Fiat Twin Cam
By Al Williams
FIAT Dual Overhead Cam Timing Belt FAQ
Note: This is a supplement to Eli Caul's belt FAQ found at mirafiori.com. Many thanks to Steve Cecchelle for the technical expertise given when writing this back in 2000.
1) How do I know it's time to change it?
If you're asking this question, it's time.
If you've recently bought the car, and the previous owner doesn’t remember when it was changed last, it's time.
If your belt hasn't been changed in years, it's time.
If your mileage is 36,000, or multiples of 36,000 miles, it's time.(60.000km)
2) Can I get a socket to the crankshaft to turn it by hand?
I can! I use a 2" deep 38mm socket on a torque wrench... it works just fine if I’m patient- even on the side of a busy highway!
3) Does the radiator have to come out?
I never take mine out to do the belt. If you're removing the crank pulley, then, yes, the radiator has to come out (if you're using an impact wrench, that is)
4) What about my tensioner?
Most people say that you should change your tensioner when you change your belt. The last thing you need is to have it freeze up on you... They're readily available at
Vick Autosports, Wine Country Motors, Bruce's Parts Bin, Caribou, and most other Fiat Parts Vendors.
5) Ack! My belt's going to slip off!
No it won't! (I said this first time I saw my '78 running without the timing belt cover) The way the cam wheels are constructed will keep the belt in place- the exhaust and auxiliary
shaft wheels have a lip on the front to keep it from falling off the front, and the intake wheel has a lip on the back for the same purpose
6) I've heard of wide belts... Are
these a good idea?
Well, belt technology has improved so much over the past few years that a wider belt really isn't necessary. Besides... they're hard to find, and may be so old that they'll be
brittle, which will lead to premature failure, something we all need to avoid. (If you get a Pirelli belt, you're getting the best)
7) What about my inner timing belt cover?
To remove that, the crank pulley ha to come off. One of the bolts that holds the cover down will not come off with the crank pulley in place. Once I have the pulley removed and the cover is off, I usually run over it with the car to flatten it so I'll never have to worry about removing the crank pulley again.
8) Do i need to replace my timing belt every time I remove it?
The quick answer is, no, unless it's a high mileage belt. New belts can be reused all the time. There's not much tension on belts. Also, belt technology has improved in the 40 years since the Spider was first introduced.
9) I have a '74-77 Spider or Brava. What's with the air pump?
Emissions stuff... It sucks. Fiat didn't think to put the air pump on the intake side of the motor, so they put it on the passenger's side. Since the alternator was already there, they decided to run the air pump off of the exhaust cam belt. This can cause major problems- if the air pump seizes, then the cogged belt that drives it will also stop spinning. This will make the exhaust cam stop spinning, which will cause major engine problems when the pistons smash into the exhaust valves.
In '78, Fiat moved the air pump location to where the alternator was, and put the alternator on the intake side of the motor. They connected the air pump to the crank pulley, like it should have been all along.
10) How do I change
First, make sure the car's cooled down... That may sound simplistic, but it IS close quarters between the engine and radiator.
There are 4 gears and one spring loaded tensioner bearing that has a smooth wheel. There is also a belt cover. It's aluminum on early models (up to '77), and plastic on later models ('78 and on)
Remove timing belt cover- it's held on with 4 bolts, 2 at the top, one near the bottom, and one in the middle. You will need to remove the top radiator hose, to get the cover out of the
way. And also remove the alternator/water pump drive belt, on some models there is a water neck "t" which will need to be removed You'll need a 38mm (1.5") socket. Turn the
engine by hand until the holes in the cam wheels (the top gears) are lined up with both the cast in marks on the cam housings, and with the pointers which are on the timing cover
bracket. Once the wheels are all lined up, DO NOT allow the engine to turn- serious damage can occur. Lock the engine by engaging gear and setting the hand brake Next, using a
3mm, loosen the bolt that locks the tensioner bracket. Then, with a 17mm loosen the nut in the center of the tensioner. (this doesn’t need to come off unless you want to change it)
The old belt can now be removed.
Make sure at this point that the tensioner is locked in the full loose position (as far to the exhaust side of the motor as it will go) and tighten up the 17mm nut to hold it there.
NOTE: If the tensioner bearing needs to be changed, the spring must be flicked out of its groove by a large flat-blade screwdriver, remove the locking bolt and washer, and don’t
lose the tensioner spacers and hardware.
Refit the tensioner onto the stud, fit the washers and spacers, fit the locking bolt (this is the one with the groove for the spring), to refit the tension spring, use a large screwdriver with a notch in the blade to lever it back into position
Now slip the new belt over the crankshaft sprocket, then past the auxiliary shaft. The timing mark on the auxiliary shaft gear, should be at approx. 1:00 or so. If it's not, then it can just
be turned to that position. It needs to be aligned so that the fuel pump cam at the end of the auxiliary shaft can’t hit the con rod of number two, which will cause damage. This is true of
all DOHC engines with the fuel pump lobe on the aux. shaft.
Next, slip the belt around the tensioner and up and around the exhaust cam gear.
The next step is to slip the belt over the
intake cam gear. The teeth may line straight up,
they may not, so, if needed, rotate the cam gear slightly with a 19mm wrench to
belt to slip on.
Now that the belt's back in place, the real fun begins.
NOTE: The slack in the belt needs to end up on the tensioner side of the motor, or else when the motor is turned the cam/crank phase can be end up being out.
Loosen the tensioner nut again and the tensioner will spring across to the intake side of the motor. Using a large flat blade screwdriver between the water pump and the back of
the tensioner, assist the tensioner to move, (THEN REMOVE THE SCREWDRIVER AND PLACE IT ON THE GROUND), return to tighten the tensioner 17mm nut. This simply
makes sure the tensioner has moved fully.
Now it's time to slowly turn the engine BY HAND with the 38mm (1.5") socket on the crankshaft.
Turn the engine one full revolution by hand, and REPEAT the previous step to ensure the slack is evenly out of the belt. Rotate the engine fully again by hand and REPEAT tension
procedure again. This takes the slack out of the belt evenly.
Now check that everything is still in phase, you can slip the cover into place to check crank position, the cam gears should line up pretty exactly. If everything is aligned, the job is almost
done. If you think the cam gears are out of phase, then you must repeat the procedure from the beginning and make sure the slack is to the tensioner side of the engine
Tighten the 13mm tensioner hold down bolt,
Reinstall the cover and radiator hose "t" piece (if removed)
Stand back and start the motor. On 1608, 1592, 1756, and 1995cc engines, the ignition timing might need to be checked as the exhaust cam and auxiliary shaft. gears won't necessarily be in the exact same place where they were before.