56 engine knock with hot engine only

[Hillbillycat]

Well, fuel pump is lubed now. Knock still there.
Ignition timing double checked (#1 and #6 cyl - no deviation) and all contacts scraped clean even on the coil and resistor.  Knock still there.
Can of seafoam through the carb. Knock still there.
With knock present and lever in DR oil light flashes.

Talked to a engine mechanic that had specialized on american V8 classic cars:
Rod bearing failure that will need the crank to come out too. From there it´s only a little step to a total rebuild. This is 10k over here.

Can´t afford that at all.
So my idea is to drop the pan on my own and check the rod bearings. Can´t just they be replaced even in case the crank journals have wear? Just to have a running motor again for some cruises. This is no daily or race car. It´s just hobby and should be fun.

[Roger Zimmermann]

You can remove the oil pan (not easy but I did it many times when the car was on jacks) and measure the play with Plastigage. If the crankshaft journeys are nice and you can determine with the Plastigage that the play is too important, you can install the next undersize set of bearings. If the journals from the crankshaft are not so nice, what to do? I don't have the answer, unfortunately.

[James Landi]

So very sorry to learn of the results of your  herculean efforts .  Yes, it could be a bad rod bearing, and yes, you might get lucky that replacement of bearings will make the difference.  I had the rod bearings replaced in one of my '56 Cadillacs way back in 1966--- oil light blinking when hot, the car was close to 100,000 miles--- the result:  When the mechanic pulled the pan, it was coated with sludge--(even though the oil was regularly changed by my parents and then by me.  The mechanic simply slipped in the new bearings, and showed me the old ones--- yes, there was uneven wear on the bearings--- he reported that the crank "looked fine."  Thereafter, the idiot oil light never blinked.    Alas, if you have a worn bearing that's knocking, the risk is that other parts of the motor may be starved for oil; however, pulling the pan, inspecting, and, putting in new rod bearing may just work out.  You;ll also have an opportunity to check out the wrist pins.  CHanneling hopeful thoughts your way,   James

[Caddy Wizard]

If you can't afford to rebuild the engine, then you have nothing to lose by dropping the pan and replacing the rod bearings.  I'd replace the main bearings while I was at it, as well as rebuilding the oil pump with new gears (but be sure to reuse the original spring in the oil pressure relief valve -- the replacement springs are too stiff and will lead to excessively high oil pressure at higher RPMs and oil leaks).  Would also be a good time to replace the rope rear main seal with a new rubber rear main seal. 


With the car on jack stands and working on a creeper, this is a weekend job.  On a lift, this can be done in about 4-6 hours.


Good luck!

[Hillbillycat]

Oil pump is rebuilt with keeping the original spring already.

You sound rather promising. A old time mechanic I talked to yesterday said that I can spare the effort in dropping, for the crank surely must come out. He said to either bite the bullet or just run the motor with additive (he suggeested non detergent straigt SAE 90 gearbox oil instead of any additive) and trying to enjoy the car for a few more thousand miles.

I´m shifting to and fro between dropping the pan and just thickening the oil.

Don´t I need to drop the pan and check all bearings with plastigauge before I can order any bearing sizes?
Or how do I determine what bearing size to order? Standrad size when crank doens´t get reground?
I´d like to have all bearings on the bench before dropping the pan to speed up the work at my pal´s place. I neither want to block his lift just to find out I have the wrong parts, nor push/haul the car around in his shop. It´s tight in there and as you know our babies ain´t no babies when it comes to weight :-)
That 4-6 hours labour ain´t so bad.

[Roger Zimmermann]

As you don't know what's installed into the engine and/or the condition of the crankshaft, its foolish to order replacement bearings before you know if there is too much play. I understand that time is a factor by having a car which cannot be moved, unfortunately, there is no shortcut.

[Hillbillycat]

Hi Roger,

that´s what I assumed. First pull the pan. Second check the bearings play with plasitgauge. Then order.

I gotta check with my pal to convince him to let the car sit in a corner till the parts are delivered.

[savemy67]

Hello Hillbillycat,

While 90 weight gear oil may help with excessive rod and main bearing clearance, 90 weight gear oil may not be good for the hydraulic lifters, so I would probably not rely on the use of 90 weight oil to solve your problem.

