Hey guys,

I am building a nitrous 408 and I would like to know what I should have for my crank shaft end play. I have a scat forged crank and clevite hardened bearings. I measure .002 of end play on the crank. According to the book I have that is acceptable, but according to engine masters i need at east .003, and according to my friend who builds engines for a racing company I should shoot for .004. The car is an automatic by the way. Thanks in advance for the help

 

To me that's kinda not enough. I like to see .005 - .012" or so. .004" strikes me as a bit tight but if somebody in the trade builds em like that all the time and they're OK, then it's OK by me. Regardless, .002" is too little.

With an auto it's not near as critical but still worth getting right of course.

When you built it, did you tighten the main bolts on the thrust cap to 20ish ft-lbs, then bonk the crank REAL GOOD from both the front and the rear with a dead-blow hammer, then torque the rest of the way? (or a regular hammer and a block of wood)

 

 

With an auto trans, there's around .100" or more of a gap in the converter <-> trans fitment, anyway. The converter is bolted to the flex plate, sometimes is held securely into the crank pilot by the flex plate and sometimes not so much (but in neither case does it interact with crank end play at all), and basically floats freely in the pump (end-wise that is). If the converter balloons enough to take up ALL THAT, there's bigger problems in the build than acoupla .001"s of crank end play.

 

 

I, too, have heard about ballooning. I think that it probably DOES happen, but that it also DOES NOT affect crank end play. Sure, torque converters "balloon" under high stress situations but that CANNOT affect crank end play. As RB04 states, in order for it PUSH the crank forward, the back side, or transmission side, of the torque converter would have to be seated solidly against something in order for it to exert pressure to move the crank forward. The back side of the T/C touches NOTHING. As RB states, it is just free floating. The hub, or neck, of the T/C is inside the trans but it is NOT in contact with the pump face, or anything else that would allow it to exert force to move the crank forward.

As I said above, I do believe that a T/C can balloon, but I think it simply means that the housing of the T/C distorts, or in some way changes shape minimally most likely resulting in damage to the internals inside over time, or over a certain # of times of flexing. If you look at how the T/C engages the transmission you would break the internal pump gears long before the converter could push the crank forward.

The only other thing I can think of that might be happening is that the impeller, and turbine, inside the T/C due to the angle of the internal fins, might cause the entire T/C to exert thrust on the crank in such a manner as to move it forward. I would think this action, if it truly happens this way, would not just be limited to when the T/C balloons, but would always to some degree be exerting this thrust in varying loads under varying conditions. I do know that transmissions thrust their internal components (typically on Chevys-towards the rear of the case). So if that internal trans thrust is pushing the gear train towards the back of the trans, then some of that rear thrust may be imparting a forward direction thrust on the internals of the T/C. If you know much about rear diffs, you know that under load, a Chevy will be trying to push the pinion gear out the front of the diff housing due to the way the gears are cut. That's a mechanical situation that can be easily illustrated. Inside the T/C the fluid is being pushed from one spinning "fan blade" into another. The liquid between the two spinning blades-I believe-can exert a forward thrust.. By forward I mean pushing the T/C housing back towards the flywheel, and then the crank forward in the engine main saddles. So, even though it is a liquid, it is acting as a hydraulic medium that is pushing the T/C forward.

The other thing that really sticks out in my mind... This idea that crank end play should be adjusted to a HIGHER clearance when using an automatic trans w/T/C just seems wrong. Even if someone comes along and proves this theory of ballooning T/C's, and forward thrust of the crank, why in this world would you want the crank MOVING farther forward than necessary? I would think the ONLY consideration here would be to insure that the crank has some end play between the thrust surface on the thrust bearing, and the mating surface of the crank that meets that thrust surface. If the crank is truly being pushed forward, and eventually stops against the forward thrust bearing, what logic dictates that allowing it to move more than necessary is a good thing? Regardless of whether it's a manual, or automatic, I would be sticking to what the manufacturer calls for. I would not go with any LESS, nor I would go with any MORE. Moving a spinning crank back and forth .015" in the engine main saddles might not make any difference in the world, or it may cause the engine to fail in a shorter time frame than a properly set up engine would. Not worth the gamble. I'd stick to what GM calls for-regardless of what type of trans is going behind it.

These are my THOUGHTS and OPINIONS only. If someone has contradicting information I will be the first to admit "I was wrong". Me being wrong about something happens at least once a day, so if this is it, I'm okay with that. Even if I am wrong I will be able to say "I learned something new today". WIN/WIN..

 

 

Torque Converter Issues

All too often, performance enthusiasts who encounter thrust bearing failure tend to blame a “ballooning” torque converter. Yes, a converter body can balloon (expand) under excess pressure, which would force the flexplate and crank forward, but this is rarely the case in a street-driven vehicle. Other converter-related issues should be considered first, such as the wrong flexplate bolts being used, the wrong converter for the application, improper converter installation or the transmission pump gears installed backward.

