Really ignorant question about timing belt replacement

[mindshadow]

I'll admit I'm definitely not the most mechanically inclined person on these boards, so keep that in mind when answering this question.

Why exactly does the timing belt have to be replaced every 70k miles on the '98 v70? More-so, is it not possible for someone to make better-quality parts that would last longer? Or is it just a case that nobody cared enough to engineer better after-market parts?

I'm sure it's more complicated than quality of the parts, so if someone can explain exactly how and why those parts wear that would be appreciated.

[polskamafia mjl]

The timing belt needs to be replaced every 70k because it breaks after that. Due to the fact that the 5 cylinder engines are interference engines, if the timing belt breaks then the pistons smash into the valves and the engine destroys itself internally. Free wheeling engines are designed differently and are not affected by a belt breaking. The reason the timing belt wears is because it is under a lot of stress. If you ever took physics then you should remember that friction creates heat and heat eventually destroys most things, especially a rubber belt. The timing belt is under very high tension and it spins at about the same speed that the engine does, in other words if you're redlining your engine at 6k RPM, your thin, rubber, timing belt is also spinning that fast. All of that stress quickly deteriorates the belt.

I have often wondered by the belt can't be replaced with a chain. A chain is much less likely to break and would require less frequent changing. I'm sure there is a good reason why no one has created a timing "chain"but for the life of me I have no idea why. lol

[tjts1]

The timing belt is made of rubber just like tires, bushings, hoses etc. It lives inside a plastic cover on the front of the engine where it spins at thousands of RPM while exposed to engine heat. Rubber is an organic compound that doesn't lasts forever. It slowly deteriorates with time, heat and wear to the point that it will break. Its not a matter of the quality of the material. Its just the nature of all rubber. Most newer cars have a timing chain that lives inside the engine lubricated with engine oil. Generally speaking a chain should last the life of the vehicle but it has been know to wear and break as well. Both the chain and belt have their advantages and disadvantages. The belt is cheaper to make, easier to inspect and replace. It also marginally more efficient and quieter than a chain.

70k miles is the expected life of a timing belt on these cars. If the timing belt breaks or the tensioner or one of the pulleys fails, the intake and exhaust valves inside the engine will hit the pistons. The engine will either have to be rebuilt or replaced which will likely cost more than the car is worth. Spending a few hundred bucks on the timing belt now will save you thousands of dollars in repair bills.
http://volvospeed.com/Repair/timingbelt.php
http://www.fcpgroton.com/category-exec/ ... by_year/48

cheers
Justin

[mindshadow]

Cool, thanks for the info. And you're right, I used to have a car that had an actual chain (looked like a giant motorcycle drive chain) and it broke. Of course it was a GM car.

From what I've read of doing the timing belt replacement it looks like a pretty advanced/expert fix. Am I right in assessing that? I'd love to do it myself but I wonder if the chance of me breaking the engine doing it would be worth the extra couple of hundred dollars. I didn't get any mechanic paperwork with the car (the dealership claimed they had it but couldn't share it because the former owners name was on it... whatever) so for all I know it could be new, but also for all I know it could be ready to snap.

[tjts1]

I've replaced the T belt on several volvos along with a lot of other people on this forum. I don't consider it a very big job but if you haven't worked on a car before I woudn't recommend this as your first project. Take a close look at the instructions in the volvospeed link i posted above. It spells out the project step by step. If you decide to take on the job yourself make sure you have jack stands and plenty of time. Don't try to rush this. With basic tools and a little patience you should be fine.

[mindshadow]

I've worked on a car before, just nothing this big. Probably could coax a few friends that are, indeed, mechanics to help me with a few cases of beer.

[FCPEURO]

I have to agree with the above. I am not sure why Volvo has not moved to a timing chain over the timing belt that they are still using to this day. I mean, Ford has been using timing chains for some time now and they have not had any issue.

[C@lvin]

I have had mixed experience trying to get service history from dealers. My suggestion is that you call the dealer back and ask them to tell you the date and mileage of the most recent timing belt change for your VIN. They shouldn't have a problem with that even if they are the typical Volvo "stealership"

[WhoaTed]

Belts and their related components (gears etc) are MUCH lighter than chain. A "belted" engine will rev and decel faster than a chain-driven one due to less weight being in motion (or lack of same). The added ability to use the t-belt to drive the water pump also eliminates the pump from having it's own drive belt and related mounting/pulleys/etc, saving more weight. And so on, and so on...this is just a very basic answer, but belts are much more efficient (and arguably as reliable) than chain.

Ever wonder why so many motorcycles today are belt-driven instead of chain...?

[MadeInJapan]

Timing belt...timing chain- Don't think it would really matter. What's over-looked is often the tensioner- it will break too after 70K miles and cause the engine to go.