96 Miata - replacing timing belt

I have read many times that the miata engine is non-interfering and no damage would result if the timing belt broke. However, in my Haynes manual under the section of replacing the timing belt, there are cautionary instructions there about turning the crankshaft bolt by hand that imply that not to be the case, but they may provide those instructions in all their manuals instead of determining if the engine is non-interfering or not.

The 1.6L and 1.8L NA and NB engines are not "zero clearance" engines. A timing belt failure will normally just cause the engine to stop running. Changing a timing belt is a fair amount of work. While you are at it, the idler spring, pully, and the water pump likely should be changed if the milage is high. Miata.net has the proceedure documented in the garage section, and the newer service notes concerning crankshaft torque in that section.

If I was making this decision about my own car, and was not able to get definite answer, I would go ahead and change it out especially if I was not certain as to how many miles the the belt has on it. This is just an opinion, and you know what they say about opinions. They're like

---holes and everybody has one. Ron.

Brian, your buddy's wrong on 2 counts. As others have indicated, the miata engine will not do itself damage (unlike most Hondas for example) and he's got his terms wrong. It's interference vs non-interference engines (on interference engines tolerances are in the negative I guess you'd have to say, not zero ;-)

Chris

Isn't it recommended to change the valve cover gasket as well? I belive you have to take the valve cover off. BTW, my timing belt was changed at 60K, and now my mileage is around 130K, so it's been about 70K.

Brian

The two areas are not related. Replacing the valve cover gasket is very easy, the timing belt is much more complicated. I would only replace the valve cover gasket if it is leaking. Doing that only takes a while because of the cleanup and removing the old gasket after taking the valve cover off. The actual removal and re-installation only takes a few minutes once you have your tools ready and everything is cleaned up. Of course, a strut tower bar adds one more step to the process. :-)

It's about time for a new timing belt at 70K. Did they do the water pump, seals, tensioners, etc.? I would have them done either way, though I would also squeeze another 10K to 20K miles out of it if they were done the first time. If the water pump is original, there is a good chance that it is getting ready to go and it would be my main worry over the timing belt.

The recommended change interval is 60K or 100K depending on if you are in California. I have never seen one break before 100K miles, so I am pretty comfortable with going 80K to 90K instead of 60K between changes. This also eliminates any decision-making on the water pump, it automatically gets replaced after 80K miles.

Pat

Is that so? I don't recall seeing that mentioned anywhere.

I didn't say it was mentioned anywhere. I am referring to my own personal car maintenance, not anything that Mazda or anyone else has published.

Once the front end is torn down enough to replace the timing belt, I am automatically going to replace the water pump because I have seen two of them fail very soon after a timing belt change. The fact that I am going about 25% longer than the "recommended" replacement interval, (unless you live in California and have the exact same timing belt), makes replacing the water pump a very good idea because I have not seen many water pumps make it to 160K miles.

One of them failed at about 75K miles after having the belt done at 60K. A new water pump would have saved a lot of money in that case.

Pat

"It automatically get replaced after 80K miles" doesn't exactly tell the reader all that.

I'll try to do a better job for everyone next time.

I do apologize for any problems it may have caused you.

Thanks,

Pat

Just out of curiosity, what happens to the car if the water pump fails? i.e. does the car overheat and you get stranded where you are? Or does it mainly leak out coolant? 10-15K miles ago my car was leaking coolant from somewhere (it appeared to be the water pump). I took it into the shop and they could find no leak. Since then I have had no problems with it at all. In fact, I changed the coolant and still no problems. Coolant level is steady and fine now.

Brian

Think nothing of it.

It depends on now badly it is gone, which is not something you can really tell by an external visual inspection like the old water pumps that could replaced without tearing open the engine. The only indication that it is really about to go would be noises from the area and/or a large coolant loss.

I have a 1991 model to deal with that showed no signs of leaking, then the water pump went all of a sudden. It did not strand the owner, but it would have in a few more miles. There was coolant covering almost everything in the engine bay.

This car has 128,000+ miles and never had the timing belt or water pump replaced. The timing belt never snapped, I believe that the water pump is at least as much of a weak point as the timing belt, if not more so, which is why I would replace it every time, but not every 60K miles for either the belt or the pump. I have done quite a bit of work on a number of miatas, enough to see three failed water pumps, but have never seen a timing belt break on a single one, even on the cars with over 100K miles.

It could also leak slowly for a long time before giving out. To be losing coolant and have the problem just go away sounds strange. Maybe the mechanic hooked up a loose overflow reservoir cap and forgot to mention it? It sounds like they are honest anyway.

Pat

Heh-heh, I felt a tug but the line came up empty.... ;-)

Have a good one, Frank.

Pat