How fast do you suppose the rubber on a timing belt degrades at room temperature?

I’ve got an old car with an interference engine. Honda recommends changing the timing belt every 60,000 miles or 6 years. It’s been about 12 years since the belt was changed, but only 43,000 miles.

I’m reluctant to spend $900 on this maintenance. My feeling is that the belt is made of fiber reinforced synthetic rubber, right?

It’s under a cover in the engine and not exposed to UV. The car is usually garaged, so it is not normally exposed to elevated temperatures. I do not imagine it is under more than a tiny fraction of the operating stress it is subject to when running when it is sitting idle on the pulleys.

That is, when the engine is running, that belt is driving the cam that actuates the engine valve and must be under tremendous load. When sitting in the garage, the forces must be tiny by comparison. Similarly, I know rubber does decay - but sitting in the garage, whatever chemical reactions that the rubber would undergo must be far slower than it happens during driving with a hot engine bay.

Finally, Honda must be fairly conservative with these maintenance recommendations.

What would you do? The car itself is only worth 3k to replace, so spending $1000 on a repair it may not even need just doesn’t seem like a good deal. I’m tempted to try replacing it myself, but I know it’s a big project.

I would say unfortunately it’s due. The age is a big factor as the belt loses flexibility. Remember, it is under constant tension and will develop micro-cracks. Check out online forums for do it yourself help and see how hard it seems. Some cars are fairly easy. If you don’t have to pull the front motor mount and jack the engine up it should be straight forward.


Wouldn’t be asking here, and it wouldn’t cost $900 if that were the case. No, it’s one of those.

I don’t know just what kind of rubber is used, but the reinforcing strands are fiberglass.

Ground level ozone acts to deteriorate the rubber; that’s where time is a factor.

$900 strikes me as really high (where do you live?). I assume that includes replacing the water pump, front-of-engine oil seals, and possibly some other items. Those additional things might not be needed.

If I knew the year, model, submodel (EX, DX, etc.), and engine size I might be able to shed some more light on the situation.

This is basically the car :

As you can see, it’s a major job. Yes, you don’t have to replace the water pump or belt tensioner or several other components, but you might as well.

No doubt they are, because of the horrible catastrophe that happens when a belt breaks in service, and the fact that there are no warning signs to tell you that you should change the belt soon.

Conservative though they may be, you are now at 2/3 of the recommended mileage interval, and fully double the recommended time interval. If not now, just how far were you thinking of pushing this?

I’ll go out on a limb and say you’ll probably be OK. The mileage recommendation replacement interval is fairly conservative, as it should be considering the consequences. The one thing that gives me pause, on the other hand is the relatively low mileage. Did the car happen to sit for several years unused or, was it driven regularly, even if sparingly? Belts tend to take a “set” in this situation. A hot climate stored outdoors generally would be worse than garaged.

If you have a set of handtools it’s doable for someone with a little DIY mentality, lots of YT videos and websites to walk you through it. Probably due for a coolant replacement and thermostat anyway.

I would change it and probably do it myself but I’ve done a lot of assorted mechanical repairs/rebuilds over the years. It comes down to do I like the car and hope to get many more years out of it. A timing belt failing while I’m driving can (not will, just can) cause some serious damage and pretty much end the life of a car; so if its one I like I’m not shooting the dice.

rubber degrades over time, and it’s false economy to try to save a bit now to spend a lot later. The belt itself is reinforced with glass fiber (as Gary T says) but there’s more than one way a belt can fail. Many failed timing belts I’ve encountered fail when you go to start the engine; the (non-fiber-reinforced) teeth/cogs on the belt harden and crack, and when you go to start the engine the belt sprocket on the crankshaft rips off an entire run of teeth (like so.) I’ve really only seen timing belts fail by snapping on the Chrysler 2.2 Turbo III engine, because the belt tension was very high to counteract “tow-roping” between the camshafts.

Another vote that a belt that’s run for a few minutes a week will last far longer than one only run every 6 months or worse yet every couple of years. A belt that’s taken a good set is just itching to self-destruct at the first real workout.

So which is it? And most importantly, which has it been in the last couple of years? Understand that all deterioration is linear for awhile then goes exponential. You really want to stay on the flat part of that curve.

If you plan to turn around and sell it immediately after, that’s right.

