Thrust bearing modification (crankwalk prevention)

[sschambers]

This thread correlates with my in-depth crankwalk explanation thread located here: http://www.dsmtuners.com/forums/articles-engine-fuel/342560-crankwalk-depth-explanation.html

I did this modification to my thrust bearing when re-building my engine and I'm a believer that this modification can eliminate pre-mature thrust bearing failure in our engines as long as surface finish, cleanliness, alignment and load are within tolerances. I would not be posting this article if I did not do it to my own engine. Since my engine has been fully broken in, it's seen redline more than a handful of times, it's seen 125 once, and a launch or two. Still, my end-play is right at .005" (right where it was when I assembled the motor). I check my end-play every oil change with a dial indicator fixed to the crank pulley.

First off, the main bearings I finally decided to go with were ACL Race Series bearings, and on top of that, had the machine shop send them out to a company that graphite coats engine bearings (around $200 for the bearings, coating and shipping). Very similar to Clevite Tri Armors.

I originally learned this trick from one of the machinist at the machine shop my engine was at. He told me that he had a buddy with a truck (can't remember what kind of truck) that had a beefed up clutch. Apparently he was chewing up thrust bearings left and right. He finally decided to do this modification to his thrust bearing and has yet to have one fail. There is also little (and I mean very little) information on the internet about this mod.

What this modification does is direct oil straight to the rear thrust surface of the bearing first. You will not lose any oil pressure, so don't worry about that.

Let me warn you before I begin that if you decide to do this, be VERY careful when modifying the bearing.


Install the upper thrust bearing in the block to determine which side is the rear side of the bearing (the side that takes the load).

Use a small flat file and increase the chamfer on the inside edge of the bearing parting line, directing it TOWARDS the rear thrust surface of the bearing. You'll have to lightly file "around the bend" to the rear thrust face. You'll get a better understanding when you're holding the bearing.

Flip to the rear thrust face of the bearing and file little by little on each side of the thrust face (see illustration).

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The red areas show where you will be filing. Just file a little bit (about 1mm) worth of material. (Sorry about the cheap illustration, I'm not an artist ).

To the upper right in the illustration is a view of the inside of the bearing (as if you were looking at the bearing from above if it were installed in the main cap).

I can't guarentee that this is a permanent fix for our pre-mature thrust bearing failures, but I had a very reputable machinist teach me about this along with the small amount of information I've seen about it on the internet. It makes sense, and so far it's working like a charm in my engine. This mod should also aid in bearing "wiping" being that there is a direct oil passge to the thrust surface. Note: this mod only needs to be done to the REAR thrust surface. The front thrust surface is not the side that receives the load.

Steve

 

[sschambers]

Here are a few pictures of my own thrust bearing that I did the modification to. I'm sorry that some are so blurry, they were taken with my camera phone. If you're wondering why my main bearings are black, it's from the graphite coating that was applied to them.

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Rear Thrust Face

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Closer shot of the mod

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Showing the chamfer from the parting line

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Another shot of the rear thrust face

 

[TOONAH]

Couple of questions for you. One. Are you saying that lack of lubrication to the crank thrust wall is the root cause of premature thrust bearing failure? Second. How long does the graphite coating last and how many thousandths do you allow for its thickness?
I examined a 4g63 with over 0.075" of crankshaft endplay. What I found was that the sintered coating from the oem bearings flaked off the thrust surfaces and got sucked into the bearing proper. This ground the bearing up. I believe and statistics prove this, that it is improper clutch operation that pounds the thrust surface of the bearing against the forward crank thrust wall. I have many photos of smashed bearings. Statistics also show that more 4g63's (7 bolt) with manual transmissions failed than with automatics. Though some automatics failed!
We also must define 'premature thrust bearing failure'. If you tear down any oem 4g63 7 bolt with over 150K miles you will see excessive crankshaft endplay.
I do like your idea of increasing lubrication to the thrust wall. It certainly must help. But the bad thrust bearings I have all are pounded on the forward thrust surface. The rear surfaces always look mint.
I can send photos if you are interested.
I like your idea about excessive ground currents in the crankshaft especially. Perhaps the thrust bearing acts like an "anode" (as on a marine outboard motor)?

