UDP/ Lightened Flywheel Cause CW?

I was surfing a couple forums the otherday and came across a thread on focusfanatics and or focus central I think… Anyway it was one of Corbys threads and he was telling them how he has went through like 5 junk yard engine either due to crank walk or oil pump failure. Some of the focus guys where saying they only run a stock damper because almost everyone of the engines they have seen with a UDP caused CW (said like one or two guys in the thread)

Anyway I am builing a engine and am wondering if I should leave the udp/flywheel off? Since the whole reason I am building his motor is to make it last! Stronger internals etc. Since I have had no luck with the stock bottom end. First time I had CW (but I wasn’t running a udp, just the stock damper) I fixed that now I have wrist pin knock.

But yeah what do you guts think? I would like some other opinions. I also plan on checking the crank out on the motor in the car right now when doing the swap since I have been running a fiddy and powder udp for over 15K.

The “crank walk” issue is due to the thrust washer wearing (this is where your choice in oil pays off…I only use a top tier synthetic such as AMSOIL) from axial loading on the crankshaft. Manual transmission equipped vehicles suffer the most and putting a high pressure clutch on creates even more thrust load. The crankshaft pulley is not responsible for “CW”. What is important about the pulley is that it should be concentric and balanced.

Oh boy… now theres an old urban-legend of zetec right there…

Good clean synthetic oil and correct oil pressure will keep crank thrust wear at bay.

As for the flywheel and udp, yes in theory the reduction of mass increases harmonic vibration but not to any extent that affects crank walk or longevity in the real world.

I’ve ran many many miles of zetecs with udps and there never has been a crankwalk issue… however when I’ve seen a udp with the guide side of it worn and allowing the timing belt to walk into the timing cover. Other people too have seen this issue and they immediately assume its a udp, crankwalk, or thrust bearing surface problem when in actuality its a timing belt idler guide or crappy timing belt and tensioner installation.


To be clear “Good clean synthetic oil and correct oil pressure will keep crank thrust wear at bay.”, is NOT what I said. Good clean oil (I prefer synthetics for their superior load and sheer characteristics) helps to reduce bearing wear period. That includes the thrust washer and crank thrust surface.

Thanks for the replys guys

Ask Corby what krux thinks about this. He might tell ya he might not.

I would rather not ask corby lol what do you think about this?

I think there junk. I have good theory’s behind it. Yet people will flame me for saying it. I have a lot of theory’s yet keep them to myself haha.

So you believe the stock is where it’s at? This is why I made this thread is to get some feed back from either point of view. I have heard more people saying udps and lightened flywheels are junk than the opposite. So… You have experiance? Explain haha :wink:

My idea and even talked to my teacher about this which he agreed that I am complete correct thinking from a engineering stand point.

The zx2 crank like any motor out there was designed to have a heavy crank pulley at the end of it. Now even though its not a balanced pulley its still a weighted pulley. Now just imagine if you put a weight a heavy weight at the end of the stick and spin it…This creates a certain balance and weight that may help balance it and a rotational force(heavy flywheel and udp). Now you put something lighter on it…the weight is no longer there and now the whole engineering stand point of the design has now changed. Who says when you put this lighter udp on that it may be off weighted and cause a balance issue that causes vibration like a rotor does when wrapped? This could cause issues in the higher rpms making it flex back and forth causing a pulse through the crank and later causes premature failure on the bearings. Also the belt’s weight isn’t disturbed out through out the crank pulley yet brought in closer to the crank and causing more of a tug on the pulley itself.

Things to think of:

Car manufacturers want the best epa wouldn’t a udp be a good solution for them to get more hp and better gas mileage?

The car’s that you see that did have crank walk was from a udp(90 percent of the time). For example. I told Corby on the phone to take it off 5 engines ago. 5 engines later and everything was stock except the UDP.

Things to think about. I am not saying I am right or wrong…just stuff I keep to myself. I can better describe in life explaining it than typing through the net.

that does make a good amount of sence hmmmmm… I am a little stumped on what I should do haha… if I sell my powder combo and fiddy that would be a nice chunk of change and not have to worry about CW. haha I dunno I guess it will all depend on how my current motor looks since I have been running both.

The heavy flywheel and vibration damper that originally came on the car serves a variety of purposes, one of which is to cancel harmonic vibrations that are inherent with a piston engine (i.e. turning up/down movement into rotational movement). Another is to cancel harmonic vibrations that occur from the valve springs, cams, driven pumps and pulleys that are being torsionally pulled on by a belt.

A piston driven crankshaft which rotates more than itself at varying rpms is not the same as a heavy weight on the end of a stick.

IMO theories are just fears based on armchair engineering and if one fears changing what Lord Ford has put together on the assembly line then one has no business modifying ANYTHING on the vehicle.

A warped rotor has to do with not a differential of weight but a pulsation caused when applying the brake pedal because of a caliper piston rapidly sliding in and out of its bore due to warpage… no weight related imbalance issue is occurring so warped rotors do not apply to this discussion.

Since the only thing thats changing on the udp is the mass and not the balance, balance is not a problem here, the only topic of discussion really is the mass, and if you want to dig further, the loss of the rubber harmonic balancer within the stock pulley which is a whole 'nutha animal to discuss altogether.

So what you’re saying is the pulley actually flexes back and forth radially under higher rpm usage? No sir, does not happen in any real measurable form.

