A friend has a 1980 Sedan deVille with the 368 engine in it. The car only has 40K miles on it and it seems to have spun a rod bearing (engine runs but sounds like a box of rocks being shaken). This hasn't been verified yet, but that's our best guess. Anyway, instead of pulling the motor and rebuilding it, I suggested that we might could drop the pan, remove the crank, inspect the crankshaft and replace the bad bearing if the crank checks out. An engine rebuild doesn't make much sense as that would end up costing more than the market value of the car.

I've done a lot of mechanic work over the years, but it's been mainly on old Volvos, so I'm a little out of my element when it comes to working on older Caddillacs.

Any advice that could be offered would be appreciated.

Thanks!

That's certainly worth a try... That was an old trick we used to do on 4100 engines with spun rod bearings. #3&5 would go bad and the engine would knock. Generally, a 368 is a very good engine, so with the low miles, it might do the trick. What happened, anyway?

I don't think there is enough clearance to get the oil pan off with the engine in the car. Usually the engine is removed and a new crankshaft and bearings installed. If the 368 has GM's famous plastic coated timing gears, you should replace those too. The biggest expense would be labor unless you have a good friend doing it for you. :)

That's certainly worth a try... That was an old trick we used to do on 4100 engines with spun rod bearings. #3&5 would go bad and the engine would knock. Generally, a 368 is a very good engine, so with the low miles, it might do the trick. What happened, anyway?

Not sure exactly. It's his late mother's car and he was driving it back to his place when it started to make noises.

Is it possible to pull the pan if the engine is supported and the cross member (if any) is removed? Sorry, but I'm looking at this as I would an old International truck or a Volvo.

Thanks!

Most rod bearing spins are result of a main bearing spin , bent crank, scored crank, egg-shaped rod end. Mostly due to oil problem to begin with.

If all is well then replace bearing shell only.

If you are used to dropping oil pans and removing crossmembers then you are going to be cursing the GM engineers. They don't see things that way. It sounds like it is definitely worth fixing though; good luck.

I understand that this might be quite a lot of work, but I don't want to bite off more than I can chew.:hide:

What would be the minimum that would be needed to verify that the problem is in fact a spun rod bearing? It doesn't sound like it's going to be as simple as removing a cross member and pulling the pan to check on things.

Any other suggestions?

Thanks!

Drop your oil and check for metal content. Usually a good indicator that something is wrong. With the engine at idle, pull one plug at a time, when it quiets down you'll have found the guilty cylinder.
Take out your trusty oil pressure gauge and tap into one of the oil passages and check pressure. Does your oil light (stop Engine ) light come on? The light generally won't come on until your down to 15 #s, but if your oil pressure is down to 18 - 26 #s something serious is going on. 35 #s is concidered normal.
These are all guidelines, if any or all are apparent then pull the engine out and dismantle it.

don't know if your interested or not but...
http://www.cadillacforums.com/forums/500-472-425-368/126393-v-8-6-4-a-2.html

Thanks for all of the replies to this thread, guys.

I'm going to get the car later in the week and I'll report back on what I find.

Anything I should do as far as cleaning out the oil system in the engine to help prevent this from happening again? I suspect some old, probably dried-out oil may have made its way down to the bearing surface when he started driving the car home and there might be some more gunk in there that needs to be taken care of. Any ideas about that?

Thanks!

My guess is the car sat around so much that the oil didn't get changed enough and turned acidic and ate the bearings up or they just got so dry from sitting that the bearings got scuffed before the oil started pumping. How does the oil look anyway? If you don't run it too much you "might" get away with just changing bearings. Good luck and I hope you can save that fine car.

I started the car today for the first time to listen to it.

I tried the above-mentioned trick of disconnecting the spark plug wires one at a time, but it had no effect on the knocking. The engine seems to be very smooth other than the knocking, which honestly sounds as if it is coming from the top of the engine in the center more than from the bottom as I would expect if it were a bad rod bearing.

Also, from looking at it, it appears that the engine will have to be pulled in order to really be able to find out what is wrong with it.

This doesn't look like much fun....:helpless:

Gee it would be nice if it just had a collapsed lifter. It seems like it would run a little bit rough if that were the case. If it wasn't thrashing too bad then it might be safe to run it a little longer to try to diagnose the exact location of the knock with a little more certainty. If it really sounds like it's higher like in the lifter area, you could take the valve covers off to see if there is a rocker arm not moving.

It almost sounded as if the sound was coming from the a/c compressor or directly under it.

Is it possible to run these engines without the valve covers? I know from working on International Harvester V-8's that it's entirely possible to do so if one has a valve cover that has been cut down the middle to form a pan on the lower side to help catch any oil on its way to the returns.

Do these engines use hydraulic lifters? Again, I'm familiar with those from working on IH engines as it's a common ailment on engines that haven't run in a long time.

We bought a two-volume set of manuals by Cadillac on Ebay tonight, so that should be a big help.

