oil pressure before at idle at 3k and once it started knocking? What kind of oil and weight are you utilizing. I pray you are running 10w-30 as factory specified (OEM). What motor oil filter is also incorporated? Look for the weakest link... keep us posted.
Later....

Oil pressure appears to have not changed, still between 2 and 3 bar.
I run 20w-50, and oil filter is actually have to check what I used. I think a fram tough guard..

[DannoXYZ]

there's a wide range of oil viscosities specified in the owner's manual based upon ambient temperatures, and implicitly, type of usage. A more pertinent chart would be based on oil-temperatures.

Regardless, the only oil that goes off the chart on the right to support ever higher temps is the 20w50. So we don't have to worry about decreasing oil viscosity under full-throttle racing conditions.

FRAM oil filter may be a no-no. Look up the list of better oil filters in the original "oil filter study". Many more have been done with similar results.

[MB968]

Suspect a wrist pin bearing, if you don't see any change in oil pressure compared to before. Don't think the wrist pin has a pressure line to it, so if it goes you'd still have normal oil pressure.