How old is yr timing belt

[trader]

No one has commented on what their belt looked like when changed one. Mine was done at 107 k's after 14years. Visually it was identical to the replacement so could probably have gone much longer. My other garage queen has done 30000 k's in 17 yrs. I spoke to a Mazda specialist who indicated that it was the k's rather than the age that determines it's life.

[project.r.racing]

MY 265K old one looked new. not a single crack in it.

[gslender]

I would not be surprised to learn that most low mileage MX5 would first need the water pump replaced (due to corrosion or wear) before the cam belt snapped. I've replaced 3 belts on 3 engines all over 100K and none of the belts looked anywhere near aged as much as the water pumps or accessory V belts.

Oh, and the accessory V belt is another "dangerous" item to fail at 110kph on a freeway - and I'd bet nobody replaces that on a schedule - it stays on the car until it snaps or someone says "gee it looks old and cracked, best replace it" and that could be 50,000 km beyond the safe life span and yet we still continue on.

Replacing cam timing belt is a scheduled convenience activity to avoid unwanted lengthy repairs when you would rather not want them.

[manga_blue]

I'm not at all keen on your idea of planning for a breakdown. It reminds me of that poor woman in a VW Golf that shut down on the South-Eastern Freeway in Melbourne and the truck behind drove over the top of her.

As well as that I'm not even sure that there'd be no damage if the belt broke. On my head I've found that inlet and exhaust valves touch each other when they're both at full lift. That means it's theoretically possible for it to bend or snap valves before the cams stopped turning altogether.

[KevGoat]

I'm no gambler. Not changing the belt etc on schedule, considering the relatively small cost compared to overall investment, just appears an unnecessary risk that doesn't make much sense to me. When I recently looked at buying a 2004 SE with only 64k on the clock, one consideration was getting the timing belt etc changed asap. It wasn't at it's 100k schedule, but as a 10 year old car, possible rubber degradation would have concerned me and personally, I would rather just err on the safe side ...

[gslender]

I'm not at all keen on your idea of planning for a breakdown. It reminds me of that poor woman in a VW Golf that shut down on the South-Eastern Freeway in Melbourne and the truck behind drove over the top of her.

That could happen for any reason, and if that was your only motivation then you'd be replacing heaps of parts on the car in a scheduled way. You have to be reasonable and know that cam belt failure won't bring the car to a screaming halt. It will just be a dead engine (like failed coilpack or fuel pump) and you can safely move to the left. If you can't move to the left, then its not the cam belts fault that the road traffic can't absorb a stopped motor car. Every day I see this and they are not all caused by snapped cam belts.

As well as that I'm not even sure that there'd be no damage if the belt broke. On my head I've found that inlet and exhaust valves touch each other when they're both at full lift. That means it's theoretically possible for it to bend or snap valves before the cams stopped turning altogether.

I'll test that and come back with it confirmed for a BP4W head.

Can you confirm that your head (where you believe this to be true) was 100% stock and not using higher lift cams? Also, you have to consider that the camshafts have zero momentum and technically would require a fair bit of inertial force to overcome a valve spring compression - so whilst maybe you are correct, the reality is that it just cannot occur as the camshafts aren't going to spin if the belt isn't driving them.

I'm no gambler. Not changing the belt etc on schedule, considering the relatively small cost compared to overall investment, just appears an unnecessary risk that doesn't make much sense to me. When I recently looked at buying a 2004 SE with only 64k on the clock, one consideration was getting the timing belt etc changed asap. It wasn't at it's 100k schedule, but as a 10 year old car, possible rubber degradation would have concerned me and personally, I would rather just err on the safe side ...

Safe side of what? If it is no more or less safe to run with an old or new cam belt, then why replace it early? What did you think you were being safe about? I'm only asking that people who are worrying about damage should probably outline what they believe will be damaged?

[project.r.racing]

As well as that I'm not even sure that there'd be no damage if the belt broke. On my head I've found that inlet and exhaust valves touch each other when they're both at full lift. That means it's theoretically possible for it to bend or snap valves before the cams stopped turning altogether.

Then it wouldn't be a non interference engine then.

