Poor compression, high leak rate = bad valve guides?

I will share a little story on my previous 1997 F355 spider I purchased in 2004 with 27k miles from FoS. Before buying the car, I reviewed all the service records and the dealer inspection report (as the car qualified for FNA's optional extended warranty program). The inspection performed three or four months prior, noted a couple cylinders with slightly lower compression (around 10 or 11% lower than the rest), and the leak down also showed higher numbers (I believe over 20%)

The remedy they used was to use a product called "GM Top Cleaner" which they ran through the intake to clean out the intake deposits. In addition, the owner allowed the lead service tech to drive and use the car "spiritedly" over the weekend. The following week they did the tests over again, and compression was fine across all cylinders, and only one cylinder had leak down at 10%, the rest were all single digits. The report recommended the owner run the engine at higher revs than previously to prevent this from recurring. They also stated they believed the 10% leak down on one cylinder would continue to improve with "spirited" use.

I ended up buying the car, owned it for 10 years, and had two major services performed at FoS and never had issues with compression or leakdown numbers (checked before and after each major). Sold the car with around 64k miles a couple years ago.

 

I also recall a tech session I attended years ago, and Nick Scianna of Nick's Forza Ferrari also mentioned they saw a number of F355s with intake deposits. He recommended that F355 owners occasionally use Lubro Moly Ventil Sauber (now called Liqui Moly Valve Cleaner), added to their gas every 2,000 or 3,000 miles.

 

WOW!!!

Great videos, and great thread! Thanks for sharing.

 

yes great stuff for sure!!! I have a few bottles here
I have a pressure cleaner for the top end also just need to make adapters for the 355-348

 

Anyone with any degree of ability and any degree of experience with 355s would have never diagnosed that car or even suspected that car as having bad valve guides.

A. They never go bad at the same rate. #2 and sometimes #7 always go bad first. So much so that typically the others will have new or near new compression numbers.
B. Problems with carbon build up is well known within the professional arena. It may not be here but you tell us nothing new.
c. Not measuring wear? WTF does that?


Your assertion that they are often misdiagnosed is not true if applied to us. It might be true among the various keyboard warriors that regularly offer advice on the internet.

 

I for one would like to thank the likes of you stepping up and posting what you find and what you are doing in threads like this. Many dont in fear of being picked apart.
The majority of what people learn and do is through people like yourself, god knows they learn nothing from the so called experts apart from the odd quip.
Kind of reminds me of a chap on here many years ago called RF. He wrote the first how to remove the 355 engine from the car, not an expert but a home diyer. His how to was the seed that today has grown into a situation that now many remove there own engines for cambelt changes.
Thanks Dave

 

Though you'll never get them to admit that.

 

Yes, on a solid tappet you need to have the lash set correctly. But on a hydraulic tappet the tappet is always in contact wit the cam so the timing would be correct, geometry wise, but if the lifter collapses more than it should then the valve will open late and close early.

 

I'd be looking for the cause of the excessive carbon buildup , an engine running properly , with a correct fuel air ratio should not be producing enough carbon to build up like that . This would go back to what fbb pointed out , something like bad connections could be the culprit , engines dont just carbon up , there is something causing it. Where it is wet in some of those pics , i'd figure that carbon could be caused by oil comsumption , possibly entering the combustion chamber and being burned leaving the deposits , thru bad balve guide seals or the guides themselves. An old car with a carb could have mixture problems , but a modern fuel injected car should run clean enough to not leave that type of carbon deposit

If it were mine , i'd be looking into some data to see what kind of air fuel ratio it was running
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I would counter that by sighting old BMWs form the later 80, early 90 with were notorious for carboning up. BMW used to recommend adding Techron to every tank of gas. Pulling the head and blasting them with walnut shells was the alternative. Apparently there is still a problem with the N54 engine.
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IIRC, that was a problem with the secondary air system with ports in the head rather than the exhaust manifold.

 

Although I didn't personally measure them, I had plenty of evidence that at a minimum the valve seals were bad, and my machinist measured them (told me the numbers which I promptly forgot and replaced the guides which were pretty bad on #2 in particular. The others weren't as bad, but since I was in there I just had them all replaced.

That nasty picture above looked like my #2 cylinder, which was eating oil... never a good sign for the valve seals/guides. Sorry about your luck... I don't have much to add with regard to the troubleshooting at the moment, the stooges covered the obvious and not so obvious.

 

Yes and that's the wrong timing and there is no way to know if the lifter has collapsed.

 

The N54 is a direct injection motor a totally different animal than a fuel injected motor. All manufacturers are having a problem with intake carbon on DI motors. The solution is simple.

On Ferraris there is also a general over fill of the oil that gets sucked into the intake. Everyone wants to run their oil level right to the max line as if more was better.

 

I would never conclude that all guides were bad on the same side. And I don't run away from high leak down. I would just drive it more aggressively.

 

The additives are nice but to work well I have had to use more that they say and it ain't cheap nor does it do as well as walnut shells. Walnut shelling is cheaper and faster and cleaner IMO. Here is a before and after on a maranello. I don't think you can come close to that with chemicals. Each port took about 10 seconds to clean and 10 seconds to suck out the shells. Tools are shop vac, blaster head, and walnut shells.
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That's why you use walnut shells. Even if there are bits leftover they won't hurt the engine. The BMW factory specified procedure for addressing the valve deposits caused by bad gasoline back in the '90s used walnut shells on an attached head. I'd be more concerned about excessive use of fuel additives.

 

You need to use Nut oil as a lubricant

 

This is why you do this, works amazingly well. I have one of these since the late 70's and still is the system

[ame]http://www.youtube.com/watch?v=wOVXPQLTbgo[/ame]

 

No worries, Dave. That's the great thing about forums such as this-- we can all learn something from one another. I've learned way more here than I've contributed, and I'm kinda-sorta in the biz.

I've seen issues very similar to the ones depicted in your OP in a 348, which were attributed to bad gas by my machine shop that did the work on the heads. In the specific case cited, I wonder if the car had been run a bunch without ever coming to full operating temp and getting properly "aired out".

My edict is to pay *very* close attention to the type of fuel being run (Shell ONLY, because I have firsthand experience of its superiority) and to make sure to run the car to full operating temp pretty much every time you start it. The worst thing you can do to a performance engine is to start it and shut it down shortly thereafter. As the owner of a track prep shop, this is an ongoing issue for me. We push more cars around the shop than we drive. The term "Italian Tuneup" exists for a reason, but very often the owners of pristine cars never run them that hard.