Yes it has hydraulic lifters. If you run it without valve covers then it might spray some oil but you should be able to spot a non moving rocker in 10 seconds or so. I suppose if the engine bay is spotless you could throw a couple blankets in there for 10-15 seconds to catch the oil.

It's making a hell of a racket. Would a collapsed lifter cause that kind of noise? The car was being driven when it started making the noise if that helps.

Perhaps I should video the engine/noise and post a youtube link to it...haha

It's starting to sound more like a rod bearing. It probably started out with a subtle knock that wasn't noticeable until it started making a racket. If so it sounds like the crank may already be damaged but the rod may be salvageable. I wouldn't recommend running it any more. If you really thought it was higher in the engine, you could always remove the valve covers and intake manifold and look for anything obviously broken. If it isn't obvious then it is probably in the bottom end.

From reading through the Cadillac shop manual that I bought, one of the first thing that is mentioned concerning a knocking noise is a bad harmonic balancer. Any thoughts on this possibility?

One thing that I noticed is that the a/c compressor is locked up and when my friend turned on the a/c, the clutch engaged, but the compressor didn't turn. I'm just wondering if a bad a/c clutch bearing could be making the noise. I figured I would disconnect all of the belts and start the engine just for a few seconds to see if the racket would go away without the accessories hooked up.

Thanks!

I have never run into bad harmonic balancers until the mid 80's GM V6's. I have my doubts but if the manual mentions it, it might be worth a look. I don't quite know how to describe it, but if the balancer was an old style type made with heavy steel then I wouldn't worry about it. Definitely remove the AC belt and see if the compressor is making the noise.

I don't think there is enough clearance to get the oil pan off with the engine in the car. Usually the engine is removed and a new crankshaft and bearings installed. If the 368 has GM's famous plastic coated timing gears, you should replace those too. The biggest expense would be labor unless you have a good friend doing it for you. :)


It took some doing but I was able yo remove the oil pan from my 81' Eldo to replace the cracked pan.

Sorry to bump this old thread about the Caddillac I was working on.

I disconnected all of the accesory belts and verified that the noise is not coming from the ps pump, alternator, etc.

I drained some oil from the enging and upon inspection, it appears that the oil has the appearance of metallic paint. Not tons of fine metal particles, but definitely enough to notice. They are very small in size, no large chunks.

So at this point from reading the factory manual that I bought, it appears that it is indeed possible to remove the oil pan from the engine without removing the engine. The would be helpful for diagnosis, but it also appears that in order to service the rod bearings, the piston/rod assemblies must be removed which means that the heads have to come off. Unless I'm misunderstanding the manual, it doesn't seem possible to fix any bad rod bearings without performing the above tasks.

Please let me know if this is not correct.

Additionally, if the crank has been damaged, the transmission must be removed in order to get the crank out. It would probably be easier just to remove the engine and do all of this on a stand at that point.

Any additional input from you guys?

Thanks!

Well ya know....a crank is a crank, and they all have rods bolted to them. You should be able to unbolt any rod in most any engine and slide it up in the bore and inspect or replace a bearing. I usually just grab them and shake them a little while they are still bolted in and can easily find the bad one.

Did you ever notice if that has a heavy steel balancer or a thin steel balancer? I think a thin one will go "ting" if you tap it with a wrench. The solid ones will have a solid thud. Those cheap tin balancers can make quite a racket when they fail. A broken rocker arm can make quite a racket too but when the engine is that loud you need to be fast trying to find it so you don't hurt the engine too much. We already mentioned that problem. The broken rocker won't hurt the engine much but a bad rod will. Good luck.

Sorry to bump this old thread about the Caddillac I was working on.

I disconnected all of the accesory belts and verified that the noise is not coming from the ps pump, alternator, etc.

I drained some oil from the enging and upon inspection, it appears that the oil has the appearance of metallic paint. Not tons of fine metal particles, but definitely enough to notice. They are very small in size, no large chunks.

So at this point from reading the factory manual that I bought, it appears that it is indeed possible to remove the oil pan from the engine without removing the engine. The would be helpful for diagnosis, but it also appears that in order to service the rod bearings, the piston/rod assemblies must be removed which means that the heads have to come off. Unless I'm misunderstanding the manual, it doesn't seem possible to fix any bad rod bearings without performing the above tasks.

Please let me know if this is not correct.

Additionally, if the crank has been damaged, the transmission must be removed in order to get the crank out. It would probably be easier just to remove the engine and do all of this on a stand at that point.

Any additional input from you guys?

Thanks!


This is correct. It would be very nice to know what the knock is before pulling engine, and pulling the engine is probably going to be the ticket. One thing that's really bad is puling it and finding something simple and quick. Worse than that is to replace a bad rod bearing without fixing the reason it went bad. Is it possible to get an engine shop to listen to it? They could have the culprit nailed in one guess because of experience.

