Generally speaking, what causes excessive crankshaft endplay? I understand it has to do with a worn thrust bearing, but what would cause the thrust bearing to wear excessively? My crankshaft endplay measures .041 and both sides of my thrust bearing are trashed. Any insight will be helpful.

 

WORN OUT MAINS AND RODS AND SOMTIMES WORN OUR PISTON SKIRTS.

THIS MAY SOUND CRAZY BUT I LIKE A LOOSE ENGINE!!!
it lets everything float where it wants and plus most of the pressure inside an ingine is not horizontal its vertical. iv seen excessive endplay caused by an alternator pulley pulling the crank pulley out a little after about 50K miles.

are you rebuilding it?

 

Tracking down a worn distro gear problem, and found this to go along with it. A little history on the engine. Rebuilt in 2002 by myself. Currently has 20k miles give or take. All clearances were within spec when built except for rod side clearance which was a couple thousands tight. Found out about the wear on the distributor gear at about 12k when the gear teeth broke and the others were almost completely worn off. Right after the rebuild, I had metal in the oil for a couple oil changes, I figured it was the rod side clearance wearing itself in but not I can see that there was bearing material as well as crankshaft shavings. Although I am not sure if camshaft endplay should be measured with the timing chaing bolted on or just the cam gear with no chain, but the cam has zero movement with the chain. If the worn gear and crankshaft endplay are related, I'm guessing cam endplay, or lack therof, is what is causing the wear.
EDIT: I just remembered, I measured the cam endplay with the distributor installed so it most likely wasn't accurate, I'll get another reading later today.

 

i didnt think of that haha i learned somthing new......

this may sound retarted but i would keep the crank from moving by shimming the flywheel (if you have the engine pulled or putting spacers between the converter(if you dont have the engine pulled apposed to replacing mains. or if it only wears out after like 30 or 50 thousand miles just kep replacing it and changing your oil filter frequently to catch any metal shavings. maybe add a magnetic drain plug ??
i would still get more advice though. im just a backyard mechanic hahaha!

 

.040" is excessive. A good amount would be something more in the .010" - .020" range. Rod side clearance should be similar; .010" - .015" or so.

Rods, piston skirts, cam end-play, timing sets, and distributor gears have NOTHING WHATSOEVER to do with wearing out the crank thrust bearings.

Likewise, metal shavings can't do that either; if there's enough metal in the oil to destroy the thrust, the only way for it to do that, is to pass through the rear main FIRST on its way. Therefore, if ONLY the thrust is trashed, that wasn't the cause.

You can't "shim the flywheel" (whatever that's supposed to mean) to get rid of crank end-play. There's nothing to "shim" it against.

Plant, I suggest ignoring everything you've been told so far. It's the Internet equivalent of "diarrhea of the mouth".

Generally speaking, there are a several possible reasons for end-play. The first and most obvious is poor machine work on the crank. Another is improper assembly; dirt or debris or a ridge left over from align-boring, or the halves of the rear main cap and/or bearing shell weren't aligned by the builder. It could be poor oiling, although if that's bad enough to tear up the thrust, the rest of the bearings will usually be no better. And of course, too much clutch pressure will do it; but that's REALLY unlikely.

What was the actual measured clearance when the engine was built, both upper half and lower half? What did the thrust surfaces of the crank look like, and what do they look like now?

 

actually you can shim a flywheel, its a racing trick. it shims aginst the torq converter wich shims agints the inside of the pump on the transmission.


i missed the fact that your distributor gear is wearing i know a fix for that
go here to get rid of the "inward" cam walk. this is also a racing application.

it will atleast get rid of your worn distributor gear problem its $11.95

http://store.summitracing.com/partde...0&autoview=sku

the lower end im stummped with without seeing it. mines got 45 thousanths endplay but i only rev it out to 7800 prm hahahaha

 

No, you can't "shim a flywheel" aginst the pump.

Anyone who has ever actually built motors and transmissions and cars knows better than that.

First off, an auto trans DOESN'T HAVE a flywheel at all.