 

[donniekak]

I have a 7-bolt i'm putting together now, i'm going to try this. I totally agree with toonah. I have been in a good amount of dsm engines. Almost every 7-bolt i have torn apart has had visual wear on the thrust surface. I have even seen a few of the 6-bolt engines with wear, not as much as the 7-bolts, but there. The 6-bolts just don't quit running because the timing sensor is mounted on the cam. In comparison i also work on a lot of 6g72 engines for the 3s platform. They use the split thrust bearing, and i have never seen a shot thrust bearing. Even when old and worn, with all the main and rod bearings showing copper, the thrust washers look new.

 

[lacroixdp]

I'm sorry but I chuckled a while back when I read your article the first time. Anytime someone makes up statistics like that just instantly makes me skeptical on the material they are posting.

Statistics

Dirt ........................................45.4%
Misassembly .......................... 12.8%
Misalignment .......................... 12.6%
Insufficient Lubrication..............11.4%
Overloading ............................8.1%
Corrosion ...............................3.7%
Improper Journal Finish ............3.2%
Other ......................................2.8%

Where did you get these little guys from? Did you perform a survey with DSM owners with crankwalked engines? Even if you did, these wouldn't be the results you'd receive - hardly anyone would have the foggiest what caused their engine to crankwalk. This looks like something you took from ACL's website citing general bearing failure, which is not what the 7bolts go through when they crankwalk.

 

[sschambers]

Just to quickly clear up the "rear and front" thrust surfaces...

The transmission side of the thrust bearing is considered the rear side. The pulley side of the motor is considered the front. So we're getting a pressure from the rear side (clutch) putting forward pressure on the crank, causing the rear thrust face of the bearing to fail. It's un-usual to see wear on the front side of a thrust bearing.

You are correct on how most of these engines fail when paired with a manual transmission. I believe this is because over 90% of people I have seen with these cars have improperly adjusted clutch pedals, which can hold the throw-out bearing against the pressure plate putting un-needed forward pressure on the crank, essentially rubbing (or wiping) against the rear side of the thrust bearing.
Another very good possibilty is because most of us usually use high performance clutch kits with these cars. The harder it is to push the clutch pedal in - the more forward pressure we're putting on the crank.

I went through with this mod because I have had 2 motors crankwalk on me in the past. (Which is partially the reason for this last re-build. My end-play was around .012 or so, nothing terrible though).

I figured since these motors are so damn fragile when it comes to the thrust bearing, why not?

I took every other pre-caution to prevent crankwalk on this engine. I 110% properly adjusted the clutch pedal (according to the manual), grounded the transmission to the chassis, used the MBCAD kit, new oil pump, and modded the thrust bearing.

As for the graphite coating, I'm glad you asked TOONAH. These thrust bearings measure anywhere from .078 - .080 (measuring the thrust face thicknesses) for each thrust face. When I got my main bearings back with the graphite, the thickness measured .081 ~ .082 (lowest reading I got was around .080 if I remeber right). As far as how long the coating lasts for, I'm not exactly sure. The same guy that taught me this modification also told me whenever they build race motors, they always send the main and rod bearings out to get graphite coated. So I would imagine that graphite coated bearings can without a doubt handle much more extreme conditions than regular bearings.

As far as the thrust washer design, you are right donniekak. Mitsu actually revised the 7-bolt block in the later 90's to be used with thrust washers. I guess Mitsu finally found out that there was a major flaw somewhere. The thrust washer design rarely fails.
I actually talked with Pat, the local Mitsu parts sales guy and he has told me horror stories about thrust washers falling out, into the oil pan; causing a much, much bigger problem.

As far as this mod goes, I'm not saying for sure that lack of lubrication is the cause of crankwalk. I'm saying that lack of lubrication on any bearing however is not a good thing. And being that these cranks like to walk (and sometimes run ), this mod definitely won't hurt.

After spending long hours doing homework, long hours at machine shops, and long hours knee deep in these motors, this modification seems like one of the best answers I've seen so far; especially paired with graphite coated bearings. Graphite bearings reduce friction, increase durability, better start-up protection, withstands extreme temperatures, and (best of all) conforms better to any imperfections (such as a less than perfect crank thrust surface).

