# bottom end knock...Help!



## Premierplowing

One of my Jeeps has developed a bottom end knock once the vehicle gets up to operating temp. Its most noticeable at low rpm, when shifting from forward to reverse or the opposite. Oil pressure does drop a bit at temp, down to 6-8 psi. But when revved, it jumps to where it should be. Any ideas on where to start to diagnose the problem? I'm thinking its either the oil pump or main bearing failure. 

Thanks for any input

Tim 

1995 Wrangler Sahara 4.0/Auto


----------



## jasonv

Premierplowing;1514144 said:


> One of my Jeeps has developed a bottom end knock once the vehicle gets up to operating temp. Its most noticeable at low rpm, when shifting from forward to reverse or the opposite. Oil pressure does drop a bit at temp, down to 6-8 psi. But when revved, it jumps to where it should be. Any ideas on where to start to diagnose the problem? I'm thinking its either the oil pump or main bearing failure.
> 
> Thanks for any input
> 
> Tim
> 
> 1995 Wrangler Sahara 4.0/Auto


A knock shouldn't be caused by an oil pump failure, though damage caused by a lack of lubrication due to an oil pump failure certainly could. That would indicate two MAJOR (related) problems, and a potential for damage throughout the engine.

Both the jeep's we've had (89 and 91) have exhibited oddities with respect to oil. Both oil pressure gauges would be pegged at all times while running. The 89 was sold mid 90's with an oil consumption problem of 1 qt per half hour highway driving. I acquired the 91 much more recently, and I intend to just keep running the thing until the engine completely self destructs itself, then replace the engine with something real. It sounds to me like yours may be ready for a new engine.


----------



## theplowmeister

Engin Knock is not subject to shifting gears. Look for another problem IE bad motor mount , tranny mount....


----------



## jasonv

theplowmeister;1514730 said:


> Engin Knock is not subject to shifting gears. Look for another problem IE bad motor mount , tranny mount....


It is subject to engine speed and load, which are affected by what gear you're in.


----------



## Premierplowing

The noise is apparant only when off the throttle WHILE at s changing gears or at an idle


----------



## theplowmeister

jasonv;1514892 said:


> It is subject to engine speed and load, which are affected by what gear you're in.


Load and speed not changing gears something else going on


----------



## theplowmeister

bad lifter ? the lifter is about midway down on the motor low oil pressure could cause knock at idle (doing bearing damage at the same time)


----------



## jasonv

theplowmeister;1515061 said:


> Load and speed not changing gears something else going on


Just for academics sake, WHILE you're changing gears, the load is LOW. If a conrod bearing is worn, you could experience a piston slap knock at this moment.


----------



## Premierplowing

I'm fairly sure it's a rod knock. Its too loud and deep sounding to be a lifter noise which is a ticking sound. This is a beater jeep that we only use for residential properties and since winter is right around the corner , I just want to bandaid the problem to limp through the winter. Can I just put in new main bearings by pulling the pan?


----------



## jasonv

My father did the rings on an '89 on his driveway. I was out of town at the time, but I know for fact that he didn't remove the engine. I presume that he must have accessed everything by pulling the pan.


----------



## theplowmeister

Yes you can replace the main and rod bearings from under the jeep


----------



## jasonv

One last thing I'd like to add... before you rip into it, be sure to get a second opinion from someone skilled who can actually be there to "experience" it. It really would suck to rip the engine apart and then find out that the bearings are all perfect.


----------



## theplowmeister

jasonv;1515421 said:


> One last thing I'd like to add... before you rip into it, be sure to get a second opinion from someone skilled who can actually be there to "experience" it. It really would suck to rip the engine apart and then find out that the bearings are all perfect.


i second that


----------



## Mems

Try a heavier weight oil as well. $15 worth of an oil change is well worth being able to see if some of the components are worn past their perspective "tolerances" and are now starting to create some knock in the engine compartment. Ultimately, yes the engine sounds like it needs a closer look, but the simple band aid of changing engine weight oil will give you a little better idea for cheap money.


----------



## Premierplowing

I ran 20w50 in it and it went away temporarily until the oil thinned out.


----------



## basher

You can access the bottom end thought the pan. I had this issue on the kid's 97 4.0L, when we dropped the oil pan we found pieces of piston skirt. My solution was a new long block, only cost about 2K total with us doing the work. Good to go for at least another 160KThumbs Up

Quick fix attempt; Lucas oil additive.


----------



## DieselSlug

This was my old WJ. Bought it, drove it 700 miles delveloped a lifter tick type of sound then turned into a full blown knock. And this was already a replacement engine supposedly by P/O...


----------



## Premierplowing

I finally got around to getting the Jeep out of storage today. After getting it running I drove it around a bit to try to Reproduce the sound it made at the end of last season. The noise ended up coming from the transmission, It would only make the knocking noise when under a load. The fluid was a little low ...topped it off and the sound seems to have gone away.
Any idea what was making the knocking noise?


----------



## theplowmeister

U joint? else no clue on auto trans


----------



## Premierplowing

No cant be, I had one of my guys trying to find the source while i loaded the drivetrain with the brakes applied. Only made noise in R, D, 2,1... Not in park or neutral...I assume because it had no load on whatever was making the sound.


----------



## theplowmeister

Premierplowing;1518049 said:


> No cant be, I had one of my guys trying to find the source while i loaded the drivetrain with the brakes applied. Only made noise in R, D, 2,1... Not in park or neutral...I assume because it had no load on whatever was making the sound.


Ya, U joint will make noise when a load is on it not so much without a load.

step on the brake so the jeep wont move shift from rev to D do you get the noise?
in drive with foot on brake but allow jeep to move do you get the noise?

is the noise frequency the same as motor or 3 times as fast as wheels?

I dont buy piston slap or bearing slap ONLY when changing gears. not going to happen

If it sat all summer could be a seized U joint IF it happens ONLY when the jeep moves. 
Bad U joint when moving or shifting D to Rev


----------



## Mems

Plus U-Joints are an easy and cheap fix. Probably need and should be done anyways. Take a few hours and $20 and swap em out.


----------



## theholycow

Wow, that'd be a pretty cool U-joint that can tell when fluid was topped off...or did you guys miss this part?


Premierplowing;1518004 said:


> The fluid was a little low ...topped it off and the sound seems to have gone away.


----------



## Premierplowing

It's not a u joint, I know what a bad one sounds like, plus you have to be moving to hear a u joint when its bad. When we did the brake stand, the noise would raise and lower with the speed of the engine ONLY when in gear. I'm thinking it could have been the torque converter wasn't full or something. Last winter we did have one of the trans lines rust out and piss fluid all out. The lines were replaced and ran perfectly for months until the last storm of the season when the noise started. Hopefully it's gone for good, but I'm still stumped.


----------



## jasonv

Well, good thing you didn't rip the engine apart 

Auto trannys suck, and auto tranny's low on lube REALLY suck.


----------



## theplowmeister

theholycow;1518405 said:


> Wow, that'd be a pretty cool U-joint that can tell when fluid was topped off...or did you guys miss this part?


doooough............I missed that part


----------



## Rockdaddy

I cracked flex plate can sound like a rod knock


----------

