mx5cartalk.com

So the car is over 10yrs now and has not got to the 100k mark.

I am pretty relaxed about the timing belt. If it goes, so what, an inconvenient tow. That's happened before (with other cars ). Not the end of the world. Yes I do know about valve interference on non mx=5 engines, luckily we are in the clear.

So how long have these belts lasted in the real world??? It may sound perverse to all you macho mechanics but I don't have time or expense to frick around. I plan to run it until the belt or water pump goes, then change both.

I wonder Has anyone done 200k with the belt intact, that would be pretty awesome?

I remember reading a thread on miata.net about people saying their t belts were going strong at 120k miles (roughly 200km). And there are pictures of them looking new after that period of time. Theres also plenty that let go as well

My water pump in my na6 was in good working order when i replaced it at 190km. My nb was leaking at 110km

Mine has 12years and 80k not worried about it unless you have a cam oil seal leaking contaminating belt with oil, common in nb2vvt 2001 on models or a leaking water pump. The belt in US has to last 100, 000 miles by law. nc has a timing chain. If you do replace cam belt replace everything all oil seals and the water pump at the same time. Water pumps commonly fail at 150.0000k

I'm running a 98 NB8A with 75,000kms without issue. Belt still looks good.

2001 NB just hit 75,000.

Just going to do it whenever it hits 100k

i brought a bp powered astina with 81K on it. removed the engine at 265K, never changed the water pump or timing belt. motorkhanas, autocrosses and sprints, never went pop.

thats a very silly plan- in fact its not a plan at all. If the belt is 10 years old its well past its use by date- it can readily develop cracks .Its what some people do with tyres- there is plenty of tread but the rubber is hard and dangerous i.e. time is a factor. Its also not correct to say that the MX5 engine's cannot be damaged with a belt breaking.

Mr Morlock wrote:Its also not correct to say that the MX5 engine's cannot be damaged with a belt breaking.

On a non-interference engine, a broken timing belt will leave you stranded and that's all. A snapped timing belt could (if free and flying about) get jammed into something it shouldn't, but that is incredibly rare/unlikely, and no different to an accessory belt (far more common) and rarely have they been known to cause damage.

What are you thinking would be damaged?

I'd be more concerned with a water pump failure and a cooked engine but that's what the temp gauge is for.


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the consensus is generally that no damage occurs in a non interference engine but you can find contrary views. "As nothing is carved in stone when it comes to auto repair, we have seen "interference" engines not bend valves when the belt breaks and we have seen "non-interference" engines bend valves when the belt fails".

I had a car and it was "interference" . A mechanic told me that the water pump was weeping and I did not take any action - the car was going to be sold and I was not aware of timing belt change frequency- later I discovered it was overdue. The belt broke with my wife driving it and I was at work. Not funny, stressful for her , but I was insured and it got towed to my mechanics workshop. What happened was the water pump seized and that caused the breakage probably coupled with a suspect belt Fortunately it did not do any fatal damage and maybe because it was only travelling slowly. I learned some lessons- don't ignore advice from a trusted mechanic and pay attention to maintenance factors.

As far as water pumps are concerned if they destruct - not just leak some engines are cooked in a blink of an eye.

No one can predict what will happen if a car stops and in what circumstances. In Melb in a well known case a person was killed on a freeway reportedly by loss of power.

Its not clever to see how long an engine can run without maintenance or servicing. A timing belt change is a bit of pain but its not inordinately expensive.

there is no consensus. fact is a non interference engine will not damage if the timing belt breaks.

if damages has occurred, then it has nothing to do with the drivetrain.

Another story showing you can't win sometimes
Bought a BJ11 Astina new in 2002. It also has a non-interference engine. Cam belt, tensioner, idler, seals etc. were changed at 100,000km as per service schedule.
Four years and just 45,000km later, the (replaced) tensioner spring broke, got into the works between the crank pulley and belt, causing the belt to slip and the valve timing to go out about 180 degrees.
Engine quit, car towed and the whole cam belt replacement process had to be repeated.
Bluddy $5 spring caused just under $800 (parts and labour) worth of repairs.

speed wrote:I'd be more concerned with a water pump failure and a cooked engine but that's what the temp gauge is for.


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Apart from on an NB8B where anything less than molten aluminium and the bloody thing sits in the middle and then in the next second flops off the end of the gauge.

project.r.racing wrote:there is no consensus. fact is a non interference engine will not damage if the timing belt breaks.

if damages has occurred, then it has nothing to do with the drivetrain.

I'd agree. Even suggesting that "timing chain failure could result in the car stopping on the highway resulting in a crash" is just an extreme level of logic to align your life on - if we made choices based on reducing every single element of risk to the lowest possible level, then you would never leave your house.

The timing belt replacement guidance is to ensure that consumers aren't inconvenienced by a significant mechanical failure that renders their car inoperable for many days when to avoid it, they simply book the car in for a major service and have the belt replaced. All other likely issues (like tyres, coolant, oil, filters, battery) can be done fairly easily by any k-mart mechanic almost anywhere. The belt is something that requires special tools with special skills etc.

Fact is, even the coil pack (which is known to fail at around 100,000 klms or sooner) would need to be regularly replaced by that logic shown by Mr M - but I'd bet he's never gonna replace that until it fails (and that could happen whilst he is travelling down a highway at 110kph). The reason that isn't on the scheduled replacement cycle is that it commonly first fails by missing (likely), and then followed by outright failure (rarely) and in both cases fairly easily replaced in less than 30 mins with the right part. No big deal.

My advice (of which would be the same from anyone like me who has actually got the skill and experience to do this) would be to do it when you have a more significant reason to do so - ie worn water pump or are pulling the head off anyway, or repair to keyway, or you don't want to be stranded somewhere and don't enjoy having the car towed back to home/mechanic etc...

G

JBT wrote: the (replaced) tensioner spring broke.

That's actually very odd - the tensioner spring isn't under varying tension on the engine (which if it was, it could induce metal fatigue and break).

It is used to initially tension the belt, and then the idler pulleys are locked into position and the tensioner spring could technically be removed. It really shouldn't break unless it was already weak metal, or more likely idler pulleys weren't locked fully (and the spring was constantly being worked/fatigued) or it wasn't installed correctly it just fell off.

Just breaking seems odd given it wouldn't be under much strain - just saying.

G