308 exhaust valves, do they really need to be replaced with unleaded valves?

Nothing to do with unleaded actually.

They are sodium filled for heat transfer, cutting edge at the time, bad idea as it turns out for the long haul. Others will chime in but if it was me, I'd shop for a nice set of stainless steel, (search for manufacturer) and buy a little insurance on all the rest of your hard work.

The stem snaps off, throwing the valve head loose into the combustion chamber, by the time the engine gets turned off it's a big mess.

Good Luck to ya! HTH

 

Those heads will be stuck on, like green on a shamrock!!!

Lot's of penetrating oil, time and patience willl be the key....are you doing all this youself???

 

I recently rebuilt my 308 GT4 engine and thought I could get away with not changing the exhaust valves. While doing a valve adjustment the very last exhaust valve broke. The head snapped right off just from the pressure of pushing down on the valve to put in a shim. Needless to say I'm glad it happened while the engine was still out. Removed the heads and replace ALL the exhaust valves with solid ones. Runs great...why take the chance?

 

Big Tex is right on the money!
They were a "bandaid" for lean mixtures necesary to meet EPA,and as the are older now, they are even more prone to breaking even while you are driing nice! if that seems an expnsive propisition, look into FULL overhaul prices compared to a top end job!
Kermit

 

We are here for you!

Not sure about the 308GT4 as far as the front head, you can adjust valves with it in the car, but to remove the heads would be easier with it out..IMO

J. Grande????

I know from watching my tech break the heads loose on these old girls that a two to three day time period is realistic! You cannot pound or pry on them vigorously without risking damage, so penetrating oil is your friend.....wood wedges and rubber mallets.

Post in the UK sections for a shop to talk you thru it. Long distance to Texas would break the bank....

 

Surely there's many older 308's out there with original valves being regularly revved to the red line. If I worried too much about what could happen, I'd probably never get in the car let alone enjoy it.

So before I rush off to change something that ain't broke, what's the real chance of failure? Anybody know?

 

Ask an OLDER Ferrari Tech that question.....they broke when they were NEW!

 

When you see one fall and hit the floor they shatter! If you're gonna do a major service then you might as well order the tensioner bearings, 2 head gaskets, cam seals, new fuel lines and a new set of exhaust valves and then forget about it for the next twenty years...you're in there...do it once. I don't know if you can take out the valves with the engine in, mine were done while it was out.

When was the last valve adjustment done?

 

I have just fitted new valve guides to my gt4. The exhaust valves were in perfect nick as were the valve seats(70k miles on engine).I do run it on leaded petrol, the seats are hardened anyway so should be ok on unleaded(I have been to Shell and had a long discussion about unleaded petrol/valve seats/Ferrari engines and it was very interesting to hear what they had to say off the record). Also my heads came of with a couple of taps with a rubber mallet no problems there also. Regards to sodium filled valves Porsche 944 turbo run with these in and my last one was pushing over 130k miles and I know of a chap with over 200K on his with no problems. I am probably in a minority with this. But good luck with the work I would suggest that you take the engine out if you can its easier to work on when out on a bench. Make sure you time it up correctly on the vernier pulleys after.

 

I can't speak from experience with this particular engine, however...

If enough people tell you they have seen problems with these exhaust valves popping apart, replace them. One thing I notice with old air-cooled bug motors is that you can bet the number three exhaust valve will be the one to go every time. Why? Because the oil cooler sits just before the number three cylinder in the cooling air path within the cooling shrouds surrounding the engine. Number three always receives hotter cooling air, exhaust valve can't cool as well, pop goes the weasel. This is a known thing with these motors. An indication of when it is going to fail is when doing your regular valve adjustments, the number three exhaust valve will be tight two or three ajustments in a row while the others are still within spec. Maybe this is something you can keep track of the same way with your motor. If you do the valve adjusts, keep track of the exhausts compared to each other. If one is getting tight frequently, change the lot.

Caveat, I just saw a 360CS motor apart on the bench in need of new cylinder liners, one new head, four new pistons and a blessing from the pope on the crank!!! And this was from something much smaller than a valve head coming apart.

If you think a top-end rebuild bill is a tuff pill to swallow, try choking down a complete motor.

 

On UK and Aus spec cars, it's perfectly practical to get the heads off in situ. Even if a bit stuck on the studs. If a US car has a whole load of sound/heat shielding it may be a bit tricky with baulkhead clearance.

I usually pull out the front cam cover studs to gain some clearance, it only takes a moment.

There is no sign or warning for the valves to break. They don't stretch and you cannot see any external evidence. Under x-ray, you can see the internal erosion at the head/stem joint, but in reality, most likely cost is more to test than to replace.

I just got a local shop to make some new valves. Wasn't too expensive at all. Also need to replace steel valve seats for stainless (test with a magnet if unsure), then you can use high octane unleaded without worry.

I've had problems with Shell optimax turning a bit jelly like if left to stand, but otherwise you can use any unleaded you like. The higher the octane the better.

 

Did they use the same valves in 308 QVs?

 

No. QV's are completely different and no known problem!

 

I think he meant that usually they are worn, at the point of the engine needing attention........

 

Basically correct, but you must bear in mind that Technical Bullitin 966 also states that while it is permissable to use unleaded fuel without modifications to the engine it also states "in case of heavy duty use of the engine (such as use on track or continuous high speed) we recommend the use of high-octane fuel or appropriate additives"

 

Like I said....Use stainless seats for "fit and forget". Once fitted, the clearances go for about double distance before needing re adjusting.....and valve clearances never need doing on a time period, so your clearances can stay set for years and years in most cases.

 

From the below Phil, I would deduce that the original seats are not that hard afterall, and may not survive unleaded like everyone says they would.

 

I replaced ALL the valves,guides and seals in my 308 just last winter. I git the valves from SIvalves aswell as the guides and seals. They were very well priced,,cheap really and the quality is very good. My valves seats were in very good condition. The machine shop said just too leave them alone.
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Both inlet and exhaust in stainless will give you years of trouble free motoring. The first thing to fail if you used unleaded solely, would usually be the exhaust, but the inlet will go too eventually.

The exact seat material needs to be clarified..there's stainless and there's stainless...I'll get the info from my cyl head guy.....