Belt Skipped a Few Teeth

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18Fiatsandcounting
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Re: Belt Skipped a Few Teeth

Post by 18Fiatsandcounting »

Well, the best of all possible worlds is that you simply have a nearly dead battery that turns the engine a bit and then is out of juice. The worst of all possible worlds is that something is bent or broken inside the engine.

A few questions/comments:

1) Did you try turning the engine a few rotations by hand, with a socket on the crankshaft nut? How did that go?
2) How are you making sure that the crankshaft is in the right position when you're putting the timing belt on?
3) If you are off by a few teeth on the belt, the engine won't run well (if at all), but it wouldn't cause it to lock up.
4) I'm not sure what you mean by "I'm not positive I have the belt on correctly."

Sorry for all the questions, but this one stumps me. Unless it's simply a dead battery or bad battery connections.

-Bryan
CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

I have not tried to rotate the engine by hand since trying to start it. I did rotate it a few times before starting.
The crankshaft stayed in place while I was putting on the belt, that part was easy. The aux pulley kept moving which is why it took me several tries. Getting the belt on the exhaust pulley was the hard part. When I got it on, it seemed like the belt was tight between the exhaust and intake pulleys but not right from the intake to the aux. The cans were on there marks.
I'm not at home now so I'll test the battery tonight but I'm pretty sure it's good.
Thanks for the help Bryan
1976 Fiat 124 Spider
CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

I just checked the battery and it is good.
I tried rotating the engine by hand clockwise and it will not budge. So does that mean something broke inside?
1976 Fiat 124 Spider
18Fiatsandcounting
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Re: Belt Skipped a Few Teeth

Post by 18Fiatsandcounting »

CharlieB wrote:I tried rotating the engine by hand clockwise and it will not budge. So does that mean something broke inside?
Not necessarily. But, and this is very important, you must (capital letters MUST) make sure that the crankshaft is rotated so that the pistons #1 and #4 are at the very top of their stroke when you align the rest of the timing belt. "Top Dead Center" as it's called, or TDC. If you put on your timing belt when you aren't at TDC for #1 and #4, there are clearance issues between the valves and the pistons that can wreak havoc on an engine.

So, to put on the timing belt, the crankshaft MUST be rotated so that pistons #1 and #4 are at the top of their stroke, that is, at TDC. Let us know if that doesn't make sense. At that point, the camshaft pulleys and the auxiliary shaft pulley can be rotated to their respective positions and the timing belt installed. And, as noted, the distributor rotor at this point should point to the #4 spark plug wire contact inside the distributor cap.

-Bryan
CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

Number 1 was at tdc. I checked several times to make sure. I just don't understand why I was able to turn it by hand before trying to start it. But when I try to crank it, it gets out of sync, for lack of better term.
1976 Fiat 124 Spider
18Fiatsandcounting
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Re: Belt Skipped a Few Teeth

Post by 18Fiatsandcounting »

Do you have the right size timing belt for your engine? The timing belts come in at least two different sizes (lengths) depending on which engine you have (1438, 1608, 1800 or 2 liter), and so I'm wondering if your belt is too long for your engine, and it's slipping around the crankshaft pulley?

-Bryan
CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

It's the same belt I've had for a year or so. I guess the next step is start taking it apart and see what's going on inside.
Ok, that might be jumping the gun. I'll take the belt off tonight and start the process over just to make sure.
1976 Fiat 124 Spider
18Fiatsandcounting
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Re: Belt Skipped a Few Teeth

Post by 18Fiatsandcounting »

Charlie, I wouldn't take the engine apart quite yet. Maybe you've already done this, but I'd take the belt back off, verify that the crankshaft, two camshafts, and auxiliary shaft all rotate freely by hand. If they all rotate smoothly, then we need to figure out why the belt "gets out of sync" as you try to start the engine, and things appear to lock up.

One question: Is your timing belt tensioner working as it should?