Yes the valves can be pushed to touch each other, but that is at least 1.5-2.0mm past what they cams would actually do. somewhere around 9.5mm lift. BP engines depending on year and torque to peak hp versions, will have 8.2-8.9mm lift from factory.

My Toda 256 duration and 9mm camshafts were still non interferring when I had them.

[KevGoat]

gs ... I don't think I mentioned damage, I have no idea whether damage can be caused or not ... somewhat mechanically disadvantaged . From what has been said here, as long as no other part failure occurs (apart from the belt), there should be no further damage. I certainly don't drive around all the time thinking about the timing belt breaking (or other possible mechanical scenarios), but still I prefer knowing that I've done what I can to keep my car as reliable as possible and if a timing belt change is recommended at 100k, I'd still prefer to have it done. This debate is all kind of funny really considering most of us on here probably service and maintain our 5's beyond the specified requirements, utilising higher spec and more costly materials than required, and even use higher cost fuel than is necessary ...

[gslender]

gs ... I don't think I mentioned damage, I have no idea whether damage can be caused or not ... somewhat mechanically disadvantaged . From what has been said here, as long as no other part failure occurs (apart from the belt), there should be no further damage. I certainly don't drive around all the time thinking about the timing belt breaking (or other possible mechanical scenarios), but still I prefer knowing that I've done what I can to keep my car as reliable as possible and if a timing belt change is recommended at 100k, I'd still prefer to have it done. This debate is all kind of funny really considering most of us on here probably service and maintain our 5's beyond the specified requirements, utilising higher spec and more costly materials than required, and even use higher cost fuel than is necessary ...

That's ok, but being "safe" is the wrong thinking and incorrectly implying there is some significant risk if you don't follow the advice given in the workshop manual.

It would seem the only thing you are likely saving is your time or inconvenience. In car that is now approach over 20 years old, it is unlikely the cam belt is the only thing you really should be worrying about. The cam belt is just as likely to fail as the fuel pump, or the coil pack, or the ECU itself for that matter. Anything 20+ years is probably as likely to just fail and will have the same impact as the cam belt.

When the car was 5 years old, if it had 100,000klms then replacing the cam belt would be fair - you'd expect that the fuel pump, or the coil pack, or the ECU would all be fine and live another 5-10 years without any trouble. The cam belt though is probably going to need attention fairly soon, so you may as well get the big job done now when it fits in with your dealer availability and your life.

Driving around in a car that is approaching 20 years of age and thinking "gee, glad I did the cam belt as per the 100,000 klm schedule - it will be really reliable now" isn't very realistic.

G

[KevGoat]

Driving around in a car that is approaching 20 years of age and thinking "gee, glad I did the cam belt as per the 100,000 klm schedule - it will be really reliable now" isn't very realistic.

G

I never claimed my thought process to be logical ....

[JBT]

...but being "safe" is the wrong thinking and incorrectly implying there is some significant risk if you don't follow the advice given in the workshop manual...

Blindly disregarding the possible implications can be just as bad.
When my daughter's car (the Astina mentioned earlier) quit because of the cam belt slip, it quit outright - no warning, just dead. I'm glad it happened in the shopping centre car park in second gear.
I dread to think how it could have played out if it had happened with her and the little ones in the car at 100 km/hr on the Ipswich motorway - especially with the traffic density and the d1ckhead tailgaters out there, especially the tailgating trucks

[Mr Morlock]

Slender seems to be in total denial about what is a universal recommendation about changing the timing belt. There is no chance that Mazda issue and state this in their service schedule without it being important. External belts are listed for regular check for car servicing amongst a number of other things.

People are also wrong in believing that age is not a factor in deterioration of rubber/ synthetic timing belts. Rubber and plastics all deteriorate over time- you easily see this. Simple things like windscreen wiper blades, tyres on cars, plastic lenses, dashboards etc. these items including internal items are subjected to a variety of factors impinging on the original spec.

If you are travelling down a highway in heavy traffic at speed and the engine stops then pulling to one side may be an extremely dangerous situation. Most people have their cars serviced-not all- to avoid breakdowns and failures .

[gslender]

Mr Morlock, how often are you replacing your fuel pump?

[Mr Morlock]

What is the recommendation to replace the fuel pump ?

[M1474]

Timing belt has very little exposure to UV light.