Dropping the oil pan to check the rod/main bearing clearances with Plastigage will tell you what the clearance is, but you won't know what size bearings to purchase unless you can confirm that the crankshaft is 100 percent original and has never been machined.  If you cannot confirm the crankshaft has ever been machined, then you cannot know whether it is already undersized, so you cannot know for certain what size bearings to purchase.  All bearing sizes are relative to the original factory journal diameters.  In order to measure the rod/main journals accurately with a micrometer, the crankshaft has to be removed.

However, dropping the pan will allow you to do an inspection of the bottom of the engine.  Before removing any rod/main caps, grasp each connecting rod with your hand and try moving it back and forth, up and down, and side to side.  Rotate the engine 120 degrees and grasp each rod again, attempting to move them by hand.  Rotate the engine another 120 degrees and repeat.

If your engine's clearances are within tolerance, you should feel little to no perceptible movement in the rods when you try to move them.  There are several locations for clearance - journal to bearing, rod to rod (side clearance), piston to cylinder - that may be felt by hand when trying to move a rod.  But these clearances are all specified as being a few thousandths of an inch - an amount that is barely felt.

If all the rods feel like they have no or barely perceptible movement, you probably do not have a rod knock.  If one or more of the rods has movement greater than the others, this rod may be the source of the knock.  You can measure the excessive clearance with Plastigage to confirm the offending rod/bearing.

Your descriptions of the symptoms have not convinced me that you have a rod knock.  That is why I think attempting to move the rods - before using Palstigage or 90 weight oil - is a good diagnostic procedure.

Respectfully submitted,

Christopher Winter

[Roger Zimmermann]

Usually the inserts are noted/stamped if standard or undersize. Maybe I'm wrong, but it would be logical.

[Hillbillycat]

HI Christopher,
thank you for the in deep explanation on how to proceed.
Roger, you´re right. I had read that, too.

So I will drop the pan for an inspection and report back with my findings. Will take some time though.

[Hillbillycat]

I did some more thinking and reading. Especially the 68 oil flicker thread caught my eye and since Christopher did mention he´s not convinced of rod knock I´m clinging to that idea.

Isn´t the knock every time the strobe light flashes an indication for a valve/head releated issue? That would match my broomstick stethoscope diagonstics: Knock coming from the head around the spark plug of one cylinder. It is the one that showed more carbon deposit on the piston face and different spark plug color.

Soooo, I was thinking if it wouldn´t be smart to first pull the valve covers before dropping the pan. They´re much easier to get to and can be done without the need of a lift or jack in the tightest place. My garage is european standard size. That leaves about two to three feet of clearance from car body to wall. You need a shoehorn to get in and out. And that´s just the side walls. Front bumper kisses the wall and tailpies the door. OK for storage but not for wrenching.

Anyway, what to look for and test when I pull the covers. Should I remove the rocker assembly for cleaning and pull the pushrods to check for bending?: I think so.

[James Landi]

YOur approach, eliminating the "upper ended" potential seems sensible, and linking it to the unusual carbon build up in one cylinder with the knock might be "the connection" between cause and effect. While you're doing this, and if there IF  no apparent issues are discovered (say a bent push rod), would it make sense to go a little further?  My suggestion (subject to careful consideration by others) would have you change out the hydraulic lifters on that cylinder.  And here's another unusual experience I had with a rebuilt marine engine that I purchased "for cheap" because it had a knock ----  in a fit of "last resort desperation," I loosened up the rocker arm assembly with the engine at idle--(while using plenty of rags to stop the oil flow off the end of the block).  Voila! the knock went away--- I found that several push rod were the wrong length-- clearly some sloppy work by the rebuiler.  Sending positive energy your way.   James

[Hillbillycat]

James,

that´s what I had in mind, too. Run the engine sans covers and finger feel the movements of each rocker arm. Then play with the bolts on the suspicious cylinder.
OK, I´ll remove the rocker assembly and check the pushrods, too.

[Hillbillycat]

OK, thank you for sending positive energy over the sea!
I gained enough courage to pull the valve cover and peek inside today. And I did not forget my camera this time :-)

What struck me -besides the grime in there- was the pushrods on exactly the suspicious cylinder:
The right one almost touching the cavity wall, the other one being flat on the tip with just a wear ring. And they are not the same length, with the flat tipped one being longer.
And most significant: They are not the same like the others with the single/double grooved ends.  Both did not appear to be bent. I need to roll them on a glass plate to check.
Does the oil that poured out of the head  when I pulled the rocker assemblies look normal to you? The two center bolts pulled out like being held back wit honey!