I don't think there is enough clearance to get the oil pan off with the engine in the car. Usually the engine is removed and a new crankshaft and bearings installed. If the 368 has GM's famous plastic coated timing gears, you should replace those too. The biggest expense would be labor unless you have a good friend doing it for you. :)



Al is right here, but if you have spun a rod bearing replace that rod and at least resize the other rods and replace the rod bolts. Check your oil pump clearances.

Well I got the pan off of the engine after a few hours of work and sure enough, it's a bad rod bearing. The bad bearing journal, which should be 2.500" was worn down to 2.436" or so. From talking with the local rebuild shop, the best thing to do would be to buy a crank kit that includes a new crank and bearings for $290 as that would be cheaper than paying for machining and buying all of the bearings separately. Once I get the engine out of the car all of the way, I'll know more. I'm not certain about whether or not the rod can be reused, but from looking at the manual, the head has to come off to get the rod/piston out, correct?

Updates to follow....

I recommend pulling heads off, they do no have to come off to pull crank. It's a hard job to get it out and back in and fairly difficult to check rod bore for size, but can be done.

Did the rod bearing move? If the rod bearings didn't move then the rod should be fine. When the rod bearing moves out of place then it damages the rod. I re-used an egg shaped rod in a 350 Chevy once and it lasted until it burned a valve. I never did trust it but it never made any noise or anything. I actually tightened up the clearance a little by scuffing the rod cap on a piece of emery paper in a figure 8 pattern. I would never recommend this but I onlly mention it because you would be surprised how forgiving an old V8 can be.

If you change the rod or resize them then you have to take the head off, buy head gaskets, probably ream the ridge or hope the rings will slide by the ridge. Then it looks like a good time for a valve job and new rings etc etc. I'm hoping your rod bearing didn't move and you can avoid some extra work. Good luck.

I don't think the rod bearings moved, (sort of hard to tell from under the engine) from the position it was in when I removed the cap, but the journal from that rod is really messed up as mentioned above. I'll check it out as best I can when I get the engine pulled. I suspect if it's anywhere near as damaged as the journal was, it will be apparent. I'm really hoping to not have to pull heads, replace rods, etc. on this engine as it only has 40K miles on it. Y'all keep your fingers crossed for me.

Update:

We pulled the engine and the sad news is that the crank is shot and so is the connecting rod from what I can tell. The rod journal is about .050" undersize now. In order to get the piston and rod out, the heads will have to come out, which is a whole other bunch of work it seems.

http://i107.photobucket.com/albums/m314/wrenwright/forum%20photo%20folder/IMG_4947.jpg

At this point, I'm debating just having the whole engine rebuilt, but from talking to the nearest rebuilder, that appears to be about a $2500 proposition as he suggested new pistons, cylinder honing, etc. The good news is that it would be a complete rebuild of the long block and would be ready to stick back in the car once the accesories are hooked up. Does that sound reasonable as far as cost goes?

There is so much sludge up in this engine from lack of maintenance that I'm sort of scared not to go this route, especially considering all of the loose bearing material that was thrown off of the spun bearing.

Attached is a photo of the rocker arms...:eek:

http://i107.photobucket.com/albums/m314/wrenwright/forum%20photo%20folder/IMG_4943.jpg


Any input would be appreciated.

Thanks!

That's a lot of sludge for 40,000 miles. The guy that sold me m 78 Coupe swore it had 60,000 miles but I knew darn well he was full of s**t and it had 160,000. It started knocking very soon afterward. I will be doing this same project next month. For some people $2500 is a lot of money and for others it's just chump change. If money were no object it would be much easier to just have it rebuilt. If $2500 is too much then a running used engine could probably be found for less than $500. A 425 should bolt right in and any 500 should fit but may need an oil pan change. I'm not positive on the oil pan part but the Cadillac 500 is a proven dependable engine.

I would definately rebuild the same engine letting the shop know the trouble (spun bearing) and they can look for the cause and fix it on the way. $2500 seems in line pricewise. If they find the cylinders and pistons are like new then that will save some money , if they find the top end good then that can save some money too.

If it was me I'd try to get a 500 engine.

I'd redo the 368 & make it bad ass, it's got the fuel injection, who want's to mess with Carbs

I'd redo the 368 & make it bad ass, it's got the fuel injection, who want's to mess with Carbs

The 80 368 wasn't injected, it got a carb. It got TBI in 81.

After a brief hiatus from working on the Cadillac in question, I've found an '81 Sedan deVille that seems to have a good drivetrain that might could be a donor for the '80 that I'm working on. The possible donor car has the V-8-6-4engine though and I'm wondering if it would be possible to swap out the long block into the '80 model that uses a carburetor (both are 368 cu engines). Everything seems to be the same save for the electronic fuel injection system. Will the intake maniold bolt up to the '81 engine?

Any thoughts?

Thanks!

I would bet lots of money that it will. I don't think Cadillac made very many different cylinder heads; probably just one.

So can I assume that the long blocks are the same from '80 to '81?

Thanks!

That's my assumption, sorry I can't say definitely. I think they scrapped it in 82 so I doubt they did much changing in the last year.