Lets Talk Crankwalk

[TurfBurn]

So it is coming up more and more on these forums so I'd like to see an open discussion on it not cluttering up a build thread or a turbo kit thread or rods thread or anything else...

The rumor mills and informed sources have started bringing up that there is belief that the FS motor will crankwalk with high horsepower loads and heavy clutches.

So first off.. what the hell is crankwalk... Crankwalk got very popular as a topic for modded motors after the 2G DSM's showed considerable instances of this where endplays on the cranks became so bad that clutches would fail to engage and pistons sets would even be destroyed from the moving crank in some instances... Essentially, crankwalk is the ability of the crank to shift side to side in the main journals greater than intended. From motor to motor it varies as to what is "acceptable" I have the spec for my motor somewhere as to what I have for clearances, but I don't want to throw out a number as I'm not 100% positive on it.. someone else can chime in unless I find it before then.

What generated the catastrophic crankwalk in DSM's was wearing of the thrust bearing. In some cases it would become so worn that the crank would actually grind into the block itself!!

Many many theories are out there and exist... but after reading many an article on the DSM forums and the like I have a couple I prefer over others, but this isn't the place to discuss DSM crankwalk... this is about FS motor crankwalk!

My point is that crankwalk by definition relies upon clearances to open up between the thrust faces of the crank and the thrust bearings/faces in the block enough for excessive endplay to occur...

Now with that said... onto the topic at heart... Can and will this happen in the FS motor?

A number of reputable and admirable sources say that it will indeed happen and is a major problem for us... other reputable and admirable sources say that it will NOT happen and isn't a problem. So this is where you all come in... Below will be my opinions and thoughts and knowledge... not that I believe I'm particularily right... or that I have a better grasp than anyone else... but I'm going to share my knowledge and listen and learn from what other's have to say and overall it should simply mean more info for the community and better motors for each of us in the end... so onto discussions!

 

[TurfBurn]

so anyway... first off.. my theory... We do not have a crankwalk issue... or if we do there is no hope other than replacing thrust bearings repeatedly.

While there are considerable forces in the motor very little of the forces created by high horsepower or actual motor running will generate lateral forces on the crank. Unless there is considerable deformation of the block or crank, very little can happen from an angular standpoint in the motor. The pistons themselves would have to generate a torque upon the rod to torque and force the crank sideways to generate that motion. This would cause the pistons to rock against the rings and contact the sides of the cylinder bore. Obviously this would create much more serious issues than a little thrust washer wear.

Arguably, the greatest amount of force exerted on the crank is exerted by the clutch pressure plate. Many pressure plates well exceed 2000 lbs of total spring force. Every time you depress the clutch you are forcing this pressure against the crank (as it is leveraged against the clutch release fork and throw-out bearing) which then is held in place as necessary by the thrust bearing. While forces may be generated due to the flexing of the motor and the loading of belts and accessories that will generate pressure in the lateral direction of the crank I believe few if any come remotely close to the levels of force that the pressure plate itself can exert.

So with that said the demon for crankwalk with our motors will be pressure plates. My previous and current motor both ran with an ACT yellow pressure plate. This is a 34% over stock pressure plate. The previous motor that I had as many of you know blew due to rod fatigue in cylinder number 4. I'll try to post pictures in the near future but this motor ran from 10 psi to 16 psi daily before I owned it and 10 psi daily when I owned it. It was boosted for nearly 25,000 miles of driving. If you look at my thrust washers and all of my main bearings none of them show any signs of unusually high wear or heavy loading. Meaning the motor did not walk or wear the bearings in that time with that clutch and pressure plate.

I believe that riding the clutch, using excessive pressure plates (no need for anything above the 34% plate... my current configuration is RATED for 500ft-lb's of torque), and poor oil pressure are the only demons to worry about in generating thrust bearing wear and futur crankwalk. I may be proved wrong in the future, but at this point I doubt it...

So please... lets here some counter opinions with good reasoning because while I'm confident in my stance, more information and sound logic is best for us all!

 

[terbow]

so based on your last paragraph there..

Is crankwalk what causes the bearing failure, or is it that poor oiling causes more friction which breaks down the bearing then the crank walks cause the bearing is worn down?

I know in cavaliers (the 2.4L) they spin the 3rd cyl bearing all the time cause of oiling issues.

