Thrust bearing problems

[92SS3908]

So I got my new engine (350 small block) together about a month ago and ran it for a little on the street doing some tuning and such then dumped the oil to see what it was looking like and is was slightly metallic had chips in the filter. We took the engine back out and tore it apart and found the thrust surface on the rear bearing was completely worn (down to the steel shell in one spot). After asking around we were told the excess thrust could have been caused by torque converter ballooning, so we got a new Coan converter. The thrust surface on the crank also seemed rough so we got it polished. Got the engine back in Thursday and ran it up and down the street a couple times then dumped the oil and again it was metallic. Checked the endplay on the crank and it was at 24 thousands it should be, and started at 8, so we ate through another bearing. The only odd thing I noticed Thursday was a shutter in the higher rpms, somewhere above 5000, on the one full throttle test I did. Anyone run across this problem? Any suggestions would be appreciated. Edited April 25, 2009 by 92SS3908

[Dave1647545494]

look for anything that could be forcing the crank against the bearing

 

unseated converter, wrong lenght input shaft for the bellhousing depth, or wrong flexplate is where I would look first.

[92SS3908]

With the trans bolted to the block, the torque converter bolts out and the converter pushed all the way back there is about a 3/16-1/4 inch of clearance between the flexplate and the converter bolt pads. From what I've read thats what it should be so that should cause any force.

[Guest Removed]

what all is driven off the crank? which trans? more info?

[92SS3908]

Trans is a 700R4 (4L60) brand new Coan 2500 stall converter was installed before the latest failure. Stock serpentine belt system: air pump delete, a/c compressor is there but not hooked up, alternator, and water pump.

[Guest Removed]

well if the trans/converter isnt doing it, something in the motor could be pulling/pushing the crank forward.

but still hard to tell what is pushing it forward. i only asked about the crank driven stuff incase you was turning a super charger or something. but trying to figure if its the trans would be first i have seen the input shafts walk outward and push the convertor on the crank harder....

[92SS3908]

Any ideas on internal engine problems? Thus far we haven't come up with much the only long shot idea we have had is if the breather is restricted under decel there could be a large vacuum building in the crankcase. The rear sealing surface of the crank is bigger than the front so if the pressure in the crankcase gets low enough the crank could be forced forward but to have enough force to do any damage we're going to have to see some very low pressures. We're going to put a gauge on it soon and see what it reads under decel. As for the trans, in the incident you've seen what do you know what caused the input shaft to walk forward?

[Guest Removed]

there are tons of cars out there with neg- crankcase pressure, and dont have crank walk issues..check the rods. see if any are twisted or not located on the pins correctly.

 

 

the internals on the trans was walking forward. pushing everything forward

[92SS3908]

I know there are cars out there with neg crankcase pressure but with my block, using the one piece rear main seal the rear area of the crank is greater than the front so there is potential for a pressure differential. In the older/ aftermarket blocks that area difference from front to back is not very big so the pressures more or less equal out. I know it’s a long shot. I don't think it’s a rod problem because that should show up as an abnormal wear pattern on the cylinder walls which was not evident when we took the engine apart after the first failure.

Did the internals of the trans move forward because of something that broke? Also what kind of trans was it?

[Guest Removed]

I know there are cars out there with neg crankcase pressure but with my block, using the one piece rear main seal the rear area of the crank is greater than the front so there is potential for a pressure differential. In the older/ aftermarket blocks that area difference from front to back is not very big so the pressures more or less equal out. I know it’s a long shot. I don't think it’s a rod problem because that should show up as an abnormal wear pattern on the cylinder walls which was not evident when we took the engine apart after the first failure.

Did the internals of the trans move forward because of something that broke? Also what kind of trans was it?

 

just cause a rod is twisted it wont affect cylinder wear.. sounds as if there isnt even enough mileage to get to cylinder wear.

 

one peice or two peice dont fucking matter.

 

the lt1 is the one with pressure differential that your thinking of. cause half the crank is internal balance, the other half is external.

and there is not way you are pulling that much vacuum in the crank case without a vacuum pump!

 

are they pressed pins

 

 

i have several different trans cause this..one was a turbo 400. but mainly stick shift cars do it..but over time. you have something major going on to cause such a rapid wear as your saying

[92SS3908]

one peice or two peice dont fucking matter.

