930 clacking noise

[Rawknees'Turbo]

Originally Posted by sunlion

I've been good about letting the Turbo cool. Not using synthetic but using 25/50 given the mileage on the motor, perhaps that's too heavy.
New finding - measured the distance form the top of the valve to the valve cover mating surface on the cam carrier at TDC for each cylinder, #5 is 22mm and #6 is 18 mm. The #6 valve is riding higher for some reason. But it's closed still nice leakdown is minimal. I think the valve is broken at the valve keeper or it's somehow sucked up into the head.....weird either way. I'm preparing to drop the motor next week.

20w50 is not too heavy if ambient temps are above about 17 degrees F (no joke - people think it is a summer only oil, but that is not accurate) for an aircooled engine, but synthetics have much higher flashpoints (resistance to burning/coking), and are much less likely to coke up in the superheated, turbocharger bearing cartridge after engine shutdown. Coke particles created in the bearing cartridge is what clogs the cam spray bars, since the dumbasses at Porsche decided the oil return from the turbocharger did not need to be filtered before it was sent to the crank, rods, cams, etc!

In my opinion, you are making way too much out of the valve stem height differences, considering your good leakdown numbers. There is no way that the valve is broken anywhere, or it would have been sucked into the combustion chamber, and have destroyed the head, piston, cylinder, connecting rod and crankshaft, a long time ago. What you are seeing is perhaps a valve seat that is worn/beaten into the head more than the one next to it, a variation in valve shaft length, etc. Unless Chris pipes up and says I am full of it ()then I wouldn't even consider pulling the engine for that.

[T77911S]

my brother has 140k on his 930. always used synthetic, let it cool before shutting down, changed it often and also use to send his oil out to be tested.
the engine is still in great shape.

I pulled my turbo apart.
the coking was in the body of the turbo. the bearings still looked good and the seals were not bad.
my theory on it is the dirt is the main culprit. that and dino oil. it just bakes onto the body of a hot turbo.

I remember seeing a thread many years ago about the filtering of oil and maybe how to change it.
I think I have seen something about changing the oil return out of the scavenge pump that dumps it into the case so it is filtered before going back into the engine.

[sunlion]

RT, you make good points. This is the stuff I don't know - variation in valve stem heights exist. You mentioned the valve seat could be worn which makes sense to me and it sounds like this is not a significant concern given the leakdown numbers. There would be more damage with a broken valve. I'll borrrow my friend JWs proctoscope and take a peak inside the combustion chamber as it put it back together.

[sunlion]

I reinstalled the #6 rocker and adjusted the valve correctly at TDC. Leakdown is 40%.

[sunlion]

Time for an update......
Found 5 of these.....split valve spring retainers

Had many of these......extra valve shims, 8 or more for each valve

Nothing catastrophic but could have been. Top end done and back on the road. Bit of a mystery as to exactly why and what happened. I'm thinking the unusually high numbers of valve shims, 8-10 instead of 5-6 preloaded the springs causing excessive pressure on the retainers which made them split.

[WERK I]

You may have had spring binding with that many shims. Did you have excessive cam lobe wear?

[sunlion]

No. The cams were fine but installed SC cams.

[flightlead404]

Originally Posted by sunlion

No. The cams were fine but installed SC cams.

What are your impressions of the new vs old cams?

[sunlion]

I've only been able to put about 50 miles. It's still pretty lazy under 2500 RPM, its more lively over 3k. I was hoping for more get up and go from a dead stop but that ain't the case. Makes more boost than before so went back to a stock spring. Difficult to assess what the result of the SC cams vs the fresh top end reassembly. Most of the original parts were reused other than 2 new valves. New steel studs and valve spring retainers.

[T77911S]

see my post on boost vs RpM.

my power comes in at 4200, full boost is 3200.
I recorded the pull in 1st gear so I could go back and look at the numbers later.

I am REALLY curious if the SC cams bring the power on earlier.

would you be able to check those with the engine in the car or even together?

[sunlion]

First gear boost only goes to .4 and comes in late, 2nd, 3rd boost starts at 2700 but I'll spend some seat/film time. Rather look at the road than the gauge

[T77911S]

that's why I had to video it.
happens too fast

[sunlion]

Never mind what I said earlier - just drove, brief video in 1st shows boost begins at 2600, .8 by 3800; happens too fast otherwise and I didn't have a passenger to film. Will get it dyno'd after 1500 mile valve adjust. But it's definitely less tame with the SC cams - feels much quicker, needs full attention.

[356911930]

Is that with the stock exhaust and muffler?

Rahl

[sunlion]

No, it has dual outlet aftermarket unbranded exhaust but stock heat exchangers and K27. Purchased this yesterday: will do the middle set up in the photo and extra iPhone for the gauge