I believe 100% that having scratches or any imperfections in between two surfaces in a tight space, with a load and having inadequate oil between the surfaces will cause wiping of the bearing. Wiping meaing exactly what the word says. The crank can 'wipe' the oil off of the thrust surface of the bearing, causing metal to metal contact, ultimately resulting in failure.

So here was my equation:
1. Make sure everything was perfect when I got everything back from the machine shop.
2. Go with graphite coated main bearings.
3. Allow better lubrication to the thrust surfaces that see the load (mod).
4. Make 100% sure the thrust bearing is properly aligned.
5. Check end-play after each oil change.

Now if (IF!) my engine's thrust bearing ever does pre-maturely fail, I must say that I might just end up throwing in the towel. This will prove that the root of the problem lies somewhere deeper.

I swear, all of these 4G63's were Monday engines......I mean, really; who wants to work on a Monday?

 

[sschambers]

I'm sorry but I chuckled a while back when I read your article the first time. Anytime someone makes up statistics like that just instantly makes me skeptical on the material they are posting.


Where did you get these little guys from? Did you perform a survey with DSM owners with crankwalked engines? Even if you did, these wouldn't be the results you'd receive - hardly anyone would have the foggiest what caused their engine to crankwalk. This looks like something you took from ACL's website citing general bearing failure, which is not what the 7bolts go through when they crankwalk.

I stated in that post that a lot of the information in it was gathered, not all of it was my own.
I never said that those statistics were 100% pointed at the 4G63's, those are general statistics.

And who are you to say that 7 bolts don't go through any of that when they crankwalk? It's not hard to overlook a simple step in assembling any motor, which would fall into the misassembly category. I have to laugh every time I come across a thread on here with someone asking "which way do these bearings go in?"

Maybe someone had a less than perfect thrust bearing put it (maybe some dirt they didn't see). Or how about the people that keep ripping through main bearings and can't figure out why they're blowing thrusts every other day...maybe a bad crank thrust surface?

I'm not trying to tell anyone that they're wrong or make people believe something they don't want to, I'm just throwing more detailed information into the DSM world about this particular problem because I've been through it and I know it's not a cheap fix. I made that post about the in-depth explanation to crankwalk just to state facts, statistics, opinions and theorys...and most of all, to be helpful.

Again, I'm not saying that everything that I say is directly related to 4G63's. All of us know any motor can crankwalk. I'm just on here because I own a 2nd gen, I have a 7 bolt, I've had crankwalk twice and hopefully someday my information, your information and everyone else's can help someone else.

 

[lacroixdp]

It is nice to post this information to be helpful - for that I'm sure we're all appreciative. However, I see a flaw in your approach. The fact of the matter is that these problems started cropping up after Mitsubishi redesigned the block. That leads me to believe that it's unlikely to be dirt or anything on the user's end, especially in stock examples. If a block was rebuilt by a person, then your list could absolutely pertain to them. Unfortunately, it's harder to categorize factory built engines with the same statistical list... at that point, IMHO, it becomes a design flaw or an assembly flaw. You see 6bolts with heavy clutches on them - why does the same on 7bolts sometimes lead to crankwalk? It is all but certain that Mitsubishi 'did it wrong' with the block revisions. I have a feeling that if it was an easy fix, Mitsubishi would have simply issued a TSB, or revised bearings, or something of that nature. Instead, they revised the block design again, this time with floating bearings. I've seen a lot of work done to fix crankwalk from machine shops I used to work with. Unfortunately, none of them have had a sure-fire fix with a 100% cure rate - they would inevitably have a customer come back with excessive thrust bearing play. I have to wonder if we'll ever know for certainty a complete cure for crankwalk.

 

[sschambers]

However, I see a flaw in your approach. The fact of the matter is that these problems started cropping up after Mitsubishi redesigned the block. That leads me to believe that it's unlikely to be dirt or anything on the user's end, especially in stock examples.

I understand how you can see my approach being a little bit off in my other thread, I should have probably initially stated from the start that I was approaching every known likely cause, from the ground up with any motor.

