Timing belt change: mileage or time determined?

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njoconnor
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Timing belt change: mileage or time determined?

Post by njoconnor » Fri Aug 30, 2019 10:09 am

My 72/1608 ate its water pump this past week, and since many of the posts I've read in research suggest timing belt and tensioner change outs at the same time, figured I'd ask. This engine was rebuilt in 2011 by the PO's mechanic, and the rebuild included new timing belt, tensioner, and...water pump. That was 6000 miles ago. Not many of those miles were put on between the rebuild and 2014, when I finally got the car sorted and roadable. Most miles came the last 2 years, and I was DD-ing it to school last fall and this spring.

I'm aware of the 30K recommendation on timing belt changeout in the past (that was my practice with my 71 coupe back in the day). Wondering if there's a consensus on age based lifespan. The car's been stored inside, covered in winters, used a few times a week for local cruising and errands, May-Oct. I'll be placing an order for a new pump soon, and figured I'd ask iso I can order anything else at the same time.

Not sure of the reason for the pump to go "so soon". Might have been over-tightening of the alternator belt. I'm going to doublecheck the pulley alignment between alternator and water pump. Any other things I would do well to check?

Neil
Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
12 Jeep Grand Cherokee
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miker
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Re: Timing belt change: mileage or time determined?

Post by miker » Fri Aug 30, 2019 11:13 am

As I recall there was a thread years ago about how bad aftermarket water pumps are, with a particular made-in-Japan brand singled out for praise. If it were me, I’d just change the pump if the timing belt looks good.
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
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rridge
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Re: Timing belt change: mileage or time determined?

Post by rridge » Fri Aug 30, 2019 11:27 am

Such a simple question. And yet you won't find a consensus answer. Modern belts seldom fail under 100k miles or 10 years unless the car is stored for many years before startup, the belt is contaminated with oil or coolant, the bearing in the tension seizes or the cam pulleys have excessive wear. None of these conditions is common in relatively low mileage cars.

The real questions may be what you find when you inspect the belt and related hardware and how much time are you willing to spend to do belt replacement. Replacement time in turn depends on the difficulty of getting the crank pulley and any protective shields off and that in turn depends on the year and engine configuration of the Spider as well as the mechanic's talent and equipment. And then there is the question of the credibility of the previous owner's records and memory regarding prior replacement.

I replace belt whenever it is relatively convenient for me do it. They are cheap and timing belt age is an inevitable question when selling a somewhat collectable 40 year old car. The work can be tedious but if you actually read the manual not that difficult.

Under no circumstance would I recommend having mechanic who may not be familiar with Twin Cams replace the timing belt based simply on the belt age. The odds of inducing new problems during replacement are greater than the potential problems you may be avoiding.
Richard
'81 Turbo Spider
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njoconnor
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Re: Timing belt change: mileage or time determined?

Post by njoconnor » Fri Aug 30, 2019 12:22 pm

Richard, Mike: Thanks for the responses.

The PO was pretty good about documentation; he gave me the work order from the engine rebuild, dated April 2011. We bought the car June 2012, with very expired plates and threadbare tires, so I know the PO didn't drive it much between those dates (he was refusing requests for test drives on public roads, using his farm roads as the test site). The belt did get doused with coolant when the water pump let go, rinsed off now; would a single exposure to coolant affect integrity that much? Planned on a 30K (my miles) change out in any case; it'll be a few years before I get there ;) . I've read the belt change process in Haynes a few times before now, and figure it's within my skill zone. This is more a "lets avoid the extra shipping costs/time of two separate orders" sort of decision in my case. If I decide against doing it myself, I'm literally walking distance from Foreign Car Service (ex-Chris Beebe) or an easy tow to a dedicated FIAT mechanic in the next city south of here.

As far as pump manufacturers: whoever Csaba is using these days for his 1608 pumps!

Thanks

Neil
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Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
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Various MOPAR's, Fords, VW's, Audis, and SAABs, and a Bimmer
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Re: Timing belt change: mileage or time determined?

Post by atruscott » Fri Aug 30, 2019 1:43 pm

My approach:

Is it more than 5 years old? Replace.
Does it deflect more (or less!! - can happen!) than it should when you twist it between the cam wheels? Replace.
Does the belt have any nicks or marks in it? Replace.
Do you not know any of the answers above? Replace.

Otherwise - you're good to go!

A
1960 Autobianchi Bianchina Transformabile
1970 238 Camper OHV
1974 124 Wagon TC
1974 124 Special TC
1975 124 Sport Coupe
1976 124 Sport Spider (The Racer)
1981 Spider 2000 (The Resurrected)
1985 Pininfarina Azzurra
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Re: Timing belt change: mileage or time determined?

Post by njoconnor » Sat Aug 31, 2019 7:39 am

Well...it flunks the 5 year old item!

