Poor compression, high leak rate = bad valve guides?

First, flame suit on

With that out of the way, I wish to share some facts regarding my experience rebuilding the motor of my 95 355 Berlinetta.

Prior to removing the motor I did a compression test which yielded poor compression on bank 1. After removing the motor I did a leak down also which confirmed the leak path to be within the cylinder head (valves)

My investigation did not stop there. I wanted to understand the complete situation. Upon removing the cylinder heads, the combustion chambers of both heads did not look too good. Lots of carbon build up and one side was wet while the other dry.

I disassembled the valves and then proceeded to measure the valve stems on the inside diameter of the valve guides. What I found is the valves and guides are well within specification, in fact, approximately .001 to .0012" of clearance.

Check out the pictures and videos I created.

I did this because I found it very troubling to hear over and over from owners and potential owners how great and strong a particular car runs yet people walk away based on compression / leak down results.

I'm not denying the valve guide issue. However, I think it's blown radically out of proportion and I think it's often misdiagnosed. I never, ever read anyone that posts about measuring valves and guides. It's almost immediately a "replace guides" answer.

Moral of the story, poor compression and leak down does not always mean bad guides. And, I'd love to see dyno results on a motor producing above 200 PSI of compression vs one producing say 160. On the street, I bet most people would never notice the difference.

Folks, do your homework. Your milage my vary

http://youtu.be/2f77G_iRUjM

http://youtu.be/oY0jqb8Ld-4

 

Compression
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Combustion chamber
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Another
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I'd bet there was a difference in cam timing R/L.

 

Hi Tim, yes, but not that much...
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Leak down
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That carbon is killer for sure
Looks like the pics we took here also

Good accurate observation.

 

Dave,

Those are some terrible numbers. Because of where you are in the process, one thing I would do for diagnostics is to leak the block without the head. It does not matter if the bottom is to be rebuild except for knowledge gained. Second before the head comes off I would leak it with camshafts out. Third any Ferrari with bad numbers gets a day at the track and run hard before I believe the numbers I get. I also tend to use both high and low pressure tests when I get numbers I don't like.

Because a solid tappet can not be used during cam timing I wonder what you think about the influence of hydraulic lifters and cam timing. No one talks about it or knows anything about it. There is a difference between the throw of a valve with lifter fully pressurized vs. leaked down. We seem to ignore that. There are claims that Ferrari lifters in general are less than completely reliable. I know more than a few good wrenches who have confirmed faulty lifters for those mechanics who bothered to check. One seemed to think the problem significant enough for him to invest the time to make a lifter rebuild program.

It is super easy to walnut shell the intake ports and valves insitu and leave no residue to get inside the engine. However, you can't clean the sealing lip of valve to seat because you aren't opening the valve to blast it clean. I make intake cleaning part of my major with injector blue printing. The exhaust can be accessed but at more work. I have seen some pretty coked up Ferrari driven too respectfully.

 

Carl, yes, I do plan to LD the bottom end but visually it looks great....yeah, I know - can't measure visually.

The leak was felt through the valves....

Doing the LD at the proper cam position is pretty much the same as no cams but I get your point.

This motor had all the typical symptoms of valve guides when they are not the problem- that is the point of this thread.

 

Good work Dave.
I agree with FBB as far as Italian tuneup. It's really surprising how the numbers can change.
Not surprised at the carbon. "Respectful" driving is bad for Ferraris. I wonder if there's some in the rings too.
Wet on one side...hmmmm
3.5 deg is a lot of advance. 1/3 of a tooth? (how many on a 355?). Heck, a degree is a good bit of cam timing.
I appreciate your approach to this diagnosis. Important to 355 owners.

 

Thanks, Bruce. I only drove this car up my driveway and in/out of the garage a couple times.

This car will be getting a full rebuild needed or not -,part of my learning

 

I agree.
3.5 degrees is a lot. That would have an impact on compression numbers across the whole side.

 

Correct, except the poor compression is on the opposite side......

 

Subscribed.

Robb

 

If the lifters are working correctly they should not be causing any problems with timing. If they aren't pressurizing correctly the effect is to reduce duration. The vales will open later and close sooner. It's basically equivalent to having excess valve lash with a solid lifter.

 

Hey Bruce, a stock 355 can be adjusted at 1.5 degree intervals. Not really an amout of a "tooth" per say as the teeth pitch must remain consistent. It's really cam rotation we are talking about here but it's semantics.

 

Those numbers look almost exactly what mined looked like prior to the engine out. The cam timing was off a full 2 degrees. Reset and the compression numbers were fine.

I hate to ask...but will...is there a snake oil remedy for carbon build up on the valve seats? <ducking for cover>

 

Haha. Where is the emoticon for "ducking for cover"? Tim had turned me on to BG 44k and it works because I did a CC on my third car. Added BG 44K, drove the crap out of it a couple hundred miles and compression improved.

This car had pitted valves though....

 

Lack of use. Condensation builds upon valves. Mixes with products of combustion. Forms acids. Evaporates. Cycle repeats. Valves, seats become pitted.

 

Just to pile on data to Dave's findings

We had some of the stooges over my place looking at this head, basically same thing loaded with carbon with total fail leakdown numbers on the head. This is a 5000 mile motor

With Daves suggestion I did get some pin guages to check valves and got same passing results on the guides and valves

These cars need to be driven for longer periods of time not just 30-60 mins.
We used to call this "loading up" when the crabon was this bad and we would take a 4 hour drive to fix it


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If the lifter or setting clearance of a solid tappet is incorrect you get the wrong numbers

 

I agree with the extended driving of these cars. The more I drive mine, the better they run. The more they sit, the more trouble I get. That 95 355 does not like to sit at all. It is also rare that I have a chance to drive it more than 30 minutes.

 

Mine seem to take a good hour before they start to run correct. Or at least drive them a few times during the day to get it to heat cycle and burn off all that gobbly goop

 

People don't want to admit it, but most of these cars have poor electrical connections that may or may not improve as temps rise. The pioneering work of Helms brought us to the next level. Many are quitely doing the Ernie Stooge connector repin to gain reliability and proper function the results of which are highly variable.