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.

 

I'm having fun now, thanks Markphd for your reply, one small thing I never mentioned though is it's decatted with spark plug non-foulers on the rear o2.

I got the heads off and found my exh valves were burnt, #6 real bad. Found a nice tool on amazon to extract the valves and am progressing nicely, I think I just need new ones. I put some oil in the cylinders and they hold nicely. Darn those cylinder head nuts were tuff to get off.
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Thanks to all your advice, plus the local guidance from an fchat’r who I know his name but not his user id, and some words of wisdom through Brewman’s long time Ferrari mechanic, and moral support from Brewman, and of course the cylinder head wrench tim355 kindly loaned me, I have got the fcar back on the streets. And FBB you were right, I cannot believe how smooth it is – in fact it has never been even close to this smooth since I bought it 4 years ago. The muscle car lope, jumping mirrors and pumpkin/gearbox noise are all gone. Feels like a Maxima now. And .. I only had to replace all valve guides and valves! (ha). Final tally for all repairs (labor by me), including tools and parts, and the mis-diagnosis path of flywheel repack, plug wires and tranny mounts is just over 5k USD. Thanks!!
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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?

 

Good question, and I don't know the answer. I checked for intake and exhaust leaks and didn't find any (still have factory manifolds installed at 38k, and tubi test pipes). Since the day I bought it with 74k miles back in 2010, it has had (now I know) a somewhat rough idle - not real rough, kinda like a cam lope, both I and my mechanic neighbor thought it was normal. I think my 2 track events must have made a bad situation worse. Long story, but when I bought it (I later found), a PO had installed an intentional fuel line return blockage that made it run real rich and throw 'too rich' codes on both banks. I removed it, maybe he knew something I don't - like maybe he thought it was running too lean. Or maybe the original guides contributed to it, although they weren't real bad in my opinion fwiw. It had the bypass wired open then, and still is now with 88k miles on it. Smooth as melted chocolate now, 300 miles since.

 

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.

 

My local 355 friend pointed me to sivalves.com. I got both the valves and guides from them. 1100 for the set of valves and around 12.50 each for the guides. I used the Elring gasket with some Permatex copper spray. For all the supplies like the cutters I used (31,46, 60 degree) and the 6mm cutter guide and guide driver, my friend directed me to cylinderheadsupply.com.

The prudent thing to do would be to unwire my exhaust valve, you're right. I just can't stand the way it acts and sounds with it like that, I've tried it. I'm takin' my chances.

 

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

 

Easy as cake with the 6mm guide driver, hooked to an air chisel at about 80 psi. Place head in oven, set on 250 degrees for 1.5 hours, remove and with about 5 blips of the chisel out each will come. Install is reverse, heat head, remove guides from kitchen freezer, dip the guide in a little oil and blip the chisel until the collar seats .. a change in tone and oil splashing up from underneath the collar tells you they are seated. Btw, some guides don't have the collar i'm talking about, not sure how you'd do those. Once you get the guides in, ream them with the 6mm carbide reamer from cylinerheadsupplies (part # k-1110c, about $100), use a big hand drill too, I reamed usually a max of 2 times, mostly once, then fine tune with cross hatch flex hones a small bit (cheap, part number BC6M24). If you over-ream and end up with too much valve to guide play, no sweat, just remove guide and replace with a new one, I messed up about 6 while getting the hang of it. I was shooting for about 3 thousandths total travel when valve is lifted slightly and moved side to side, which translates I’ve read to 1.5 thousandths stem to guide clearance. I think 5 or 6 thousandths was the max limit I allowed without re-doing.
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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.

 

One's a 31 and 46, the other is a 60. Part numbers from cylinderheadsupplies is 103 – seat cutter and 111 – seat cutter. I learned a lot by watching '3 angle valve job' videos on youtube. Good luck!

 

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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I spun by hand until I got consistent cuts, then used the lapping compounds with a drill motor attached via a rubber hose to stem. My goal was to be able to blow compressed air into the intake or exhaust while holding slight pressure on the rubber hose and not see any air bubbles in the soapy water it was holding. Then let it sit for 15 minutes and not see any water leaking. I did have to have my stems ground down some in order to fall in the stem height spec. But I've read where that's common too.

 

Jeff, are you referring to the guides or seat? I was asking about seats, just want to be clear

 

I was talking about the seats. For the guides, use a big hand drill. A small one will stall out half way through. Seats = hand turn with the t-handle shown, then lap (I used a drill for the lapping, search youtube for 'lapping valves with a hand drill').

 

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