For reference, here's a quick summary of how I put on a belt: Line up all the pulleys. Put the belt over the teeth on the crankshaft, and guide the belt roughly into position but leave it hanging off the two camshaft pulleys. Where the belt goes around the exhaust pulley, put the belt into the area between the pulley and the front of the cambox housing. Guide the belt onto the driver's side of the auxiliary pulley, and pull the belt tight up over the teeth on the intake pulley. Go back down and guide the other end of the belt up past the passenger side teeth of the auxiliary pulley and around the timing belt tensioner. Now, the important part: Stand on the driver's side, and with the palm of your left hand pushing on the timing belt tensioner so that it moves away from you, slide the belt with your right hand onto the exhaust cam pulley (sliding it on from the rear of the cam, not the front). Release the belt tensioner, check your timing and tighten everything up. Don't forget to tighten the two nuts that secure the tensioner (one 13mm and one 17mm).

-Bryan
Last edited by 18Fiatsandcounting on Mon Jun 15, 2020 2:29 pm, edited 1 time in total.
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RRoller123
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Re: Belt Skipped a Few Teeth

Post by RRoller123 »

Just a thought..... could you have the longer, 2L belt, instead of the shorter one used on previous engines? Other than the belt tensioner either not working, or not set properly, that is all I can think of that would repetitively cause a slippage like this.
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CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

I'll take the belt off tonight and see if it rotates by hand.
Bryan the procedure you described is exactly how I attached the belt except I pushed the tensioner with my hand and tightened it down until I had the belt on then loosened it to take up the slack. Then retightened it.
I'm going to redo the whole process tonight...hopefully.
I went home for lunch and looked at the car for a few minutes and the belt is tight between the cams but pretty loose from the aux. pulley up to the intake pulley. Anyway I'll get everything lined up and give it another shot tonight.
Roller, I know it's the right belt, however at this point I probably need to replace it. It is not a new belt.
Thanks guys
Charlie
1976 Fiat 124 Spider
18Fiatsandcounting
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Re: Belt Skipped a Few Teeth

Post by 18Fiatsandcounting »

When you say "loose between the aux and intake pulleys", how loose do you mean? Loose like a beagle's ears flapping around hanging outside of a car window, or loose as in "not totally taut"?

If the latter, here's what I do to fix that: put the belt on as you describe. Before tightening the tensioner bolts, take a 19mm wrench and very slowly and gently turn the intake cam counterclockwise (looking from the front) by the bolt so that the belt tightens between the auxiliary and intake pulleys. Just enough to snug up the belt, and if you turn too much, the pulley usually jumps a tooth and you're back to square one. Then turn the exhaust cam very slowly counterclockwise as well to snug up the belt section between the intake and exhaust pulleys. The tensioner should now have moved outwards a tad, which is expected and you can tighten it up. Recheck to make sure every timing mark is still lined up, and at this point the belt should be timed and taut.

-Bryan
CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

Well not like a beagle's ear in the breeze, just not as tight as I think it should be. Great idea on turning back with a wrench, hopefully I will not need to do that but good to know.
Thanks Bryan
Charlie
1976 Fiat 124 Spider
18Fiatsandcounting
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Re: Belt Skipped a Few Teeth

Post by 18Fiatsandcounting »

You're welcome. I like to re-check the tightness of the belt after it has run for a while, using the same procedure. I also do not have a timing cover on either of my cars, so adjusting belt tension is as easy as changing a spark plug. The downside of no timing cover is that I no longer have a crankshaft timing mark for TDC, so I have to use the tried and true "long screwdriver down the #1 spark plug hole to find TDC" method.

-Bryan
CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

Yeah I don't have a belt cover either.
1 more question: If the belt was off by a tooth or 2, would that prevent the engine from being able to rotate by hand?
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CharlieB
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Re: Belt Skipped a Few Teeth

Post by CharlieB »

OK, I took the belt off, left the cams and aux. pulley lined up with their respective marks and tried to rotate the engine by hand.
It still won't budge. It's definitely hitting something inside. I can feel it bump.
Not sure what to do now besides taking a look inside the head. I'll hold off on that for now.
I replaced the head gasket a few years ago, so I know I'm at least capable of pulling the head. Of course, that's the easy part.
Thanks
Charlie
1976 Fiat 124 Spider
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