If you want to to drive it, then think of money put into repairs and maintenance as contributing to the transportation value of the car to you. Consider whether you’d rather spend money on this car, or on its replacement.

If you want to sell it, sell it as is. Replacing the timing belt is very unlikely to enhance the sale price as much as the repair costs.

There’s really no reliable way to judge the likelihood of imminent belt failure other than removing the belt to inspect, closely, the toothed side while bending it back. Thus we can’t answer your main question (how degraded is it) with any kind of certainty, which leaves us to talk about the risk. If the belt breaks and a valve is bent, the repair cost could increase by 1,000 or more.

So fix it, sell it, or take your chances, unfortunately with minimal information to assess the chances.

It’s true that there’s a significant savings in replacing oil seals, tensioner and idler pulleys, and the water pump while the timing belt is off over doing those things separately later. But if the seals aren’t leaking, the pulleys turn smoothly, and the pump is smooth and leak-free there’s no compelling reason to replace them. If the low mileage mentioned in the OP is an indicator of future use, it would take a long time for those items to reach the point of requiring attention.

It is one of the more complicated belt procedures due to the balance shaft set-up, meaning there are two belts to replace. Loosening the crankshaft pulley bolt requires the special tool shown in the video, or an impact wrench, and occasionally an acetylene torch.

It hasn’t sat more than a month at at a time. I just live a lifestyle where I avoid driving when possible, but I also live in a Southern state where I have no choice, so it does get driven periodically.

My skepticism primarily comes from the fact that whatever deterioration happens due to simple time must be extraordinarily slow. As for when to replace it - well, ok, the issue is I have a long drive (about 900 miles) coming up in a month. And little spare time to do it in, and if I try to DIY and blow my engine, I would have a rough time finding a replacement car to make the drive with. On the other hand, if I DIY, I save almost $800, the full belt kit with the Aisin water pump is a mere $111. Plus $20 for the tool, and $70 for a nicer socket set, and maybe $100 for a decent torque wrench and breaker bar. So I actually save more like $600…

tires are rubber too, and there’s a reason they legally must have a date code on them.

Ok, I’ve ordered all the parts. Tools and parts are $250. I’ve seen the videos, and there’s a cheat way to bypass the most difficult part (removing the bolt from the crankshaft pulley). Basically it requires 2 breaker bars and then just body weight. And the alignment stuff is just a matter of following directions and double checking the many, many alignment marks.

Come back and tell us how the procedure went when you are done.

Just out of curiosity, what are “all the parts?”

Timing Belt, Water pump, Balancer Belt, 2 springs, a water pump seal, and 2 bearings that one of the belts rides on. The kit sold by Aisen on Amazon for $110. Supposedly, their pumps are the best, and the kits come with Mitsubishi branded belts.

Then I will need all new coolant since the water pump is coming off, and I wanted a higher quality set of sockets so I bought a Tekton branded metric set, 1/2 drive, and a Tekton brand breaker bar and torque wrench. $211 spent so far, and I’m going to buy a cheap, big breaker bar from Harbor freight, some high grade radiator coolant, a cheater bar length of iron pipe, and a 50mm socket.

 I was not able to break loose the crankshaft nut at home. I had a road service mechanic drop by and impact it off for me. I have a small home compressor that would not build and sustain enough pressure for my impact.

The plan is to use the tool to secure it, and send the force to the ground. Then a 2 foot breaker bar and about 4 foot of cheater bar iron pipe. I’ll just put my bodyweight on it.

Should easily reach levels of torque that are the same or greater than what an impact driver can reach.

So, no oil seals*.

It’s possible to replace the front crankshaft seal, camshaft seal, and forward balance shaft seal when the timing belt is off. If they show no signs of leakage, I wouldn’t worry about them. If they show some seepage, they’ll probably be okay, but they will get worse, the question being how bad how soon. If they show significant leakage, it would be wise to replace them, as oil getting on a timing belt can deteriorate it rather quickly. Be advised that replacing these seals can sometimes be a bit tricky/challenging.

Note that this is not a typical socket for fitting over a bolt or nut with a 50mm head, but a special tool that fits INSIDE a hex in Honda crank pulleys. I wouldn’t call it a socket.

*Note that oil seals are for rotating shafts and look like this. What you’ve called a water pump seal is normally called a gasket (or in this case perhaps O-ring).