When cold it sounds fine, but over 165° it starts to knock and gets worse at 200°+. Sounds worse at idle. I pulled the plug wires one at a time with no change until #8. Oddly it seemed to get worse. I thought it was supposed to get better if it was a rod bearing? Anyways, does this sound like a pretty typical case of rod bearings or maybe something else? I'll see what I can do to post a video.

Video added.
L98 with knock:

Thanks.

 

a rod bearing is loudest when you let off the accelerator temp shouldnt make that much diffif it is a rod
good luck

 

The video says
private" ????

regardless, a rod will be more of a "rapping" sound that does get instantly louder the instant that you LET OFF the gas after revving it. That is due to the reciprocating forces slamming the opposite direction in the loose rod bearing and the slack in that bearing makes the noise.

If the noise is all the time, it may well be a lifter collapsed, or something in the valve train. It COULD even be external....TC bolts, flywheel or dampener.

Get the stethoscope and listen to isolate the exact area of the noise and what makes it louder.
Next, might drain the oil and strain it thru a white sheet to see if there is any "silver paint" in the oil....(bearing material and debris)
If you did find something like that, the noise location becomes irrelevant as the engine has serious mechanical issues and has to come apart anyway....

 

Sorry about the link. That was my first video upload, so I'm still figuring it out. It should work now. The noise sounds low in the motor. I don't know if you just don't notice it, but it sounds good if you give it a rev. Doesn't seem to fit the "let off the gas after rev" MO. You can hear it very clearly on the video. Just trying to do my due diligence prior to yanking the motor....again.

I should add that though the clutch has been bled several times, its still not disengaging properly. Its like its dragging all the time wanting to pull the car forward and grinding reverse so bad you can only get it in when the motor is off. Not sure if the two things are related. When hot the oil pressure reading is super low too.....5 or 6psi and sometimes drops to 0.

 

Pull it.

 

sounds like crank and/or rod bearings

 

yup...


Low oil pressure @ idle when warm is the classic sign for worn/gone mains. If the mains are gone, good chance the rods are too !

How many miles on this eng? or is it a case of abuse? These are usually good for 150,000 to 200K if taken care of.

Then again,. I knew a guy that believed that you filled the engine with Mobile-1 and NEVER had to change the oil again....just top it off once in a while....I wonder what mobile-1 looks like after 100,000 miles?

 

126,000 miles but this car has a long story. It has basically been almost completely overhauled. It even has a new crank. The first mechanic did all that work but things didnt seem to be put back together correctly. Had a second fix those issues and now I'm looking at this. I honestly can't tell you if the first mechanic replaced all those bearings or not. Seems like something went really wrong with his install though. Sucks!

 

126K ????????????? That's not even considered to be "high miles" anymore.

and someones been in there before?

yeah, sumthins seriously wrong !

Good luck !

 

I was thinking a dual mass f.w. is a possibility (?), but 86's didn't have them I don't think. and that wouldn't have anything to do with the low oil pressure. That is an odd "knock" sound though.

 

Sounds like you have a cracked block. My 88, 43000 mi. had same symptons. Pulled engine and had it magnafluxed, sure enough cracked. Sounds like first mech. replaced crank and bearings, to get running. Then sell.
Good luck Joe

 

Well, that definitely sounds like a rod knock from the video. If you pulled the 8 plug and it stopped, then there you go. Hard to say about causes and conditions at this point.

 

He didn't say the noise stopped when he pulled #8 wire...Based on that, + the oil pressure...At this point it doesn't really matter what the issue is; he has a bottom end issue and it needs to come out and be torn down.

 

I'd pull the pan and be prepared for the worst...no...the worst would be to NOT pull the pan and have the engine grenade on you.

 

What all should I be looking for in pulling the pan? Anything besides metal fragments? Is it guaranteed that I would find something if any of those bearings are bad?

Either way, it sounds like the consensus is that it has to be yanked out of there and rebuilt. If that's the case, im sure I am looking at having to hone the cylinders, new pistons and rings, bearings, what else? Whats the price tag for something like this? I say pistons, because those are the only things that weren't done last time. Doesn't make sense to pull in apart again without doing everything.

It has a new crank, new cam, new heads and valve train.......I assume all of that should be fine, since it doesn't even have 100 miles on it all. Please correct me if Im wrong so I know what im getting into here.

Also, has anyone seen a good write up or how to on pulling an l98? It'll save me a ton if I pull in and install it myself.

 

If you pull the oil pan.Pull the bearing caps and inspect bearings. If they are smooth, clean and use plastigage to check clearence. Same with rod caps.

 

Might be easier to cut open your filter. If there are metal flakes (silver or copper), your motor is toast. If there aren't, keep looking.

 

I missed that, oops.

But yeah, at this point it doesn't really matter which cylinder is knocking.

 

shut that motor down dont run it,pull it befor you blow it! and have to get a complete motor.

 

Yeah, sorry to say, but that's rod knock. I know that sound well.
If you can, get a cheap automotive doctor's stethoscope at your local auto parts store and when it's running, see if you can pinpoint which cylinder is the loudest. On a later L98, you can check each centerbolt valve cover holddown bolt with it to instantly pinpoint which cylinder, but on an '86 that has conventional four bolt valve covers, it will be a little harder. You will have to probe around with it.

After that, I would get underneath and drop the oil pan. It is surprisingly easy to do on a C4 without pulling the engine (just make absolutely sure you support the car properly with a real floor jack and proper jackstands before getting under it) and once it is off, it is not hard to figure out which rod has the bad bearing. Just jiggle each rod cap...anything making that much noise will be readily apparent. Once you confirm, you will likely have to pull the motor.

In the meantime, try not to run the motor too much...bearing material from that one bad rod is likely going everywhere through your engine via the oil resulting in increased wear or worse. If you catch it early enough, you may get away with just polishing the crank although at this point you might even be past the point of grinding the journals undersize on that one problem area. Might be cheaper and easier to get a replacement crank in good condition. Also, you may find that you need to have a good machine shop re-size the big end of that one rod. If it is a spun bearing, tolerances have likely gone out of spec. If they weren't before then they are likely to be now. Make sure everything is to spec or else you will find yourself having to do the job all over again.

Some people will pull the motor and do a quickie disassembly and slap it back together, but keep in mind that the bearing material from that one bad area has travelled everywhere within the motor. The right way is to completely disassemble the motor and do a proper rebuild after cleaning out all the oil passages (rifle brushes or engine cleaning kit) to ensure there is no leftover foreign matter to injure your fresh new parts. Personally, I would have the block magnafluxed and hot-tanked as well which is the route I took with mine. Don't forget the oil cooler (if equipped) either as bits of bearing can get stuck in there, only to come loose into your freshly rebuilt or repaired engine at a later date wreaking new havoc.

Wishing you the very best...I've been there before and it really sucks, but it is not the end of the world, but rather the chance for an even stronger and better motor.

Roy