Second, the thing that an auto trans DOES have, a FLEX PLATE, does just exactly that; it FLEXES.

Third, an auto trans torque converter should NEVER EVER bottom in the pump; it should in fact be about 1/8" or so OUT IN FRONT OF bottoming. If it bottoms, it will destroy the pump. As those of us who have actually done this stuff before all know, when you assemble the motor & trans, the TC should be fully bottomed in the pump; it should then have to be pulled out by that 1/8" more or less, in order to bolt to the FLEX PLATE.

Fourth, it's not a "racing trick".

Fifth, even if there WAS such a thing as this "shim" business, the motor would STILL need an intact and functioning thrust bearing, for the crank to run against.

Moving right along:

The thrust bearing in the link, requires MACHINE WORK to install into a timing gear. so for most of us it's cheaper to buy a timing set with the Torrington already installed in it at the factory, like this one.



All it does, is provide a lower-friction arrangement than the stock system of the back of the cam sprocket sitting against the front of the block; and doesn't do ANYTHING AT ALL about "eliminating" cam end play. Especially since with a flat-tappet cam, there's NOTHING holding the cam in AT ALL, except the lifter face shape, and the distributor gear (oil pump) load, and the timing chain; in other words, end play IS NOT an issue AT ALL, by design.

And of course as stated earlier, the cam has NOTHING WHATSOEVER TO DO with CRANKSHAFT end play and CRANK thrust bearing surfaces.

 

BAM! Sofa lays the smack down!

Fortunately, he's allowed to do that becuase he happens to be right.

Sounds like that motor was doomed somewhere in the build 20K miles ago. That's too much stuff worn out to be any single problem (short of a general oil system problem).

Any chance you were running a high volume/high pressure pump in that motor? What weight oil did you run? That could explain the cam gear problem over thousands of miles.

Thrust wear (assuming the motor was built right to begin with) is usually from the torque converter/line pressure inside the trans or a bad converter. It tries to push forward the more pressure there is inside the converter. Thrust bearing faces can't support anywhere near the kinds of pressures that say, a main or rod bearing can. Few hundred pounds of forward pressure on the crank and it'll tear hell outta them. Heard about this problem a few times before with 700R4s, although I have never experienced it personally.

 

How likely is it that .040" of crank end play will = time for a new crank?

 

Isn't that what ended Stephen_Iroc87's racing season prematurely last year?
I know a guy who tore up his thrust bearing on his 400cid engine with a standard tranny and he's at a loss as to how.... Some good insights here.

 

I was wondering what the rest of the main/rod bearings looked like.

The reason I ask is that with the distributor gear chewed up, IF the oil filter bypass was not blocked, some of that metal also went through the engine. With the thrust bearing trashed on both sides, this is something to check.

Another item which Damon touched on is the torque convertor. However, I'm thinking differently, carefully check the splined shafts going into the transmission. Look for a notch in the splines where the mating TQ splines can hang up. There have been instances of improperly heat treated input shafts.

Over time a notch gets worn in the splines. Then when the TQ expands under load it hangs up in the notch and puts excess forward pressure on the engine thrust bearing.

RBob.

 

I have only pulled the thrust bearing cap at the moment and the bearing looks normal. I am not running an oil filter bypass. This shortblock has been with three different transmissions, two different 700-r4s when I had it in my old Formula and now with a 200-4r in the MC, I will check the input shaft splines tomorrow as well as snap some pics of the thrust bearing and crank. Cruzin brought up a good question, is my crank trashed? Damon mentioned improper assembly, what could I have done wrong? I can see improper assembly leading to it running for 20 minutes, but I have 20k and never had any oil pressure or bottom end noise issues.

 

im siding with the transmission problem. if there is a small nick on the inside of the pump keyway, and for some reason it gets hung up when accel/decel it could be momentarily putting pressure on the thrust bearing. I had that exact thing happen on my 545 BBF in my truck. I nicked the inner pump keyway with the converter snout when i was putting it in. 100 miles later i had a trashed thrust bearing and a completely demolished front pump. make sure the trans it tightened down too.

