Blown Ring?

[mueller944s2]

I was driving the old 911 (1975 with an SC engine) during a hot summer day and came across a big problem. I floored it up to 6000 and let off and white smoke start pouring out of the exhaust. That was 4 years ago. Now when we start it up it wont constantly pour smoke out, it'll be smokeless then a huge cloud. If you put your hand over the oil filler cap there's a little bit of blowback (correct term?). We think it needs new rings. Any other ideas?

[47silver]

I think a compression test and/or keakdown test may let you know if you have a problem.

[E Sully]

As 47silver suggests do a leakdown test and listen for where air is leaking. If into the crankcase, rings leaking. If intake or exhaust, valve leak.
Worn valve guides don't show in a leak down, but smoke when letting off the gas is a sign they are worn. This seems to match your situation.

[mueller944s2]

Well it's not every time I let off the gas, just the first time when it blew. Now I have a compression tester, for the leak down what would I need?

[47silver]

You need compressed air and a leakdown device. It has 2 gauges. Essentially you put a cylinder to top dead center. Pump air into it and watch the gauges and listen for leaks. The bad cylinder should be very different from the others cylinders.

[Flat6pac]

Bob, that was aftermarket P&Cs wasnt it..I recall you buying the engine.
Bruce

[mueller944s2]

Bob, that was aftermarket P&Cs wasnt it..I recall you buying the engine.

Bruce

Actually I'm his son, the car is still his but I blew the ring. I've got the 944S2 now. I don't believe they were aftermarket, it used the oem p&c but we might be switching to a 3.2 short stroke if there's a lot of damage. I think I remember coming to see you, North Carolina right? Black 3.2 targa and a light green 930 3.0?

[Flat6pac]

Yes, you and your sister were with Bob to visit and now youre all grown up.
Bruce

[mueller944s2]

That was a long time ago, 8 years? I never would've guessed that 2 years later I'd have my own. I might as well throw every paycheck at that car because that's what it takes to keep it running! I've always admired that green 930 you had, that was a beautiful car