Rod Bearings in car?

[FiatRunner]

The warm sunny days are unfortunately over here in Chicago, so it's time to get some work done.

I believe the rod bearings in my car are slowly getting worse. It isn't very bad, but there wasn't any noise when I bought the car a year ago, but a bottom-end noise is very slowly getting louder. It's surely a bottom end noise, as I have checked all of the tappet specs, listened with a large screwdriver, and it's definitely coming from the bottom. It sounds like a knock, not a tap or a click. I drive the car hard, and I would imagine they're just tired from 48 years of abuse. I've talked with the original owner, he is sure that they are the originals.

I have been running Castrol non-synthetic 14w40, and while there definitely hasn't been a ton of metal in the filter, there is enough very fine metal to barely see it. The oil pressure gauge stopped working about 8 months ago, and I haven't gotten around to fixing it, (yes, I know) but I've been noticing that the warning light takes a little bit longer to turn off on startup and no longer goes out when cranking.

Is it possible to lift up the motor, open up the pan, and put in new rod bearings and a new pump? As a college student, I don't have the resources to pull the motor and do a proper rebuild. I need this motor to last me another summer, maybe two at most, and I'd rather not damage the crank. Is this something that's possible? Or is there another plan of action that might be better?

Thank you!

[18Fiatsandcounting]

Is it possible to lift up the motor, open up the pan, and put in new rod bearings and a new pump?

Yes, it is possible although I don't think this is the best course of action. It would be IF (and this is a big "if") you knew for sure that it was just a rod bearing problem and nothing else. However, with an engine this old and that has been driven hard, there could be other issues. Plus, if the engine is 48 years old and hasn't been rebuilt, it really is time to do this.

Note that Fiat oil pumps usually show very little wear unless the oil has been unusually dirty. Issues are usually with bearings (main, rod, and aux. shaft). So, unless you find the oil pump to be damaged, you might not need to replace it.

Here's what I would do. I would try 20W-50 oil just as a test to see if the rod knock is quieter. If it helps things, you could switch to 20W-50 although that is likely too thick for Chicago in the Winter. But, if you only drive the car in the warmer months, then you might be able to get by with thicker oil for a year or so.

You could also try removing the spark plugs one at a time and see if the knock goes away with a specific spark plug. That would at least tell you which cylinder it is.

-Bryan

[FiatRunner]

Yes, it is possible although I don't think this is the best course of action. It would be IF (and this is a big "if") you knew for sure that it was just a rod bearing problem and nothing else. However, with an engine this old and that has been driven hard, there could be other issues. Plus, if the engine is 48 years old and hasn't been rebuilt, it really is time to do this.

The only reason I wouldn't immediately consider a full rebuild is because the rest of the engine seems to be in good health. Compression is between 155 and 160 on all four, the cams, springs, tappets, and valve guides/seats were all replaced fairly recently and all clearances are well within spec. It doesn't smoke at all, runs real well, and makes great power. It's wasn't driven much either, it's got just shy of 30k miles. I'd really hate to spend the money and time to pull apart an engine just to find that it doesn't need a full rebuild.

I only suggested replacing the oil pump because it easily can apply to the "do while you're in there" mentality.

Here's what I would do. I would try 20W-50 oil just as a test to see if the rod knock is quieter. If it helps things, you could switch to 20W-50 although that is likely too thick for Chicago in the Winter. But, if you only drive the car in the warmer months, then you might be able to get by with thicker oil for a year or so.

I'll try 20W-50, as I don't often drive the car when it's less than 55 degrees outside, although I do start the car and let it warm up once a week in the winter. Would a thicker oil take longer to warm up? I struggle to get the car warmed up as quickly as I'd like already.

If the cause of a knock could be crank bearings, rod bearings, or aux. shaft bearings, what would be the diagnosis route? I'll try pulling a plug to see if it goes away on just one.

[18Fiatsandcounting]

Would a thicker oil take longer to warm up? I struggle to get the car warmed up as quickly as I'd like already.

Regardless of the oil viscosity, it should take roughly the same amount of time for the engine to warm up. If it takes a long time to warm up, you could have a stuck thermostat.

When starting the engine at any temp above freezing (32 oF), you should the temp gauge needle move off of "zero" after a couple minutes, and it should be fully warmed up within 10 to 15 minutes. It will warm up faster when driving as opposed to just idling to get it warmed up. If it takes longer than 20 minutes to fully come up to temp, you likely have a thermostat issue or a bad temp sensor. The former is more common than the latter.

-Bryan

[FiatRunner]

So, I hate to be that guy that revives a dead thread, but I wanted to post an update on my situation.

I continued to drive the car, from Oct. of 2022 until early June 2023, and the knock slowly got a bit worse. I decided to weigh my options, and I decided to change out the rod bearings, and if that didn’t solve the issue, then pull the entire motor and do a full rebuild.

I’ll keep the story short, but I was able to successfully change out the connecting rod bearings with the engine in the car. I raised the engine by disconnecting the engine mounts and exhaust header, and then put a piece of 1x6” in between the rubber mount and engine bracket. This allowed for just enough space to remove the oil pan.

