How old is yr timing belt

[Mr Morlock]

gslender what does the NBOwners Manual say - have you checked for NA owners manual in your glove box.

For NB it says "Replacement of the timing belt is required at every 100,000 km. Failure to replace the timing belt may result in damage to the engine".

Do Mazda in gslenders words fit the bill as "mechanically aware and capable people" Did the " may result " just get thrown in for no reason?

I replaced my belt soon after the service interval and it seemed like a reasonable idea.

It might not answer Hejira's question however about age versus KM.

[gslender]

It also may result in parting of money for unnecessary service maintenance


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[gslender]

To install the cams I have to position both cams at their set points and not rotate them until the belt is on. I've done that a few times but I do remember that I started doing it when I had standard cams because they caught once and I almost bent the valves until I realised that I had interference at the valve rims.

You must have something non standard.

I've been able to check this of the following heads....

NA6 B6 Head - can rotate both cams with lift on both intake/exhaust, no interference.
NA8 BP05 Head - can rotate both cams with lift on both intake/exhaust, no interference.
NB8 BP4W Head - can rotate both cams with lift on both intake/exhaust, no interference.

I was able to inspect the NA8 and NA6 heads as they were off the engine, and with both valves open there was several mm of space between each valve. I have no idea how you'd get them to interfere so I can only assume magna_blue was extending the valves beyond the cam lobe profile.

The NB8 head was installed, but I could turn them with no resistance or hitting anything, so can only assume nothing cam into contact with either piston or valves.

The B6 and BP engines are both listed and confirmed by Mazda as non-interference - that means something and you can choose to ignore that and follow the "guidance" in the user guide book in the glove book and pay a mechanic every 5 years to replace the cam belt early before it needs replacing if you feel so inclined. Most folks who have no clue about how engines work are happy to pay mechanics to perform routine maintenance on their cars for all sorts of reasons - if you're convinced your saving yourself from "maybe damage" and that's worth paying for, then so be it. I frankly don't care as it's your money.

Fact remains, the B6 and BP engines are non-interference and nothing I've seen has yet to demonstrate otherwise. How you use that information in cam belt replacement is up to you - some will stick to their limited understanding of engines and follow the user guide, others who have a better understanding will choose their own maintenance schedule.

Let's leave it be at that hey?

[manga_blue]

Can't see any logical reason why there's so much diff between your heads and my heads. No big deal, just strange.

I do know that original factory machining on mine were both pretty shyte, but not that shyte.

[gslender]

Can't see any logical reason why there's so much diff between your heads and my heads. No big deal, just strange.

I'll try and take a photo so you can see, but there is no way the stock cams can push the valves out enough - if you see the angle and space between them you'd only get interference if you removed the springs and push the valve down/out much further than the cam lobe would.

Perhaps your memory is different, but on the 3 heads tested, no interference is what it seems to mean.

[project.r.racing]

Mine's a BP05 head with standard valves and seat heights. The cams in there now have lifts of IN 9.2mm/EX 9.6mm, versus 8.6/8.6 standard. IN and EX valves interfere by quite a long way, about 2mm, if I set one pair of EX valves to full lift and rotate the IN cam independently. To install the cams I have to position both cams at their set points and not rotate them until the belt is on. I've done that a few times but I do remember that I started doing it when I had standard cams because they caught once and I almost bent the valves until I realised that I had interference at the valve rims.

I think the situation could be safer with a BP4W head because it's high-ported and the valves sit a bit more vertical.

Are you saying the new cams make it non interference, or the old ones were?

stock BP-05 cams on an mx5 are 8.15/8.66.
96-98 323 ones were 8.30/8.89, with the exhasut camshaft having reduce duration of 9 degrees.

but then lift isn't the only thing that will cause contact, duration is a bigger factor.

[gussy]

I don't understand why people are so relaxed about changing the timing belt and water pump. I always do it as scheduled on my cars. At least you can have confidence neither of them will fail and Murphy's law dictates it'll be in the middle of nowhere / at 1am / in the overtaking lane on the highway when it fails.

