[MEDIA]
Two main things pointed out about the 308 engine - TLDR version if you want to skip the video. This may help qualify why the 308 engine is called "bullet proof" by some. Cylinder head studs: studs provide the ability to obtain much more accurate torque values because the studs don't twist during tightening as do bolts. Because the studs remain stationary during nut tightening, the studs stretch in one axis alone, providing much more even and accurate clamping forces. Dual Springs are a good option for performance engines with a heavy valvetrain. The two springs rub against each other and act as a damper. The second spring also acts as a safety measure. Broken springs can be found before they drop a valve into the engine.
That engine has sodium-filled exhaust valves. Wall thickness of the hollow stem is only a couple of millimeters. Very prone to failure. I just finished an engine-out refurb of my 1975 308/GT4 (exact same engine) and swapped out the exhaust valves for solid stainless steel valves. You're probably going to do a valve job so the labor involved for the swap is negligible, less than $1000 for the valves.
Nowhere near all of them have sodium valves and of those that do nowhere near all of them need a valve job. Then there is the matter of how many have heads that will be difficult to the extreme to remove due to corrosion between the studs and head castings. It can be a very major additional expense to replace sodium valves for some. No expense at all for most.
I have also heard "anecdocally" that the air injectors being disabled (pump removal/belt disconnection) reduces the chance of a sodium valve failing. There is some connection between cold air being injected into the hot exhaust port and sodium valve failure - localized temperature variances? A local Dallas independent I spoke to, said, they have done a few but the sodium valve concerns are usually overblown by the Internet.
Well the reason air is squirted in there is to restart the fire in the 1400 degree exhaust gasses. Do you really think there is anything cold in there? The 2nd Ferrari I ever worked on was a 250 Lusso with a broken valve, that was around 1974. Even then broken Ferrari exhaust valves were pretty famous. It was also built about 15 or so years before we had air injection. That was a long time before the internet. The last V8 Ferrari built with sodium valves was 1982. The 12 cylinders used them a little longer. Point is in 2022 most of those cars are driven very little so its not real surprising it doesn't happen a lot. There are a lot of internet wives tales. This is not one of them.
That is not what I wanted to hear as a 308 2V driver Would you recommend a proactive valve replacement the next time the engine is pulled out?
Well I never suggest waiting until they fail. If the engine is tired I'd plan on working it around whenever you can do whatever other work it might need. Pulling the engine out of one is somewhat rare. Waiting until there is another reason could be a long time.
Found something online that I will save here for others. Sort of a scientific analysis of why the sodium valves fail. -----Original Message----- From: ferrarilist [at] pless.com.au To: ferrarifixer [at] aol.com Cc: ferrari [at] ferrarilist.com Sent: Wed, 16 May 2007 11:16 PM Subject: Re: [Ferrari] Why a 308GT4?.......sodium valves Found out some interesting information....not applicable all areas "Why do sodium cooled exhaust valves fail? When valves are removed inspection revealed that some corrosion in the area where the divergence from the stem to the head occurred on high mileage cars. Low mileage cars showed no corrosion. I have found that if valves are dropped onto a concrete floor from 1200MM some valves snapped. Also when adjusting valve clearances if the cam bucket hold down tool was removed quickly causing the valve to snap shut a valve head may snap off. Inspection of the fractured area revealed spots where fractures had been in existence prior to the final drop shock that separated the head from the valve. Eccentricity existed between the outer diameter and the sodium filled core. This was very much predominant on one valve, but not detected by naked eye on the remainder of the valves. The quality of sodium in the core was highly irregular from one valve to another. This was determined by carefully removing the sodium with a suitable hand held drill bit. Analysis of valve material by spectrometer revealed the following:- Carbon 0.70% Manganese 5.70% Silicon 1.00% Sulphur 0.005% Potassium 0.02% Nickel 1.40% Chromium 20.00% Molybdenum 0.58% Copper 0.12% Titanium & Nioberin 0.01% Remainder Iron This analysis matches very closely with German valve steel known as German Standard (DIN) 1.4881 The metallurgical report on these valves examined is as follows:- 1. The alloy appears susceptible to interangular corrosion and pitting when used with leaded fuels. This corrosion causes stress concentration and structural weakness just below the head of the valve. (This was observed by dark patches at the fracture face aforementioned). 2. This metal when maintained at its critical temperature of between 540-800 deg C for prolonged periods suffers from a reduction in toughness caused by the chromium precipitating out and the alloy becoming in the embrittling "Sigma" phase. 3. Eccentricity of the bore to OD of the stem would lead to some localised stresses, thus causing failure. 4. Variation in sodium quantity on individual valves would not make the heat transfer optimum. 5. As the valve appears to be investment cast, the final product could be quite variable in analysis from batch to batch, hence exacerbating the problem. In conclusion, the original sodium cooled exhaust valves are basically under-designed for our standards. Thicker stem and increased gas resistance flow would solve problem from the start. Vehicles that have dropped valves are 246, 308, 365GT4, 365BB, 512BB 400.etc. These valves have letters stamped above collets like EL BM ST FS. I would suggest changing exhaust valves to Nimonic 80A or equivalent material of local manufacture".