 

the lt1 is the one with pressure differential that your thinking of. cause half the crank is internal balance, the other half is external.

and there is not way you are pulling that much vacuum in the crank case without a vacuum pump!

 

 

All i'm saying is the possibility is there because the facts are the rear surface of the crank is larger than the front surface. This is true on the one piece but not the two piece that the only reason I mentioned the seal. And yes I know its not likely that i'm pulling enough vacuum but it is possible if the crankcase is sealed (or almost sealed due to a clogged breather) becasue manifold pressure does get low enough during high rpm decel.

 

are they pressed pins

 

They the rods and pistons are stock the only thing that was done during the rebuild was stronger rod bolts and the big end resized so the pin position shoudn't be a problem, it was never taken out.

[Guest Removed]

All i'm saying is the possibility is there because the facts are the rear surface of the crank is larger than the front surface. This is true on the one piece but not the two piece that the only reason I mentioned the seal. And yes I know its not likely that i'm pulling enough vacuum but it is possible if the crankcase is sealed (or almost sealed due to a clogged breather) becasue manifold pressure does get low enough during high rpm decel..

manifold pressure gets low under WOT.like 0. and gets high with the throttle closed on decel. like full idle vacuum or higher.and i guess it would help to know or be looking at your crankcase vent system, which i have no flipping idea of or how you have it setup. and i have never seen vacuum pull a crank forward.at most it will suck oil out of the crankcase harder.

and if your thinking the breather is clogged, why not go check it?

 

They the rods and pistons are stock the only thing that was done during the rebuild was stronger rod bolts and the big end resized so the pin position shoudn't be a problem, it was never taken out.

 

does not mean that they are striaght or if infact in there wrong holes.

 

i have seen the wrong bearings riding on a poorly turned crank do this well. where the ends are radiused but the bearings are not.

 

and if i remember right, 8 thousands is high! to start with.

with the wear being all at the rear, something is pushing it forward. suction is not going to be enough to cause this as fast as your saying.

[92SS3908]

manifold pressure gets low under WOT.like 0. and gets high with the throttle closed on decel. like full idle vacuum or higher.and i guess it would help to know or be looking at your crankcase vent system, which i have no flipping idea of or how you have it setup. and i have never seen vacuum pull a crank forward.at most it will suck oil out of the crankcase harder.

and if your thinking the breather is clogged, why not go check it?

 

 

with the wear being all at the rear, something is pushing it forward. suction is not going to be enough to cause this as fast as your saying.

 

I have a PCV system. It’s a simple hose going from one valve cover to the manifold. I think you have it backwards on manifold air pressure. Under WOT the pressure in the manifold approaches atmospheric (I’ve recorded right around 96kPa atmospheric=100kPa). During decel the throttle plates are closed yet the engine is still trying to pull air so pressure goes low (I’ve recorded as low as 18kPa under high rpm heavy decel). So with that into consideration the crankcase is exposed to that low pressure and I did check the breather it is not clogged but restricted so it may not be able to keep up with what the PCV is drawing, so although crankcase pressure will not be as low as manifold pressure it will still be low. As for the force this will create we aren't talking about suction there's no such thing. Its pressure differential from outside to inside. Pressure outside is higher than inside so in pushes in, not the inside pulling. Although I do not have the exact numbers, which is what I will be measuring when I get back to the car, here's a scenario to explain my theory. Let’s say the front diameter of the crank is 1.5 inches that’s an area of 1.767 square inches. Let’s say the back diameter is 4.5 inches that’s an area of 15.904 square inches. The front area will cancel the back so the area that can act on the crank is the front area minus the back area which is 14.137square inches. Now calculate pressure. If the crankcase pulled down to 30kPa that is equal to 4.41 psi. Atmospheric pressure at sea level is 14.7 psi approximately 14.3 psi here in Ohio. That’s a pressure difference of 9.89psi. Multiply the pressure by the area and you get a forward force of 141.6lbs. That’s a significant amount of force pushing the crank forward and a possible cause of failure.

 

 

does not mean that they are striaght or if infact in there wrong holes.

 

 

If you're talking about pistons in the wrong bore that isn't possible we marked all of them as they came out and double checked that when we tore the engine apart after the first failure. Even if they were slightly off (which I don't think they are) I’m told by my engine builder it shouldn't be a problem. On Pro Stock engines the crank journals were offset from the bores on purpose and it did not cause a problem.

 

 

and if i remember right, 8 thousands is high! to start with.

