1975 cj5. 258. 3 spd. Just bought this jeep and it was running great until I drove it on the highway. The engine was rebuilt before I bought it. When I got off the highway and hit a stop light I noticed the knocking. I checked the oil. Nothing. It looked like all the oil blew out of the dip stick. I filled it up with oil but the knocking is still there. I took off the valve cover and checked the rockers, they seemed ok. I suspect a main bearing but want to take all suggestions before taking the oil pan off. I am planning on swapping engines evenutually but would like to stop the knock even if only temporary. thanks.

I drove my jeep for a while with a knocking 258. After a year of it running like shit, I figured out I had a blown motor. Then I did a two year ordeal putting in a 4.0. Most of that time I was off working and it sat in the side yard. Dan

Is there any way to pin point the problem? Or am I right about the bearing? thanks for your reply.

I've seen this exact thing on a 258 a buddy of mine used to own!  It had a knock that was so loud it was embarrassing to drive around town.  He had to put a piece of rubber tubing with a bolt stuck in the end of it over his dipstick tube and keep the dipstick in the backseat to keep the oil in it.  His was from a cylinder being out of round and the piston skirt was slapping the cylinder wall.  It caused major blow by.  His was caused when, shortly after a rebuild, a rocker arm retaining bolt broke and allowed a lifter to jump out of the galley.  This made him lose all oil pressure.  Being extremely non-mechanically inclined he kept driving it with the low oil pressure.  It had enough pressure to keep from trashing all of the engine but not enough to spray up on the #1 cylinder wall.   Sandy '80 CJ5    

Thanks for the info. How can I find out if is a bearing or piston or anything. Would a compression test tell me if this is the problem. I'm trying to pinpoint problem before I take any action. It is embarrassing.

Sandy

A compression test will tell you if it's the piston.  With so much blow by that your oil comes out the dipstick there has to be something wrong piston wise.    

I wouldnt suggest wasting your time on the mystery fix oils.Nothing will fix a collapsed lifter. Thicker 20w50 oil will help. But ultimately replacement is the cure.Than i would suggest worn out lifters.All the cases of rod knock i have seen gets horrible with more RPM. Also on a high mileage engine i wouldn't suggest punting in new bearings...without the crank being check and turned.
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