The rod bearings were toast! I couldn’t believe that the engine was running on those bearings. The crank journals, on the other end, looked brand new.

https://drive.google.com/file/d/1iLU9aN ... p=drivesdk

Having the engine apart also revealed some information to me: this engine is a 1608, not a 1756 like I thought! What does this mean? The car is a ‘73, not a ‘74 like I was told! I couldn’t believe it, and I ended up buying three sets of bearings before I was able to get the correct ones.

https://drive.google.com/file/d/1y3uCof ... p=drivesdk

With the new (and correct!) bearings in place, I was able to use plastigauge to find the clearance, which was well within spec. I also repainted the oil pan and exhaust header, and replaced the faulty oil pressure sender.

https://drive.google.com/file/d/1PT0Azc ... p=drivesdk

https://drive.google.com/file/d/15wQG1n ... p=drivesdk

With it all back together, it runs great! 60+ psi of oil pressure cold, and 20ish at idle when fully hot. I drove it around cautiously for about 250 miles, then changed the oil. The used filter didn’t have any metal in it when I cut it open with my filter cutting tool.

https://drive.google.com/file/d/1-41spY ... p=drivesdk

So again, I apologize for reviving an old thread, but I wanted to post an update just in the slim case that someone else was in the same situation as me. Thank you all for the help!

[Nut124]

Apologies not needed. Good job!

I'd like to see your pictures but you'd have to share the folder in Google Photos.

[FiatRunner]

Thank you!

Here’s a link to the folder: https://drive.google.com/drive/folders/ ... 5RnYfrDju7

I also updated the permissions to the previous photos, but who knows if that’ll make them work.

[18Fiatsandcounting]

Great job! I can see the pictures now.

Last November, I rebuilt a 2L engine for a friend because the engine had pretty serious rod knock. Like yours, the main bearings (and journals) were fine, but the #1 rod bearing was toast. It had pounded on the #1 rod journal long enough that it required me finding a new crankshaft. I still have the old crank, but the eccentricity is about 0.006" around the rod journal. Unacceptable to just put in new rod bearings, although you could grind down the rod journals by 0.010" or 0.020" and then use oversize rod bearings.

Surprising (at least to me) was that it was the #1 rod journal that failed first, not the ones further from the oil pump, like #3 or #4. But, in talking to another Fiat friend, he said his experience was that the #1 rod journal usually fails first. Not sure why. The main journals are very beefy and so it's rare to have significant damage unless the engine has really been abused.

In my friend's 2L engine, it was a bashed in oil pan that started the whole chain of events. The bottom of the oil plan was pushed up against the oil pickup screen so oil flow was limited.

Anyway, good to hear you're back in business. On your '73, I actually would have expected this to be a 1592cc engine. The 1800 didn't come out until 1974, and the 1608 was used through early 1973. In between these years, the 1592 briefly appeared. I don't know why Fiat didn't just go directly from the 1608 to the 1800, but there you have it.

-Bryan

[FiatRunner]

Surprising (at least to me) was that it was the #1 rod journal that failed first, not the ones further from the oil pump, like #3 or #4. But, in talking to another Fiat friend, he said his experience was that the #1 rod journal usually fails first. Not sure why. The main journals are very beefy and so it's rare to have significant damage unless the engine has really been abused.

Anyway, good to hear you're back in business. On your '73, I actually would have expected this to be a 1592cc engine. The 1800 didn't come out until 1974, and the 1608 was used through early 1973. In between these years, the 1592 briefly appeared. I don't know why Fiat didn't just go directly from the 1608 to the 1800, but there you have it.

Yeah, the #1 bearing was the worst, but they were all quite bad. The rest didn’t look much better than that one. I thought that there was a slight chance that the oil pickup was cracked, as the pan was pretty beat, but it was fine.

And you’re right, I assumed it was either a 1592 or a 1756, which share the same journal size iirc.

[18Fiatsandcounting]

And you’re right, I assumed it was either a 1592 or a 1756, which share the same journal size iirc.

Correct. The 1592 and 1756 were the same with offset oil holes up through 1975, and then 1976 and onward had centered oil holes for the 1756 rod bearings.

-Bryan

[howelljd]

Great job on all the productive work! A better way to determine bearing wear before it becomes excessive - such as when knocking gets progressively worse - is to get your used oil analyzed by a lab. I use Blackstone-Labs.com analysis at each oil change. The reports are comprehensive for wear metals, additives, contaminants, and physical properties of the oil itself. It is not necessary to do this at every change but having a history of the engine baseline in parts per million rather than in visible metal parts could prevent a catastrophic failure. Enjoy your improved smiles per gallon!

Cheers,
Jonathan

[FiatRunner]

Just wanted to post an update to this thread in case anyone might be in a similar situation or wanted a long-term update.

I've been driving the crap out of the car, I think I've put close to five thousand miles on it since I put the new bearings in. Not easy miles either. It's held up great- still can't hear any knocking, and it actually survived a couple moments of zero oil pressure when the oil pan bottomed out on a huge bump and the plug got ripped off. New oil pan, oil, and it's fine.

Not long after my previous update, the oil pressure dropped a bit. Above idle it's ~35+, and at 4,000RPM it's 55+, but at idle, in traffic, on a really hot day, it's pretty close to zero on the stock gauge. It's stayed at those levels ever since, I assume the higher pressure was just because it was breaking in. I've never seen the low pressure light turn on at idle, so I haven't worried about it. I do run Valvoline VR1 20W-50, which has been great. I really drive the heck out of the car.

[18Fiatsandcounting]

... it actually survived a couple moments of zero oil pressure when the oil pan bottomed out on a huge bump and the plug got ripped off. New oil pan, oil, and it's fine.

Wow, what kinda roads do you have there in Elmhurst....??

As for the oil pressure, you're likely fine. Except for newly rebuilt engines, most Fiats I've seen have pretty low oil pressure when hot and idling. The oil warning light sometimes flickers under these conditions, and while not ideal, it's not a huge concern since there is little stress on the crankshaft while idling.

After going through the filter, the first bearing that the oil flow encounters is the front auxiliary shaft bearing. These don't usually go bad, but when they do, a lot of oil pressure can be lost there. But again, it sounds like your engine is fine in terms of oil pressure.

-Bryan