Crank Thrusting Foreward Issues

-
T56MaxTorq

T56MaxTorq

Well-Known Member
Joined
Dec 21, 2010
Messages
1,023
Reaction score
376
Location
CO
Well I built my 318 turbo Magnum from the oil pan up but I noticed an issue the other day. I have a trigger wheel installed on my balancer and when I give it a little rev, the balancer and bolt all move foreward about .020" to .035"

I noticed this first when I was putting on the custom 36-1 trigger wheel. But the bolt wasn't torqued just yet. I torqued the bolt and it didn't happen anymore. I've had a lot of issues with this wheel setup and have had it on and off many many times and finally got it right and bolt torqued. But I don't recall if it was ever ran hard with the bolt only snugged down, not torqued. The thrusting hasn't affected the crank sensor...yet. I always put that crowbar on and thrust the crank when torquing that main cap. Any ideas??

Thanks fellas
 
Too much play between the crank and thrust main bearing.
When you use the bar to push the crank forward all you are doing is aligning the top and bottom halves of the bearing to acquire the most surface contact area of the surface of the crank where the crank and thrust bearing contact each other.

If the distance between those two surfaces is worn you get excessive crankshaft movement.
This is most common on stick shift cars because when the clutch is depressed the entire load of the clutch cover springs are transferred to those two small surfaces and they wear faster.

So even if a brand new bearing was put in the surfaces on the crank can be worn to allow that forward thrust amount to be excessive.

spec.jpg
 
Last edited:
Yo seat the thrust bearing (#3 main) I torque the cap, then loosen to finger tight, then whack the crank forward and back with a soft mallet. Then retorque the cap. You measure by prying forward and aft to get the clearance. But I would pry to set it. Not that it will give you 3 times what you should have anyway - just saying that's how I've always done it. Too much thrust means not nough bearing, or not enough crank surface. One is cheap to address as long as you can find out why it went away. The other isn't. I've seen factory engines with crank sensors not misbehave until there's .030+... but some aftermarket systems will misfire with more than .010 of movement.
 
I would also make sure that the balancer is not old, with a cracked and deteriorating rubber ring between the hub and balancer ring, allowing the ring to move back and forth, relative to the hub and crank.
 
nm9stheham said:
I would also make sure that the balancer is not old, with a cracked and deteriorating rubber ring between the hub and balancer ring, allowing the ring to move back and forth, relative to the hub and crank.
Click to expand...

I think if the balancer ring was moving around forward and back .035 it would be gone already. LOL
 
Easy 'nuff to find out if it is moving...just part of the equation that needs to be looked at.
 
This engine only has about 10 hours run time on it. The balancer is new and a prostreet type, but that is a valid concern of it being old.

Trailbeast, come to think of it, when tearing down the junkyard block for rebuild, the bearings were trashed, all the metallic layers were showing and they crumbled in half in my hands. Likely why the truck (which was an automatic) was in the junkyard in the first place. That being said, I'm sure the crank journal where #3's thrust bearing rides took some excessive wear. During install, I simply pried the crank and torqued the cap. I should have done a full blueprint on this engine but unfortunately didn't, so I don't have the actual endplay measurement, but I feel it was on the low end.

Needless to say, I'm putting down some power to this crank, 13 lbs of boost worth (10 psi if I were at sea level). I'm sure thats close to 450 torque, so I was wondering if I it's possible for #3 bearing cap to come loose or shift a little? It's hard to say.

As always, thanks for all the knowledge and advice. I'm gonna try and upload a video cause everybody enjoys a video.

 
I had similar issues with a 360 I bought. Tore it down to find that the thrust bearing was eating into the crank. New crank, new bearings and the machine shop charge to balance everything wasn't cheap nor overly expensive, but I think it was money well spent.
 
Whoa.... that is moving a ton more than .030" ! That's gotta come out; dang. At least you caught it.

I think I would pull of the damper just to be sure it is the crank that is moving, and not the damper loose on the snout. Have you re-tightened the bolt? Does it have the very thick retaining washer under the bolt head? Just wondering if something is awry there.
 
Last edited:
Not sure what balancer you're running but consider a really good on, like an ATI. Made a world of difference in my race engine, which was a 2500cc ministock with 13:1 compression and a manual transmission. I know the 4 cylinders vibrate more, but a good balancer can still make a difference in longevity once you get your problem corrected.
 
