Non Interference Motor??

[Pro5driver]

I was told that I have this type of motor and that if the timing belt goes everything will not go bad like in other motors? Is this true or a myth?

[tsunami7]

myth

[NCZ13]

to the best of my knowledge, this is a non interference motor.

although replace your timing belt at the intervals and youll be fine.

[magnumP5]

FSDE is non-interference so if timing goes off you won't destroy your valves. This does not mean you won't cause other damage however...

[Suomi]

FSDE is non-interference so if timing goes off you won't destroy your valves. This does not mean you won't cause other damage however...

I'm curious what other damage you're referring to. I can't think of anything else that could be damaged by just a broken timing belt.

[YelPro03]

I'm curious what other damage you're referring to. I can't think of anything else that could be damaged by just a broken timing belt.
Let the belt break and find out. The point here is you really don't want to find out so it would be in your best interest to change the timing belt at 60,000 intervals. While you're at it might as well change the water pump and other drive belts. Preventive maintenance is the key.

[ogsp5]

Our engines can go up 100k miles before doing the belt change. But good preventive is always wise.

[slavrenz]

myth

I'm so tired of this being spread around(I'm not trying to single you out tsunami, I'm talking to everyone who reads this.) If you only read that this was an interference motor from somewhere else, don't spread the "myth" that it is. I have spoken with several mazda techs about this, as well as Mazda corporate, and have been assured that it is a NON-INTERFERENCE motor.


FSDE is non-interference so if timing goes off you won't destroy your valves. This does not mean you won't cause other damage however...

Yes, if your timing belt breaks while you are on a mountain road, you may freak out and drive off a cliff :). But otherwise, you're not going to do any other damage :bs:


Let the belt break and find out. The point here is you really don't want to find out so it would be in your best interest to change the timing belt at 60,000 intervals. While you're at it might as well change the water pump and other drive belts. Preventive maintenance is the key.

Don't try to freak him out by imagining what damage could occur if his belt breaks, unless you know first-hand. In 99 cases out of 100, the only thing that will happen is your car will stop running, and you will have to take it to a shop to get the belt replaced, and have your valves re-timed.


Our engines can go up 100k miles before doing the belt change. But good preventive is always wise.

Agreed. Unless you live in an extremely cold climate, you can wait until 105k miles to change the belt (that is what is listed in my manual). I realize other manuals may say 60K, but again, unless it's very cold year round, you will be fine.

[magnumP5]

I'm curious what other damage you're referring to. I can't think of anything else that could be damaged by just a broken timing belt.
While no physical damage will occur directly you run all sorts of risks when running with severely screwed up timing. Chances are the belt just won't snap but it will stretch or tear. This will through off your timing, which could lead to detonation issues and those are never good.

[cbrcrx]

I bought my belt a long time ago and was going to see how long the original belt would go bofore it broke and prove that there was no damage. Well, I got tired of waiting and changed it at 156,000 miles.

[Suomi]

Let the belt break and find out. The point here is you really don't want to find out so it would be in your best interest to change the timing belt at 60,000 intervals. While you're at it might as well change the water pump and other drive belts. Preventive maintenance is the key.

In fact, I know that nothing in the engine will be damaged by this, but was curious to hear the response. If the P5 were my daily driver, I would be inclined to let the timing belt go until it breaks. But it's my wife's car, and she uses it for some work occasions when she can't afford the breakdown. Her car is at about 107,000 miles (service interval is 105,000), and I'll be changing the belt when it gets a little warmer outside. My point is that telling people that a broken timing will cause some sort of collateral damage is just silly.

[YelPro03]

In fact, I know that nothing in the engine will be damaged by this, but was curious to hear the response. If the P5 were my daily driver, I would be inclined to let the timing belt go until it breaks. But it's my wife's car, and she uses it for some work occasions when she can't afford the breakdown. Her car is at about 107,000 miles (service interval is 105,000), and I'll be changing the belt when it gets a little warmer outside. My point is that telling people that a broken timing will cause some sort of collateral damage is just silly. Even if a broken timing belt doesn't do any damage to your engine doesn't mean you should run it unit it breaks because you just don't know when and where that will happen. If you're lucky it will break on a clear sunny day just as you're pulling into a repare shop or a garage just to ask a simple question or it can break in the middle of winter, at night, with 3 inches of snow on the ground or in a down pour and you're miles away from home with a loaded car. Then you'll have to call a tow truck, find a repare shop near where ever you might be at the time, find a way to get home with all your stuff, and find alternate form of transportation while it is being fixed. My point is its not just getting stuck when the belt breaks but all the problems and logistics involved in getting it to a shop and getting it fixed.

[Suomi]

Even if a broken timing belt doesn't do any damage to your engine doesn't mean you should run it unit it breaks because you just don't know when and where that will happen. If you're lucky it will break on a clear sunny day just as you're pulling into a repare shop or a garage just to ask a simple question or it can break in the middle of winter, at night, with 3 inches of snow on the ground or in a down pour and you're miles away from home with a loaded car. Then you'll have to call a tow truck, find a repare shop near where ever you might be at the time, find a way to get home with all your stuff, and find alternate form of transportation while it is being fixed. My point is its not just getting stuck when the belt breaks but all the problems and logistics involved in getting it to a shop and getting it fixed.

The point is that no actual damage will come to the car as a result of the broken belt. Obviously a broken belt will cause some sort of inconvenience, but I honestly wouldn't be too bothered by towing a car home and just throwing a new timing belt on. I wouldn't go on a road-trip in those circumstances though. That's just pressing your luck.

[YelPro03]

The point is that no actual damage will come to the car as a result of the broken belt. Obviously a broken belt will cause some sort of inconvenience, but I honestly wouldn't be too bothered by towing a car home and just throwing a new timing belt on. I wouldn't go on a road-trip in those circumstances though. That's just pressing your luck.
Basically that is my point. Why limit yourself to where you can go? Why not just get it changed and be free to drive where ever and when ever?

[Suomi]

Basically that is my point. Why limit yourself to where you can go? Why not just get it changed and be free to drive where ever and when ever?

I think you are agreeing with me then. That's why I'm not waiting. The idea is that if the limitation on where you can drive is a non-issue, then a broken belt is a non-issue. I honestly take my GTI most places just because it's faster and more fun to drive, although the P5 does handle a little better and beats it in mileage.

[Pro5driver]

Thanks for the answer guys. I will be changing the belt next month cause I have no idea if it has ever been changed.

[tsunami7]

I'm so tired of this being spread around(I'm not trying to single you out tsunami, I'm talking to everyone who reads this.) If you only read that this was an interference motor from somewhere else, don't spread the "myth" that it is. I have spoken with several mazda techs about this, as well as Mazda corporate, and have been assured that it is a NON-INTERFERENCE motor.

OOps. I read the post wrong, I was saying it was a myth that the car had a interference motor, LOL. Curse my poor reading skills.

[Suomi]

OOps. I read the post wrong, I was saying it was a myth that the car had a non interference motor, LOL. Curse my poor reading skills.

And still wrong. It is not a myth that this is a non-interference motor. It is in fact a non-interference motor.

[i12drivemyMP5]

The "myth" part is that for some mythological reason people won't believe that it is in fact non-interference & these well maybe it is or maybe it's not threads keep going on forever. See previous 5000 int/non-int threads..............If shit don't hit, you must quit, believing the bullshit

[mgrinshpon]

The "myth" part is that for some mythological reason people won't believe that it is in fact non-interference & these well maybe it is or maybe it's not threads keep going on forever. See previous 5000 int/non-int threads..............If shit don't hit, you must quit, believing the bullshit

This. ^

It's not hard to do the timing belt install yourself, either. Grab the service manual and read it. Really really easy to do if you have a bunch of hours. It can all be done with hand tools, too.

[flash75]

The interference (myth) comes up because the Gates timing belt chart lists the Protege 5 as one of the few Mazda's that have an interference engine.
http://www.gates.com/downloads/download_common.cfm?file=428-1466_web.pdf&folder=brochure

Most of you don't agree with them and perhaps you are right. I don't know, but I have not seen any Mazda reference stating the P5 is a non-interference engine. I did a search and didn't find a lot of information on the subject. I have a shop manual and cannot find any reference that mentions if it is a non-interference engine. I know a Mazda technician said it's non-interference in another thread.

I have changed a few timing belts in other cars and it's not necessary to know if car is non-interference to change a belt. If the belt breaks that's different story. My son had one break in an Isuzu Stylus, it is a non interference engine and no harm was done.

I do have a question for those who have removed a Protege cylinder head. Do the pistons have valve reliefs cut in the top of the piston? That information would help.

Clifton

[tsunami7]

And still wrong. It is not a myth that this is a non-interference motor. It is in fact a non-interference motor.

Damn I still can't seem to read or write correctly, good thing you're here to clean it all up

[Diehonda]

I bought my belt a long time ago and was going to see how long the original belt would go bofore it broke and prove that there was no damage. Well, I got tired of waiting and changed it at 156,000 miles.

(lick) I lasted longer than you! 184K on the original timing belt!!! W00t!