When I got the cover off I found a fair amount of rubber dust. The belt was positioned at the very forward edge of the driver side cam wheel, and took a slight (maybe 5 degree) angle back to the center of the passenger side cam wheel. I'm thinking the forward edge of the belt may have been rubbing on the cover as well. No cracks or exposed cord seen. So, I'm going ahead with the replacement, along with the tensioner bearing. Any reason to also replace the tensioner spring as well? Want to get the pump off the car to make sure I don't need anything else before I send in the order.

Thanks, all.

Neil
Neil O'Connor
Madison, WI
72 Fiat 124 Spider
14 Ram 1500 Ecodiesel
12 Jeep Grand Cherokee
71 Fiat 124 Coupe (long ago and far away...and very much missed!)
Various MOPAR's, Fords, VW's, Audis, and SAABs, and a Bimmer
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Re: Timing belt change: mileage or time determined?

Post by rridge » Sat Aug 31, 2019 8:18 am

Like the 124 disc brakes, the rubber cam belt was a pioneer and is unlike modern cam belt drives in some details, which is why attention to the manual is more important than experience in installing modern belts. One is that the tensioner spring is used only to set the initial tension. Once the tensioner pulley is bolted down during installation the spring's job is done. I've not heard of a spring failing. Others may weigh in on the "walking belt". Not an issue my 2L.
Richard
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Re: Timing belt change: mileage or time determined?

Post by atruscott » Sat Aug 31, 2019 10:36 am

Agree on the spring purpose.

The belt walks. The timing belt cover no doubt also doubles as a way of stopping new purchasers from complaining that ... the belt walks :). I believe that it’s been proven that the belt can walk so that part is not on a wheel, and the increased tension of the piece still on the wheel walks the belt back on again. I hope someone will chime in on that.

If the belt walks a lot then it can rub and you get the dust.

I would check that the pulleys are on tight and true (simple to do when the belt is off).
1960 Autobianchi Bianchina Transformabile
1970 238 Camper OHV
1974 124 Wagon TC
1974 124 Special TC
1975 124 Sport Coupe
1976 124 Sport Spider (The Racer)
1981 Spider 2000 (The Resurrected)
1985 Pininfarina Azzurra
2017 124 Spider Abarth Elaborazione
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Re: Timing belt change: mileage or time determined?

Post by cgranju » Sat Aug 31, 2019 12:11 pm

And for what little bit it’s worth, I have taken apart many twin cam engines to find that in some location the timing belt cover was rubbing against a cam gear (or gear + belt) so I’m guessing that contributes to early belt wear (and other issues)
Chris Granju
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Re: Timing belt change: mileage or time determined?

Post by hayesbd » Sat Aug 31, 2019 2:02 pm

I'm new here, but have been wrenching on Fiats (and other cars) for decades. There are some differences between these belts and modern timing belts that may suggest we keep to a fairly low mileage replacement interval (25 to 36K as compared with ~105K which is fairly typical of modern belts):

1. The tooth form is different. There have been a lot of automotive advancements since 1966 when Fiat pioneered the belt driven cams, and this is one aspect of belt design that I think has probably been vastly improved. Similar to gear flank profiles, modifying the tooth form makes a big difference in wear and loading. It looks like the old Fiat design uses a straight flank instead of an involute form (just eyeballing, though, so I could be wrong). Straight flank teeth will inevitably wear faster.

2. The tooth pitch seems to be very different from new stuff. Modern belts have a different pitch/tooth spacing that has probably also been optimized for better reliability on modern engines.

3. Routing and tensioning methods. This may or may not make much difference, but managing the tension, flex, and belt pitchline velocity have very likely been optimized on modern engine designs.

4. We also have to remember that Fiat DOHC engines turn a lot more revolutions per mile than modern cars. There aren't many modern engines turning 4000 rpm at 70 mph, so this would also suggest that replacement intervals would have to be shorter on our cars.

I have no idea if the materials and construction methods have been updated on modern Fiat-compatible belts, but they probably have. The Flennor belts I have are from a German company, but are made in the UK so I don't have any feel for the quality control, but after 20K miles, the last one I replaced seemed to be fine. I replaced it only because I was doing head work anyway.
As far as time goes, I judge by the surface condition since atmospheric ozone is the main culprit for degrading rubber components. Just like old tires, surface cracking can be age related and is a hint that it's time to replace.
And to this day, I don't have a clue why Fiat declared that once tensioned, a belt could not be reinstalled. Perhaps someone else knows; I doubt this is important these days.
Finally, the "walking" phenomenon would be eliminated if the teeth had any amount of crown to them (similar to the old leather belts on pulleys that were common in old factories). I don't know for sure, but I would imagine that Fiat engineers were smart enough to know about this and incorporated it in their original designs. I don't see any walking of the belt on my '73 with the engine at around 129K miles or so; if your belt is walking, you may be in need of new pulleys or something is out of alignment.
Just my $0.02....

Brian
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