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Discussion in '308/328' started by Bobby Butler, Feb 17, 2020.
One belt has 0 miles on it, the other has 27k miles and 25 years.
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I would like to add a story, that is belt related. It's true and involves me and one of the most famous Ferrari dealership in the world, the Belgian Franchorchamps Motors. I got in 2014 a GTB turbo (a 328 GTB with a 2 litres turbocharged engine, made for the Italian market only), from the first and only owner of the car, an 80 years old gentelman. That (excellent) car had a 20 years old belt: I only drove the car at low RPM (under 3000 RPM) and then after some days I found another car like that even better, so I sold the "20 years old belt" to Francorchamp Motors. I told them that the car needed a service and a new belt too, as it was 20 years old: I asked if they wanted the car serviced, telling them that with some more money I could have it done and so the truck driver that had to carry the car to them could move and load the car without the fear of a belt failure (I was at the time very worried about a belt failure). They answered: "No, thanks: well installed belts don't fails at low RPM, there is some risk only at High speed on a motorway. We prefer to change the belts and service the car by ourself as we know how doing the work in a perfect way, so we can give the new customer a full warranty. That old belt is correctly installed as it worked for 20 years and it just has to work some other minutes and no more. Don't worry."
Learnings: do it not so often, but do it with the correct materials and in the correct way.
Before buying the car, they sent here one of their mechanic to inspect it: they do things in the best way possible
Exactly why visual inspection is worthless and supports changes based on time. Thank you for the example.
Not, that I would have expected anything different from you.
A destructive tensile strength test of both belts on a calibrated machine would be highly interesting. Too bad, that I have no more access to such equipment.
Best from Germany
And neither has enough light to be able to actually discern anything.
Nevertheless, I could post a similar pic of a 25 year old tire from a garage queen and a new tire, and say "they look the same, voila!" Yet we all know that aged tires, more than ~6 years old, have age-hardened rubber with much less traction/grip than new tires, and are more fragile and prone to failure. Visually, identical. As Rifledriver posted, the visual condition is NOT a valid determination for belt replacement. Period. (Since we're doing that in this thread )
Testing the hardness of the rubber, shear strength of the teeth and loss of elasticity would be what I'd want to see.
Tire manufacturers say 5-6 years on tires for exactly the same reasons and we accept that but when it comes to timing belts suddenly age makes no difference.
This is, because old tyres can be life-threatening, especially on our still speed limit free Autobahn, while old belts are just wallet-threatening
It's almost five years ago. Last time, when I hit the upper limit of my car on our empty public road without speed limit. And I have to admit, I thought 'tyres' and not 'belts'.
Best from Germany
Hmm..I have a pair of Ho Chi Minh sandals (which were made from car tires). They were in 'operational' jungle use in 1968 and they work fine. But maybe I should retire them due to age!
What are your criteria for "work fine"? I have hiking shoes with Vibram soles, and once they get to 6+ years age they stop "working fine" - with that being defined as providing original levels of traction over rocks, gravel, etc in dry, wet, frozen, snow/ice conditions. Sure, if you wear your 1968 sandals in warm, dry, level ground, smooth surface, for strolling around, they will still do a fine job of keeping the soles of your feet from touching the pavement, if that's your only criteria. Throw in a bit of running, climbing, higher stress traction scenarios in lower grip and uneven surface locations, and I'd bet a bunch that those 1968 car tire sandals are slippery as banana peels.
Ancient tires work fine for holding the wheels off the ground for a garage queen show car, but they are dangerous and useless as actual moving car tires. Ancient timing belts work fine for keeping the cams fixed in relation to the crank when the crank doesn't turn, or only idles...
Well, I can tell you one thing about the old and new belts I posted a picture of. Both easily survived 100 lbs tensile load and neither stretched more than a fraction of a mm under that load. (I was interested in belt stretch. It's insignificant. Less then the manufacturing tolerance on length.) Also the 25 yr old belt showed no visual signs of cracking at the roots of the teeth when flexed backward to expose the teeth, and no signs of cracking on the flat side of the belt, again when flexed tightly.
Frankly, with all the wacko method of tensioning belts I have read I think belts often get tensioned too high and that has a significant effect on belt wear and life.
I tried the tensioning methods described in various places but I must say they did not feel solid and repeatable. Relying on a spring setting the tension when the cams are pushing and pulling the belts, the tensioner locking may add some extra tension ... and the old engine may be out of acceptable tolerances too.
