Freshly Rebuilt 1958 Olds Oldsmobile 371 knocking at idle

[Rockabilly Hooligan]

Hello Everyone,

Need some of your expert Olds 371 knowledge. My friend and I recently rebuilt my 1958 Olds 88 371. On initial startup engine sounded good but smoked a lot (Moly rings?). Too eliminate smoking I Rebuilt carb, replaced fuel pump, changed oil, changed plugs. my first fuel pump leaked fuel into oil pan but I did not drive more than 100 miles until I replaced pump and oil. Hoping it did not mess up my bearings. Engine starts, idles, and runs strong just knocking.

Oil Pressure has always been 30-40PSI. Was able to finally able to set rings for most part and does not smoke as much. Engine friend says I still need to put more "hard" miles on engine to completely set Moly rings. Compression is all good in each cylinder. My engine now has a knocking/rattling sound at idle and appears to be getting worse the more I start it up and idle her. When I rev the engine it appears to go away (or at least less noticeable).

I listened to engine block with stethoscope and did not hear any different or louder noises from cylinder to cylinder and noise appears to be coming from the lower rear engine/ front transmission area. One of my friend thinks its "thrust bearing". Another friend thinks it might be transmission related.

I pulled the starter and flywheel cover to check to see if flywheel is loose or cracked but and all bolts are tight. I also verified very little flywheel play/movement (1/4"?). Before I drop oil pan to see if bearings are loose/damaged, could the knocking/rattling sound be something in transmission? Any suggestion besides before I drop pan and check out bearings Thanks Erol

[Stude Light]

Knocking usually is a bearing or piston pin. One thing you might try is just grounding one plug at a time and see if the knock changes tone or intensity. If so, you'll know what cylinder it is. If not, it may be something else.

Scott

[Rockabilly Hooligan]

Thanks for response.  When you say " grounding plug " are referring to dis-connecting plug from distributor so it does not fire?

[Guest]

Just pull the boot up a bit and ground it out with a screw driver.

[carbdoc]

I once had this problem with a '63 Buick 401; it turned out to be a worn shaft key in the harmonic balancer's keyway.  Remove the bolt and washer from the balancer and try to "rock" it back and forth on the shaft by hand; you'll know pretty quick if that's the problem.  And when you reinstall the bolt and washer, be sure to torque it to spec (or just as tight as you can get it!).

Edited December 27, 2018 by carbdoc (see edit history)

[Aaron65]

A rebuilt engine shouldn't really ever smoke, regardless of the ring type.  It might use some oil, but if it's smoking profusely, something is wrong.  If the engine is knocking back by the transmission, I'd be first checking my flexplate for cracks, looseness, or something else that has gone awry in that area.  If the knocking is getting worse, I would stop driving it until you figure out the problem.  Good luck!

[DonMicheletti]

 

There should be no play at all at the flywheel other than the about.005" end play of the crank.

 

Lots of smoking  suggests that rings may have been put in upside down. Especially #2 scraper. It has a tapered edge and if in wrong will force oil up to the combustion chamber.

 

Any knocking on a new engine is bad news.

[JACK M]

I have found some fuel pumps will mimic a rod knock.

[dl456]

If the flywheel really has 1/4'' lateral movement and the smoking is that bad. I suspect the engine will be coming back down.

I would not run it anymore until you find the problems.

Bummer!

[herm111]

On 12/26/2018 at 7:58 PM, Rockabilly Hooligan said:

Hello Everyone,

Need some of your expert Olds 371 knowledge. My friend and I recently rebuilt my 1958 Olds 88 371. On initial startup engine sounded good but smoked a lot (Moly rings?). Too eliminate smoking I Rebuilt carb, replaced fuel pump, changed oil, changed plugs. my first fuel pump leaked fuel into oil pan but I did not drive more than 100 miles until I replaced pump and oil. Hoping it did not mess up my bearings. Engine starts, idles, and runs strong just knocking.

Oil Pressure has always been 30-40PSI. Was able to finally able to set rings for most part and does not smoke as much. Engine friend says I still need to put more "hard" miles on engine to completely set Moly rings. Compression is all good in each cylinder. My engine now has a knocking/rattling sound at idle and appears to be getting worse the more I start it up and idle her. When I rev the engine it appears to go away (or at least less noticeable).

I listened to engine block with stethoscope and did not hear any different or louder noises from cylinder to cylinder and noise appears to be coming from the lower rear engine/ front transmission area. One of my friend thinks its "thrust bearing". Another friend thinks it might be transmission related.

I pulled the starter and flywheel cover to check to see if flywheel is loose or cracked but and all bolts are tight. I also verified very little flywheel play/movement (1/4"?). Before I drop oil pan to see if bearings are loose/damaged, could the knocking/rattling sound be something in transmission? Any suggestion besides before I drop pan and check out bearings Thanks Erol

Did you check all the rods for twist, bend, and offset?

 

Herm.

[ted sweet]

sounds the fuel weakened  oil did major damage and likely rings never seated

[lump]

Rockabilly, 

 

One final suggestion for you: 

As I see it, the knowledgeable folks here on the AACA forum have given you some very valuable information so far, and nearly all of it suggests that something serious may be wrong. The advice you got about not running it at all any more until the problem is found was very good and very sound advice indeed. 