I agree with you 100% that with our 4g63's it is very unlikely to be the builder's fault for bearing failire (although I have seen quite a few people not knowing what they're doing, trying to re-build an engine). You, me and everyone else knows that it is a design flaw somewhere in these blocks. But there have been plenty of times I've spent hours thinking about "what if the cause of the problem is so simple and easily over-looked?" Maybe an external problem (which would fall into the clutch category) or something else external...

Then there are other times I think to myself that the problem is so severe and so deep in these motors, they'll never be 100% cureable.

Although, like I said with my engine - so far, so good. Lately I haven't been being gentle with my engine because if it's going to happen, it's going to happen now or later. And to this very second, I'm still at .005".

What leads me to believe that this modification *may* fix the problem is that I like to call it a permanent bandaid fix. (Bandaid fix meaning someone came up with a modification to assist in problems - this does not include zip-tieing the front bumper cover to the car). Such as people adding a washer under the t/o fork pivot ball because of wear to get it back in spec. It works with no consequences (that I've heared of). The only way I see my modded thrust bearing eliminating crankwalk is if these motors had in-adequte thrust lubrication from the start. Either way, it's worth a shot...And I'm all about making sure there is a good oil film between those surfaces, especially on a re-built engine. And honestly if I were to rebuild any other engine that wasn't a 4G63, I'd do this same mod to the thrust bearing just for added insurance.

 

[lacroixdp]

I gotcha now. I have no doubts that the clutch plays at least a small part in this problem - the evidence pointing to that is strong since automatics have a very low failure rate. However, that still doesn't answer why 6bolts with heavy clutches don't have thrust bearing failure. If I sounded like an ass initially in the first post, I apologize. Years of hearing my friends gripe over their 2G's engines got old when I gave them a perfect suggestion for a fix - switch to a 6bolt, and they refused to take it. As time went on though, they either swapped or moved onto different cars. Because of that, the subject itself threatens my sanity at times I absolutely won't deny that it would be great to have a permanent fix for the 7bolts though - I hope your modification yields fruit!

 

[sschambers]

I gotcha now. I have no doubts that the clutch plays at least a small part in this problem - the evidence pointing to that is strong since automatics have a very low failure rate. However, that still doesn't answer why 6bolts with heavy clutches don't have thrust bearing failure. If I sounded like an ass initially in the first post, I apologize. Years of hearing my friends gripe over their 2G's engines got old when I gave them a perfect suggestion for a fix - switch to a 6bolt, and they refused to take it. As time went on though, they either swapped or moved onto different cars. Because of that, the subject itself threatens my sanity at times I absolutely won't deny that it would be great to have a permanent fix for the 7bolts though - I hope your modification yields fruit!

It's cool, we're all here to get and give information, and I also hope that this mod does shine some light on to the dreaded 4G63 crankwalk issue.

Clutches as well as torque converters do play a role without a doubt because both of them are an external device exerting forward pressure on the crankshaft. Like I mentioned in my other thread, one of the most common problems with automatics is the ballooning of the torque converter putting constant pressure on the crank.

Another thing I had mentioned in that post was the difference in main caps between the 6 bolt and 7 bolt. When assembling my engine, I honestly considered cutting the center (thrust) cap off from the cradle so it would be seperate. I know that the bed plate (or cradle) design is suppose to be a "better" design and aids in cap walk and keeps everything tied together. But the 6 bolt didn't have a bed plate design. It was just a thought that I had. Not to mention, most older motors had seperate main caps as well. I just found it somewhat odd that no one else has really taken this into consideration.

Also, as far as Mitsu's revised 7 bolt block (the one that uses thrust washers and not the flange style) - if all that was changed was going from a flange style to a thrust washer style, then maybe it does has something to do with oiling to the rear thrust face? Maybe the thrust washer design allows for better oil flow in these blocks? I'm not too sure because I've never got too in-depth with their newer designed 7 bolt. And unfortunately we can't just swap thrust washers into our flange style blocks... But if that were the case then I can only hope I hit the nail on the head with this modded thrust bearing. I guess only time will tell...