 

[BlkZoomZoom]

Finally a thread about this. I am with Turfburn on this in that I have never known, or seen any type of crankwalk issues on any Fs motor. Now granted, my end of the spectrum is typically "normal" drivers with stock vehicles but I have seen several turboed MP3's go through. I know for my original engine it lasted 11k miles of serious abuse with outputs of around 250-270whp and also a ACT yellow pressure plate. All bearings and thrust washer were in perfect condition with no unusual signs of wear whatsoever. I also agree that it has to be caused more by a very high clamp load pressure plate than a higher hp ouput.

I am curious to see pics. or a description of what conditions an FS failed or exhibited crankwalk conditions.

 

[SpicyMchaggis]

For the most part our crank's are quite balanced. However, I've heard from a couple owners pushing 250+ that they are starting to develop problems related to the crank and axles..Axles, are obvious, but I was suprised to hear people getting moderate to harsh crank walk. Wasn't there some MSP that was converted to an all out drag comp car that had a really nice balanced crank made for it?

 

[TurfBurn]

crank walk is from the bearing wearing down from not enough oiling or too high of loads on the crank thrust bearing. Unless that bearing wears down or the main webs break there is nowhere for the crank to go to... therefore until you cut that bearing down you can't get it to go anywhere... I have heard of a few people blaming this and that on crankwalk but I haven't seen any actual issues or actual photos showing a failure that would be crankwalk related. There is rumor of spun bearings... but that again is an oiling issue... So dunno! Part of why this discussion.. I want it all out in the open because the only way all of us can be faster and more powerful and do it safely is to learn from what everyone has to say!

Later.

Steve

 

[Wiggles422]

bump/subscribing

for my own info... isnt the thrust bearing the same as a throw out bearing?

 

[TurfBurn]

thrust washwer is internal on a main web and prevents the crank from moving side to side in the block... the throw out bearing is attached to the clutch release fork and presses against the fingers of the pressure plate on the clutch assembly and is what transfers the force of your foot to release the friction disc when the fingers are pressed down and the friction surface in the pressure plate releases.

 

[TurfBurn]

and btw... there are some 600 horse FS motors in 323's and P5's down in Puerto Rico, and i don't know if they even worry about crankwalk or not!

 

[BradC]

What about oiling problems due to a super-rich A/F mixture watering (with gas) down the oil?

Can't a mixute as rich as stock wash the cylinder walls off, thus causing poor lubrication?

 

[low_psi]

I agree with you Turf. Only some serious lateral pressure would enable the crank to move enough to start walking, and I don't see anyone doing this. I believe the blocks Mental Addiction have magnafluxed have shown cracks around the thrust bearing surface(not the actual bearing) but BlkZoomZoom has stated he's seen this aswell and is just a normal by product of the casting process... and that its not just around the thrust bearing that these cracks occur.

I think everyone building their motor just needs to maintain very tight tolerances within the rotating assembly to avoid any possible gremlins. I think the FSDE has larger issues to address when trying to produce 400+whp and a quality build should eleviate concerns.

 

[low_psi]

What about oiling problems due to a super-rich A/F mixture watering (with gas) down the oil?

Can't a mixute as rich as stock wash the cylinder walls off, thus causing poor lubrication?

Atleast one member here has spun a rod bearing due to gasoline in his oil. Even in stock form, I don't think the MSPs are prone to overly rich related failures though.

 

[TurfBurn]

I agree with you Turf. Only some serious lateral pressure would enable the crank to move enough to start walking, and I don't see anyone doing this. I believe the blocks Mental Addiction have magnafluxed have shown cracks around the thrust bearing surface(not the actual bearing) but BlkZoomZoom has stated he's seen this aswell and is just a normal by product of the casting process... and that its not just around the thrust bearing that these cracks occur.

I think everyone building their motor just needs to maintain very tight tolerances within the rotating assembly to avoid any possible gremlins. I think the FSDE has larger issues to address when trying to produce 400+whp and a quality build should eleviate concerns.

That's one of the major reasons to have the block align honed and have everything checked. I had my block magnafluxed and it came up clean before we did this build. So it's a matter of good and bad blocks too. Gasoline in the oil is catastrophic in all cases, not much you can do if that's the case! Always good to keep the AFR's reasonable... my car ran insanely rich for a while when I first got it.. (before this rebuild) so who knows what all went there... but it's another good reason to periodically check and smell your oil and look at it in various light just to verify that you don't have gasoline or coolant in it at all... but again... when it comes down to crankwalk... I just don't see a major issue yet... but again, that may prove out wrong.. we only have a smattering of 300+ whp cars... and maybe one or two ghost 400 cars... I think transmission gears will be a far bigger issue than block issues at this point.

