How much tension in the tensioner before tightening?

[ScoopMan]

Is it OK to crank in plenty of tension into the timing belt by prying out the tensioner with a bid screwdriver before tightening it? Or is it better to just let the spring take up the slack, and THEN tighten? I did the former, in thinking that a tight belt is usually a good thing, like when thinking of a V belt that drives the alternator and water pump. But then I had second thoughts, as a toothed belt is obviously not a V belt, and I might be putting too much force into the system and risk a premature belt breakage with all the attendant carnage to engine internals. I remember seeing a spec that wants you to put a 60 pound load on the tensioner, by using a fish scale or something similar, but how do you know that is correct when you also have that spring pushing out on it....?

[djape1977]

according to late 60's fiat workshop manual, timing belt is properly torqued when you can just achieve 90" rotation between intake and aux shaft sprockets.
this will require pushing tensioner with a substantial screwdriver before tightening. spring is there just to make sure there's some tension at least if nut holding the tensioner somehow gets loose

[bradartigue]

Only as much tension as is generated by the engine during manual rotation (2 turns) of the crank...

Read your shop manual, starting around p 10-63 is the entire procedure for timing belt replacement...specific to the tensioner:

Place timing belt over tensioner pulley
Loosen tensioner bracket bolt and allow tensioner pulley to take out play
Do not apply additional force to tensioner pulley
Turn crankshaft two full turns
Check that timing is correct
Tighten tensioner bolt.

[ScoopMan]

As I was afraid, two very different answers. My sense is I may have overdone it. The engine runs fine but I now hear a whine in there so I started getting nervous. I think I will follow Brad's advice and back off the tension a bit. The 60 pound load is clearly shown in a photograph from an early 70's shop manual that I have. Did the tensioner always have a spring?

[bradartigue]

Are you looking at a FIAT manual? The official early manuals had supplements for the TC motor and they don't have you tension the pulley until you finish installing the belt and rotating the engine (by hand). The early instructions are a bit hokey:

loosen belt stretcher pulley mounting nut (6,
fig. 731) and belt stretcher pulley bracket locking
screw (5); in these conditions the spring will act
on the bracket, tensioning the belt;
then secure belt stretcher pulley mounting
nut (6) and bracket locking screw (5).

The early manual has the tension at 32.5 ft.lbs.

[ScoopMan]

I have 3 manuals, the Brooklands one still in print; Chilton's 'Fiat 2' from 1974, and the 'Fiat 124 Sport Shop Manual' from Henley Press, 1971. The last one has far more original Fiat engineering drawings in it than the other two combined, and is pretty excellent. In it it shows the use of a fish scale type device to put a load of 27 Kg pulling outward on the tensioner, which is basically 60 pounds. Then it says to torque the tensioner bolts to 35 ft-lbs. The pictures show the spring.

As it is a torsional spring, it could be rated in ft-lbs per degree, but I don't know who would check such a thing. I cannot see these springs ever weakening as they are statically loaded 99.99% of the time, only getting flexed when the tensioner is moved during a belt change.

[bradartigue]

Just be careful using them, most of the aftermarket manuals have typos in the wrong places (e.g. the head bolts at a dangerously low value, the wrong way to set the suspension, etc).

The 35 ft lbs is on the bolt. The spring sets the tension - the bolt doesn't really lock it so much as keeps the assembly from flying apart. I don't know what they're doing pulling on the spring or bearing, that is not how you set it. That is how you set some cars, but as you noted it is continuous tension at a rate determined by that fat little spring, at near full load all the time.

[ScoopMan]

Well the Henley manual I have is pretty impressive, almost seems like an English language reprint of the factory manual. However, you have convinced me to ease off on the tension and let the spring do its job before the final tight down. I am worried that I cranked too much load into the system.

Your contributions to the Fiat owners community are legion. I am just a shade tree mechanic who likes old cars and wants to keep them going....