Opinions sought on odd engine knock

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nm9stheham

nm9stheham

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- 225 /6, original 52 year old engine
- Occassionally has a knock that sounds very much like a rod knock on start-up that quiets down as soon as the oil pressure light goes off; happens maybe 1 out of 4 times at cold start; never seems to happen at warm startup
- A few days ago, this knock persisted at a lower level after oil pressure was up for > 1 minute; backed up to turn around on the steep incline in my driveway; stopped on the steep incline with front of car pointing downhill, and the knock quieted and went completely away while on the incline.... ??

So....what could cause this? My thoughts so far:
- Loose piston pin on the rod
- Cracked crankshaft
- Worn thrust bearing
- Multiple issues??

Any ideas on these possibilites (or rejecting them), or other casues, would be appreciated.
 
How do you know it's knocking on an odd cylinder???

It could be knocking on an even one or both.....


Engine knocks suck....
 
It's old. Maybe it is time to refresh it. This could be almost anything. I had an old six once that was so gummed up the oil pumped up to the lifters and couldn't find it's way back to the pan until it warmed up a little and thinned out.
 
Using a Fram oil filter? I had start-up ticking on a 78 318 that I bought new. After reading a shocking filter comparison on EEK I switched to Purolator. Instant fix! Up until then I had used Fram filters exclusively. Yours sounds more like a heavier knocking and I think mine was valve train. But it may be worth a try.
 
They don't last forever. If you wait until a rod comes through the side of the block...
Good luck with it
 
Sounds like main bearing knock.
 
52 years old would be 1962. Yours doesn't have hydraulic lifters to "pump up", and I understand there aren't even oil passagess to your solid lifter bores. There is a gap at the valve tips to rockers, but that should make a slight ticking sound all the time.

I have read that a worn main bearing is a deep sound (never heard). You can check/replace the main bearings and rod bearings from below after removing the oil pan (I need to jack my engine up slightly). If so, also replace the rear main seal (push rubber half around crank). Check compression first and do a complete rebuild if <100 psi in all cylinders. At a minimum, turn the engine over 2 times by tugging on the fan belt and see if you fight 3 tight "air springs" each rev and hear them hiss down. If so, your compression is great regardless of what your gage test says.

Most likely it is something more benign like "piston slap" or timing chain slop.
 
Thanks for all the input. Odd cylinder ... nyuck, nycuk, Curly Joe. Guess I walked into that one....

Using WIX or Hastings oil filters, so no joy on that simple fix.

Tming chain was changed due to trying to eliminate a low pitched rattly sound in the crankcase (as well as get rid of all the chain slack) but that rattly sound is still there (different sound than the knock). No change in that sound, and that is also concerning; it remains after a process of sorting out noises and eliminating the water pump bearing noise, the 3 exhaust manifold leaks, worn timing chain noise, etc.

Yes, a mechanical lifter cam; this is definitely a lower end knock, not a valve train tap. Main bearing? I HAVE heard that once but it was really bad.... as it tends to be when the main webs crack.... that was a bad day.

Compressions all in the 115-130 range. Reluctantly, I think all the ideas to tear into this are probably the best; I was starting to think the same as Redfish: no need to allow something to keep eating up the insides. I've been trying to keep this car as original as possible, but looks like I gotta get inside and flush this one out. Sounds like time to at least pull the pan and then probably the head..... BRRRRR!

Many thanks for the input. And I'll keep in mind that a greasy day under a hobby car is better than a clean day working.
 
A couple things to check,
Torque converter bolts if automatic.
Crank shaft end play.
 
I have heard crank end-play rattle at one time, if I parked the car at just the right angle. If its a stick car, it goes away when when you push the clutch in. The Thrust-bearing was done.I once heard a fuel pump rattle when the return spring went missing. Rod knocks are pretty distinctive.And mains have a deeper base tone to them.And then theres cam end-play, but I imagine you checked that when you replaced the chain. The sound is similar to the crank end-play sound,but higher in pitch and more random in nature.The only sounds that are normal inside that old girl are of course tappet clatter. All other sounds are from excessive clearance somewhere.Sometimes they run for years that way, and sometimes, they dont. I had a rod come through the side on a slanty once.I guess I waited a bit too long.
-Yeah, what redfish said. A cracked convertor flex plate can give you fits to diagnose.
 
OK. Manual trannie car. Pilot bearing and such seem to be good. (It takes several seconds after the clutch is pushed in for the input shaft, clutch disc, and countergear to spin down to where you can engage the non-synchro 1st gear).

Crank end play: may be. I have tried lightly pushing it in and out with no obvious excess clearance but I use a bit of leverage to really see if it moves excessively.

Yeah, just recently changed out the fuel pump on the chance that it was noisy.... and it WAS. I mean a reeeeeally loud knocking at highway speeds. That has been one of noises eliminated to date.

No I did not check the cam end play with the new chain. But I thought that the cam thrust was set by the cam sprocket on one end; not sure what keeps it from moving forward unless it is just the tappets being centered a bit forward of center on the cam lobes.