I figured the only way was to develop a sonic measurement that can be performed at a few positions of rotation, after locking the tensioners. I do not know the exact tension Ferrari aimed for, but the spring action on the belt pushes it to about 110N on my old springs. Then, I don't know if the springs are a bit relaxed so I bought new ones which had a bit higher spring tension (at the same compression). The identical geometry of the belt could also be found in the tension meter manual from SKF where they proposed an install tension of 122Nm. So, I figured this is the ballpark the belt should be in.
The rest is just calculations to get the frequency of each part of the belt run ..
Honestly I think, some are overcomplicating things, regarding the belt tension.
I think thermal expansion of the engine is more significant, than a difference of 12 N spring force. 12N is much less than than the difference, as if I push my keyboard keys relaxed or being in anger
Regarding thermal expansion; I can definitely feel a significant difference with my fingers in belt tension between hot or cold engine. With the engine being hot, the belts are significantly more tight.
Best from Germany
I don't think 12 N is that important, but I figured I wanted a few data points anyway.
Belts are not measured on each part of the run and they are always measured in a specific crankshaft position. Cams, depending on their position will try and turn, sometimes forward and sometimes backward and it has an effect on the tension of the belt.
But as Martin said, you are over thinking it. Some of the motors with active tensioners like 355 and 360 are sensitive to correct tension and are set with sonic tensioner. I have one, I use it a lot but never on a 308.
I had no idea what a sonic tensioner was. I had to look it up YouTube on a gates model. Neat.
I bought my 308 qv in 2001 @ 47k, now has 72K. I changed the belts every 6 years and that always felt like it was just done. Belts and bearings always looked new and I believe I still have both old sets. Do what you're comfortable with, but 3 years IMO is crazy, especially since many here don't drive their cars all that much.
Change the oil regularly and let the car get warmed up properly before you drive hard and things tend to work better and last longer.
OH! A belt thread! Its been a while!
I'm changing the belts on my car one more time..........then that will be it for this lifetime. So I'm hoping to get 20 years out of them. When I bought the car I was good for 14 years. Time to push the envelope a bit.
Beats the what are they worth threads or the idiotic thread on some set of aftermarket rims from japan and the guy winds up bitchin to the one person trying to help him - only on fchat.
I Always find very interesting belt threads about 308. They show and incredible thing: there still are many who don't want to see the evidence. The evidence (proven by 47 years of story) is that 308 belt system is rock solid and it's the last thing that gives problems on that car. The only way to have problems with a 308 belt is this: remove the old (well working) belts and replace them with bad installed new ones. I NEVER heard of a 308 belt that failed due to age. I heard SEVERAL times of brand new belts that failed. A typical error is a wrong belt tension or bad installed bearings and tensioners. But the funniest thing about 308 belts is not that there still is someone that replace belts every three years, throwing away money, as everyone can do what he wants, of course. It's another: there still are several that try to say that it's wrong going over the three years with your belts!
Let me say that this is amazing...
It is fun to analyze designs to understand it, find flaws and make it better.
I overthink things all the time ... and there does not seem to be any cure for this.
. . .but how many here change their timing belts and tensioner bearing themselves. I for one do and have always used Ferraris suggested method of setting tension. Like I said about every 6 years.
On my Boxer I've read every 8 years. Did them in 2016 and their configuration looked like it was under less load at the tensoner. Never heard of belt failure on a Boxer and would hate to hear of one. The diff failure issue is bad enough, but I put tgat to bed with Newmann carrier and did the belts because it's all right there.
I still say it's really up to the persons tolerance for risk, on when they change them.
This is probably the first time I have seen this discussion lean towards a leave them alone opinion without much push back, if any, from opposition.
Probably a sign that the general opinion is evolving towards longer intervals and less paranoïa? Statistics are not sufficient to draw clear laws, but yes it seems that when failures do occur, they tend to happen just after a change (leaving the question of tensioners aside). Perhaps those who have been working for a long time on these cars do know of age-related failures on the belts?
As for yours truly, I trust my mechanic completly; he has been working on these cars since 1983. In 2008, when he was still in the official factory network, he said "every three years" and that's what I settled for. Nowadays, he says "five years is fine", and I have settled for five years. I have made my mind a long time ago that once agreed between us, I won't question the interval; I'm fine with five years and the associated cost and my mind is at peace.
I read the threads on the belts just out of interest, but even if many solid arguments are used here and there, as for myself: five years it is, period.