Yeah it's worse then I previously thought. I have a Prostreet balancer and it is new, and I have verified torque on the bolt, it's damn tight. So it's a little complicated how the balancer, bolt, pulley and trigger wheel is installed so bare with me. First I installed the balancer and the timing cover. Then I installed a small diameter aluminum pulley onto the balancer. I needed a way to fixate the trigger wheel to the crank so I purchased an extra long snout bolt and stacked washers behind it to reach all the way to the crank, the most aft washer is the big oem washer. So the breakdown from aft - forward would be: crank snout, balancer, big washer, 2.5" of little washers, the trigger wheel, a washer, then the extra long bolt. The pulley is deep and surrounds all the stacked washers. The trigger wheel then has a bolt that fastens it to the pulley so it does not become out-of-time during operation.

Here is a walkthrough for a /6 that shows basically what I did except we V8 guys have a little different pulley and balancer, but you get the point.

Installing a DIYAutoTune.com Crank Trigger - DIYAutoTune.com
 
OK, was wondering if the thick washer was there. It is important for clamping force to lock the damper to the crank. Were you able to get the full torque on the long bolt into the crank snout? How long is the long bolt and how much threading is into the crank snout?

I'd take this stack up apart and look for evidence of movement and in the damper key way. And make sure this long bolt is not too long and bottoming in the hole in the crank. You may well find nothing wrong, but it is easy compared to pulling the pan! If nothing bad, then off with the pan.....

Just as an aside: The one problem that I think you could have with this stack up is that the clamping force has to be transmitted through a whole series of metal to metal interfaces, rather than just 2 (bolt head to washer and washer to damper). These all give the chance for movement, and if they are plated washers, that is even more likely. That stack of washers should be replaced with a solid steel sleeve. Understand that the damper is being locked to the crank with the bolt and thick washer; this is what actually transmits the high frequency crank vibrations that the damper is designed to counter. So, if you have even a miniscule amount of movement in the bolt clamping setup, it can interfere with the damper action.
 
The crank bolt has a bit to do with the balancer working properly - but the balancer has nothing to do with excessive endplay. Yes, main caps move - but they are not supposed to. If you used stock caps and stock main bolts they are probably moving. If the engine is getting detonation, they will move more. You can see the movement at the cap parting lines and the bearings themselves. You have a lower end issue. Best tear it down and check it all out. It's a lot cheaper before it fails...
 
And then while doing the autopsy, figure out what ate the thrust bearing.

If it's an auto, you can bet that the converter was incorrectly installed.

If it's a stick, some cranks weren't drilled deep enough. You see this when you buy an unknown crank, or convert from a stick to an auto.

If you don't figure out what happened, it will happen again.
 
I'll check the bolt depth and ensure it is not giving me a false torque from bottoming out in the snout, and you're right, a steel sleeve would be a better option. When threading the bolt in, there is only about 1/2" or so of threads until it all tightens up. I likely have to take the pan off anyways for an oil leak but would naturally love to avoid pulling the engine. Now with the pan off, I should be able to see if the #3 cap or bearing has failed.

Now, I have to admit, I remember putting the balancer on when it was all on the engine stand. It was very tight, even when warmed up. I don't recall though, if I helped force it on with some dead blows. I'm wondering if I did, that the #3 cap could have shifted aft and then now the crank has lots of room to thrust forward since the cap loosened up. Is that the last nail in the coffin for a crank, cap, and bearing combo? I'm grabbing at all ideas now on how it happened whether it was me or machine.

The bolts and caps are oem, yes. I don't believe I have been detonating, my entire rotating assembly is oem. I pull lots of timing and give it lots of fuel (E85) in boost. I figured it would explode the pistons if I had some detonation going on.

Not sure how anyone could put a converter in incorrectly. I fed the converter into the 904, engaging the slots into the pump and the splines into the shaft. Hoisted the trans into the pegs and bolted it down. Didn't have much problems there and it spun freely when lining up the flexplate bolts.

Is the converter what causes the crank the desire to thrust forward? The action of the fluid on the turbine rotor and stator?
 
It's easy to not get the converter all the way in. When you bolted the converter to the flex plate, you should have had to grab the converter and pulled it to the flex plate. Should have moved a bunch.

That is issue number 1 when a thrust bearing goes out.
 
yellow rose said:
It's easy to not get the converter all the way in. When you bolted the converter to the flex plate, you should have had to grab the converter and pulled it to the flex plate. Should have moved a bunch.