I have seen this video before. IMHO, a clueless YouTuber who has never worked on a Ferrari and is somehow amazed that it isn't the same as a GM or Ford engine. By the way he talks about low horsepower and carburetors he wasn't around in the days of early emissions regulations when computer driven fuel and ignition management was in it's infancy. It kind of reminds me of the "deer in the headlights" look that you get when you tell someone that you need to put oil in SU carburetors.
It's cool that you know about SU carburetors but I had to google it. But the guy in the video is some one who is maybe starting to appreciate the details of a classic Ferrari engine. So what if he has not worked on Ferrari engines a lot? Everyone started with their first job before their 1000th job. Why do we have to shoot him down as a noob? Unless there is a way for anyone to skip being a noob at some point in theri life or career. I don't think that is the case. Internal combustion engines are dinosaurs that are going the way the dodo bird went soon so it should be appreciated that younger people still like them.
Yes, if you're tearing down the engine by all means change out the valves. It's the weakest link in the 308 engine.
No one expects everyone to know everything but anyone who chooses to put themselves in a position of educating about anything has a responsibility to be well versed in the subject matter. I don't advise anyone on taxes or legal matters but you tube and the internet has spawned a whole new generation who just cant help themselves. This place is a great example. It dispenses an unbelievable amount of misinformation.
Fuels unleaded theses days and has been a few years in the EU / U.K. . I asked my Ferrari tech and told me he had with his techs a combined years of over a 100 working on older stuff and he can count on one hand a dropped valve the sodium thing .U.K. based . Could hardly remember the last time he saw one . He then went on the go further to say inadequate belt changes not done properly for what ever reason were in his experience the leading cause of broken valve .Obviously in the older modals listed above ^ all sodium. It’s a big shop and cars come from all over the EU for work . I would like it to be black or white but I suspect it’s multifaceted.The neck and stem dimensions are just one of many .Easy to hang your hat on thoses as the cause and preach “ thou shalt change “ You need all to come together for a failure . Maybe in the states the proportion of DIY belt changes is substantially greater than the U.K. The classic F market in the U.K. is heavily influenced by service history at time served marque specialist less populated by DIY enthusiasts. I mean @ rifledriver have any one of your cars that you regularly look after to do the belts dropped a sodium ? You know customers who follow your additional advice where necessary like new tensioner , pulleys etc and maybe a dial gauge to time it as well ? Regular valve adjustment as advised with your correct tools and full box of shims . Never quibble on the Labour kinda guys ? I honestly don’t know where the truth lies .
As others have already said, the stem walls are very thin and unfortunately the weld between the valve head and the stem is right where the air is injected which further increases the temperature and the risk. On top of this, when the relatively soft original valve guides get worn, mine were all quite loose at 36,000 miles, then the repeated eccentric closing of the valves due to the loose guides creates small bending moments and that fatigue stress in the super heated region of the thin, welded stem can lead to failure.
Yes read ( maybe you ? ) the valve stem wears and oscillations set in ….wobbles . It’s the exhaust valves that are sodium .Are the inlets sodium too ? But crappy oil or extended oil change Fq , or just plane not warming the thing up or too many periods of inactivity = the heads dry up along with valve stem lub , and guy thrashes it out of the blocks chasing a 911 he’s just seen .= premature valve guide wear = wobbles = fatigue = fracture . See what I mean . It’s not just one thing it’s a bit of a lot of tiny things added up together. Where as a guy who regularly uses his 308 with sodium’s , warms it up before letting rip .religiously follows the oil change regime etc etc and gets a good tech to do the belts + what ever else at the time needs doing might never get the dropped valve . I don’t know .
The issue I have with the video isn't that he's never worked on one. It's that it's got misleading information in it. At the end, co-worker OJ is pulled over to give some information on financial aspects, and clearly states that replacing the 308 timing belt is a $6,000 job that requires the engine to be removed. There are other more minor things that struck me as amusing: - His observation on the double valve springs: "Weird, I've never seen these in such a low-performing engine. But I'm sure Ferrari knew what they were doing." Personally, I don't know why the springs are double... but if I had to guess, it would be to combat the valves floating. Again, I don't know either, but I'm also not making a video in my shop and discussing a $18,000 engine job I'm charging a customer for. - Shimming a lifter = nearly the same thing as replacing a lifter. - Several mentions on how slow the car was/is, without much context at all. In 1977, the 308 had more 12%/24% (L48/L82) more HP than the Corvette, weighed 30% less, and was faster both 0-60 as well as top speed. Hell, the 1977 308 has more HP than the 1985 Corvette, beats it by 3 seconds in 0-100. - He's laid his cam parts down on labelled cardboard (good idea), but also not in the correct relative positions to each other (bad idea). Hope they put them back in the right spots.
Engine out and north of 6k for timing belts. The kind of misinformation that scares people away from Ferrari ownership…..
