Guest bastaad525 Posted May 23, 2004 Share Posted May 23, 2004 MYSTERY SOLVED! for anyone who's been following along with this topic already, you can skip to the bottom... Okay... so... I keep trying to find ways to get it to move. For anyone who hasn't heard, I've apparently got a bad thrust bearing on the crank... when I was having the clutch changed, and the clutch/flywheel/tranny were out, the mechanic was able to move the crank a significant amount... I eyeballed it and it looked like 1mm or so. I know The bearings gotta go... been planning on trying to swap the bearings sometime soon here, but it's been delayed for a couple weeks. Anyways... I'm curious. After getting the new clutch in, I hit a snag... where I was going to HAVE to drive the car pretty much every day, regardless of the fact that I knew the bearing was bad (luckily that has been cut down a bit but I still gotta drive it sometimes). I wanted to measure the fore/aft play of the crank and keep an eye on it to see if it was getting measurably worse after driving it (was gonna measure it like once a week/every 250 miles or so). I went to try to pry the crank forward or push it back with a crowbar, but I could not get it to budge. This confused me... it had seemed pretty easy to move at the shop. So then I had my wife rev the engine and pushing the clutch in and out, in and out, all the while watching the crank pully... it never moved other than spinning of course. I even had her slip the clutch out in gear to put load on the motor (used wheel blocks of course) and still nothing. I thought the fore/aft movement of the crank occured when the clutch was operated? The movement when it was at the shop was pretty obvious... I didn't have to squint to see it or anything... yet getting as close a look as I could at it when my wife was revving and operating the clutch... no sign of fore/aft motion at all. A friend of mine even verified that he saw no sign of fore/aft movement either. I know this doesn't mean that the bearing has magically repaired itself or anything (though it wouldn't be the first time the car has fixed itself!!)... I'm still driving the car as little as I possibly can, and am planning on replacing the bearings in two weeks either way (I HOPE!!! life keep throwing me curve balls and keeping it from happening).... I'm just trying to understand why it might be doing what it's doing? I know there are plenty of guys on here who have had enough L6's apart... can someone give me an explanation for this? Quote Link to comment Share on other sites More sharing options...
blueovalz Posted May 23, 2004 Share Posted May 23, 2004 This is not direct experience here, but just thinking out loud. I would think the forces pushing the crank forward are the clutch pedal action. This pushes the pressure-plate forward to disengage the clutch, thus pushing the flywheel forward, and pushing the crank forward as well. With the motor running, oil pressure should fill this void you are writing about, and not allow the movement you are looking for. If it does, you've got other problems as well. I'd use the clutch to push it forward, and a prybar (behind the sway bar or whatever else is available, with a block of wood on the damper to push on) to push it back to the rear. Do this several times to squeeze out any oil that is between the bearing and thrust surface. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 23, 2004 Share Posted May 23, 2004 I did try it with the motor off as well, having my wife push the clutch in and out, and there was no movement of the crank pulley at all. To me this kind of makes sense as well, seeing as the crank itself is pretty heavy... now that I'm back to a near stock pressure plate... I dont think enough force gets exerted on it that would move the heavy crankshaft as well.. but then again there are the rules of leverage involved there so I really dont know how much force is getting transmitted onto the flywheel when the clutch pedal is pushed. Very interesting and good thought about the oil pressure keeping it from moving.... I never would have thought of that. One thing I'm curious about... seeing as I still do need to drive the car a bit. You say oil is filling the gap between the thrust bearing and the crank... this is good right? I mean... if it's not being allowed to move with the engine running, additional wear should be very minimal right? I am running 10w-30 Mobil 1 oil... hoping this will be my saviour in keeping the engine from getting any worse. At the same time this is kind of confusing.... if you're right about oil pressure filling the gap between crank and thrust bearing, shouldnt the pressure have been there all along and kept the bearing from wearing out at all? I want to clarify, you're saying if the crank WAS moving with the engine running and oil pressure present, that would mean I'd have other problems as well? What would the 'other problems' be? BTW, Blueovalz - your car is friggin awesome dude Quote Link to comment Share on other sites More sharing options...
