timing belt: tight

[RRoller123]

I think we are going to look at the mounting plate too on this. There is a clear design flaw in that there is not remotely enough play designed into this system to get the belt on easily. Everyone struggles with it, even at full extension (moved left) of the tensioner bearing plate. It should have more play, and then the tension is set by the return spring, as it should be. But with the damned adjustment all the way over (left), and still struggling to get the belt on, and it's being tight, the belt tension is then pretty much not being regulated by the return spring as it should be (before lockdown of the nut).

So I think Tim and I will run some experiments on my spare engine this weekend and see what we can come up with. All it would take is some modification somewhere, remove some material, whatever, to get more adjustment capability into the flawed system.

[18Fiatsandcounting]

So I think Tim and I will run some experiments on my spare engine this weekend and see what we can come up with. All it would take is some modification somewhere, remove some material, whatever, to get more adjustment capability into the flawed system.

I agree with you that it's not the greatest design, so let us know what you find out.

Meanwhile, and I know I have mentioned this before, but here's how I put the belts on: Route the belt as it should be around the crankshaft pulley and auxiliary shaft pulley, and on the intake cam pulley, but leave the belt hanging behind the pulley (towards rear of the car) on the exhaust cam. Make sure the timing marks are all lined up. Turn the intake cam (wrench or by hand) very slightly counterclockwise so that the vertical run of the belt on the driver's side is as taught as you can get it, but be sure not to jump a tooth on the crankshaft or intake cam. Using the heel of your left hand, push the tensioner pulley away from you, and with your right hand, slip the belt over the exhaust cam pulley (from the rear forward). Sometimes I "help" the tensioner spring with a large screwdriver, pulling the tensioner towards me, and then let it relax. Recheck timing, and tighten the tensioner bolts.

-Bryan

[tima01864]

Not much help on this issue, I have the belt on. Timed and running. I am concerned with the tightness of the belt since the tensioner spring is not in play. I had the cylinder head refurbished, The exhaust cam was worn to a point i had to replace. So I am not sure this is a new problem.

[RRoller123]

We are going to look at a machining solution, to get the tensioner adjustment within the range of the GD belt! It is a clear design error; as moving the tensioner to its extreme should yield plenty of free play so that any mechanic can fairly easily slip the belt on. They just screwed up and placed the belt at the very edge of the available adjustment range. I bet we can see a way to easily and safely remove some material somewhere to add a little more adjustment range.

[Nut124]

My recollection is that one of the two studs, nuts involved in the tensioner go thru a slot in the tensioner brg base plate. Filing that slot should allow for more "left" travel of the tensioner.

[RRoller123]

Good tip! We will check that out!

We ARE going to solve this age old design flaw problem, and relieve this burden from the Fiatista community of the tight belt! LOLOL

[Nut124]

The slot that sets the range of tensioner travel is actually the tensioner brg journal on the base plate. It could be hard to file.

[RRoller123]

There is always an ECO that can be written to correct these design flaws..... hahahahah!

[tima01864]

Impossible to alter, But the centering washer could be altered? I think the smaller idler would be a good fix, But I have been advised against reason being the spring may not apply the right tension on a 2L.
Any thoughts?

[Nut124]

The Fiat TC tensioner is not a "live" tensioner. Once tightened, the spring does nothing.

All that matters is that after all bolts, nuts have been tightened, locktited, and the engine run a bit, the belt tension is correct. I would not depend on the spring to set the correct tension. Expect to have to adjust it by hand and check results.

There is a spec for how to assess, check the belt tension by deflection, twist. Too tight can be heard, too loose is assessed by belt deflection, force.

[RRoller123]

That is correct, but it is the spring that sets the tension.

[tima01864]

The early tension 1438cc ? was set with a spring balance, According to the shop manual. That was obsoleted with a spring mechanism. This was designed to set a correct force on the idler to belt. No added force, The spring sets the tension.
I can not find anything about belt flex other than word of mouth from experience. No answer on belt flex between idler and exhaust cam.

[18Fiatsandcounting]

The early tension 1438cc ? was set with a spring balance, According to the shop manual. That was obsoleted with a spring mechanism.

Correct, and the changeover from using a tool to the spring/tensioner assembly happened in early to mid 1969 as far as I can tell. My 1438 spider was manufactured in the summer of '69, and it had the spring mechanism on the tensioner bearing plate.

-Bryan

[tima01864]

I really think it comes down to the Diameter of the tensioner bearing.

[RRoller123]

On our 2L engines, I totally agree. After doing all the investigation we did yesterday, there is no other logical answer right now.