Well, does this look like I found the culprit already?

How would you proceed now?

Btw, after seeing all this dirt I pulled the driver´s side valve cover, too. After removing all the acssories that are in the way on this side that make removal impossible if let in place, I think.
Nothing special in there except for all pushrods being inserted with the single groove end up, wheras the passenger side had them with the double groove end up?
My Motor´s Auto Repair Manual says the 331´s had the single groove up and the 365´s the double grooved end up.
Someone definitely had messed with it down the line......

[Caddy Wizard]

I believe that all pushrods are supposed to be the same length.  I have never seen on with a flat end.  Moreover, these two look like something from a non-Cadillac engine that someone installed after bending the original pushrods.

If a pushrod is too long, it could be holding a valve open.  Also, it could be opening the valve to such an extent that it hits the top of the piston at times.  Can you stick a bore scope into the spark plug hole and look for any signs that one of the valves is hitting the top of the piston?

[James Landi]

."...  And here's another unusual experience I had with a rebuilt marine engine that I purchased "for cheap" because it had a knock ----  in a fit of "last resort desperation," I loosened up the rocker arm assembly with the engine at idle--(while using plenty of rags to stop the oil flow off the end of the block).  Voila! the knock went away--- I found that several push rod were the wrong length-- clearly some sloppy work by the rebuiler."   

I'm quoting myself here.  The wrong sized push rods are creating, at the very least, a timing problem that is likely causing the knock --- I suggest that you get the correct push rods, put them in according to the service manual and button up and test the engine --- I think you stated that you have more than adequate compression in every cylinder, so perhaps you've uncovered the "ghost: in your machine."  James

[Daryl Chesterman]

I would also closely inspect the respective rocker arms for those two different push rods—they might be worn such that new push rods will not fit correctly in the cup portion.  I don't think your engine looks especially "dirty".  The oil looks like it is needing changed, but I don't see sludge in any of the pictures.  If an engine does a lot of short-trip driving like in parades, trip to the store, trip out for dinner, etc. the engine doesn't get properly warmed up and the oil gets diluted with moisture.  Once you get the engine "knock" fixed, you can take it for a good drive and drain the oil when you get back.

Daryl Chesterman

[Hillbillycat]

You didn´t see the underside of the rocker assembly......lot´s of gunk in the corners and recesses. Oil holes are clean and free luckily.
I´m gonig to take the assemblies apart for thorough cleaning.

Would you recommend using a new set of pushrods or just replace the two mismatches?

[James Landi]

Regarding your question, I've limited experience with "finding the correct push rods" for decade's old engines, so I'd be inclined to very carefully measure them---(it THINK you should be able to spin  the two push rods for each cylinder when that piston is in top dead center position--- but please verify this--- It's been a long time).   Also make certain to put each part back in its respective individual places--- that certainly includes the specialized bolts that transfer the oil up to the rockers..."randomizing" what looks to be identifical parts will cause all kinds of squeaks as these parts don't wear uniformly.  I also encourage the "video" exploration that was mentioned above, as there may be damage to that piston and, perhaps the valves (although good compression would provide confidence that all is well--so if you saw some minor impact where a valve was hitting that piston, you'd have good evidence that your knock has been identified) --- all this said, I'd be much less inclined to remove everything, and I'd concentrate efforts on the cylinder with the problem.  (As my father used to say, "James, if you're looking for trouble you'll find it!)    Hope this helps,  James

[Hillbillycat]

Guess what - I made a cardboard fixture to keep the pushrods in order. Now what happened? Right, it tipped over and five of them fell out, right beside the engine. That was some Mikado game in the engine bay......
I hope it doesn´t make things more complicated now.

I checked the rocker cups for wear. And yes, the one with the strange pushrods has some marking in the cup. The others look clean. I´ll have to upload pictures.

All but one pushrods are straight. One is out of round less then half a millimeter- but not from the suspicious cylinder.

I still feel that it´s a lifter that isn´t working right on the suspicious cylinder. Is there a way to test them in the engine now that the rocker assemblies are off?

Valve springs are all non-broken and can be rotated by hand with some effort. When pressing down on them with your thumb they give in a little.