Interference engine (Ford content)

Ok, ford focus with the zetec engine. Is this an interference engine or not? Chiltons, Haynes AND Gates says it is, everybody on two different Focus forums say it's not. I have one engineer tell me it's freewheel.
So, I have some spotty repair companies telling me it's inteference, some focus fanatics (I would like to thing enthusiasts of the marque would know) are saying it's not, and a Ford engineeer telling me it's not (but I've also had engineers tell me engines need back-pressure to run right, so some of them ain't so bright either).
What say you? And more importantly, why? Have you had a timing belt break on one and had no damage or have you had the belt off and turned the crank independently of the cams?
Thanks.

All sources I've seen say it's dependent on rpm when the belt breaks. A coworker of mine has his zetec's timing belt go while idling at a intersection, no damage...

If you're doing highway rpms, passing etc, I'd imagine it would be another story.

paul wrote: All sources I've seen say it's dependent on rpm when the belt breaks. A coworker of mine has his zetec's timing belt go while idling at a intersection, no damage... If you're doing highway rpms, passing etc, I'd imagine it would be another story.

I'm sorry I can't help, but can't resist asking because it's the first time I ever heard of such a thing.

Depends on the RPM? Is that because of variable valve timing?

friedgreencorrado wrote:

paul wrote: All sources I've seen say it's dependent on rpm when the belt breaks. A coworker of mine has his zetec's timing belt go while idling at a intersection, no damage... If you're doing highway rpms, passing etc, I'd imagine it would be another story.

I'm sorry I can't help, but can't resist asking because it's the first time I ever heard of such a thing. Depends on the RPM? Is that because of variable valve timing?

Valve float, maybe?

Dad's '99 Contour 2.0zetec with VCT is thankfully NOT an interference engine. Glimmer of hope?

Ford Focus 2.0L Zetec with stock cams is non-interference. I have helped put aftermarket cams in 4 engines and in the process we have turned the crank and cams independently with no problems. Have not done anything with an SVT with VCT so I can't be sure about that engine.

Exceptions:
1. Some aftermarket "Stage 3" cams are very close or may be interference.
2. If it breaks at high RPM (6K+) you could always have some valve float and bend one.

m4ff3w wrote:

friedgreencorrado wrote:

paul wrote: All sources I've seen say it's dependent on rpm when the belt breaks. A coworker of mine has his zetec's timing belt go while idling at a intersection, no damage... If you're doing highway rpms, passing etc, I'd imagine it would be another story.

I'm sorry I can't help, but can't resist asking because it's the first time I ever heard of such a thing. Depends on the RPM? Is that because of variable valve timing?

Valve float, maybe?

Anybody got any data on valve float on cars with hydraulic lifters? I thought VF was an artifact from our past, considering modern valve actuators/springs & lubricants..

Not dissing your question, m4ff3w! You're making a good point.

In reply to friedgreencorrado:

valve float still happens, it'll take out the whole valvetrain on a k20a2 at about 9100rpm.

Valve float is actually a product of poor spring choice. OE engines are usually not designed for 9100rpm duty. The springs are light enough to reduce parasitic drag and heavy enough to close the valve at a specific RPM for XXX,XXX miles. For higher RPM application proper valve springs are a must.

The lower RPM is more related to piston speed. In VW land we might see a 1.8T stop at idle and the lower piston speed pushes the valves back with little or no damage, the pressure walking the cam around a little. At higher RPMs those valves are more likely to get bent because of the higher piston speeds.

no, factory rev limiter is around 8100, but they'll reliably run up to 8900 without killing anything. just have to make sure its a later k20a2 with the double valve springs. same valvetrain as the s2000.

John Brown wrote: OE engines are usually not designed for 9100rpm duty.

Again MOST OE engines are not designed for that duty. Some are, which is why it is so easy to track an S2000 or an Si.

The Zetec engine is most definately a non interference engine. Revs don't matter.

It seems valve floats only when the spring can't pull back the valve as fast as the piston is returning to the top?

If that's the case, then if the engine is non-interference, then a moderate RPM valve float isn't going to cause contact between piston and valve because the valve would have to have so much inertia that it goes past the normal point at which it would stop and then return.

Anyone with me on this? or no?

Agreed.

In reply to DrBoost: From other sources: http://duratec.wikispaces.com/
Differences from the Zetec: Interference: The Duratec engine is an interference engine, while the Zetec engine wasn't. Except: The SVT has an interference engine. Regular Zetecs are not interference Do you have an SVT engine or not? From FORD: https://www.fleet.ford.com/maintenance/vin_tools/pdfs/VIN2003.pdf Engine code 3 > 2.0L DOHC ZETEC I-4 Gasoline Ford 130 Engine code 5 > 2.0L DOHC HP ZETEC I-4 Gasoline Ford 170, Available only on ZX3 SVT Focus

gonzomuppet wrote: In reply to DrBoost: From other sources: http://duratec.wikispaces.com/ Differences from the Zetec: Interference: The Duratec engine is an interference engine, while the Zetec engine wasn't. Except: The SVT has an interference engine. Regular Zetecs are not interference Do you have an SVT engine or not? From FORD: https://www.fleet.ford.com/maintenance/vin_tools/pdfs/VIN2003.pdf Engine code 3 > 2.0L DOHC ZETEC I-4 Gasoline Ford 130 Engine code 5 > 2.0L DOHC HP ZETEC I-4 Gasoline Ford 170, Available only on ZX3 SVT Focus

Good stuff Gonzo.
This board has a wierd quirk that requires to hits of the spacebar twice before hitting the return bar if you want to single space your text. I have edited your repy in the fashion I think you wanted it.

Mardini wrote: It seems valve floats only when the spring can't pull back the valve as fast as the piston is returning to the top?

One quick correction. Valve float has nothing to do with the piston. Valve float is when the spring can't keep the valve lifter/cam follower in contact with the cam after the cam passes maximum lift. The shape of the cam changes so radically that the valve is flung off the tip of the cam like a bike jumping off a ramp. The spring is supposed to prevent this from happening, but sometimes the momentum of the valve is too high for the spring to compensate.

A floating valve can be hit by the piston though, because the valve ends up in the wrong place at the wrong time. It's supposed to be closed (or closer to closed than it is), but it's not and the piston comes up and hits it.
Bob

Confirm on the standard Zetecs - NOT interference

Confirm on the SVT Zetec - DEFINITELY interference

SVTF wrote: Confirm on the standard Zetecs - NOT interference Confirm on the SVT Zetec - DEFINITELY interference

Quoted for Truthiness. My (former!) SVTF grenaded a pulley and ate all the valves.

I've also heard of valve float being responsible for bending a couple on standard Zetecs if the belt/pulley lets go at high RPMs.

Soon, when my ZX3 comes apart for its first belt change at about 160k, I'll confirm with my own eyeballs whether the standard Zetec freewheels or interferes - though all signs point to the former.

When a timing belt breaks on an engine at speed the camshaft may continue turning for a moment but out of phase with the engine & pistons as it shows to a stop I'm talking milliseconds here. This could lead to contact of one or more valves with a piston. It depends on a number of factors: engine speed, where the break occurs in the belts cycle, how close the valves are to the pistons in normal operations, etc. . I think it’s more a matter of luck then anything.

If it happened at start up or when the engine was idling I don't think this could happen, but at 6-8000 rpm who knows.