Then, from later in the article; they will also cause the same force on the pump gears, since all of these problems will put equal force in both directions from the torque converter. So any of these conditions should also cause serious pump damage very quickly—within minutes or hours. This last statement seems to indicate-as I mentioned above-that the pump gears WOULD be damaged if the T/C truly was expanding, or ballooning, as Che70 is alluding to. If the pump is not being broken, or damaged, the T/C is not "ballooning". I think there are two different things happening here... There is THRUST that will flex, or bow, the flywheel towards the engine.. And then there is ballooning, which is the actual case, or converter housing, actually expanding. In this video; you can see a situation where a T/C is THRUSTING the flexplate, and bowing it, towards the engine, but they are *attempting* to use the term ballooning. I think THRUSTING is what is being shown in the video. You can watch the shape of the T/C and it does not change visually. If you watch the relationship between the flywheel and the engine, you CAN visually see that the flexplate bows, and moves towards the engine block. It's curious to note that as the flexplate bows, the T/C neck is being pulled slightly OUT of the transmission pump. This should indicate how vitally important it is to get the T/C seating depth in the transmission spot on. If when bolting the T/C to the flywheel you pull it too far forward-meaning the air, or free, gap between the T/C and the flywheel is too great as measured with the T/C seated all the way into the face of the trans, you run the risk of breaking the pump gears later IF the flywheel bows and allows the neck of the T/C to come out of the pump. In that scenario, you could lose pump tang to T/C neck engagement and snap the pump gears. Again this would be a flywheel FLEXING or BOWING problem-NOT T/C Ballooning!!!!!!!!Taken from here; https://www.motor.com/magazine-summa...tion-analysis/

Lots of good information in that article for those that care to read it. And yes, Che70, I took your advise and researched ballooning torque converters and found that information. It seems to support the idea of keeping the crank end play within factory specifications. They go on to discuss how the T/C pilot can bottom out in the back of the crank IF and WHEN the flywheel flexes, or bows, enough to allow that to happen. I think the distinction here needs to be made between ballooning, and flywheel flexing, or bowing. Flexing, or bowing, is a direct result of THRUST due to internal hydraulic action and would explain how the flywheel flexes, or bows, in the first place. I think watching the video above PROVES that ballooning is not really happening. At least in that video. If the T/C were ballooning-would it not expand in BOTH directions, or contract in WIDTH, and increase in outside diameter? I think so. What we are seeing in the video is that the T/C *appears* to maintain the same dimensions, it just moves towards the front of the engine due to the flexplate bowing.

It's all still about as clear as mud. What is obvious is that flywheels bow, or flex, and that crank end play is critical to control this issue. I think people are erroneously calling this forward movement and associated flexing/bowing "ballooning" when in fact it is simply forward thrusting. Until I see a video that shows me a T/C actually expanding in outside diameter, or increasing in width in BOTH directions, I'll remain dubious. OR, if someone can post an autopsy of a T/C being cut open showing signs of stresses, or metal damage, inside the unit from the T/C dimensionally changing internally.. That would be eye opening for me. Is it possible that both of these phenomena are occurring? That's the most likely situation. But my $$ is on flywheel flexing or bowing as the bigger culprit of the two, and most likely what most of us are seeing-but calling ballooning. From the article-as vague as it is-they are indicating that this is the result of a mismatch of parts, or equipment.

I know both Brian, and Chris, at Circle D specialties. If I remember, I will call them on Tuesday and get their input on the situation.

 

Yes sir I did, but not at 20 pounds(it was 15 i think ) and maybe I didn't hit it hard enough? my dead blow hammer isn't very large.

 

I was just assembling my LS with a Lunati crank and discovered that I needed to chamfer the mains slightly.
I always use an inch pound torque wrench to look at running torque once the crank is in place.
I had 15 to 20 inch pounds and the crank didn't feel quite right rotating by hand.
I pulled it back out and noticed the edges of the mains were "polished". The filet radius was catching the edge of the mains. I carefully chamfered by hand and reassembled. Crank now spins "easier" by hand and takes less than 10 inch pounds to rotate. End play went from barely 2 to 3 plus.
If you feel you must have more, I use a piece of glass and fine emery paper with WD40 sprayed on it and polish the thrust faces a touch. I grasp both halves firmly on polish together in a figure 8 motion to adjust the clearance.

 

 

I understand why you might want a bit more clearance for a nitrous build but specs show 0.0015-0.0078" which is a large variance. Does anyone see a problem with .002 end play for a mild street build with a 4l80e trans ?
Because that's where I'm at

 

My end play is .004. I just had to realign my thrust bearing!