Is the FS an interference engine ?

Pretty much both, a lot of places have it listed as non interference and there have been several members break timing belts and bend valves while others had them break and not hurt it at all
 
I was thinking he should remove the plugs and slowly turn the crank shaft because he wouldn't be working against the spring tension of the cam shafts so he's more inclined to feel the "hit" but he'd still have to move the cams at some point.
 
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Just turn the cams lol. I doubt the valves are so weak that they bend from turning it by hand.
 
I'm still confused about all this interference. Perhaps they had racing cams or running the red line when it snapped and the valves were floating ???

I get really nervous running up to the red line figuring if something is gonna break, that's when it'll happen.

I know a guy that bought a car off a little old lady who only drove it to church. It was a great deal but he killed it the first day. It had never been anywhere near red line until he drove it.

The rings hit the ridge at the top of the cylinder walls and broke all of them.

Maybe that's a good reason to install heavy duty valve springs.
 
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No to what exactly ??

Everything or just the heavy duty springs ?

I bought my car knowing it was an interference engine.

It had 142,000 km on it and couldn't track down the original owner so I went ahead and replaced the timing belt at just under 200,000 km.

I ended up replacing a belt and water pump that had already been replaced.

I've got 205,420 Km on it now and all is well, but I would have ignored the belt until it broke if I knew it wasn't an interference engine.
 
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yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no..............and the debate continues
 
i12drivemyMP5 said:
yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no yes no..............and the debate continues
Click to expand...

It can be but just barely, it's enough to cause some damage. Just rebuilt the block (to stock specs) and for the hell of it my dad has a camera that you can use for remote work (kind of like the cameras surgeons use for throat exams). Sure enough had the intake valve open to 100% from cams and rotated the crank up to TDC and a clink noise where it hit (rotating by hand...). It was touching it, which is why i think they consider it an interference. It would take a MAJOR(scratch) screw up to get the timing that bad though.

tweety2300 said:
Pretty much, just change the belt every 100k miles and not worry about it
Click to expand...

EDIT: @PCB ---- There's misinformation even in that thread. A lot of the people that rebuild these motors especially for horsepower gains are using lower compression pistons/shorter rods to get those compression ratios down in the 8's and low 9's for the boost. (ricer)(ricer)

Therefore they may not be getting the interference, but a stock engine can. Even in the shop manual it says that it is, I would be cautious and take the extra 5 minutes to insure that the timing is correct before I'd rely on a few people's opinions that it's a non-interference. My $.02.
 
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interference vs. non-interference definitions are very misleading. Mazda calls it a non-interference design for a couple of reasons, although in very specific situations a piston head can come in contact with a lifted valve with a completely stock FS engine.

Engines with solid lifters do not rely on oil pressure for tappet lash. So in the event that an engine 'breaks', is no longer running, and doesn't have oil pressure...physical spring tension with solid lifters will more often than not seat the valves properly...not having the cams stuck in a fully lifted position...you can verify this when changing the timing belt...you'll notice when you release a cam gear, it'll shift to a more or less neutral position through lifter pressure...some valves might be slightly lifted, but its tough to get a pair to remain completely opened...

i'm guessing this is where mazda is getting away with calling the FS a 'non-interference' design. In 95% of circumstances in which a timing belt slips or breaks...the cams will stall at a position in which no valves are fully lifted...and a piston will never come in contact with them. Even when fully lifted, the valves can only barely be bumped by a piston head...and it'll usually just load up the lifter and move the cam a little. I had mine slip from a bad tensioner years ago...nothing happened other than destroying the belt...

it is luck though...if the belt breaks as a piston is approaching TDC with a cam that stalled with the right valves hanging open...at very high rpm...that slight bump can bend a valve stem...but its still unlikely enough that the powers that be call it a non-interference engine...older designs with hydraulic lifters could leave valves fully lifted, with much more possible contact...that is guaranteed to break something...its such a small possibility on ours i wouldn't worry about it.
 
If the stock version of the motor can hit s*** and bend or break s*** if timing is not set right or if timing belt breaks then it should be classified as interference. Saying that it is not an interference motor "MOST of the time" or "in MOST situations" is basically bulls***, a lie & mispresentation. If is was really non-intereference then nothing would clash ever as that is the definition. Mazda & everyone else should just say WTF it is...........interference. Consider it that if erroring on the side of safety and saving yourself time and money matters at all.
 
Installshield 2,
Do we have solid lifters, or is there a hydraulic component to the valves/
Thanks




Installshield 2 said:
interference vs. non-interference definitions are very misleading. Mazda calls it a non-interference design for a couple of reasons, although in very specific situations a piston head can come in contact with a lifted valve with a completely stock FS engine.

Engines with solid lifters do not rely on oil pressure for tappet lash. So in the event that an engine 'breaks', is no longer running, and doesn't have oil pressure...physical spring tension with solid lifters will more often than not seat the valves properly...not having the cams stuck in a fully lifted position...you can verify this when changing the timing belt...you'll notice when you release a cam gear, it'll shift to a more or less neutral position through lifter pressure...some valves might be slightly lifted, but its tough to get a pair to remain completely opened...

i'm guessing this is where mazda is getting away with calling the FS a 'non-interference' design. In 95% of circumstances in which a timing belt slips or breaks...the cams will stall at a position in which no valves are fully lifted...and a piston will never come in contact with them. Even when fully lifted, the valves can only barely be bumped by a piston head...and it'll usually just load up the lifter and move the cam a little. I had mine slip from a bad tensioner years ago...nothing happened other than destroying the belt...

it is luck though...if the belt breaks as a piston is approaching TDC with a cam that stalled with the right valves hanging open...at very high rpm...that slight bump can bend a valve stem...but its still unlikely enough that the powers that be call it a non-interference engine...older designs with hydraulic lifters could leave valves fully lifted, with much more possible contact...that is guaranteed to break something...its such a small possibility on ours i wouldn't worry about it.
Click to expand...
 
All vs engines 98 and on have solid lifters.

i12 I totally agree. It is bs. It's another issue like 'harmonic balancers', and if certain engines aactually have them...or not.
 
i12drivemyMP5 said:
If the stock version of the motor can hit s*** and bend or break s*** if timing is not set right or if timing belt breaks then it should be classified as interference. Saying that it is not an interference motor "MOST of the time" or "in MOST situations" is basically bulls***, a lie & mispresentation. If is was really non-intereference then nothing would clash ever as that is the definition. Mazda & everyone else should just say WTF it is...........interference. Consider it that if erroring on the side of safety and saving yourself time and money matters at all.
Click to expand...

Mazda does consider it an Interference engine...(scratch) says it right in the service manual in the timing belt change sequence in bold print at that. I don't see why so many people piss their pants calling it non-interference and when it bends a valve poop their pants and blame everybody. Time is precious money is even more so...damn bills.

I guess some people just have gotten real lucky.
 
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Agreed on what manual says. Have had this car for 10 yrs and have covered the manual pretty thoroughly if not completely. Have had and worked on both non-interference and interference motorized vehicles. If anything hits at any time regardless of positioning - interference, if not then it's not. What I meant was that Mazda does and EVERYONE ELSE should just consider it intereference to end this neverending debate and misinformation. Whoever's car s**** the bed timingbeltwise without any other damage just consider themselves lucky and not try to say that it is non-intereference motor just based on their stroke of luck that time.............
 
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