F355 - Clicking noise from pumpkin

Too answer your question regarding the bypass valve, maybe.

If the motor was getting significant backflow of oxygen that was impacting the operation of the O2 sensors or causing combustion in the header tube/valve seat area, it could do a number of nasty things, both in closed loop and open loop conditions. Examples running too rich or lean leading to excessive EGT's.

With the valve wired open below 4,000 rpm and at part throttle, the gases will go through the bypass (as it offers the least flow restriction), but atmospheric air could be drawn through the exhaust past the O2 sensors and cause the ECU to think the engine is running lean. This would then cause the ECU to add fuel, which if unburnt would continue to burn in the exhaust and past the valve seat, raising EGT's to levels that could damage exhaust components potentially including the valve guides, seats, and seals.

Potentially, in open loop conditions (above 4,000 RPM and part throttle when the valve is supposed to be closed) could lead to a lean condition due to increased flow and insufficient flow, once again raising EGT's dangerously high and cooking the exhaust valves. Although this is less likely since the engine still has mass air flow data and "should" be close enough in fueling the engine to avoid a dangerously lean condition.

Generally, the real culprit is boogered up catalytic converters which result in excessive overtemps in the exhaust and since (correct me if I am wrong) cylinders 2 and 6 are the two hottest running cylinders with regard to port exit EGT temps. This is what leads them to fail first. Much of this is conjecture based on what I know about the engine and what I have seen happen with other motors, but I suspect that I am not too far off when I implicate the exhaust system in general as a source of the valve problems.

 

CONGRATS!!!! Great job.

 

+1! Great job!

 

Glad to see that you're back in business!

 

wow...that is some DIY thread. Congrats!

SO do you have any clue as to what led to the exhaust valves getting fried like that?

Did the wired open bypass valve contrinute to this?

 

Jeff, what did you use for head gasket oem ferrari?

 

Nice job

What valves and guides did you use?

 

Maybe unwire the bypass valve? Why take a chance with your newly redone heads? Straight pipes must sound awesome.

Congrats on getting it all back together! What a beautiful color.

 

This is just a guess but, one reason could be do to the design of the exhaust system. The diameter, length, and pairing of the primaries and secondaries. The same goes for the bypass tubes and the bypass valve. Ferrari has the primaries paired non sequentially. That maybe all fine and dandy when the bypass valve is closed, but when it opens it could be changing the harmonics, and thus the scavenging affects inside the headers change. My guess is that #2 and #6 are getting over scavenged when the bypass opens up. The harmonics could be changing in such a way that it causes a harder pull on those primaries. Instead of the fuel mix staying inside the cylinder, it's getting pulled into the primary where it's lighting off. Or maybe even the change in harmonics when the bypass first opens could be causing some sort of reversion.

With that said, the design of the cams and the cam timing can also be a contributing factor. The overlap and duration could be such that when the bypass opens it's allowing some of the intake charge to be briefly pulled into the exhaust, because of a brief change in harmonics. The 355 doesn't have variable cams, so as you well know, once the timing is set that's it. If the cams are set for top end then that is where they will run best. If the cams are set for midrange then that is where they will run best. The 355 cannot adjust the cam timing based on the engines speed, or bypass, to get the optimal low/high power. It also can't adjust the cam timing to help prevent over scavenging. The cams are set where they are set, and if they briefly have a negative affect on scavenging then that's the way it is.

Then throw coolant temperatures into the mix. If the thermostat has gone belly up and isn't opening/closing normally the engine can run cool (below 176°F). It may get out of the initial start up enrichment, but could get stuck in post warm up enrichment and never get into full operating temp mapping. Meaning the engines will be running rich. More fuel to get over scavenged into a primary, to light off inside the primary............

That is my Stooge guess as to why #2 is the first to go. What would be interesting to see is the whole thing played out on some sort of CFD like solid works. I guess the only real way to know would be to put an f129 on the dyno and run it with O2s and thermocouples on each primary, plus pressure sensors, then see what happens when the bypass is closed vs open, and.......see what happens during the transition between the valve opening/closing. You could also test what's going on during various coolant temps during various scenarios, try different cam timing, even different header designs. That's a lot of R&D, and who is gonna have the gumption, time, and money to do that???

 

Excellent, Thank you

How was it removing the OEM guides? Any tricks to share?

I would like to try this myself also

 

Jeff Thank you so much

Its been 25 years since I did a valve job and think I will do it myself, I have the time

Are those 31 and 46 degree seat cutters?

May need a few more tips in time

 

Wow...a DIY valve job. You guys are the best. Very impressed.

 

Nice work, Jeff. FYI, the valve clearance specs are in the WSM, see below. And, you resurfaced the seats by just hand spinning the cutter shown above or did you use a drill motor on it?

.002" is the max per the spec of .06mm. .004" is the wear limit
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Jeff, are you referring to the guides or seat? I was asking about seats, just want to be clear

 

Ok. Thanks. So, I assume you are lapping the seat to valve interface and not the valve stem to guide interface?

The WSM shown a seat grinder for the seats, it would seem this would be difficult to cut the seats with the t handle with no real RPM to speak of.

And, the new guides are steel correct? They must not be very hard if you can ream them (which the WSM states although it references the copper bronze guides)

 

I hate it when amateur mechanics make most of us look like children playing in a sandbox.

 

Trying to find a valve installed height in the WSM with no luck

Doing this in my head a few dozen times first