Timing belt failure log MTBF

[instarx]

Listing parts replacements before a failure isn't going to be very useful in determining mean time between failure (MTBF) and I suspect that's what you are going to get reported in this survey. Owners whose TBs have failed aren't likely to be active in this forum. I'd be very surprised if you got 30 data points.

I am positive Volvo and every other manufacturer lists replacement intervals with tons of safety margin. If the recommended replacement interval for a belt was 100,000 miles and its MTBF was 100,000 miles half the belts would have failed by that point. Manufacturers pretty much know what a safe replacement interval is. I do not know what formula they use but I would assume even a 10% failure rate at the recommended change interval would be unacceptable for them from a reputation point of view. I've always assumed that the recommended change interval results in a failure rate of well below 1%. For that reason I do not constantly worry that my timing belt is going to fail, even when it reaches its recommended change interval.

[abscate]

Using replacements before failure data obviously gives a lower bound to MTBF vs actual MTBF, but for the purpose of this study, that will suffice.

The 1% failure analysis above is exactly why I commissioned this study (that makes it sound more scientific) and I suspect it is probably even better than 1%. Remember, most of us here are driving vehicles well past their "service life" in the eyes of the product line management of an automaker, so that reasoning might not apply.

Gaussian statistics need about 30 data points to overcome shot noise behavior - speaking loosely. The more the merrier of course.

[erikv11]

Please specify what information you actually want.

[abscate]

The goal of this thread is to get > 30 logs of timing belt failures with mileage to see if we can get an idea of how long these parts last.

Entry format

First line: year, model, engine, year replaced, mileage replaced,

Second line - mechanical commentary on what failed, if anything

[erikv11]

Lee..I would love to have the data on your cars...how many miles they had when they got them, since those are all TB lifetime data points

I need 30 to get a good set for analysis

OK so you didn't really mean this, you don't actually want TB lifetime data points. Gotcha - that seems like a huge can of worms.

No failures to report, cap'n.

[rspi]

Ok, here is my slant on this stuff.

Belt = 105,000 to 120,000 before failure providing that everything else is fine. 10 Years to 17 years depending on climate (providing that mileage is less that 20% of limit).
Idler = 10 To 17 years providing that mileage is not exceeded by 20%. Also, 120,000 to 180,000 miles.
Tensioner Roller = 10 To 17 years providing that mileage is not exceeded by 20%. Also, 140,000 to 180,000 miles.
Hyd Tensioner = 15 Years or 200,000 miles.
Water Pump = 12 Years or 200,000 miles.

Here is my deal, age does matter. Seen a guy with a "new to him" 960 the other day. Claimed the car had been sitting for about 6 years, had 106,000. Claims that the timing belt had never been changed. I suggested that he never start the car again, just have the stuff changed. A belt that old that sat for that ling is likely brittle. Same with the rollers sitting in the same position, they are ready to blow. But a car that runs 40,000 miles per year may go 120,000 (3 years) with no problem on a belt and new rollers. I use to put between 30,000 to 40,000 per year on my red block 740 GLE. The belt suggestion was 50,000, I always went 75,000 between changes. Never had an issue.

What I usually do is inspect the idler, tensioner, and tensioner roller at the belt change. If the roller is good and tight, I usually re-use them. If they seem worn, I change them. Has worked for me so far except for a belt that someone else changed for me. The idler was bad 18,000 miles later. Not sure if they checked it. It may had been loose then.

[rspi]

Roller inspection:

[polskamafia mjl]

1995, 850 t-5r, 5/2013, 207,783mi

Nothing had failed, no service records from previous owner so no idea how long that belt was on there. I replaced all the rollers, tensioner, and water pump as well.

[precopster]

Our first 850s timing belt system including hydraulic was done at around 65K miles and now has about 94K miles.

Our second 850 (wagon) was done at around 130K miles when I replaced the motor (overheated) and the car was sold with about 138K milles.

My current 2000 V70 has 150K miles and has a Volvo foil sticker from 2004 @ 112K and I'm about to change the timing system again due to time and a startup squeal I don't like.

My project '01 XC 70 has 100K miles and is getting a full timing system. The motor is a used example which was replaced by a local garage by the previous owner (ran out of oil) so I don't trust the history.

[januwan]

First TB changed at 83K (only two belts), second changed by me at 155K (big thanks to Lee, C90, and rspi). I replaced everything except pump. All the components were in perfect shape I felt really bad throwing out, in my mind, good parts. Even belts did not show any signs of wear.