knoxville

So, i'm in the process of replacing my oil pan gasket and tracking down the typical 4.0 knock while i'm under there. I checked the rod bearings which seem okay ( a little side to side play but not up and down ) and after following many members' advice I checked the flywheel bolts and i got between 1/2 and 3/4 turn on them. Do you guys think thats enuff to give me a knock (only at idle)? I looked for flexplate cracks and didnt see any. Just wanted opinions before I put the pan back on. Also just for grins, would you guys replace the oil pump (40lbs press now) and bearings or just leave it alone; other than being noisy and leaky it runs fine. As always thank you your help is appreciated!

93 sport 4.0 auto 4wd 185xxx

miglia-spyder

im guessing thats enough to make the flex pate make noise. You should take them out one at a time and put thread locker on them!

Hommersimpson

I would at least pull a few rod caps and a main cap and look at bearings.. and def replace rear seal so theres 1 main cap then needs to come off.....

were the bolts tight ? and you got them tighter ? or when you went to tighten they moved easy at fist then got tight after 1/2 3/4 turn ? if you put wrench on them and moved them easy at first.. then yes that could cause a knock...

knoxville

Yep I'm gonna, Thanks

knoxville

They were kinda tight but I put a wrench on em and got em tighter.
If I do pull the rod caps, do i replace the bearings? If so do i put the same size back in? Or do i reuse the old ones? Kinda scared to get into plastigauge and torquing the bearing I never did this before and dont wanna screw up my motor, it still runs great, just noisy

Hommersimpson

well.. its easy.. you will need a torque wrench and thats the only special tool...take one off and look.. take a pic and post.. if it has any copper showing at all.. replace them all.. you can take one to parts store with you and they will match it up.... just to make sure you get right ones..
its not hard.. and if the top end is still working good.. a fresh set of bearings means the motor might go 100-200k more..a new oil pump wouldnt hurt... but its not manditory if it was working well before..

knoxville

Hmmm, alright Hommer, i got a torque wrench so, I may do that. Do you happen to know the torque specs? I got a Chiltons but I dont really trust it, seems they aint what they used to be very vague on info and minimal / maybe incorrect info. Thanks alot guys I really appreciate the help and FAST responses !

Hommersimpson

33 ft lbs
http://jeephorizons.com/tech/99_40l_torque_specs.html

make sure you put caps back on the same way they came off and on same rod....

mikeXJ1020

So common for the flex plate bolts to be lost. My flex plate was cracked almost all the way through. That was a fun job pullin the tranny off

-Mike

knoxville

Well Mike, the oil pan wasn't exactly a walk in the park either Ya know??!! LOL

Jeepman659

haha i feel ya on both i had to do the oil pan for the rear main seal and had to replace my flexplate as well. now on to the damn rattle from the cracked exhaust manifold! but deffinetly use lock-tite on those flexplate bolts.

knoxville

10-4

5-90

"Portion of a turn" is immaterial - make sure they're torqued properly!

IIRC, proper torque for those screws is 105 pound-feet, but you can check the lists in the Tech section of my site to get the FSM value.

Definitely use threadlocker! If you're reusing screws, clean the threads and then use threadlocker! A wire wheel will work on the screws proper, you can make a "thread chaser" for the internal threads by taking a 1/2"-20 screw and cutting three or four longwise flutes in the threads using a thin cut-off wheel. Run it in and out of the hole by hand - this will remove any debris and scrape off any old threadlocker that will get in your way. Apply new threadlocker and torque.

Why is the portion of a turn immaterial? I can take a screw torqued to 105 pound-feet, and get a good two full turns out of it without too much trouble (provided the screw holds up.) It will then be torqued beyond utility. I'm a big guy, and it's no trouble (I did the "industrial mechanic" thing for a bit, and having to crank big-*** screws and nuts down to 300-400 pound-feet was common. And I did it using hand tools, since the boss was usually busy with the airgun taking the next thing apart.)

If you've had the screws reasonably tight before you cranked them down another half-turn, you may have stressed them beyond the "yield limit." Steel, recall, is "plastic" - in the engineering sense of the word. This means it can be deformed recoverably up to a certain point (which is called the "yield limit." Also called "Yield Strength" of a fastener - it's the internal tensile preload that may be applied and the fastener will still return to its original shape reliably.)

If you torque a screw past its yield limit (like a "Torque-To-Yield" cylinder head screw, as used on Diesels,) you've just wrecked it. TTY screws can only be used once and then they get thrown away - they're deformed when they're pulled out.

If you've got the screw torqued resonably well, and you crank it down some more, it's a good chance you've overdone it and will need to replace it. I found an ARP kit that will work to replace the screws if you have a flexplate - I don't recall the number, but it's the flexplate screw kit for Pontiac V8 engines. 6 pcs 1/2"-20x.590", 3/4" 12-point head.

NB: Do not use hardware store screws! They're the wrong head style, and won't give you the clamping force that is required! You can check a "farm & fleet" or a Diesel mechanic's supply house, ask for a "place bolt" with the dimensions above (you can use 1/2"-20x1/2", and probably 1/2"-20x5/8" if you grind the end down a bit for clearance with the engine block casting. You wouldn't be able to find that dimension of screw at the harware store anyhow.) Getting a "place bolt" is vital - the head style is different underneath, and is designed to allow for maximum clamping load when the join is loaded in shear - the clamping force is provided by stretching the screw, but the joint usually loads the screw additionally in tension (pulling.) Shear (sidewise loading) requires a different head design, if you're dealing with a single shear joint with power transfer (like a flywheel or a flexplate...)

Oh - and if it's an automatic, check for flexplate cracks! They're probably more common than loose screws. Get a big flat screwdriver (or a short prybar) and a small flashlight - shine the light up toward the hub of the flexplate, then use the screwdriver to prise it back and forth. If you see the flexplate detach at the hub, you're in for a replacement. Pioneer/Barnes is an aftermarket part I've had good fortune with - and get new screws (installing new screws with a new flexplate or flywheel is cheap insurance... Chase threads and use threadlocker as before.)