Engine knocking...

[pvt.tadpolxj]

Hey everybody I need some professional advice. My engine is knocking pretty loud after warm-up time and continue's loud until i get on the road. then when i get to a stop somewhere it is a lot qiueter. this could be bad main bearing's. But i read on Cherokee Forum. sometime's a cracked misaligned flywheel can cause engine knock. Can somebody help me with this?:stars::stars::stars::stars:

[4.3LXJ]

Generally a bad main bearing will knock when revved with no power to the wheels and stop when power to the wheels is applied.

[pvt.tadpolxj]

Thank's 4.3l XJ do you recommend any kind of oil treatment or a diffrent oil wieght?:stars:

[Mudderoy]

I recently developed a low tone, low end knock near the rear main bearing. There's a post on here somewhere...

Anyway as I recall the knock would get louder as the engine slowed down, almost like a rattle.

I pulled the inspection cover and the bolts that attached the flywheel to the torque converter were FINGER tight!

I was so happy that it wasn't the main bearings I quickly tightened them up and failed to put lock tight on them!

Oh well I'll put lock tight on them twice next time!

[4.3LXJ]

Thank's 4.3l XJ do you recommend any kind of oil treatment or a diffrent oil wieght?:stars:

I run Valvoline 20W50 racing oil. Many people swear by the lighter weight oils. However, the oil recommendations by manufacturers are the lightest weight they can get away with so they can increase gas milage. Some of these get like water when warm. I have always had good luck with this oil since I started using it 30 years ago. It is designed for engines that are used hard. You will notice that your oil pressure will go up which may take care of your knock. It can also make the difference in a lifter that is marginal. My oil pressure in my Cheyy 4.3 stays at about 50# when warm, 70# on start up. Good pressure and the flow that goes with it is the key to good bearing life.

Most oil additives like STP and others only increase viscosity, but not lubrication qualities of the oil. So why don't you just give your engine a transfusion and go from there. If you do need to change the bearings, that can be done without pulling the engine and you can put in a new rear seal while you are at it.

[bigjim350]

When my flexplate bolts were loose, it would knock at Idle. If you were driving down the road it would not knock until I came to a stop. If I would rev it up in park, it would knock as soon as I hit the pedal then go away as the revs went up, then come back when the revs came down. Its pretty easy to check for after you get the inspection cover off. Check for loose bolts, and shine a flashlight up there and check for cracks.

[pvt.tadpolxj]

Thank's everybody. I need to know what the word viscocity mean's like in oil treatment's?:stars:

[pvt.tadpolxj]

I have never used any oil's other than 30W. or 10W30... Will this factory 4.0 be O.k. with 20W50. 4.3 LXJ.. Muddy, BIGJIM !!!:stars:

[bigjim350]

I run 20w50 in all of my vehicles, including the Jeep.

[pvt.tadpolxj]

Thank's Jim.. I'll get it in today and get back this evening...:smiley-laughing021::smiley-laughing021::smiley-laughing021:

[Punisher]

I had this problem a while back when I first got the jeep and its the flywheel that cracked all around the bolt holes...
But if your flywheel is not crack then the next think to look at is that rod knocking... you wont hear knocking if the meain bearing spun out unless all of then went bad at the same time but thats highly rare... and theres no oil treatment that will fix a rod knock, it may only make it quieter... but I heard you can use gear lube to make it quiet for a little bit but you will need to do a rebuild....

[steph74]

I had this problem too on a renix engine though.... I put Rotella dyno 15W40, upped the low idle to 750, and knock was just there but quiet.... then I had an illumination and I grabbed a random knock sensor at the JY and Knock is gone ;)

[4.3LXJ]

Thank's everybody. I need to know what the word viscocity mean's like in oil treatment's?:stars:

Viscosity in a nutshell means resistance to flow. Honey is more viscous than water. When you have a more viscous oil, it does not flow out of the bearings as easily. This has two benefits. First, it protects the bearings more under load, especially when lugging. Second it stays in the bearings longer when the engine is not running so there is no bearing contact when starting.

[4.3LXJ]

I had this problem a while back when I first got the jeep and its the flywheel that cracked all around the bolt holes...
But if your flywheel is not crack then the next think to look at is that rod knocking... you wont hear knocking if the meain bearing spun out unless all of then went bad at the same time but thats highly rare... and theres no oil treatment that will fix a rod knock, it may only make it quieter... but I heard you can use gear lube to make it quiet for a little bit but you will need to do a rebuild....

Yes you can. But eventually that will take out the camshaft. You need splash from the little holes in the rods to lube the lobes of the camshaft on flat tappet engines.

[xj4life2]

I would highly recomend that you get a stethascope and locate the source of the knock . I have seen alot of cherokee's that are mis diagnosed with a rod knock and its actually a bad lifter, just a thought !!!

[pvt.tadpolxj]

Thank's everybody. this post is such a big help fpr me. I did install the 20W50 0il today and it is still knocking, but man it is running a lot smoother. I really appreciate the qoute about checking my lifter's I know there is no adjustment, but it will be worth the check anyway. Maybe I will be lucky and some of them have worked loose and need to be retorqued.:driving::driving::driving:

[Punisher]

Yes you can. But eventually that will take out the camshaft. You need splash from the little holes in the rods to lube the lobes of the camshaft on flat tappet engines.

Your right, So that why I said ya might as well do a rebuild if it's a rod knocking, unless ya going to sell it adding gear lube is to just to keep the knocking queit for the mean time :D

[mw14c]

PLEASE DO NOT PUT GEAR LUBE IN YOUR ENGINE!! Gear lube is not the same as engine oil. It is "Hypoid" oil and does not have have any lubricating properties related to engines. Check your flex plate first. Pull plug wires one at a time. If the knock goes away with one you probably have a loose rod bearing. The reason the noise is coming from the top end is because the piston is traveling to far upwards via loose bearing and hitting the head. Removing ignition to that cylinder will relieve stress and allow piston to "free float". Everyone thinks connecting rod bearings should be heard in the bottom end but its seldom the case.

[pvt.tadpolxj]

Thank's Friend.....I have solved most of the engine noise by running Valvoline VR1 oil....10w30......It is Racing oil and has diffrent propertie's than conventional oil's....It is also very high in Zinc/ Phosporous......:watermelon: