timing belt: tight

[18Fiatsandcounting]

I also agree. The crankshaft is fixed in place, the block is fixed, the head is fixed, etc. Unless you have done something really odd like use ridiculously thick head-to-cambox gaskets, or an aftermarket cam pulley that isn't quite right, it's hard to imagine that the problem is anything other than the wrong belt length or the wrong tensioner diameter.

-Bryan

[tima01864]

Seems like the vendors sell 70.5mm bearings, I was told that finding a 70mm is very hard to come by. I found and measured the old bearing and it was 70.5mm. 67mm seems, from the math, Would put the bearing in the other direction of possibly too loose. All you have is the space between the 10mm stud and the clearance of the bracket.
Hard to say if the 0.5mm would make so much of a difference. Decided to let it go and move on. In another four years Iwill investigate it next belt change or other.

[greenspider]

Geo - Great to read that your timing belt replacement turned out ok. Is the belt still overly tight? Did you use Bryan’s technique? BTW - My 2021 registration was $148. I noticed that your’s was 2018.
Also, would it be a sin to not replace the bearing (assuming it spins freely) since that could be the culprit of a too tight belt? Greenspider

[RRoller123]

I also agree. The crankshaft is fixed in place, the block is fixed, the head is fixed, etc. Unless you have done something really odd like use ridiculously thick head-to-cambox gaskets, or an aftermarket cam pulley that isn't quite right, it's hard to imagine that the problem is anything other than the wrong belt length or the wrong tensioner diameter.

-Bryan

Yep, we measured the Adjustable Cam Wheels diameter, they were very close to factory, and Tim put the factory wheels back on anyway. He did use a HiPo head gasket, but the difference is minimal. The key is that tensioner bearing, because a small change in Radius yields a big change in circumference, and the belt travels along quite a long portion of the circumference. Same with the Exhaust cam wheel, where it travels around almost 3/4 of the circumference. So one could easily see a 0.05" or so change, and given the absolutely sihtless design of this tensioner system, that has way too little free play, that could lead to the common difficulty in getting these belts on. It just shouldn't be this hard! The tensioner should be levered to the Left, and that should yield enough free play for the belt to slide right on, but it never does.

Pete

[18Fiatsandcounting]

It just shouldn't be this hard! The tensioner should be levered to the Left, and that should yield enough free play for the belt to slide right on, but it never does.

Yep, I agree with you there! Anyway, let us know what you find out regarding the tensioner and/or its bracket.

-Bryan

[tima01864]

I think
i did

[18Fiatsandcounting]

I think
i did

Maybe I misunderstood, but I thought you and Pete were going to look into modifying the tensioner bracket to allow greater travel. That's what I was referring to.

-Bryan

[tima01864]

Ah, Impossible me thinks Bryan

[RRoller123]

Yeah, agreed. It looks like the only thing that could be done would be to increase the diameter of the tensioner support tube that goes over the stud coming out of the block OR to actually decrease the diameter of that stud. A third option would be to move the position of the stud slightly. All of these are terrible solutions, hard to implement, costly, and they weaken the system. This whole damned thing pisses me off, lolol. OR.... risk trying the smaller diameter tensioner bearing, and then possibly find out after all that work that it is now too loose. Blechh.....

[Nut124]

Is the belt too tight once everything is tightened up?

If not, who cares if the belt is hard to install? Once the belt is on, you can adjust the belt tension looser if you want and tighten it up when to your liking.

Regarding modifying the tensioner bracket: It does not have to be drilled out. You only need more clearance in one direction.

If you are willing to put in the time, you could get a carbide burr and cut the inside of the bracket hole on one side only. 1 to 2mm would go a long way. I would not try a smaller diam bolt.

Do you lock the tensioner in the fully loose position before attempting to install the belt?

[RRoller123]

I care about it, but that is besides the point. The belt is tight once installed, and there is not enough play to loosen it either before or after installation, that is the whole problem. Yep, you are right, there is no good machining process to create more free play, it is just a sihtty design. I think filing down one side of the tube to create more free play would probably induce high stress points and it would be better just to re-bore the hole, but neither approach is any good, they both weaken the system. All one could gain is a few thousandths without critically weakening the tube. Yes, the Tensioner is locked fully loose before installation.

[tima01864]

I dont think you are getting the picture here Nut124

[aj81spider]

I've been reading this thread with interest, although not really relating to it, as I've had two Fiats (81 and 74), neither of which I would describe as having overly tight timing belts. After reading what's been going back and forth for days and thinking about it, here's my 2 cents.

When shipped from the factory I'm pretty sure the belts were not particularly tight to install (I have personal experience with two different model years where that is the case). The design is probably pretty closely toleranced, as you want to tighten a belt with a spring that doesn't have an exceptionally long range of motion, and which has to exert a reasonable amount of force.

Over the years Fiat changed the design in subtle and not so subtle ways (length of the belt, size of the wheels, whether there is a spring or not). People who have owned the cars have also modified them over the years. I'm guessing that, in some cars, the narrow range of motion that was necessary by design, and which was perfectly adequate when manufactured has been consumed by other things (a pulley that's a larger diameter, a slightly thicker head gasket, etc, etc). Short of figuring out everything that's not perfectly stock and putting it back I suspect it becomes an intractable problem.

I wish Pete and Tim good luck in finding a way of increasing (or moving) the range of adjustment, but it probably won't be easy, as the engineers at Fiat would probably have put that range in if they could have. To increase the range meaningfully I think you'll probably have to completely change the way the tensioner operates.

[Nut124]

I think this thread may just have saved my engine from total destruction.

Last nite, I decided to check my timing belt tension after having driven it maybe 500-1000 miles since rebuild last fall.

The belt was totally loose. The long run between intake and the aux had over 1/2 of slack play. I disconnected the battery.

I'm pretty sure the tensioner has not moved. I have the Vick pulleys. I wonder if the Vick pulleys do not quite mate correctly with the belt causing the tightness you are seeing. Perhaps the grooves in the pulley are too narrow and the belt runs "high" on the pulley until the belt wears a bit. I have never seen the belt tension change with factory pulleys.

I will have to remove this belt and examine it.

[18Fiatsandcounting]

Last nite, I decided to check my timing belt tension after having driven it maybe 500-1000 miles since rebuild last fall.

The belt was totally loose. The long run between intake and the aux had over 1/2 of slack play. I disconnected the battery.

This might be normal, but I've always "retensioned" a new belt after it has 500 or so miles on it. Loosen the tensioner, very slightly nudge the pulleys so that all belt runs are tight, and retighten the tensioner.

By the way, I sense we're all on the same page here, just that some of us have engine/belt/tensioner setups that make it ridiculously hard to install a belt. I'm still not totally sure why, but it looks like minor differences can have a big impact.

-Bryan