Top-Gun

Ever since I bought my 95 a year and a half ago, I've struggled with a metallic ticking noise from the drivers side of the motor. I've done the following thus far;

- Used a mechanics stethoscope to try and pinpoint the location; the sound is most obvious on the #3 cylinder exhaust valve cover but I can hear it on the other cylinders as well

- Replaced all of the exhaust lifters with Porsche INA lifters, still ticks

- Drove the car ~500 miles last season, tick didn't change

I came to the conclusion that it must be a worn valve guide that was making noise, decided to just go ahead and do the top end this winter as I was going to pull the motor to do a MWF/RS clutch and refresh the gear box. Car has 65,000 miles on it and spent half its life in Texas with the engine cover in place so my thinking was its plausible the guides are cooked.

Before pulling the motor, I opted to do a leak-down test just to confirm my suspicion of bad guides. Warmed it up and got the following results;

**All tests completed at 96 PSI (gauges range 0-100 psi so didn't want to peg them)**

Cylinder #1 - 95 PSI (~1%)
Cylinder #6 - 93 PSI (~3%)
Cylinder #2 - 94 PSI (~2%)
Cylinder #4 - 94 PSI (~2%)
Cylinder #3 - 95 PSI (~1%)
Cylinder #5 - 95 PSI (~1%)

From what I've seen these leak-down numbers are excellent, am I wrong to think a guide worn bad enough to make audible noise should be obvious on a leak-down test?

I hate to tear into what appears to be an excellent motor, my concern is if it is a loose guide perhaps it hasn't been long enough for the valve/seat to wear substantially?

What would you do, leave it well enough alone or just do the top end since the motors out anyways?

Thanks.

amondc

A worn guide won't show in a leak down as long as the seat and valve are ok.

Quadcammer

typically the worn guide results in a beat up valve seat.

anyway OP, what I would do is this:

take the valve cover off, remove the rocker and check valve stem movement. Thats really the only way to know without taking the whole thing apart.

btw, got a video of the sound? Could it just be a noisy air cooled motor?

How about cam wear? How about a bad wrist pin?

LexVan

What oil and what viscosity are you running?

shadow993

What about intake lifters up top? I have the same tic and I believe that is the culprit.

It isn't too loud but I can hear it with the deck lid up.

Top-Gun

Mines silent from the top, loudest with your ear by the drivers side tire. Running Brad Penn 20W50.

If I pull the valve cover can I check the guides with the valve springs installed? If not how hard is it to remove the keepers/springs without pulling the heads off?

IainM

Sometimes I worry myself into believing I can hear valve tapping and the imminent doom of worn valve guides. But then I get driving and everything is right again.

Does it always tap or only after warmed up? or only when cold? Is it really just one out of the 12?

If you really think it's valveguides I'd do the test as Quad says and find out for sure before laying down some big green.

bcameron59

New lifters shouldn't tick - even at startup after sitting for days - unless you got a bad one, oil is too light, or you have an obstruction in the oil line (omnipotent deity forbid).

Try 15-50 weight oil which seems to eliminate ticking for many folks, YMMV. Also check for / eliminate exhaust leaks, apparently they can imitate ticking lifters. Failing these, check valve guides per quadcammer.

Steve Weiner-Rennsport Systems

Well,......you will NOT remove the keepers, springs & retainers here; you use a pair of screwdrivers to "measure" the movement in the whole assembly with the valve on the seat.

This takes some skill and experience to determine how much sideplay is excessive and if you've never done this on a 911 engine, I'd strongly recommend having an experienced professional do this for you so you get constructive results.

The most accurate method to determine guide wear is by removing the heads & valves and both measuring the valve stems for wear & taper as well as using a dial-bore gauge in the guide bores.

Oil consumption is another indication of guide wear so I hope you track that very carefully as part of your records.

OverBoosted28

How loud is this "ticking"? Are you sure it's valvetrain and not normal injector noise. The induction on these cars is fairly noisey. If your car runs fine, doesn't use/burn/ leak excessive oil amounts and you haven't noticed loss of power or throttle response, stop worrying. Spend money when you HAVE to. Not when you think you might need to.

Top-Gun

Its pretty loud in my opinion, enough that people that have no idea about engines ask "why does your car make that noise". I do have a video but its pretty large, if someone would like to take a listen I can share it via Dropbox or something similar. I'm a mechanical engineer with a perfectionist streak so its possible I'm being too critical but it really doesn't sound normal to me.

Unfortunately I don't believe theres many air-cooled Porsche experts near me to execute the valve play test with the screwdrivers. I agree that sounds like a "feel" thing that you just need experience to make useful. Furthermore I've got the car torn down to a point where I couldn't drive it to a pro so the best I could do is bring the entire motor once its out.

I've only put maybe 500 miles on it since my last oil change; no noticeable oil consumption in that short period. I did the overrun test a few times (i.e. wind it out in a low gear and lift/coast while watching out back for smoke), nothing noticeable. After sitting for extended periods (like a couple weeks) it does puff a blue cloud on the initial start. If I drive it regularly theres no smoke on startup.

Its sounding more and more like the best bet is to bite the bullet, pull the heads and send them to Steve W. I'm not so much worried about the cost, more intimidated getting the timing set right when I reassemble it.

Top-Gun

Sorry I missed answering a few questions above.

Cams looked good, I inspected what I could when I did the exhaust lifters. Lobes all had a similar polished finish with nothing marked up. Exhaust rockers all looked identical wear wise.

I did do a search for exhaust leaks, couldn't really confirm the heat exchanger to cylinder head flanges as I saw imminent 3rd degree burns coming, but the rest of the system is tight/leak free.

Can't hear it when the car first starts from cold, loudest once it warms up and is most noticeable at Idle. Once the revs come up the noise just blends into the normal sounds of the motor. Hot oil pressure at idle (750 RPM) is just a tick over 2 Bar and is 5 Bar by 3000 RPM so I believe that's right in line and I shouldn't have any oil supply/system issues.

cgfen

the first time i changed mufflers i didn't get a good seal and the resulting leak sounded much like a "tapping valve".
i reseated the muffler and noise was gone.

just something to check

axl911

What is your oil consumption?

Worn valve guide would increase oil consumption to the point of 400-600 miles a quart. Other indicators are smoking at idle when engine is warm, and smoke upon decelerating at high rpm.

If your oil consumption is at that level, I don't think it's valve guide.

axl911

BTW, upload the video. Some 993 is pretty loud....like mine.