The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

  • Update Your Password Today!

    We have implemented tools to identify member accounts using insecure passwords and will be locking those accounts until their passwords are updated. Don't get locked out of your account - update your password today, and ensure your account has a valid email address on file. Read more here...
Please Support Morrison Fabrications
Please Support STM Tuned

1995 Eclipse GSX - 2.3 Stroker 400WHP

95REGF150

10+ Year Contributor
433
221
Mar 7, 2012
Elk Grove, California
Thanks for the very good pic of the "one piece" thrust bearing that you found in your 98 GST engine (post #8).

I'm curious, when you rebuilt the engine from the "early 1995" GSX, what kind of thrust bearing did you put in there? You say in post #68 that you put in a "non split thrust". Is that actually the same design as the one you found in the '98 GST?
I'm trying to wrap my head around all the thrust bearing variations in the 2g DSMs and the early evos. Evo 4 for example, which seems to have the reputation of being one of the "worst" ones in this area.

Lots of interesting stuff with really good pics in your thread here. I'm probably going to cook up a Word document to index some of it so I can find it again later LOL.

Thanks for reading, glad all the extra detail was useful for someone haha.

I had 3 blocks total between the 3 cars. My original 99 GST, the 98 GST, & the early 95 GSX. So not sure I mentioned it in the thread so far but I ended up tossing a rod out of the block on the 99 GST years ago shortly after I started the build on the red car. I still have never torn down that block to see what actually happened but there went my for sure split thrust block. That car now sits in the back yard and I use it for parts.

So I thought no problem I had read that the 98-99 cars should all be the split thrust. So that is why I went for the 98 GST block first. I was kinda disappointed when I tore it down and found it was an earlier single piece thrust so it must have been an earlier built 98. At that point both the block from the 98 & the early 95 car were exactly the same so I just used the standard bore block from my the 95 in the end.

I researched the crankwalk/thrust problem pretty extensively at that time. There's tons of information out there, everything from guys cutting 7 bolt blocks apart to look at the oil galleys to adding more thrust washers to the other journals on a split thrust block trying to figure out why these engines have this problem. As far as I know there are only 2 thrust configurations in 7 bolt blocks. The traditional 1 piece design like most engines have as shown in post #8 and the so called 2 or 3 piece design where all of the main bearings are the same without the thrust flange and the thrust bearing is made of 2 separate "washers" that go on either side of the #3 main journal.

The main take away that I got from all that I read is that the cars that walked early in their lives that Mitsu warrantied most likely had machining issues on either the block or the crank which caused an uneven contact surface and killed the traditional 1 piece thrust bearing quickly. They then went to the split thrust washers to gain a little bearing area but more importantly it removed the need for the sides of the crank journal to be perfectly parallel with the block and bearing itself. The separate thrust washers will "float" slightly and tolerate some machining error in this area. Also on a traditional 1 piece thrust the 2 bearing halves have to be lined up perfectly during assembly or the surface between the 2 can be uneven.

So as far as the 1 piece design vs the later 2 piece design everyone wants a split thrust block because it is the later revised design. However, I came to the conclusion that with proper machining and assembly the split thrust design really is no "stronger" than the traditional 1 piece design. What I found was to be the bigger issue for both of designs and what causes crankwalk today on built motors is the that both of these thrust bearings are too small to withstand the a heavier than OEM clutch.

Our engines are a small 4cyl and the drivetrain they received to match that. Meaning our clutches are very small in diameter and they didn't take much clamping force to hold the 200 HP we originally had. But now we up to 500 HP and we need a clutch the same diameter to be able to take that. And there is only so much you can do with friction materials so the clamping force has to go up. ACT 2600 lb pressure plates are the most common that everyone runs. Even when you get into the multi-disc stuff the pressure plates are usually 2900 lbs. That means extra pressure is going to shorten the life of the very small thrust bearing in our engines. The engine running or how much HP it has does not effect the thrust load. The thrust bearing is only there to take the axial load pushed on the crank the biggest of which by far is the clutch.

So small disclaimer, there is no concrete evidence or actual science to back up all that I have said above. A lot of people went searching for the 7 bolt thrust problem and they never found any 100% answers. This is all just my opinion and conclusion I have come to after a lot of research.

The cliff notes version on my 7 bolt crankwalk opinion for those who don't want to read all that:
1. Use whichever 7 bolt block you can get your hands on but make sure the machine work and assembly is top notch. I used a 1995 7 bolt - 1 piece thrust with ACL race bearings.
2. Don't use a clutch heavier than you need to. If you only have 300hp you don't need a 2600lb clutch. I went with the 2200lb plate from South Bend specifically to try and save the thrust.
3. Disable the starter lockout and start the car in neutral without your foot on the clutch.

I have a lot of updates to the build as well. I will try to post em up soon.
 