As for the “weight” of the belt… since the belt is made of a rubber like material it absorbs vibrations itself, and since the udp actually slows down the items its driving it actually reduces the vibration pulses caused by the driven accessories. Many people report a smoother idle after installing a udp and I can attest to that as well.

Yes they would, but they also must address the alternators and a/c compressor’s ability to produce maximum amperage and cooling at idle speed, thats why they are spinning the accesories at a faster rate. Also, They assume that the typical driver will be operating the car in extreme conditions, be it subzero weather or desert heat.

I don’t know the Corby situation you’re referring to but I’ll bet lots of times what was being called crankwalk failure was nothing more than eroded udp thrust surfaces due to timing belt (not crank) walk from bad cam belt idlers or tensioners causing the belt to chafe forward more than it was designed to.

Bottom line… EVERYTHING you do to your car will affect the engineering of it one way or another, and ANYTHING that was replaced, repaired, or altered from the factory as it left the assembly line is a compromise in the vehicle’s quality.

BUT the good news is that many compromises are good ones, and compromise exists within the framework of the car’s engineering itself, meaning economy and emissions on our cars were considered more important than outright performance.

Assuming the 130hp ZX2 motor will last to 250k miles if left stock, then perhaps a 30hp boost with aftermarket add ons will take that figure down to lasting only 150k miles.

I’d trade 100k of usage for 30hp but thats just me looking for 150k miles worth of silly grins when I step on the throttle instead of 250k miles worth of generic automotive boredom.

Besides, from an economics perspective, we’re not talking a lot of sheckles here if we reduce engine longevity a bit, if at all. We’re not working on $10k porsche motors, we’re tinkering with a $500 motor in a $2500 car.

My original S/R, which now has 120k on its original motor, has seen lots of performance parts added to it over the years (headers, cams, udp’s, cam gears, injectors, intakes, mufflers, pcm tricks) and it’s still running without any issues of crank walk, or bearing failure.

I HAVE, however, had to replace udp’s damaged from bad cam belt installs done by yours truly (cam belts trying to run off the front of the pulleys, wearing a groove into the back of the udp). The replaced udp has been on the car 50k miles without issue, and the motor has had a udp since it had 20k miles on it.


What he said. I was too lazy to type all that. The Zetec is an internally balanced engine.

Thanks for the info guys both sides are argued well. The bottom line for me is to see how my rebuilt motor looks when I pull it for the new build (I cant wait by the way LOL.) And I have been running a UDP/ Fiddy Flywheel combo since the day I rebuilt it.

Rob I would reply to your comments but Ill leave it be. I have said my words but see a lot of wrong points in there. Biggest thing is there are cars having crank walk and now more than ever and you might not even know it. 5 motors and a person to claim it was his fault is ridiculous. They were perfectly running motors except one mod which ended them fast. Yet ill leave this subject since this could get super hot super ugly super fast.

Piss best of luck to your decision.

Here for reading:


the main reason our engines or a lot of engines have crank walk is that stupid have thrust bearing design.
Im thinking about machining a main cap milled to accept a thrust bearing also to see how that works. Then ill have twice the main cap thust surface.

Also if your worried about balance and torsional vibrations have a performance shop rebalance the cranks, rods, pistons, udp, flywheel and have them check it with the flywheel, clutch kit and UDP installed.

I wonder if anybody has tried having the thrust surface on the crank welded up and reground to make a harder thrust surface? Or at least shot peened and nitrided? I wish I had the time and the money and the test engine to try out some different methods of reducing thrust wear that we used back in the day on our big Chevys.

thanks krux, not looking for a verbal war either, but the point i was trying to make was that theres a good chance the crank walk people are referring to is a mis-diagnosis.

as for one guy having the same problem 5x, well either he is the most unluckiest guy in the world, or something is occurring that is being overlooked.

I buy and sell used zx2’s locally and I have yet to see/find a zx2 with crank walk. i know they are out there but its surely no epidemic, and doubly sure they’re not caused by udp installs.

I understand why people point to the udp as being the culprit for crankwalk when they are holding a pulley that has teeth worked into the backside of it. It however is not the cause of the problem, but rather the result of something else. let me explain…

the oem crank pulley is made of carbon steel which has superior wear resistance to an aluminum udp. the aluminum, although softer, will work fine without issue providing it has limited exposure to being chafed by a walking cam belt. But… if a cam belt wants to walk forward off the gear, there is another culprit thats causes the endeavor, such as excessive play in the idler bearings or tensioners, or a warped timing belt due to it being bent and stretched over the gear instead of placing the belt on a removed intake gear and then placing it on the cam. These instances will wear out the backside of the pulley and allow a belt to walk itself right into the timing cover and start to shred. Now think if a guy with 5 bad engines kept putting this same worn udp on his “fresh” engine. He’d keep shredding the belt and that would lead him to believe he had another bad motor since it had the same result.

Another big problem, and this is an engineering goof by Ford in my opinion, is that the small timing belt idler that sits near the crank received a design change in late 1999 from a concave to a flat on the pulleys belt riding surface. The concave pulleys are superior in keeping the belt from walking forward since they have a low point that the belt will naturally want to gravitate to, away from the crank pulley and the timing cover. These concave pulleys have since been discontinued by Ford and one can only get a new flat idler pulley. It’s a shame because the concave pulleys IMO are the solution to the walking belts.