10+ Year Contributor
- Mar 7, 2012
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 .
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.