Confirmed....broken valve spring

fumanchu · 09-13-2010, 11:33 AM

well,
the title says it all. Replacing the valve spring is not such a big deal, but the question is that of the slippery slope that occurs when you get into the motor.

Before Identifying the broken spring, I did a standard baseline compression test on a cold motor. 165,165,165,157,160,157. The broken valve spring cylinder was 165. It now blows a puff of smoke on start-up for the past year....this is what propmted the compression test. I thought maybe I had a broken valve spring by the excessive ticking on the left bank. Pulled the rocker and confirmed.

Would you:
1. replace known offender, engine in car... and be done.
2. same as above and also replace valve seal?
3. Drop motor and replace all the valve springs and seals.
4. Do #3 but if your gonna go that far, do a topend. Guides cant be great at 147k

what would you do? I drive the car 1500 miles a year and It really runs great considering the broken spring.

don gilbert · don gilbert's Garage

I would just fix it in the car, not hard, done it several times. Your #'s are not bad at all.

rcaradimos · 03:06 PM

More details please and good documentation.

I'm thinking I may have a broken spring on the left side. I get a little extra tacking noise at about 2500 RPM when engine is hot. It appears to be #3 intake but I have not listened to #3 exhaust with a stethoscope.. need someone to hold the throttle open to right RPM and get under there to listen. Could be worn valve guides allowing the valve to slop around.. but that can be checked once the spring and seal is off. If thats the case; new seals at this time and place, then I'll save up to have the heads done.

Was it exhaust or intake?
How did you determine which cylinder it was before you removed the rocker?
How easy did the rocker come out?
What type of seals do you think would be best?

Pics or video of procedure would be nice. I just picked up the spring compressors and some viton valve stem seals, I'm thinking of replacing the exhaust stem seals on all six sometime soon. I'm getting some oil seeping into my exhaust ports/manifold while car sits for awhile. The oil starts to burn out the exhaust once it gets hot then stops.

Heres a link I started about my issues:
How much oil in the crankcase?

All the best,

E Sully · E Sully's Garage

Do you run high rpm? Valve could be damaged from hitting piston. With that kind of mileage, I would consider pulling the heads and checking it out. About $200. for a cylinder head gasket set, plus cost of having a shop check tolerances. It can be reasonable cost if you do the labor. Gets expensive if you send it to a shop.

fumanchu · 09-13-2010, 05:20 PM

some resonses.

The valve tick was not remarkably loud. Sounded like a bad valve adjustment on the left bank, but I just did the valve adjust and they are never out when I do them. One clue was that particular intake valve was "easy" to screw in or better to say that when adjusted to zero lash it seemed that I could screw in the adjuster easier than the others actually compressing the valve spring which of course it's integrity questioned. Thank god for dual valve springs as the inner spring is the only thing keeping things short of catastrophe.

It never made noise when cold, and typically made its loudest "ticking" on overrun and at idle.
Cylinder is #2 intake.

Removing the rocker is easy...5mm allen, pin slides out, pull rocker, done. Grab a flashlight and a small inspection mirror, also put your fingers in there and feel around. Its easy to spot and feel.

Like Sully said I was worried about piston to valve contact, also part of the reason for the compression test. That cylinder has one of the highest compression readings too, and I have been running it pretty hard like this and it runs great. So I feel I dont "need" a valve job, of course it could use one at 147k miles. But then if I did a top end, I would probably do rings and that intermediate shaft bearing is always worn and so on it goes......

I am leaning towards changing all the springs and seals with 964 seals. The intakes seem to go on the SC's and it's really cheap... 14 bucks a spring. This decision is partly based on getting it smogged every other year and trying to control oil burn is a realistic issue. The seals will hold only so long if the guides are shot but at least they are not 30 years old and crispy.

More opinions please.

EarlyPorsche · 09-13-2010, 05:23 PM

I would just put on a valve spring and keep driving the vehicle. No reason to rebuild an engine that has that strong of compression. The puff of smoke could be top end related so you could see if you need a set of valve guides but I also don't think I've seen a 911 engine that didn't puff on cold start. I assume you mean it does this after sitting and not every single time you start her.