 

I`ve heard about OD thrustbearings. Cheaper than a new crank

 

The thrust bearing is part of the rear main bearing shell.... ¿¿¿ ??? Can't say as I've ever "heard of" any such thing..... this looks alot like the earlier "contribution" of entertainment up there... not real informative, at best.

Given that a crank is less than $200 for a new one or even less than that if you go with a reground stock one, even if you DID have to go that route, it's not really anything to get all wrapped around the axle about, anyway. Kiss it good-bye and move on.

Somehow I find it hard to believe that about anything going on inside an auto trans can come ANYWHERE CLOSE TO the forces generated by a manual trans, which are typically 2500-3000 lbs or so of force on the clutch; DIRECTLY APPLIED to the crank thrust bearing. I'd look for something else, inside the motor. Most likely incorrect machine work or assembly, as detailed above.

 

Here are some pics. On the main bearing pic, I was able to see the separated piece sticking out between the crank and the bearing itself, it looks like there are some hairline cracks in the top layer and that small piece completely separated. Seems like a defective bearing.

 

The one that's missing a piece, looks like the result of detonation, hammering on it. What do the rods look like?

On the rear main: is that damage in the very center of it; about the size of a dime, right directly in the middle?

I don't see anything that looks like a bearing defect to me. That's kind of looking for an easy way out, and not facing up to whatever the REAL cause is. I know it sucks to see your own handiwork fail; but you'll never get any better at it unless you analyze the results honsetly, and squarely face whatever the truth is, and learn the lesson that's there to be learned whether pleasant or humbling or what. Weaseling out and blaming a failure on some magic or voodoo or something you can't explain, about guarantees that it'll happen again.

 

That spot on the rear main lines up directly with the oil pump bolt hole, I can't tell if its heavily worn there, or not worn at all. Notice the same 'look' of that area also shows up where the two bearing halves meet. As far as the other bearing goes, I wasn't aware that detonation would have that effect on a main bearing. I haven't completely pulled apart the engine but when I do, should I notice more of the same?

 

The only force applied to the thrust sides of the bearing is the force of the clutch fork pushing on the pressure plate. And how much could that be?
Lets say the clutch pedal moves 10inches. And the throwout bearing moves an inch.
And a it takes 10lbs of force to move the clutch pedal...so 10 to one advantage we got 100lbs. And that force is only there when you press the clutch. I could be way off on my numbers but i know there isnt 3000lbs of force on that cheasy throw-out bearing thats hooked to the fork.

The thrust bearing in my mopar got wiped by a ballooning converter. And I guess its not a super rare thing because higher end converters come with "Anti-ballooning" plates.
Note the gap between the bearing and the crank at the very top of the pic.
Wiped the crank and if left alone would have killed the block.

 

That's exactly what I was getting at; it looked that way to me.

I'd almost bet money that if you look at the back of the bearing, it has the mark of the end of the (non-)oil pump bolt.

That's supposed to be a "special" bolt. 1-15/16" long IIRC. If you use a std bolt (2"), or a head bolt or something, it will bottom into the back of the bearing. It's especially common for people to do that on 400s, with their larger main journal bore and consequently slightly thinner rear cap.

If the bolt is OK, look carefully at the bolt hole itself; it may have a little burr thrown up around the hole. If so, chamfer it before re-assembling it.

Yes detonation affects bearings. It usually shows up on the rods first. What I'm seeing there, looks JUST LIKE detonation damage to the rods. It's a form of "hammering", where eventually the thin soft coating of the bearing fatigues and fails from the constant pounding. Expect to see the rod bearings looking about the same.

Oh... and as to the clutch pressure: look at typical clutch specs for the "draw" number. That's the tension in the diaphragm or springs or whatever. Whatever it "seems" like, the fact is the fact: a typical street clutch puts a couple thousand pounds on the thrust. And, it takes typically something more like 50-80 lbs to move the clutch pedal; it moves 6-8" or more; the throwout moves less than ½", usually about ¼" - 3/8". The multiplication of force is the inverse of the distances moved. Do the arithmetic. (8" / 3/8") x 80 lbs = 1706 lbs, for example.