It's all good in saying that it's a non interference engine too but if the timing belt isn't done, then there could be a chance that the water pump could fail due to it not being changed on schedule either - and I know my missus rarely looks at the temperature gauge so the only indication that anything is wrong to her is when the engine seizes and grinds to a halt in plumes of steam - cheers love - new engine.
Best case scenario - you're stuck at the side of the road and you need to get a tow AND get the timing belt and water pump done anyway, so why not get it done earlier and avoid any unnecessary hassles? And if you're going to sell the car soon and don't want to bother doing it then I'm sure any prospective buyer would wonder where else you have skimped on servicing also and probably factor the job into his offer anyway.

[aviper4u]

I don't understand why people are so relaxed about changing the timing belt and water pump. I always do it as scheduled on my cars. At least you can have confidence neither of them will fail and Murphy's law dictates it'll be in the middle of nowhere / at 1am / in the overtaking lane on the highway when it fails.

It's all good in saying that it's a non interference engine too but if the timing belt isn't done, then there could be a chance that the water pump could fail due to it not being changed on schedule either - and I know my missus rarely looks at the temperature gauge so the only indication that anything is wrong to her is when the engine seizes and grinds to a halt in plumes of steam - cheers love - new engine.
Best case scenario - you're stuck at the side of the road and you need to get a tow AND get the timing belt and water pump done anyway, so why not get it done earlier and avoid any unnecessary hassles? And if you're going to sell the car soon and don't want to bother doing it then I'm sure any prospective buyer would wonder where else you have skimped on servicing also and probably factor the job into his offer anyway.

+1

as previously suggested it's usually every 100,000kms OR ten years which ever comes first............ these are just conservative averages to reduce breakdowns,
for example;
carA short shifted at 2,000RPM
carB raced regularly

as everything is spinning more carB would fail first, similar to most motorcycle engines and service intervals compared to most cars

[gslender]

All true, but no different to fuel pump


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[Mr Morlock]

Gslender you are just stuck in a groove everyone seems to get except you. There is no recommendation by MAzda or probably any other maker to replace fuel pumps at service intervals. Feel free to ignore replacement of timing belt and usual precaution of water pump at 100k intervals.

[project.r.racing]

the recommendation is 100K or 5 years. whichever comes first.

i guess if you are gonna run with mazda recommendations, then maximum is 5 years life.

[gslender]

Mazda recommends checking tyre pressures before driving, do you do that? Every time? Without fail?


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[gslender]

Gslender you are just stuck in a groove everyone seems to get except you. There is no recommendation by MAzda or probably any other maker to replace fuel pumps at service intervals. Feel free to ignore replacement of timing belt and usual precaution of water pump at 100k intervals.

The official Mazda workshop manual for a 1990 MX5 only lists oil, coolant, spark plugs and filters as R (replace) items and the timing belt is the only other item listed to be replaced at 60,000 miles (it does not specify time so technically, according to Mazda you could run indefinitely as long as you don't go over 60,000 miles traveled).

I've just checked these facts against the PDF that I have on the 1990 Mazda MX-5 Workshop Manual.

Can you honestly imagine owning the vehicle for 15 years and only following that guide. Do you really think your car would be in good running condition and not at risk of regular failure??

To any half intelligent person (with a mechanical background) it would be seen that these are provided for "guidance" - they are not predetermined facts.

The facts, (for those that like to base their decisions on truth instead of made up stuff) is that the timing belt will eventually fail, and when it does, that act itself will not cause any damage - the engine is non-interference and this means that the valves, will not in their normal use, hit anything if the belt fails to align the camshafts to the crank.

Will the belt (when snapping) cause other damage? - it is possible though unlikely (no more or less than any other component that when failing can cause damage etc). There are heaps of things that can cause damage to the engine when they fail (and they will).

Will the belt snapping be inconvenient. Yes. More inconvenient than a failed fuel pump. No. More risky. No. Exactly the same.

These are the facts.

Anything further is just opinion and speculation.

[JBT]

the recommendation is 100K or 5 years. whichever comes first.

i guess if you are gonna run with mazda recommendations, then maximum is 5 years life.

Mazda recommends 100,000 kms - no time is mentioned in the owners manual.

[manga_blue]

The Maintenance Table starts on page 102 in the NA Owners Manual, attached. Make of it what you will.

https://dl.dropboxusercontent.com/u/890 ... Manual.pdf