 

Of course this is unfortunate and unpleasant to contemplate. But when you think about it, removing that engine is not a giant task. I suggest that you drain all fluids, pull the engine out and hang it on a good quality automotive engine stand. Then rotate it 180 degrees and remove the oil pan. If you are not an accomplished engine rebuilder yourself, have someone come take a good look at it at this point for you, BEFORE dismantling anything further than the oil pan. (If no issues are visible when the pan is removed, a competent engine builder will want to see for himself or herself what each engine component looks like as they take it apart).

 

The worst that can happen with this action plan is that you'll find something minor, and could possibly repaired it without removing the motor. But that's a GOOD thing to find. And it really is not that big of a deal to put it back in the engine bay.  

 

IF you would find something minor when you get the engine out and the oil pan removed, just re-install that oil pan with new gaskets, and put the engine back in place. Reconnect everything, refill all fluids, and fire it up again. Hooray! The alternative....trying to start that engine over and over while trying to diagnose the problem and/or follow various theories of what it "might be," could be disastrous. The knocking sound you are hearing is likely some kind of metal hitting against some other piece of metal, with enough force to do real damage on every impact. And that could entail a MUCH bigger hassle than simply removing the engine and having a look before ever trying to start it again. 

 

We all wish you the very best luck with this. Please keep us posted. We all learn every time one of us goes through something like this, and shares their experience with the rest of us. We'll all have our fingers crossed for you, and be anxiously awaiting to find out what you learn about your engine knock. 

Edited January 3, 2019 by lump (see edit history)

[Rockabilly Hooligan]

Hello Everyone,

 

I appreciate everyone's concern and suggestions.  I agree.  I am not starting nor running car at this time.  The last time I drove the car to a another mechanic friend #2 whom adjusted/tuned the carb, the engine smoke greatly decreased and I believe the rings have set for the most part.

 

My other friend #1 who is a professional mechanic and helped me rebuild the engine thinks it could be a cracked flexplate since I was running the engine very hard doing jack rabbit starts and stops trying to set the rings.  The last time I started engine I put a sethoscope all around the engine block listening to each cylinder and the rattling noise appears to be coming from the rear engine/flexplate area

 

He suggested that before we drop the pan and disturb the rear main seal that we drop the transmission and check the flexplate and driveshaft connection at his shop that has a car lift.  If that is good than Plan B is to drop the Pan and check bearings/crankshaft.  His shop is full right now and waiting on him to free up space and time for us trailer car to his shop.  When he comes over to pick-up car he will hear first hand the noise and can hopefully confirm it is not bearing related.  Will inform everyone what we find when take her back to his shop

 

Regards

Erol

 

Edited January 3, 2019 by Rockabilly Hooligan (see edit history)

[Frank DuVal]

21 hours ago, Rockabilly Hooligan said:

I was running the engine very hard doing jack rabbit starts and stops trying to set the rings. 

 

Another old wives tale?  Never heard of doing this. Common ring seating is run car at various speeds for an hour (watch temperature gauge, quit if getting too high), with acceleration run ups between speeds. You need to load the engine in spurts, hence the acceleration run ups, but no need for quick stops, nor starting from a standstill. This is after the initial 20 minute run at fast idle, and by fast I mean 1500 to 2K rpm.😉

[Rockabilly Hooligan]

Maybe "Jack rabbit starts" was not the best choice or words.   I  accelerated the car from stand still/low speeds up to 40-50 MPH and back down several times, loading the engine in spurts. 

[Spinneyhill]

On 1/4/2019 at 6:33 PM, Rockabilly Hooligan said:

I  accelerated the car from stand still/low speeds

Hopefully not in high gear. That will be hard on the bearings.

[Pfeil]

8 hours ago, Spinneyhill said:

Hopefully not in high gear. That will be hard on the bearings.

The owner says it's got a flexplate, so it's a HydraMatic and a HydraMatic would downshift under load unless it was above 65 - 70 mph and at that speed the engine would not be hard on the thrust bearing.

 

 About 40+ years ago I helped a friend rebuild a 64 Morgan +4 ( Triumph engine ) everything went well, later  my friend buttoned up the engine ( accessories / water pump, belts etc. I was over to help for the start up. This Morgan developed after about ten minutes a knock which progressively was getting worse. I sounded like the # 1 rod bearing except the sound was deeper like a main bearing. The sound came from the front of the engine, so I decided to first check the vibration dampener because I knew everything ( because I did that part myself )  Crank, Mains, rods, pistons/ Pins were right on, plus I had done the rods resizing and balanced the rotating assy. myself at my machine shop at work.

 It was puzzling and damning for sure and the vibration dampener appeared OK so I hooked up the timing light to make sure the dampener hadn't torn loose and see if the timing marks hadn't shifted. That's when the strobe revealed a chunk of fan belt 1/2" long 1/8" deep missing in the bottom of the V groove of the fan belt. When my friend assembled the front of the engine he used the old ( not worn looking) belt. It visually wasn't noticeable with the engine running , however the strobe revealed it.