Last edited:

We're on Boost

15+ Year Contributor
1,630
450
Aug 25, 2007
Seattle area, Washington
Man, I really appreciate that writeup on the 7-bolt DSM thrust bearings and crank walk. It sounds like the right stuff to me.

So “2 piece”, “revised 2 piece”, and “3 piece” are all the same thing, right? It’s not 3 different versions.
The only other version is the “one piece”.

I think the naming is what has confused me for a long time. I mean when I look around and I see people writing about one piece, two piece, revised 2 piece, three piece, Split Thrust, how many of these fricking things are there ? is what I’m thinking. LOL

So ok, there are only 2 versions for the 7-bolt. The “one piece” and the “3 piece”.

Then just to verify - the "3 piece" actually has 6 pieces, right? There's an upper main bearing half and a lower main bearing half. Then there are 4 thrust washer halves (front and rear, upper and lower). To make a complete center main bearing. Right?

Yeah, even with my 6-bolt I have had my starter lockout switch bypassed for a long time so it isn't starting with my foot on the clutch pedal. And I am in the process of getting a lighter springed clutch in there right now. At least it is supposed to be lighter pedal, going by what other users say. It's a QM twin with the blue spring. Their "Yellow" spring, if you can get it, would be about 2,200 pounds clamp force. And on their spring chart they show one more spring even lighter than the Yellow - the Orange which would be about 2,000 pounds.
 
Last edited:

95REGF150

10+ Year Contributor
433
221
Mar 7, 2012
Elk Grove, California
So “2 piece”, “revised 2 piece”, and “3 piece” are all the same thing, right? It’s not 3 different versions.
The only other version is the “one piece”.

So ok, there are only 2 versions for the 7-bolt. The “one piece” and the “3 piece”.

Then just to verify - the "3 piece" actually has 6 pieces, right? There's an upper main bearing half and a lower main bearing half. Then there are 4 thrust washer halves (front and rear, upper and lower). To make a complete center main bearing. Right?.

Yep there are a lot of different ways to refer to it but all of those things are the same.

1 Piece thrust on the girdle/main cap side:
crankwalk-okthrustbearing.jpg


1 piece thrust on the block side:
crankwalk-okthrustbearing2.jpg


Notice how you get thrust surface all the way around 360° on both sides. So the two halves when they meet together must be even and flat.

To combat this Mistu just said ok lets ditch the bottom half and jut put larger floating thrust washers on the block side. So with the later 2-piece/3-piece/split thrust design you only get 180° of thrust surface on each side of the crank. Nothing mechanically holds the washers in. They just sit in this little groove in the block and cannot come out because they are captured once the crank sits in on top of them:

dsc02122-jpg.401405

thrust_washer-jpg.98051


But that being said there are only 2 washers total. One for each side. The reason for this is that the girdle/main cap does not have the groove for the washer on the bottom side. This is by design. If they tried to put 4 washers and go 360° without something retaining them then the bearing would just be able to spin. So the main girdle creates the bottom side of the pocket for the washer keeping them from spinning around with the crank. But this is why the washers are wider than the single piece design as they only go 180° on each side.

So in final for the number of pieces. The early traditional thrust design referred to as 1 piece is actually 2 pieces - an upper and lower half and gives you a 360° thrust on both sides of the crank. The later revised design referred to as split thrust is a total of 4 pieces - an upper an lower radial bearing half the same as all the other main bearings and then 2 thrust washers giving you a 180° thrust on either side of the crank.

All in effort to prevent this (pic stolen from RRE):

crankshaft-caughtwalking.jpg
 

We're on Boost

15+ Year Contributor
1,630
450
Aug 25, 2007
Seattle area, Washington
I'll be darned. 180 degrees only for those thrust washers. Well if they are wider enough, then I guess the effective area could be pretty similar to the one piece type.
Thanks for the good pics and the explainer.

In the Chilton manual for 1990 to 1998 they give a kind of sensible proceedure for getting the upper and lower halves of the #3 main bearing lined up, the thrust surfaces lined up. It seems like this could work ok if you have the engine out of the car and you are doing a good careful assembly job. I wonder though, if you were trying to replace the main bearings, or even just the #3 main bearing, with the engine still in the car, I wonder how hard it would be to tell if you are getting the thrust surfaces lined up.

I guess what I'm going to look for next is - what difference if any is there between main bearings for the 6-bolt and 7-bolt. When I look at Rock Auto, they show the same exact Mahle Clevite part number for main bearing sets from 1998 all the way back to 1990. Looking at the actual Mahle Clevite catalog, they show the same thing. The tri-metal type is MS-2039P, for "block 11" ( 1989-1992) and also for "block 10" (1993-1994) and also for "block 12" (1995-1998). But it gets more confusing when I look at their Aluminum bearings (instead of tri-metal). It's also more confusing looking at their "H" suffix bearings (instead of "P" suffix) which are in a different catalog.

It looks like the Evo 5 was the first Evo to use the multi piece thrust bearing arrangement.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Top