blueovalz Posted May 24, 2004 Share Posted May 24, 2004 The oil, at pressure, simply developes a film of oil between the two metal surfaces. 1mm is a lot of gap to fill, but none-the-less, the oil film will in effect reduce the movement. If oil pressure is still good, meaning normal or better, then the bearing gap(s) is most likely good, and not excessive. Again, I'm only thinking this out and have no experience on this particular issue. BTW, pressures on the throw-out bearings can range from several hundred pounds to over a 1000 pounds and more. The 3" movement at the pedal is leveraged down to about .500" at the throw-out bearing (if memory serves me correctly) and only about .050 at the pressure plate itself. I'm guessing you'd only use the throw-out bearing ratio in trying to determine the force on the end of the crank, but it still comes out in the hundreds of pounds. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 24, 2004 Share Posted May 24, 2004 oil pressure is about 10-15psi at idle, about 40-50psi while driving. When cold the pressures are higher... 60-70psi at idle. I've got a strong feeling that the wear surfaces of the bearings are for the most part a-okay so wouldn't expect to see lowered oil pressure.... I'm betting my money that it's only the thrust surface of the center bearing that is worn like this. So even at minimum I'm putting a few hundred pounds of pressure on the pressure plate... should definately be enough to move the crank... but yeah the oil film being present makes sense for why it probably isn't moving. I spoke with technicalninja on the phone today who also pitched in with a lot of good info to help explain some possible reasons for why it's doing (and not doing) what it's doing. Maybe I'm being a bit optimistic but so far what I'm hearing is telling me I dont have to worry as much as I thought about HAVING to drive the car like this for a little while, while waiting for my opportunity to fix it. Doesn't sound like it should be getting worse much faster as long as I keep my foot offa that clutch.... very relieving to me as I was expecting stuff to break any day now He also gave me a couple other things to check out to get a better idea of what's going on... hopefully I can get around to that tonite at work if there's any quiet time. I'll check this stuff out and see if I can't get the crank to move fore/aft a bit by hand again. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 24, 2004 Share Posted May 24, 2004 I'm thinking out loud... Why are we assumming that crank moves forward and back? Could the crank just be pushed forward and stay there? I'll be the mechanic used a pry bar to move it back and then pushed it forward again? Maybe in the car the crank is just always pushed to the forward limit (from pressure palte usage) and there's no force pushing it back? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 24, 2004 Share Posted May 24, 2004 The pressure plate would just be clamping not pushing forward until the clutch gets depressed. Then it would push forward. I've been watching this, but I can't figure it out either so I haven't said anything. But here's my SWAG: the pilot and clutch disk in the back and the belts in front are going to put a little friction on the crank and try to keep it from moving. Jon Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 24, 2004 Share Posted May 24, 2004 Actually on technicalninjas advice I tried a little test last night, removed the spark plugs and loosened the only one belt that runs on my engine, and got the crank to where I could turn it by hand with some effort... I still could not get it to move back and forth at all though. I figured it would most likely already be moved all the way forward, as well... but then shouldn't I still be able to force it back? Other good news at least, technical ninja actually had a bearing set on hand, and measured the thickness of the thrust surfaces on a new center main... each lip was about 1.9mm thick... so even if my crank is moving back and forth 1mm, that at least means the bearing still has some wear area left, thankfully... I was VERY worried that the bearing may have been gone or very close to it and that the crank would be contacting the block and causing problems. So the crank should be okay once I get the new bearings on it. He also reminded me that there is quite a bit of free play at the top of the rods where they connect to the piston, enough that even if the crank can move back and forth 1-2mm, it shouldn't be putting side load on the pistons and scuffing cylinder walls... more good news for me Other things I've noted that suggest the crank seems to NOT be moving while running... timing seems to be rock solid, the engine still runs silky smooth, not shaky at all - no excess vibration, and my clutch pedal and action does not seem to vary at all... something that really gives away crank walk, or so I hear, is when the clutch pedal action starts varying... clutch doesn't want to disengage or pedal stuck to the floor in severe cases, but I have noticed nothing unusual. I'll still be glad to finally replace the bearings and be able to say the engine is fully rebuilt... man I picked the worst way to do it, going in patches like this (first the head, then rings and rod bearings, then front/rear main seals and oil pan gasket, now main bearings...) but I will get it on the road and STAYING that way! Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 25, 2004 Share Posted May 25, 2004 I'm thinking out loud... Why are we assumming that crank moves forward and back? Could the crank just be pushed forward and stay there? I'll be the mechanic used a pry bar to move it back and then pushed it forward again? Maybe in the car the crank is just always pushed to the forward limit (from pressure palte usage) and there's no force pushing it back? this actually makes sense. This would explain why even with my wife operating the clutch, with the motor running or not, I see no movement at all... but still odd that I can't seem to push it back either, again, motor running or not... well when it's running the oil pressure thing makes sense, but not running, I should be able to move the darn thing one way or the other. So if it's always pushed forward, would that mean the bearing would just constantly be wearing on the rear thrust surface? wouldn't the oil coming out from the main/journal bearing surface just all get forced out thru the front of the bearing, leaving the rear dry? Kind of a scary thought.... another question though... if oil pressure creates a film that is constantly present between the crank and thrust bearing, then there shouldn't be any additional wear at all on the bearing accept right after startup, right?? Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 26, 2004 Share Posted May 26, 2004 My threads always seem to have a lifespan of only two days hmmmmmmmmmmmmmm well a little update. I had my friend lift up the front of my car with his tow truck last night, got under there and started levering on the crank pulley with a large bar... didn't notice any movement again but then had him push in the cluth pedal and THERE it was!!! Definately some noticeable movement, hard to tell how much though, but I would say too much. I noted the gap between the CAS sensor, and the toothed gear that mounts behind the crank pulley. Haynes manual calls for a gap of 1-1.5mm here. Just eyeballing it, with the crank pushed fully forward (enlargening the gap) I'd say there was about 2mm there, maybe even less (will measure this in about an hour when my wife gets home and shows me where there's a ruler in this house!). So ASSUMING that the sensor was adjusted right to begin with (heh yeah right.... ) That means the crank is only moving forward maybe .5-1mm. What I REALLY wanted to do was measure this gap with both the crank pushed all the way forward and all the way back to see EXACTLY how much it's moving, but again... friend was in a rush so.... Anyways... so no more mystery, it's definately still moving, so, no getting out of replacing the bearing for me I guess. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 26, 2004 Share Posted May 26, 2004 seems you figured it out on your own... The key to endplay measurements is indicating play with the crank one way, then forcing it the other. 1mm of movement is around .040", and your endplay should be a few thousandths, not .040! I once had a VW Type 1 engine that came in to my place with an owner complaining of a bad oil leak and noise from the back of the car. The pulley was hitting the tin! The play was around .125"!!! This is for a vehicle set up with "oilclearance endplay" of .008 TOPS! In most cases the endplay of the crank on the thrust bearing will be around 0.006" to 0.008" for the simple reason that if you go any closer, the oil will not have sufficient space to form a proper hydrodynamic wedge and float the crank on the oil. This is what the thrust bearing is supposed to do, and how it functions. You shold see maybe .006" to .010". If clearance is too large, you loose oil pressure from an "uncontrolled leak" around the periphery of the bearing. To tight, and it "wears itself in" and that's not good... Like you surmised, starting the engine cold, with your foot on the pedal of an overweight high-performance pressure plate is a sure way to kill your thrust bearing. (Take a look at bearings designed after the federal laws mandated a "clutch interlock device" for manual vehicles! WAAAY bigger bearing area, on bearings most likely designed to fit within the old machining of the block to minimize engine-plant tooling costs.) So you can guess I have removed the clutch, seatbelt, and neutral "safety interlocks" in all my vehicles. I'm such a dare-devil... My god! Call the government, I am thinking for myself and am defying their attempts to think for me! Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 28, 2004 Share Posted May 28, 2004 Again, my oil pressure seems normal, at least from what I've been told here. Fully warmed up, I get about 10-15psi at idle, and 40-50psi when driving. So there's no indication there of any problem. Anyways... after much searching the house I found the perfect thing to use as a 'pry bar' to force the crankshaft back. So I just went down and finally was able to end the 'mystery' and get an actual measurement of exactly how much play there is... First off... I gotta say, I got a good eye The first time I saw the play in the crank was from a good 6 feet away at the tranny shop when the guy was showing it to me... and I guessed 1mm right there. Second off... no more wishful thinking... it's definately got too much play, the bearing has got to go, and I really got to try to find a way to stop needing to drive the car. I moved the crank back and forth a few times to squeez any oil out, and then pushed back as far as it would go, and used a feeler gauge to measure the gap between the CAS wheel on the pulley, and the CAS itself, and got .483 mm. Then I pushed the crank all the way forward via the clutch, and got 1.778 mm. Grand total of 1.295 mm of play there . One other odd thing I noticed, is that it definately is 'happier' pushed forward. I pushed the crank back, and then had my wife start the car, and slowly (within about 5 seconds) the crank worked its way back forward by itself. I wasn't expecting this, as I park on an incline (nose high) and expected gravity to sorta 'pull' the crank back instead of forward. So I'm HOPING this is just oil pressure forcing it forward. Technicalninja suggests that a possible cause of the worn thrust bearing might be the wrong sized throwout bearing carrier or collar... that this can exert constant pressure on the pressure plate and hence the thrust bearing. So I gotta wonder if THAT is what moved the crank forward and is holding it forward whenever the motor is running. However, I did notice that on many occasions, after I turn the motor off, if I have my wife push the clutch the crank will still move a little bit forward, so I'm gonna assume and hope that this means that it's not being forced ALL the way forward, to where it's rubbing on the bearing, but rather is just being forced forward by oil and then being 'suspended' in the middle by oil on both sides. Again, the is NO noticeable movement when the clutch is operated with the motor running, for whatever that's worth. Would there be any good indication (audible maybe?) if the crank were rubbing up against the bearing full time? Well.. at least now I know w/o any doubt that it's gotta be changed, and at least if I DO have to keep driving the car, and dont get a chance to fix it soon, I now have a measurement, and can re measure it every so often and see exactly how fast it's getting worse. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 28, 2004 Share Posted May 28, 2004 the bad news is that if you rock the crank enough, it can cause pin locks to move out, and other odd wear patterns evolve on the pistons due to the rods not operating where they are "supposed" to be. Normally you only move about .004" (0.1mm) and the rods can handle that. But you move beyond rod side clearance, and the sides of the rods start running on the fillet, and stresses them at an andle, instead of perpinducular to the crank journal (anyone wonder where "tapered" journals are formed?) Make sure when you go in, you check the sides of the rods, etc etc etc... Good luck on the repair. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 28, 2004 Share Posted May 28, 2004 Yeah but I thought there was a LOT of free play at the small end of the rod where they attach to the piston? I know I've seen rods with a lot of side-to-side clearance on the piston pin... man... I know it's bad... and I do worry a lot about 'collateral damage' from this... I dunno what else to do... just not drive the car as much as possible, get it fixed as soon as possible... keep my eyes open for another block Let alone trying to figure out WHY this is happening in the first place... I've never really seen Z engines with this problem before and was surprised to hear it's as 'common' as it is with the L6, for whatever reasons. Well I can only hope collateral damage is little or none. Compression is still good on all cylinders. No other real signs of anything funny going on. And it really would seem the crank does NOT move at all while the motors running or small enough amount as to not be visible, even when operating the clutch in and out and when it's under load and at high rpm, no fore aft movement at all... the crank just seems to settle in one spot... Like I observed today, even if I push it all the way back, as soon as the motor starts it moves itself back forward. And no signs of metal in the oil, pan or filter tells me the wear must be keeping to a minimum at least since I've owned the motor. If it's all working the way Blueovalz describes it really is going to be wearing very slowly as long as oil is buffering everything, and oil pressure is definately good. Just gotta keep telling myself all this... hoping and praying this car is DONE screwing with me like this, and after this fix everything will be alright.... Well, if all goes as planned, I will be able to keep the car parked all week, and if I can get all the parts I need together I will do the bearing swap next friday. Quote Link to comment Share on other sites More sharing options...
