Hi All, I'm having my major done right now. My trusted mechanic did a leak down annnnnnnd a few cylinders are starting to go. Really bummed as I have records of the car being fine at the last major only 4 years ago. He is sending everything out to be rebuilt right now. It sounds like they will use different guides. He did say he believes my valves themselves are okay. If so they will clean and reuse them. Also turns out my clutch is pretty much toast - which I was expecting. Any thoughts on anything else to do while it is apart? This is a '97 GTS gated. Thanks!
How many miles. My Feb 97 355 spider had its last major (before I sold it) at around 57k miles and compression/leak down was still fine.
Dirty valve seats. Just built up carbon on them. leak down testing is not a good indicator of valve guides. Just the sealing ability of the valve to seat. If the heads are out, have the machine shop measure value guide clearance. Most likely you just need to do a standard valve job. Not valve guides…
Good point. When I bought my car in 2004, it had around 27k miles and in the records from earlier in the year (previous owner), it had some 14% to 17% leak down on three cylinders, while all the others were single digits. Ferrari of Seattle suspected carbon build up on the valves and recommended their technician running GM "Top Cleaner" or something like that through the intake system, then run the car "spiritedly" for a weekend, then bring it back for another test. The second test showed the previously high leak down numbers now around 7 to 9% and they said in the notes it will probably continue to improve if the customer quit driving so sedately. I owned the car for ten years and went through two major services and never had another issue with compression or leak down numbers.
There's a cottage industry of people on Rennlist who are certain that 993's don't really have valve guide problems. Sure, maybe you had some carbon on the valve seats. But you probably have worn guides. Very easy to check with the engine out. Don't get your hopes up that it just needs an Italian tune up.
^^^Exactly. The old adage if it aint broke... Blue smoke, and oil consumption would worry me before I would tear my engine down and replace valve guides. Although I suppose if this car is being used in a racing application where every ounce of HP is critical then why stop at guides?
No smoke. He tried snapping the valves into place but was still getting over 60% on multiple cylinders. He's quite positive it is my valve guides. The heads are being sent to CA to someone who makes his own special guides. He's hopeful the valves themselves are fine though.
60 percent is crazy. This is from guides being so worn the valve heads have beaten up the seats. You must have had significant oil consumption?
And what part makes sure those skinny little valve faces land on the seat in such a way it has a chance of sealing? The valve guide. Sorry but you are wrong. A leak down test is a good and widely accepted method of diagnosing valve guides....at least to those of us who understand how a piston engine works.
A dry sump engine does not always have a high oil consumption issue from guides. One of the advantages of a dry sump is the amount of vacuum it produces in the interior of the engine. That vacuum helps reduce the amount of oil that can flow past the guides. A 308 with bad guides will smoke like a choo choo train. A 348 or 355 will not.
This is what I wanted clarification on. My car suffered no smoke at all and didn’t have excessive oil burn between annual services and yet the valve guides were shot.
So rough running and poor power output isn't a reason to fix it? If that is your standard why even have a Ferrari. Just get a clapped out Toyota.
Out of curiosity, what is excessive consumption? If the average 355 driver puts on 2k miles in a year and consumes a quart of oil is this excessive? Personally I won’t find out how much oil I use until next year since the car is new to me.
Obvious question. Did the mechanics listen to see if he heard leaking from the exhaust or intake. Usually before you assume bad guides you listed to see if you can determine where the cylinder is leaking.
If the engines out anyway then its a no brainer, purely for resale if anything, essential to be able to prove that the one thing buyers of 355s panic about and that is if the guides have been done recently.
Interesting. Most of my experience is working on air cooled 911's and they are dry sump but drink tons of oil when guides are worn.
Great thing is a well built 355 runs and sounds like a scaled cat! Your wallet is going to hurt but the smile on your face will be priceless. Maybe get some new sticky tires and have fun. These cars see few miles and often ride on old tires.