 

Factory spec is 5-8 thousands and some race engines are even higher than that.

 

Also please understand I’m not trying to shoot down everything you say I’m just trying to think through this logically. I have thought about a possible rod problem and bad crank grind and plan on doing more checking on that. I’m just trying to search every possibility so I don’t get everything back together and have to replace another bearing. Thank you for all suggestions thus far. Keep them coming.

[Guest Removed]

I have a PCV system. It’s a simple hose going from one valve cover to the manifold. I think you have it backwards on manifold air pressure. Under WOT the pressure in the manifold approaches atmospheric (I’ve recorded right around 96kPa atmospheric=100kPa). During decel the throttle plates are closed yet the engine is still trying to pull air so pressure goes low (I’ve recorded as low as 18kPa under high rpm heavy decel). So with that into consideration the crankcase is exposed to that low pressure and I did check the breather it is not clogged but restricted so it may not be able to keep up with what the PCV is drawing, so although crankcase pressure will not be as low as manifold pressure it will still be low. As for the force this will create we aren't talking about suction there's no such thing. Its pressure differential from outside to inside. Pressure outside is higher than inside so in pushes in, not the inside pulling. Although I do not have the exact numbers, which is what I will be measuring when I get back to the car, here's a scenario to explain my theory. Let’s say the front diameter of the crank is 1.5 inches that’s an area of 1.767 square inches. Let’s say the back diameter is 4.5 inches that’s an area of 15.904 square inches. The front area will cancel the back so the area that can act on the crank is the front area minus the back area which is 14.137square inches. Now calculate pressure. If the crankcase pulled down to 30kPa that is equal to 4.41 psi. Atmospheric pressure at sea level is 14.7 psi approximately 14.3 psi here in Ohio. That’s a pressure difference of 9.89psi. Multiply the pressure by the area and you get a forward force of 141.6lbs. That’s a significant amount of force pushing the crank forward and a possible cause of failure.

 

im talking vacuum gauge readings. hook one up to any car and watch it under WOT and decel from that.

 

Theres one mounted in the dash of my mustang just for this reason. at WOT its 0 " of vacuum. close the throttle, and it slams 21-22" then settles back down to its 10-8" it normally runs. even at part throttle, i had 16" or so, just cruising around. its great for trying to squeeze out max fuel economy. but i just love the sound of 14.5 to 1 barking thru 3 1/2 race bullets on the street, so staying out of it was my issue.

 

now yeah i looked the clearnces up after i said that. but when you close the throttle on yours, the pcv valve is going to close off. and remember what opens the pcv valve is crankcase pressure.breather being clogged will just make it worse, if not make it work harder. and look at a lot of the late model stuff, all they have is a tube going to the air intake, for suction on the crank case. but thats before the throttle blades. now i can only assume your pcv valve is in the front of the valve covers. but alos think that there other cylinders moving downward at the same time some are pushing up, with pressure coming down thru the ring seal.

i mean it could be possible, but highly unlikely, in suck a rapid

rate that you are saying!

[Guest Removed]

in which im almost starting to wonder about ring seal. when its running at idle, does the pcv click really fast? or suck open? is the pcv new? and is the hose show any sign of oil being drawn in?

[92SS3908]

im talking vacuum gauge readings. hook one up to any car and watch it under WOT and decel from that.

 

Theres one mounted in the dash of my mustang just for this reason. at WOT its 0 " of vacuum. close the throttle, and it slams 21-22" then settles back down to its 10-8" it normally runs. even at part throttle, i had 16" or so, just cruising around. its great for trying to squeeze out max fuel economy. but i just love the sound of 14.5 to 1 barking thru 3 1/2 race bullets on the street, so staying out of it was my issue.

 

 

Got it. I agree with you there, I read pressure you read vacuum, but same idea.

 

but when you close the throttle on yours, the pcv valve is going to close off. and remember what opens the pcv valve is crankcase pressure.breather being clogged will just make it worse, if not make it work harder. and look at a lot of the late model stuff, all they have is a tube going to the air intake, for suction on the crank case. but thats before the throttle blades. now i can only assume your pcv valve is in the front of the valve covers. but alos think that there other cylinders moving downward at the same time some are pushing up, with pressure coming down thru the ring seal.

i mean it could be possible, but highly unlikely, in suck a rapid

rate that you are saying!