technicalninja Posted May 28, 2004 Share Posted May 28, 2004 Factory Nissan pistons do not have pin locks and they have a large amount of pin side clearance at small end (.250-.375). When I get home this evening I will measure this clearance on a set of L28ETs that I have in a box and post results. Floating pins with pin locks are a feature of forged aftermarket pistons. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 28, 2004 Share Posted May 28, 2004 I remember observing that when a friend and I pulled the pistons last year to replace the rings. GOD I wish I had known I could have replaced the main bearings then.... I always thought the engine had to come out and crank be removed..... otherwise I could have saved myself a lot of hassle. I do remember the large amount of side-to-side play on the small end of the rods though, so I'm not too worried about abnormal piston wear, however I am worried about the other stuff you mentioned technicalninja... increased wear on just about everything else like front and rear oil seals, dizzy/oil pump shaft, harmonic balancer... *grasps head and starts spinning* Wish I could mount a camera pointing right at the crank pulley though and drive it around normally and see when or if it moves..... Quote Link to comment Share on other sites More sharing options...
DAW Posted May 30, 2004 Share Posted May 30, 2004 All things considered, with the oil film/spacer effect at the thrust bearing and role of oil pressure as key factors here, I'd make a change from the Mobil 1 10W-30 you're using, to 20W- 50. DAW Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 31, 2004 Share Posted May 31, 2004 Good idea... I was thinking about 'upgrading' to a thicker oil as well, but just didn't see the point as I was always 'one week away from fixing it'... especially with the cost of a synthetic oil change. I'll be ordering the parts I need tommorow (bearings, gaskets) and hope... really really HOPE this friday will be the day. Would thicker oil make a difference in this situation, putting a better 'buffer' between the thrust bearing and crank? One kinda odd thing, I do remember, not that long ago I did try switching to the thickest mobil 1 I could find, in an effort to slow down some leaks that I had, but it didn't seem to effect oil pressure, at least not by the Z's guage. And on top of that, it made my leak worse.... I do think the 10-30 is just too thin for my car in general... I dont think the clearances on this motor were tight enough even new to get away with it really, so will probably switch to at least 10-40 when I swap out the bearings. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 31, 2004 Share Posted May 31, 2004 I know there are people at this site that have extensive knowledge on oil viscocity effects, and my input here is purely anecdotal based on my own experiences only. My impression is that thicker oil increases pressure and takes up space but that higher weight synthetic oils aren't necessarily thicker yet they meet the load ratings of the equivilant non-synthetic weight. I've begun using semi-synthetic Castrol 20W-50 in most of my higher mileage or higher clearances engines and if there is a specific high clearances issue I would run 30 weight in the summer in that engine. DAW Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted June 1, 2004 Share Posted June 1, 2004 Ugh... wouldn't the Castrol Syntec not hold up well going thru the turbo? This is the main reason I'm running full synthetic... To keep oil from being cooked and destroyed when it passes thru the turbo. Well I can say the 15-50 Mobil 1 definately comes out of the bottle thicker than the 10-30. I dont know for sure that there is a straight 30 weight in the mobil 1, and really I dont think I'd want to switch to Syntec. But then... all my oil knowledge is based 90% on manufacturer hype, and every other person I talk to tells me something different (synthetic is EVIL, synthetic will triple the life of your engine, synthetic makes NO difference over non synthetic, sythetics are NECESSARY in a turbo engine, etc.). Wish someone else would comment on this and some of the other things brought up in this thread, I keep hearing some very good ideas mentioned but they dont get completely followed thru on. Heheh probably because you guys know... if I thought I could run thicker oil and not worry about a 'measely' 1.3mm of crankshaft play I'd do it! but I'm sure that just aint gonna happen. Man I miss driving my car.... Well... still on schedule to swap bearings this friday. NOT looking forward to it at all... so sick of working on this damn thing and not really ever getting to just DRIVE it. I envy you guys that just pull your engines or other major operations at the drop of the hat... like it's just like mowing the lawn or something.... "well it's friday, time to pull the engine again..." Quote Link to comment Share on other sites More sharing options...
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