Exactly How Do The 308 Cam Belts Fail And So What?

Wanna start a fight or something???

The belts are the most often needlessly changed part on these cars, behind the wheels probably!!!

The belts are only PART of the engine out 30K service, but failure is so disasterous to piston/valve contact that it's cheap insurance, to most owners. This is referred to as "zero clearance" engine. Some designs can fail without this damage, but ours cannot!!!!

Often overlooked is the bearings, hoses, valve shims that should also be done at the same time!

They shred usually, or jumping teeth is also possible, but this would be most likely due to tensioner bearing failure.

 

There are several way that the cam belts can fail.
cracks from dry rot
age (usually contributes to above)
On the 308 if the com cover seals are leaking the oil will run down on to the belt and cause failure.
most of the maufactures of these belt state the belt life to be 100,000 miles under normal use. Since Ferraris do not usually get normal use age is the predominant factor.

What happens when it fails ( YOU WRITE A BIG CHECK)

In an interferance engine like Ferraris the purpose of the cams is to open the valve to either let in fuel or expell gasses from combustion. This is a times occurnace and if timing is off or if a cam belt breaks then the valves are not opening at the precise time when the piston is coming up to creat the combustion. So, if the valves are off then the pistons hit the valves and subsequently bend them and damage the head and the top of the piston. Which usually the valves, pistons, need to be replace and the heads need to be repaired.

Oh yeah forgot to mention the dreaded tensioner bearing seizure,


Wade
www.fortunemotors.com
www.308qvregister.com

 

20 years might be pushing it! I've heard five years is the Factory recommendation, regardless of mileage.

Otherwise you would be getting them, and tensioner bearings, at your 60K mile service.

 

The belts are streaching continuously from new until either they are changed or they break.

If one streaches too far or if one breaks, the valves impact the pistons. If this happens at slow speeds, the low end TQ of the engine is effected, however at higher RPMs, this can bend con rods, bend the crank shaft, or send a broken rod throught the block. It does nothing good for the valve seats, and can break the cam bearing caps.

In a pendanic way, the age of the belts does not matter. What matters is to keep the valves from hitting the pistons. However, keeping the belts new is one excellent means to avoid valves hitting the pistons.

 

The 308 engine is an 'interefering' engine. ie: If a piston goes up while a valve is down, things will be very expensive($5K & up). The valve will get bent or broken. The piston can get anything from a ding to a hole in it. The head and/or cylinder sleeve will require repair.

Check out the dinged pistons in this thread:

http://ferrarichat.com/forum/showthread.php?t=16098

Most common failure is for one or more belt teeth to get stripped off, altho broken belts have been reported. Also, the belt tensioner bearings can sieze & wear the belt to the point that it breaks.

5 years or 30K, whichever comes first is the generally accepted interval for this service.

Search the archives for topics with titles containing 'cam' and/or 'belt'.
Don't forget the Old FerrariChat, it's where most of the info is.

 

Oh yea!! Figure $10K.

See why they sell so many $30 belts???

But I hope you understand what I'm saying here. Fuel lines, hoses, evap lines, all these are also potentially expensive (How loud can you scream "Fire"?) problems that are addressed during periodic maintenance.

CAREFULLY read your owner's manual on interval's and don't scrimp!!

You'll be SO happy! You'll sound like that Bobby McFarren dude, whistling!

 

Mitch,
The belts do NOT stretch. The fibers are made of kevlar which is like dacron in that it doesn't stretch, it keeps a fixed length up to the point that it breaks. This is why the belt tensioning is a one time set & forget.

 

Do later model 3 series cars have only one cam belt? It would seem that, if that is the case , a broken belt means even more damage than if just one broke in a two-belt confifuration. Right?

I ask this because I thought I saw a pic of a later model Mondial engine, and it looked like one belt.

 

[QUOTE

The belts are only PART of the engine out 30K service, but failure is so disasterous to piston/valve contact that it's cheap insurance, to most owners. QUOTE]


Correction, the engine does not normally come out for a 30k or "major" service...20 years on the belts??? Holy cow...sounds like the 78 308 GTS I bought in 1999, had the original belts in it!!! I drove it for about 3 weeks before having a major performed with all new coolant hoses and fuel hoses. I felt like I was driving a hand grenade with the pin pulled and the spoon ready to fly off!

Do people get away with this foolishness? Yes, many times, but it is a terrible risk. My mechanic gets one or two 308's or Mondials each year with a snapped timing belt (actually, I think it is the teeth on the belt that shear off).

 

The last in the Mondial series, indeed had a single belt.

 

Now THAT's efficiency! You can trash both heads with one belt failure!!!!

 

Sometimes ya gotta let 'em hang low, bro.

I'll give ya'll a tale on 5/18, if I survive!!!

My b'day is 5/17, the day my father died. Let's roll...........

 

My gf's like "Hey, wait for me... I'm coming, too!"

 

Well, I think it'd be OK to drive it over!

The cross baffle lines are a good idea. I heard a tale where a shop came in to find a 308GTB sitting in a big puddle. 16 gallons on the floor!

Good thing it was a non smoker. Can you say "WHOOSH!!!!"????

 

Donald I own a 75 GT4. I have done mine since I have owned the car in 82. I can do your fuel lines, tensioners and belts for 1,000 including parts. All new cam seals also. I am in San Diego, if you want, I can do the work in your garage.

 

I disagree, however we are talking microns of stretch per use, but stretch happens nonetheless.

Kevlar is a wonderful material, however it, just like every other material used in tension slowly yeilds. Even a solid flawless diamond cut in the shape of a bolt and torqued above 1/2 its plastic limit will slowly yeild.

 

If you go to over to any goof ferrari shop or somewhere like TRutlands--there is always a big box or barrel full of pistons with big dents in them from valve impact--no matter where the cam stops--some valves are extended--and sope piston is gonna crunch um--bad--if you are lucky it will not destroy the block and head too

I have seen valves brake into pieces and chunks of valve go back up the intake and into other cyls--tearing up cylinder liners, heads, pistons in 3 or 4 cylinders. AND at that point a connecting rod usually snaps and pokes a hole thru the block-----got 8000.00 to spare?????

 

Now THAT's interesting!!!!!

No wonder they cost a lot!

 

"The fibers are made of kevlar"

Not in a 20 year old belt I'll bet.

 

I know, I'm an engineer also, however from a practical 'layman's standpoint, the stretch on the belts is negligable.

 

Interesting, since I am contemplating rebuilding my own 308 in the near future, curious as to your comment as a 308 being an "interfering engine". Can you explain what you mean by this?? Thanks (I'm another dork engineer)

 

THere are two types of engine, interference and non interferance .


What it reffers to is if valvetrain will interfere with pistons if one movens when the other dosent.