Sorry, this is a long one with lots of questions.

I have done a lot of shade tree mechanical work in the past, and I'm pretty confident in the work that I have done. That being said, I haven't done a lot of work on the inside of an engine, (rotating assembly and camshaft stuff). My 390ci has a slight knock. I only notice it after it warms up, and I don't hear it at idle. Because of this I do not run the engine; I don't want do anymore damage. I assume it is either the crank bearings or rod bearings, (my guess is probably rod bearings), but I don't know 100% for sure. I plan on pulling the oil pan off and taking a look at the engine. I assume if my rod bearing are worn enough to knock, then I would be able to notice some play of the rods at the crank. I've read that a spun bearing is a common cause for an engine knock. I really hope this is not what I'm dealing with. Since it's just a slight knock, is there a chance that it may not be a spun bearing? I do not have an engine stand or a cherry picker right now, so I'm hoping to fix this in the truck, however, I assume a spun bearing would require machine work, (i.e. removing the engine).

Best case scenario: I don't have a spun bearing, and the crank journals aren't scored. Do I just replace with the same size bearings that I took out, and torque to spec, or is there more too it? Should I use Plastiguage when I do this?

I'm sure these questions probably seem real simple, and I'm sure some of you have done this many times. This will be my first time doing this, and I just want to ensure I'm doing it correctly. I would love to pick your all's brain about this. I do intend sometime in the future to have a complete rebuild done, (or a crate 390), when funds permit, but for now I'm just trying to get my truck on the road so I can enjoy it, and the satisfaction of knowing I fixed it myself. Thanks.

 

What does the oil look like? Any metal?

Pulling the pan and checking the rod bearings might be worthwhile, but if it's a spun rod, you can't fix it as you have to pull the pistons out the top.

If you don't find any bad rods, you could make sure of the rod size and just replace the shells with new ones of the same size. IMO a bit of a gamble. If it's knocking, the rod could be out of spec and your new bearing shell could quickly produce a spun bearing.

So you go through the aggravation of pulling the pan, working under the truck etc, with a less than 50-50 chance of fixing the problem. Again, jmo.

I would rather pull it and go through it top to bottom and make mild to hot powerhouse out if it. Again, ymmv.

 

I've had bearings spin on be in an air cooled VW and in a mid nineties Chrysler. It's a kind of 'thud' sound that's hard to communicate in text but is very distinct. One thing I can tell you is it happens all the time from the moment your start it up though.
I hate to be the one to ask this, but you've checked you oil level? Spark plugs?
A mechanics stethoscope might help. I agree with the previous poster, check out the top end.
Also, exhaust leaks can sound kind of like a knock and get worse when everything warns up.

 

"85e150six4mtod" is right. If you have a knock, you almost have to take it apart, or it's a BIG crap shoot!! It will all have to be measured to see what is out of spec and which size bearing is needed. Or maybe you may need a new rod or crank. If you replace just the crank bearings (assuming the crank is still in good shape), then the rod bearings might go out next, or the wrist pins in the pistons. Unless your x-ray vision is working better than mine( and mine quit) you don't have a lot of options. I think S and D engines still has an 8 year warranty on their reman engines. Or you might be heading down to Harbor Freight for that engine lift for your birthday present. Let us know what happens

 

I appreciate all the advise. I was hoping to fix it in the truck, but I agree with the consensus here. Looks like I get to make a Harbor Freight wish list now. I have done almost no mechanical work to the truck since I've owned it. I did install a new oil filter. I tried to open up the old filter to inspect it for metal particles, but I ended up adding metal shavings from cutting it open, so I wasn't able to accurately inspect the filter. The oil is old though, and I'm going to change the oil soon. when I do that, I might go ahead and pull the pan, and inspect the sludge, if any, in the pan, and have a look at the engine. I also need to do an entire tune up, and carb rebuild. This truck was sitting for a long time before I bought it, and I've only started it maybe 3 - 4 times in the last 2 years. Again I appreciate the advise. I'm going to start saving up for a rebuild.

 

Other Engine Knocks are caused by
Carbon on top of pistion.
Broken piston skirt, or badly worn piston/cylinder wall
Piston Pin worn in piston or possibly in rod end.
these are top end engine knocks.
remove a spark plug wire on each cylinder untill knock becomes less to help determine which cylinder is Making Knock. You may have more than one cylinder knocking.
good luck
20w50 or Heavy weight 40 straight weight oil may dampen the Bearing knock. This is not a long term fix.
Just some info to know in addition to the posts you have.

 

Worn bearings usally cause low oil pressure, metal in oil, cut open oil filter to inspect.

 

 

2X check oil pressure. A sludged up oil pump pick up screen can cause low oil pressure also. It would choke the oil pump. We don't know why the truck was parked those years ago. Drain that old oil out. See if there is metal bearing material in it. I have a feeling there won't be. IMHO it is a problem caused by sitting so long then being started. Is the oil sludgy? Pull the valve covers. Tons of sludge there? If you find sludge, oil pressure low, and no metal in the old oil, pull the oil pan and check that pick up screen.
Again, we don't know why it was parked originally. But I know Penzoil oil used to cause sludge back in the day.

 

I do not know why it was parked. From what I can gather, the son of the guy I bought it from was going to fix it up. He had most of the interior stripped out. I guess at some point he lost interest, and gave it to his dad, who didn't really need it and just left it sitting. when you said that in your opinion it's a problem caused by sitting so long then being started, Do you think it has done permanent damage, or just needs fresh oil, and a clean screen? I hope you're correct about it being the screen, that would defiantly allow me to get it on the road quicker. Thanks for the advise, I really appreciate it.

 

You should do the general maintenance items.
1) Oil and filter (you may want to add a little Marvel Mystery Oil, this is good for the top end of the motor).
2) Plugs, wires and points.
3) Check the exhaust manifolds and pipes, likes can sound like a knock and get worse when hot.
4) Check the tranny and rear end.
5) Brakes and steering.

Once that is done you need to find out if the noise is still present. If it is you need to find out if its in the bottom end or top end. Get a mechanical oil pressure gauge and hook it up. Run the engine to temp and see what the oil pressure does. If it drops below 20psi at idle when warm it will need to be refreshed. Remember you are dealing with a motor that is over 40 years old, it could have well over 100,000 miles on it at this point! 390's have been known to go on a long long time.

 

Absolutely. I will try to get this done soon. I know the exhaust is in terrible shape. P/O hacked the exhaust to make dual exhaust that clears the saddle tank using flex exhaust tubing. I'll try to get a picture of it so you all can see just how terrible it is. There are definitely exhaust leaks. The transmission leaks like a sieve, and I think it might be the front seal, so I want to pull that and put new seals on it. I looked at the odometer and it shows around 80k miles, I don't think it has rolled over, but I honestly I don't know for sure. I really hope some basic maintenance, and cleaning is all I need for this engine for now. Otherwise it will be a while before I can muster the money for a rebuild. I will try to keep you all posted with updates as soon as I have them. Thanks again everyone.

 

What is the best way to open up an oil filter with out contaminating it?

 

New blade in a razor knife (don't try to cut all the way through in one cut, it will take several passes) and metal snips (avaition shears).