The idler was loose, the tensioner spring was shot, but the belt was good. I got the Gates kit and replaced it all. Only had to get a tnesioner spring from the dealer.

[igdrasil]

i know this is an old thread but as my experience...the FSDE is an interference engine (for me). I have bent a few valves before.

This could be in fact a different case...but...there you have it. It does have valve reliefs so its not supposed to bent valves.

For now, I would say its a non-Interference.

[flash75]

You say you have bent valves, yet you say it's a non-interference engine?

With valve reliefs in the pistons valves should not bend when the engine running normally. Both valves will be slightly open at TDC on the exhaust stroke. That is valve over-lap and normal for most all engines. However, some engines do not require valve reliefs, it depends on the type piston and combustion chamber shape. Higher compression ratios can make a difference on what is required.

The relief's are in the pistons to provide additional clearance between the the valves and pistons during the valve over-lap period of normal operation. They are not there to make it a non-interference engine in the event of a broken timing belt.

Assume your timing belt breaks. The cams will stop turning but the crank will continue to turn until the inertia is used or until you get the transmission in neutral.

When the cams stop turning some valves may be fully open. Guess what will happen if the piston moves past TDC in the cylinders that have some valves open. BANG.

That makes it an interference engine. The Gates manual also calls it an interference engine.

Clifton

[Suomi]

Well, bent valves are pretty convincing. So I stand corrected, as it clearly is interference. Who were the first to declare this motor to be non-interference, and why? No actual experimentation could have been done to come to that conclusion.

[ucMP3]

I do not have extensive knowledge on this "myth", but I can say this. I blew my motor out at 86k miles (I bought it at around 80k) due to a timing belt issue that caused me to bend a valve and throw a rod as well. I wasn't driving hard, I was merely on the way to work. So my situation seems to correlate with this discussion.

[slavrenz]

Well, it seems we are at an impasse. I have asked four different Mazda technicians at 3 different Mazda dealerships, as well as the support at Mazda corporate. All 5 individuals have told me that the engine is non-interference.

I don't know about the first guy who said he bent a valve, but to the poster who also threw a rod, broken timing belts don't throw rods. It's obvious that something else happened along with the belt that likely contributed to the valves bending.

My last argument for this is that I have owned 2 cars before with interference engines (an Accord and a Sonata), and the owners manuals were very clear to state that not replacing the timing belt would cause damage to the engine. Don't you think Mazda would have included anything if the engine could be damaged when the timing belt breaks.

Like someone above said, these posts have become a waste of time, and this argument could continue all day. Those are my final points as to why our engines are non-interference; you guys can take them how you want.

[igdrasil]

You say you have bent valves, yet you say it's a non-interference engine?


Because I dont know for certain what happened when the engine blew. My thougts is that it threw a rod cap, sending the piston higher on the chamber and eventually bending valves. I did not attach the picture where it shows the region in the piston where the valves got the hit...but for sure it wasnt on the reliefs, so it must have rotated slightly as it was released from the crankshaft.

But Im not an expert...thats my theory.

[Suomi]

Seeing that the bent valves mentioned in this thread both resulted from piston/rod problems, I am again unconvinced. I think the only thing to convince me (and likely most people) would be to see a video of someone free-wheeling the crank with the timing belt off. I was planning on checking this a few weeks back when I changed my timing belt, but I was running into some headache-inducing issues, and I decided to just finish the job without any extra-curriculars.


Well, it seems we are at an impasse. I have asked four different Mazda technicians at 3 different Mazda dealerships, as well as the support at Mazda corporate. All 5 individuals have told me that the engine is non-interference.

I don't know about the first guy who said he bent a valve, but to the poster who also threw a rod, broken timing belts don't throw rods. It's obvious that something else happened along with the belt that likely contributed to the valves bending.

My last argument for this is that I have owned 2 cars before with interference engines (an Accord and a Sonata), and the owners manuals were very clear to state that not replacing the timing belt would cause damage to the engine. Don't you think Mazda would have included anything if the engine could be damaged when the timing belt breaks.

Like someone above said, these posts have become a waste of time, and this argument could continue all day. Those are my final points as to why our engines are non-interference; you guys can take them how you want.

[slavrenz]

Someone get a video clip posted - settle this once and for all ;)

[i12drivemyMP5]

Depending on what happens, it's an interference motor.
Depending on what happens, it's NOT an interference motor.
Hope that clears things up a bit.

[magnumP5]

I wish someone suggested this sooner as I have a spare engine sitting in my garage. Too bad I have already removed the cams from the head and the head from the block otherwise I could have very quickly found out.