 

[TOONAH]

I do some times get things "bass ackwards"!
I can tell you that "aligning" the 7 bolt mains cap girdle is a complete mystery to me. I tried tapping it fowards and backwards before tightening the arp bolts. It did not move a single thousandths. Once its in there, its in there. I did pay a machinist a lot of money to 'align hone' the mains with torque plate installed. Like everyone here I really do not know what is the root cause of premature thrust bearings is.
I do like your improved oiling technique and wish I had done it to my 7 bolt. By the way I used the ACL Race bearings because they do not have the hard final sintered layer.
Time will tell. If my crank walks, it'll be walking to the junkyard and I'll never touch another 7 bolt again!!

 

[sschambers]

Lining up the 7 bolt caps is a total pain in the ass because they're all tied together. Like you, I also had my block align honed with a torque plate on the block. What I ended up doing was after assembling the bottom end, I only torqued the mains to about 15ft lbs or so and finger tightened the oil pan on. I assembled the rest of the motor, dropped it into the car and after getting everything hooked up and good to go I then went to line the thrust bearing up.
Took the oil pan off, un-torqued the mains and just made them finger tight.
I tapped the main girdle as far as it would go to the rear of the motor, and had my buddy push the clutch in.
I then continued on with the torque sequence.
I figured this would be a more reliable way of lining up the thrust bearing instead of just tapping the mains to the rear, then prying the crank to the front. Constant pressure from the clutch being held down just seems like a better idea to me.

 

[Artago]

Hi all. I've had my motor rebuilt twice and it's walked twice.

Right now it's at 0.009" so time is ticking. What I would like to know is.... has this mod had any success? Basically, I want an update.

I've been reading everything I can about this issue including magnus' oil passage/squirter/lack of flow theory and it seems like that this mod could aid in getting more oil to the thrust bearing.

I'm going to be replacing my bearings soon and would like to know how this mod has held up in your car? Maybe I'll try it myself.

Thanks,

Tom

 

[lacroixdp]

Hi all. I've had my motor rebuilt twice and it's walked twice.

Right now it's at 0.009" so time is ticking. What I would like to know is.... has this mod had any success? Basically, I want an update.

I've been reading everything I can about this issue including magnus' oil passage/squirter/lack of flow theory and it seems like that this mod could aid in getting more oil to the thrust bearing.

I'm going to be replacing my bearings soon and would like to know how this mod has held up in your car? Maybe I'll try it myself.

Thanks,

Tom

Yup - .009 is the service limit. I'd be interested to see if he has any news on this mod. I can tell you however, if you choose to stay 7bolt for some strange reason, I'd suggest replacing the block with a different one. Several people have had better luck after switching blocks, which coincides along the 'casting' theory.

Have you considered switching to a 6bolt?

 

[Artago]

if you choose to stay 7bolt for some strange reason........

Have you considered switching to a 6bolt?

I have considered a 6-bolt however I've spent a lot of $ on the 7-bolt I have so I'm reluctant to throw it all away.

It's very frustrating having to make a decision to fight a problem or give up, cut your loses and move on.

I just wish I hadn't spent so much on the 7-bolt (pistons, rods, water pump, oil pump, flywheel, clutch, the list goes on) and had done a 6-bolt swap in the beginning.

Tom

 

[lacroixdp]

You could sell the parts to cover the costs of swapping to a 6bolt. Otherwise, I completely understand your pain. I had many, many friends back in the day that went through the exact same crap.

 

[sschambers]

Hey sorry I haven't been on here in a while. The car's thrust is still perfectly in spec, right around .005. I ended up selling the car, however. I couldn't pass up the price I was offered. But I have driven it and seen it since then. The motor has around 7,000 miles on it already (possibly more now) and the last time I checked the end-play, the dial indicator read a consistant .005 - .0055; never spiking at or around .006. The entire motor still sounds and runs like brand new and is still being very well taken care of by the guy I sold it to (washes and waxes it nearly every other day ). I am confident that this motor will last years to come with as much research, time, money and hard work I put into making a 100% reliable and solid build out of a 7-bolt. If you have any other questions about CW please feel free to PM me or just post them on this thread.

