930 Timing Marks For Valve Adjustment

sand_man · 11-01-2005, 12:20 PM

Can anyone please tell me if the following picture is true for a 1987 930:

I used the left mark as "Z1". At this pulley mark, my dizzy rotor was lined up perfectly with the notch on the dizzy for number 1. I wonder if I should have used the mark on the right!!?? Might explain why my car is running like ass! Please advise as I'm about to tear into this thing for top end rebuild.

a-dougk1 · 11-01-2005, 01:47 PM

Yes, your photo is correctly marked.

What do you mean "running like ass"? Perhaps if you were more specific, we could help. Just because a 930 motor is running "like ass" doesn't necessarily mean it needs a rebuild.

Doug

2.7RACER · 11-01-2005, 02:39 PM

Sand_man,
The intake valve closes 50 degrees after bottom dead center on the compression stroke. The exhaust vale doesn't open until 60 degrees before bottom dead center.
This means both valves are closed 130 degrees before the piston reaches TDC and stays closed until 120 degrees after TDC at the compression stroke. These numbers are absolutely closed, no 1.0mm clearance.
So if you were anywhere near TDC when you adjusted your valves they would be OK.
Now here comes the kicker, If you adjusted the valves at the crossover TDC, (TDC overlap), 360 degrees from compression TDC, the valves would be opening and closing later and probably clattering badly.
My point being it isn't critical to have the engine at a perfect TDC compression stroke to adjust your valves, but it can't be at 360 degrees later or sooner at crossover (TDC overlap).
I would double check your ignition timing with a timing light. Make sure it is advancing (towards the right hand mark) as you rev the motor.
Are you confident the cams are timed properly? Did this happen shortly after some work? What is the compression? S/B 120PSI or better.
If the compression is out of spec, I would do a leak down.
Really quiet valves could be burnt.
What is the boost gauge showing?
Bad gas, (low octane), will destroy a turbo with detonation, (pinging).
I hope it's something simple.

sand_man · 11-01-2005, 04:35 PM

Thanks for the responses. Sorry I wasn't clear in this thread, I have posted questions regarding my problem(s) in other forums.

The engine only has 42,000 on it, but recently my original rubber centered clutch disc completely disintegrated as I was accelerating hard under full boost. The engine went to redline as the disc let go...I backed off quick, but maybe not quick enough.

I pulled the engine to completely redo the clutch. As the engine was out, I went ahead and did the valve adjustment (I've literally adjusted thousands of valves over the years, so I'm no stranger to it). The engine fired on the first try after it was installed (and after the oil pump was cycled a few times). Seems to sound fine at idle, but as soon as a load is put on the engine, it quickly sounds like an old Beetle or Harley. I can find no obvious cracks in my B&B headers. The headers look snug on the exhaust ports, too. I have checked my valve adjustment twice. I have checked my spark plug connections and firing order one billion times. I have pulled each plug wire one by one as the car idles to determine if one of them is not firing. I have also replaced my spark plugs and checked to be sure they were seated and torqued properly. All is good.

Nope, I'm afraid I have a broken head stud...or some other probelm with the top end - broken ring, burned valve, etc!!! I was just hoping that maybe I picked the wrong "Z1" mark and that perhaps that was causing the horrible and dreaded "ppfftt", "ppfftt" sound! Sort of like the car has a REALLY nasty exhaust leak!

I have posted a question in the "engine rebuilding forum" about how involved to get with my top end rebuild. I haven't decided if I'm gonna split the case and freshen the entire shootin' match up. I'm really looking to keep this as a practical rebuild. I have a B&B intercooler, B&B Headers, K27-7200 turbo, and a stock waste gate spring.