That is issue number 1 when a thrust bearing goes out.
Click to expand...

Well to touch on that, I roasted the rear clutch by accident shortly after its first engine start from forgetting to set the kickdown right. So I had to pull it, fix it, and put it back in.

So what you're saying is that I may have bumped the flexplate with the converter, pushing the crank forward and fucked #3 bearing?
 
YR is right on the converter possibility and that you should have to pull the converter forward to do up the flex plate bolts.

On the balancer... they should not be hammered on, or pushed on with the balancer bolt. An installer is $100. Buy one. Hitting the crank with a steel hammer hard enough can hurt the thrust.
 
T56MaxTorq said:
Well to touch on that, I roasted the rear clutch by accident shortly after its first engine start from forgetting to set the kickdown right. So I had to pull it, fix it, and put it back in.

So what you're saying is that I may have bumped the flexplate with the converter, pushing the crank forward and fucked #3 bearing?
Click to expand...

Nope, I'm saying you didn't get the converter all the way into the pump, and that forced everything forward and ate your thrust.

Happens all the time.
 
yellow rose said:
Nope, I'm saying you didn't get the converter all the way into the pump, and that forced everything forward and ate your thrust.

Happens all the time.
Click to expand...

Wow I've been doing nothing this for a while now and haven't heard that one. Hey I love learning new things, thanks! I don't care what they say about you, yellow rose, you're alright in my book. I cannot confirm that that's what happened but it makes sense. I remember the first time I installed the 904 it was a complete pain, the second time not so much. So to fix this I need to remove, inspect, and retorque #3 cap?? Or is my bearing and cap now trashed??
 
Last edited:
T56MaxTorq said:
Wow I've been doing nothing this for a while now and haven't heard that one. Hey I love learning new things, thanks! I don't care what they say about you, yellow rose, you're alright in my book. I cannot confirm that that's what happened but it makes sense. I remember the first time I installed the 904 it was a complete pain, the second time not so much. So to fix this I need to remove, inspect, and retorque #3 cap?? Or is my bearing and cap now trashed??
Click to expand...

Bearing and quite possibly the crank where the bearing rides, as it normally wouldn't hurt the block unless the bearing spun.
If you put the converter in and were able to turn it easily by hand to put the first bolt in it's probably fine, because they either miss the pump ears and are bound up or not.
There really isn't an in between unless you had to force the converter to turn to line up that first bolt.
Not to mention a bind like that would have taken the trans pump WAY before it wore your thrust bearing.

Converters can balloon under load though, and that's hard to find out except for the end result(which is a trashed thrust bearing and bearing surface on the crank and even a trashed trans pump from the converter pushing the center gear of the pump back)
You did say you run boost right? :D
Again, if you were able to pull the converter forward 1/2 inch or so to the flex plate to put bolts in then converter ballooning is probably not the problem.

THE most likely thing that happened is you missed checking the clearance on the thrust bearing to crankshaft so you didn't notice the crank being worn there.
See the thing with a thrust bearing is that you could literally cut both ends of the engine off and only have 6 inches of the center left and still only have that same amount of forward and back movement at what was left the crank because of the thrust bearing.

I doubt it has anything to do with your front balancer install not being tight either as some mentioned, and the easy way to find that out is to check the flex plate end and see if it also moves forward and back that much there when you move it.
If it moves the same (and I suspect it does) then you have excessive thrust bearing clearance and need to determin if you just missed it or something caused it after.
 
Last edited:
It is entirely possible that the thrust was bad from the gitgo. It should have been checked, torqued with a dial indicator.

Since I have a tiny bit of experience with crank grinders...it's also highly UNLIKELY that the thrust on the crank was bad while it was up in the grinder. Almost everyone I know kiss the thrust while the crank is in the grinder. It is possible it was missed, but it falls into the statistical category of highly unlikely. I have seen some crank that were so poorly done that they were sent out to be welded strokers (yes I am that old).

I still say most likely the converter was not in the pump.

The big deal is that the OP nail down EXACTLY what when to poop on him or it will happen again. I don't think anyone wants that.
 
Take a look at the balancer when you tear into it, some aftermarket ones are designed to be honed to fit the end of the crank, never tap or hammer one on.
 
You must log in or register to reply here.
-

Back
Top