Thanks,

Steve

 

[sschambers]

Hi all. I've had my motor rebuilt twice and it's walked twice.

Right now it's at 0.009" so time is ticking. What I would like to know is.... has this mod had any success? Basically, I want an update.

I've been reading everything I can about this issue including magnus' oil passage/squirter/lack of flow theory and it seems like that this mod could aid in getting more oil to the thrust bearing.

I'm going to be replacing my bearings soon and would like to know how this mod has held up in your car? Maybe I'll try it myself.

Thanks,

Tom

.009 is right there at service limit. I actually have a friend who owns a 97 GSX at the moment with 130,xxx miles and his end clearance is .013 and he has no problems while driving, and his play hasn't opened up at all since the last time I checked it for him (4 months ago or so). As far as just replacing your bearings - make 100% sure that your crank's thrust surface isn't chewed up when putting new bearings in, or you're just wasting money on a temporary fix. If your crank's thrust surface is fine, then I would highly recommend getting the bearings that I went with and doing this mod. It's very simple to do and doesn't take long. I am by no means saying that this is a 100% cure all for CW, but like I just mentioned in my last post a few minutes ago, it's holding up EXTREMELY well.
There is obviously a design flaw in these motors and I believe that giving the thrust bearing a swift kick in the ass (the mod) definately, without a doubt, aids in keeping a nice, constant film of oil on the thrust areas.

Steve

 

[DSM Jeff]

I just came across this thread as I'm working on a 97 7bolt for a friend. From my manual the standard is .05-.18mm with the max of .25mm. He appears to be around .17. Looking to buy some more time out of this engine, the manual says to replace the thrust bearing. So would I be able to just change these bearings, recheck clearances and go? Can main bolts be reused?

 

[Artago]

Can main bolts be reused?

I would also like to know this.

 

[sschambers]

11 D-61 (in my FSM)

(1) Since the main bearing bolts are torqued using a new procedure, they should be examined before reuse. If the threads are necked down, replace the bolts.

(2) Necking can be checked by holding a scale or straight edge against the threads. If all of the threads do not contact the scale, the bolts should be replaced.

So...they CAN be re-used but with something like that I would always use new bolts (or convert to studs like I did; however an align-hone must be done)...So if you're not looking to get that far in-depth, buy new main bolts or check the ones that you have and make sure they're ok.

.17mm is around .0066" so that's not absolutely terrible; could be worse.

Look at it this way (in standard units)

Standard value: .0020 - .0071 with a service limit of .0098 (which is exactly .25mm).


Also, if you guys are replacing the thrust bearings while the engine is still in the car, PLEASE read through this thread and make 100% sure to align the thrust bearing properly or you're asking for more trouble. Oh, and check the cranks thrust surface.

 

[DSM Jeff]

Thanks for the info. I actually came across a local selling some arp main studs for half the price of new, and they are new. So we may replace the bearings and check clearances. I was talking to a kid at work and he started telling me about this mod to the thrust bearing before I even said anything. He's into sbc's and said a few builders he know does this. So I'll go ahead and try it. While this engine is not at the max limit, its near the max standard value. The owner would definatly like to keep having fun and have a longer life while saving for a swap with forged internals.

 

[Artago]

To anyone who tries this:

Can you please document the process so that others may benefit from it. Please take pictures and notes. Personally, I'd like to see bearing swap done while the crank is in the car.

Thanks all,

Tom

 

[DSM Jeff]

Bearing swap in the car is called the "dirty" I'll actually be doing this but the engine is out. Head and manifolds are already on. The car was going back together with the play before I kinda stumbled upon this thread. Found some new headstuds local for very cheap. Going to be picking up some bearings and will try this mod. Will be taking off the rms cover and the pump is out since balance shafts were pulled. Hopefully I can get the crank up, bearings out, clean the block and install the new bearings. Bolt the gurdle down with some plasti gauge and check the tollerances. Then get the arp's in. Car has 140k on it I do believe with some track time. Not too bad. I hope everything works out and this kid can get a another year or 2 out of the car while still having fun with it. May not be the best way to do this but with limited time/budget, its the best bet.