Non Interference Motor??

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
 
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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.
 
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.
 

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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
 
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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.
 
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.
 
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.
 
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.
 
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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.
 
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.
 
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.
 
The FSDE is absolutely interference. I've seen the result of this first hand countless times.

The clearest example I could give is this:

I once watched the timing belt jump on a protege AT IDLE. It instantly bent all 16 valves and lost all compression.

It's also very easy to prove that it's an interference engine. Take your timing belt off. Turn the cam so the valves in cylinder 1 are at max lift. Now rotate the crank. SLOWLY AND CAREFULLY. You will eventually feel resistance. That's the pistons hitting your valves.
 
The FSDE is absolutely interference. I've seen the result of this first hand countless times.

The clearest example I could give is this:

I once watched the timing belt jump on a protege AT IDLE. It instantly bent all 16 valves and lost all compression.

It's also very easy to prove that it's an interference engine. Take your timing belt off. Turn the cam so the valves in cylinder 1 are at max lift. Now rotate the crank. SLOWLY AND CAREFULLY. You will eventually feel resistance. That's the pistons hitting your valves.
9 year bump?!
 
The FSDE is absolutely interference.

No It's Not !!! Not always !;; Especially if you're not a race car driver !!

It's also very easy to prove that it's an interference engine. Take your timing belt off.

I cut mine off, is that OK ??






I cut the other belts too ...




Turn the cam so the valves in cylinder 1 are at max lift. Now rotate the crank.

Max Lift... You Got It !!








SLOWLY AND CAREFULLY. You will eventually feel resistance.


Slowly my ass.. I wound Er' up Good...





Faster than idle dude !!! 1600 RPM 's !!!
(or whatever my drill spins at ??)


That's the pistons hitting your valves.[/QUOTE]

OMG !!;

No clacking of Valves !!;

What Am I Doing Wrong !!!

It's An Interference Engine !!


Ya know,.. My car is at 238,000 km and I'm gonna run it till my belt snaps, and join the happy club of people who have also done so !!

Snap a belt, tow it home, replace belt, drive on....

If you spend all day on the dino Mr. Kool, then yea, you'll bend your valves ...

PS... Downshifting is really bad for your connecting rod slap...
The piston is being pulled down instead of pushed down causing wear on both ends of your rods...

Ya know ... My parts car ran fine before you made me wreck it !!!
 
The FSDE is absolutely interference. I've seen the result of this first hand countless times.

Countless ?? Really ?? Have you Ever seen an FS-DE engine survive a T-belt snap or skipping of teeth ??
(I just did in my backyard!!)

Your statement is quite misleading... You're suggesting that if your T-belt snaps, you need a new car or at least a new engine or rebuild and that simply is not always the case.

If anyone here on the forum snaps a T-belt on their P5 it is certainly worth the $35 and effort to throw on a new T-belt and give it a try.

PS... I'm gonna give the interference another go...

I'm gonna put a drill on the two camshafts as well as the crank and spin them all up at different rpms, forward and reverse...

Any suggestions on how to get things to hit ??

It's been suggested that the interference is valve to valve not piston to valve... I'll try that too.

I want a big crash... The engine is shot anyway.. It burns more oil than gas...
It's getting pretty good mileage at about 30 mpg... (that's per gallon of oil).
 
Someone get a video clip posted - settle this once and for all ;)

I'm working in it dude but Photobucket wants $300 out of me and Postimage doesn't do videos and Tapatalk I can't figure out but !! Maybe I can release a few images from this site (which does have a limit) and try to post a video here on thus forum (which must be less than 'x' number of megabytes) then you can all watch my parts car spun up wildly with three drills on the crank, and both cams...

Wish me luck!! I'm hoping for all kinds of ungodly interference!!;
 
Youtube is free. If you flag it as unlisted when you post it, it won't show up in general search results but you can post the link here and it will take you to the video if you click the link.
 
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