 

[TurfBurn]

What about oiling problems due to a super-rich A/F mixture watering (with gas) down the oil?

Can't a mixute as rich as stock wash the cylinder walls off, thus causing poor lubrication?

It usually takes a lot of extended time at or below 10:1 to cause that kind of washing... the lower you go the faster it can happen.. but mid tens and up is usually "safe" I try not to run richer than 11:1 though..

 

[TurfBurn]

And for the record I'm running about 1.8 to 1.9 thousandths of crank clearance for the main bearings.... I want to say my thrust clearance is betwen 4 and 6 thousandths.

 

[Mental Addiction]

Since I am the one who has felt the FS has crankwalk issues,brought it to this board and the only one that address's it, I will only assume this was intented to bring up a debate.To make it real simple and not type huge paragraphs of mombo jombo the FS does have problems when pushed hard..As you build HP you will need a clutch to hold that.As HP increases RPM's do to and with a heavy pressure plate the crank will push and slightly deflect forward off the thrust bearing.This deflection takes it's toll on main #1.This is why you see spun #1 main bearings from guys making some power.
The Thrust bearing is roughly 40% of the total diameter of the crank.Our cranks are made from 4130 forged steel.This material is weaker than 4340 and is known to move easier than 4340.To make it easier from some try this.
Start walking and have someone put their leg out in front of you.Once you make contact you fall forward.Same thing applies with the crank when it makes contact with the thrust bearing. Now if you walk and go straight into a walk their is no forward movement.This is the same thing we do when we add a thrust washer into the main cap.The FS is not a 1gen DSM.The block is completely different.Our blocks are a thin wall casting that is low nickel.Then take into consideration that our crank rests onto of very thin main webbing.

 

[TurfBurn]

Beau, I certainly don't mean for it to be a debate or to be contrary to what you guys are doing. I purely want this out in the open and discussed outside of threads where it doesn't belong so that the information is there. Myself, and others have one set of beliefs, and I know there are contrary beliefs held by others too. People like you who have more engine building experience and high power motors are the people who's voices need to be heard so that we can all be more educated about it... If I seem argumentative at any point, I do apologize, I have a strong tendency to play "devil's advocate" as part of my engineering training... I'm sure you should understand that with your engineering background as well... I ask questions not because I think something is wrong, but because exploring a problem from all angles is the only way to explore a problem...

So thus a couple questions I have regarding your above statements...
Why don't all the people already running 30% over pressure plates (any of the ACT, Clutchmaster, or basic SPEC guys) and pushing up to stock 6800-7200 rpm redlines see any of the issues with the "tripping" of the crank as you put it or the deflection?

I also have a hard time picturing what you are trying to get at with the analogy of tripping versus running into someone... are you saying you won't cut through the thrust washer film all the way and less likely to wipe the washer than if you had a full face or are you indicating actual deflection to be the issue? I'm assuming you mean the film because I have a real hard time seeing that portion of the crank flexing or yielding in any way before the main web itself would tend to give way. If you mean crashing into the thrust washer through the film from the higher pressure levels of a full up pressure plate then I can understand where you are coming from there.

I realize our blocks are very different from DSM blocks, but I would expect to see a lot more webbing and block problems rather than the bearings themselves.

From my understanding at this point though... but I need to confirm it fully... there are several 500 and even one 640 whp FS motor's in some Protege's and 323's (the FS swapped in) that are not modified for crankwalk in any way and are seeing good life racing at this point...

 

[SpicyMchaggis]

Atleast one member here has spun a rod bearing due to gasoline in his oil. Even in stock form, I don't think the MSPs are prone to overly rich related failures though.

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[MrDiggler]

Anyone want to update this thread? Are there any pics yet to illustrate the problem? I just bought a spare race motor that has supposedly been modified to try and prevent crankwalk, but I don't fully understand what was done to it. I think I'm going to have to pull the pan on it before it goes in, just to see for myself.

 

[69RMSP]

im subbing for beau responce. I plan on doing a rod/piston combo but thats all. I have no plans to fortify the crank. I just heard of someone screwing their motor over at 260 whp due to crank walk. if this is the case i'll settle for 220whp. I'll see if I can get him to post here.

-adam

Anyone want to update this thread? Are there any pics yet to illustrate the problem? I just bought a spare race motor that has supposedly been modified to try and prevent crankwalk, but I don't fully understand what was done to it. I think I'm going to have to pull the pan on it before it goes in, just to see for myself.