pzull

My engine is bone dry, not smoking but tappet noise is slightly louder than normal when engine's warm and seems to be consuming more engine oil than normal. It's got 55k miles on it and its a daily driver mainly in the city with occassional runs on track and highway.

What's the estimated cost for parts for top end and complete rebuild?

Thanks in advance.

Kevin

pzull;

I'd have your valve guides checked. You can do this yourself or take it to a shop. How much oil are you using? At worst $3,500.00 for a top end rebuild.

Drew_K

I've heard $5000 to $6000 for a top end rebuild on a 964. Prices will vary by location and mechanic to mechanic though. Part of the high cost is that, once the engine is out and open, you might as well replace other parts while you're in there.

johnfm

If its dry, not smoking etc, get a 'reputable' shop to do some diagnostics - leak down & compression etc.

No point cracking an otherwise OK engine - oil is cheap!

pzull

I had to top up about 3 liters for the last 3k miles (6 mths). Used to be only 1 liter before.

Just that lately I feel the car is sluggish but it could just be a psychological desire for more power and acceleration

My wife did say if it ain't broke dont fix it.

With that money I think maybe it's better spent on a programmable engine management system. What do you think? My mechanic recommends Autronic as it gets rid of the "barn door" VAF sensor which is supposed to be very restrictive to air flow - is this true about the barn door?

The Autronic is similar to motec albeit with less features (which I probably don't need) and uses throttle position and manifold pressure for fueling instead of a VAF or MAF.

Is checking exhaust valve guides expensive?

Thanks

Christer

pzull

Your engine is using a perfectly Ok amount of oil - 1litre per 1000 miles. The fact that the oil consumption has increased is of course of concern but as there are no leaks etc (I presume you don't get a lot of smoke in the exhaust) then I think you have to consider that this MAY be a sign that the engine is getting a little 'tired'. If this is so, and it can be confirmed with comp test and/or leakdown I would not spend money on performance products as any gain would be significantly lower than you would expect. As I say, I would get it thoroughly checked before you do anything to the car. In the meantime enjoy!

pzull

Hi Christer,
No smoke at all.

I did ask the mechanic to do some diagnostics first like compression test but he says that worn valve guides dont show up in comp tests. What's a leakdown?

The only thing clear that isn't quite right is the tappet noise - it's louder than other 964's I've heard. Adjusted valve clearance during last service and it did get softer But now the sound's back. Mechanic says it's a sure sign of valve guide wear.

Maybe I'll do a Gtec test to see if performance has indeed suffered and maybe also a dyno to see if it's really off the mark. What do you think?

Got to do all these tests by next week as my header system will be fitted in 2 weeks.

BrokeAss

The only way to check for exhaust guide wear is to remove the heads, pull out the valve guides and have them measured.

I brought my car (60k miles) in to have the valves adjusted and a severe leak inspected. We decided to pull the engine to fix the oil leak. (Seals on two through-bolts were failing and letting oil leak) As part of the tear down process, we're going to pull the heads and measure the exhaust valve guide wear. I'll probably have them changed even if they measure "good". It's only a matter of time.

Trust your gut instinct - it's making a strange noise. You know it's not normal, you know it sounds expensive and you know it's not going to get better by itself. Just bite the bullet and have it taken care of before little bits of metal shear off and corrupt something else.

tom964

My car currently has 68k on it. I've owned it since it had 48k. The tappet noise in my car also seems rather loud to me. I've had two valve adjustments. After the first one, it quieted down, but came back later. After the second one, it didn't, but the second mechanic told me that the valves had been adjusted too tight before. Both told me that the noise was what they expect from these cars. So I don't know what the answer is either. There are too few 964s around here for a good comparison.

I also notice performance going up and down at times. Like you, I don't know if it is imaginary, or if fuel or atmospheric conditions are the cause. I used a G-tech and my best time on 0-60 was 5.4 seconds.

J-McDonald

I think that valve noise varies pretty widely among different 911's, but all 911's have some.

I thought that the valves in my car were somewhat noisy, until I took the car to a PCA show and listened to approximately 10 other 911s run (all the way from a 2.4 liter 911T, several 3.0 SC's 3.2 Carrera, a couple of 964s, and even a 993 Turbo S (!)) - I came away thinking that mine was just fine. Remember, your car has an air-cooled engine with mechanical lifters - it's going to have a certain amount of valve tapping noise. Go to a Porsche car show and walk around when people start up their cars- you'll see.

A 911 with less than 60,000 miles should not have any problems with its valves. However, you say that your car has done most of its duty as a daily-driver, which is harder on its valve guides due to engine higher temperatures from low-speed operation. Also note that a batch of 3.2 Carreras had a problem with premature valve guide wear that was, I believe, traced to a bad supply of metal being used to construct their valve guides (I read somewhere that, if a 3.2 Carrera is going to have this problem, it will be evident around 60-70,000 miles).

Given that your mechanic has given your car a clean bill of health, as long as doesn't start smoking or using *much* more oil (like 1 quart every 200 miles), I wouldn't worry about it.

Leakdown test are performed by pumping compressed air into each cylinder and analyzing how much air escapes, both through the piston rings and through the intake and exhaust valves. The thinking is that an engine with worn valve guides will leak air from the valves (usually the exhaust valves), due to the wear preventing the valves from seating properly.

"Normal" reading are supposed to be in the 6-10% range, with large discrepancies among cylinders being a cause for concern. Note that leakdown tests are notorious for giving false negative results (i.e., high percentage leakage), due to carbon deposits on valves preventing the valves from seating perfectly, along with other reasons. As a result, if you do have a leakdown test done and you get a high reading on one or more cylinders, the conventional wisdom is to add some Techtron (or another fuel additive) to your gas tank, run the car hard for a hundred miles or so, and have the test redone - it will probably improve.

Note also that Bruce Anderson of Excellence Magazine has said that leakdown tests are unreliable for 964's, due to the internal shape of 964 cylinders. However, you'll see that some mechanics swear by leakdown tests.

I've also noticed variations in my car's performance - some days it just feels stronger than others. Hot, poor quality air definitely has a negative effect (due to less oxygen). I also think that, due to its relatively high compression ratio, it's unusually sensitive to poor quality gasoline.

pzull

Thanks guys...all very useful info.

If I do get my valve guides replaced, should I go for the hard wearing phosphorus bronze ones which are supposed to be better than the factory bronze ones?

Talking about Gtech...has anyone got the new competition version with memory, shift indicator, rev meter, downloadable data, etc, etc, etc? Looks sweeeet! Loads more features. I got someone interested in my old one and am thinking of upgrading to their latest model.

johnfm

Topic: When is it time for engine rebuild?

Answer:

According to most Porsche garages I've been too, any time you have an oil leak!!! Well, since they make £2-3k from a top end, I'm not surprised that we get this sort of advice!!

I was dropping a 1/2 drop every now and then - its been a week since I took off my engine tray & cleaneveything up. I have left the tray off to check on the leaks and the engine hasn't dropped anything yet! I still use less than the suggested oil consumption of 1.5 litres/1000 km.

Kevin

Pzull;

A good mechanic can tell you your valve guide wear with a screwdriver. He can pull your valve covers off and check the play. I have done it myself. For me my first experience was on my first '84 Carrera. I had to do a top-end. Phosphorus bronze guides are the guide of choice. Years ago it was silicone bronze. If you have the option I would get a leak down, and have the mechanic move the valve to try to unseat it.