 

I'm not quite following what you are saying here but here's how I understand the PCV valve. It is a simple check valve with a lightweight that allows air to flow from the crankcase to the throttle body below the throttle blades. The valve gets seated if flow is the other way around (in case of a backfire so the flame does not go into the crankcase and ignite the potentially flammable gasses in the crankcase.) So when the throttle is closed pressure difference between the crankcase and the manifold is at its greatest making flow greatest. There is no reason for that valve to close off. I think the hose you are referring to on the late model stuff is the breather hose which allows filtered air to enter the crankcase as the PCV draws it out. The blow by you are talking about is what the PCV is designed to evacuate and hopefully sometime today when I do a pressure check on the crankcase under load we'll know how much of a vacuum it can pull with a restricted breather.

 

 

in which im almost starting to wonder about ring seal. when its running at idle, does the pcv click really fast? or suck open? is the pcv new? and is the hose show any sign of oil being drawn in?

 

No the PCV does not click or buzz at idle as far as I know. It was replaced within the last year or two. And I don't know about signs of oil I didn't specifically look.

[Guest Removed]

well this is why i love the internet, cause all common knowledge that could have been forgot is found once again!

 

The PCV valve is only one part of the PCV system, which is essentially a variable and calibrated air leak, whereby the engine returns its crankcase combustion gases. Instead of the gases being vented to the atmosphere, gases are fed back into the intake manifold, to re-enter the combustion chamber as part of a fresh charge of air and fuel. The PCV system is not a classical "vacuum leak." All the air collected by the air cleaner (and metered by the mass air flow sensor, on a fuel injected engine) goes through the intake manifold. The PCV system just diverts a small percentage of this air via the breather to the crankcase before allowing it to be drawn back in to the intake tract again. It is an "open system" in that fresh exterior air is continuously used to flush contaminants from the crankcase and into the combustion chamber.

 

The system relies on the fact that, while the engine is running, the intake manifold's air pressure is always less than crankcase air pressure. The lower pressure of the intake manifold draws air towards it, pulling air from the breather through the crankcase (where it dilutes and mixes with combustion gases), through the PCV valve, and into the intake manifold.

 

The PCV system consists of the breather tube and the PCV valve. The breather tube connects the crankcase to a clean source of fresh air, such as the air cleaner body. Usually, clean air from the air cleaner flows in to this tube and in to the engine after passing through a screen, baffle, or other simple system to arrest a flame front, to prevent a potentially explosive atmosphere within the engine crank case from being ignited from a back-fire in to the intake manifold. The baffle, filter, or screen also traps oil mist, and keeps it inside the engine.

 

Once inside the engine, the air circulates around the interior of the engine, picking up and clearing away combustion byproduct gases, including a large amount of water vapor, then exits through a simple baffle, screen or mesh to trap oil droplets before being drawn out through the PCV valve, and into the intake manifold.

 

The PCV valve connects the crankcase to the intake manifold from a location more-or-less opposite the breather connection. Typical locations include the opposite valve cover that the breather tube connects to on a V engine. A typical location is the valve cover(s), although some engines place the valve in locations far from the valve cover. The valve is simple, but actually performs a complicated control function. An internal restrictor (generally a cone or ball) is held in "normal" (engine off, zero vacuum) position with a light spring, exposing the full size of the PCV opening to the intake manifold. With the engine running, the tapered end of the cone is drawn towards the opening in the PCV valve, restricting the opening proportionate to the level of engine vacuum vs. spring tension. At idle, the intake manifold vacuum is near maximum. It is at this time the least amount of blow by is actually occurring, so the PCV valve provides the largest amount of (but not complete) restriction. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. Sensing a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. At full throttle, there is nearly zero vacuum. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn in to the engine's intake manifold anyway.

 

Should the intake manifold's pressure be higher than that of the crankcase the PCV valve closes to prevent reversal of the exhausted air back into the crankcase again. It simply means there is a constant and definite flow of air through the system, as compared to the hit-and-miss road draught system used previously, in which air may flow in either direction or not at all. In many cases PCV valves were only used for a few years, the function being taken over by a port on constant depression carburetors such as the SU. This has no moving parts or diaphragm to jam, block or rip like many PCV valves. It also doesn't have a 'one-way' function but the lack of it was never a problem in intake backfire.

 

Not sure if this will help, but is the basic's of a pcv system and its components, and yes i copied it from somewhere else.