Just now I thought of the oil pickup tube.... maybe it is goofed up and hitting the crank....
 
Crank end play, watch the balancer while reving engine to see if it walks back and forth. Had the thrust bearing wore out on a 383 stick car and you could see the balancer move in and out at different RPM. Just a thought..
That noise is quite common in the slants. Like said above after 52 years it's still running,may continue for many years to come.
 
Very good and thanks for the comment; I was outside splitting some wood (good cold weather work...) and took the time to put a little force on the crank end play. While I did not have a dial indicator on it, it looked to be beyond the spec of .002-.007"; maybe in the range of .012-.015" by eyeball. That could be the source of the rattly bottom end noise (the damper pulley wobbles a bit and that could be moving the crank in and out), but probably does not cause the start-up knock. It's probably a general wear indicator; I remember now that the oil that I got out of this thing had been seriously diluted with gas due to an unattended-to carb leak by the PO.
 
Anything that gets quiet with oil pressure is a bearing since there aren't hydraulic lifters in there.

When it gets to the point that it doesn't completely quiet down, turn it off and build the engine. Otherwise you might get one of those famous Slant Six vent holes in the side of the block.
 
Well, it never has not quieted down, and just once did it have any noise past the oil pressure coming up. But it is coming out this week just for precautionary reasons f not a whole rebuild.... if this cold WX will relent a bit.

It is just a shame that we could not keep this never-torn-down, fully original engine going happily along. But any driving beyond just rolling around 1-15 miles from home base seems to indeed be risky. We may find more than just a 'rough' bearing.
 
Since compression is fine, and you see end-play, I would change the main bearings (one is the thrust bearing). That would be many times easier than a full engine rebuild. Change the rear seal while down there. I did this in my 383 from below. I did a full ring & hone job (removed head & pistons), but you don't need that.

You simply push the top of each bearing shell around the crank w/ a blunt screwdriver. I expect this works the same in a slant. I pushed a rag w/ ethanol around the gap to clean oil from the block surface to insure the bearing shell will stick, though a tab on the bearing keeps it from spinning. Same deal for the rear seal, if you have the split rubber type. If the original woven rope, I think it just pulls out. There is a special wire puller to re-install a rope seal, but nobody does that today. Good these engines aren't like my 80's M-B diesels that have a steel pin that locks the rope seal so you can't pull it out, frustrating owners. Ideally, use plasti-gage to check the gap, but you could just measure the thickness of each old bearing to insure you don't have any special thick ones (for over-ground crank position). That is rare, and your block should be stamped (behind alternator?) w/ a Maltese falcon mark or such if an under-sized crank. That was a way for the factory to salvage an incorrectly forged or machined crank. Also, easy to change the rod bearings while in there. Do all one at a time, to support the crank and not risk swapping caps. The caps should be marked for location and orientation, or do so if missing. With new bearings, you should see higher oil pressure.
 
I have had several hi miler vehicles with that "hollow" main brg knock for the first few revs,,

My son has been driving one for years,, a Jeep Cherokee 4 litre, with 350+ k,, it knocks every morning and has since I bought it 8 yrs ago..

We seviced a Taxi fleet back in the 70's,, they all ran /6s, cuz they could get 250k outta them, when no other engine could last that long,, they often had that rattle over 200k,, but lasted way longer..

One of my customers 51 Dodge has same noise.. been there over 20 yrs,, he won't rebuild it..

If you really don't want to take it apart,, you may find it'll outlive you, just as it is, maybe not.. but......

hope it helps

PS, as Bill mentions, slipping new brgs into it isn't a bad idea..
 
All good points guys and well considered; many thanks for the ideas and time to wiret them up. I have done 25-30 engines for racing and plain jane street use, so all the processes are pretty easy for me and I did consider the idea of just changing bearings form underneath. But, at this point, I know I will rest better if I get it apart and see everything. It occasionally will go through some oil fast; new stem seals helped for a bit but I kinda suspect a broken oil ring spring or some bores are worn too; if oiling, the compression would show good just due to the oil. And I suspect there are a few sticky valves and maybe some weak valve springs; the car sat for about 19 years at one point so I can only imagine an open spring might lose some strength. Not to mention the massive oil sludge .... you guys might remember how badly Pennzoil and Quaker State could sludge up; this is one of THOSE engines!

The garage had a space cleaned out today and the old Dodge Travco motor home engine lift (that can reach in and yank a 383 through the motor home's side door!) is set up and we'll see if we can pull this tomorrow despite the sub 30 degree temps. We'll tend ot the clutch chatter and some other issues at the same time.
 
Just an update on this... pulled the engine.... 28 degrees in the open is not too bad if the wind is still!

The startup engine knock appears to be the #3 main bearing worn out. The main surfaces were down to the copper in some areas, and the thrust surfaces were very badly worn, worse than I have ever seen in a still-running engine. We noticed that the crank pulley wobbles at least 1/8" forward and backwards around its periphery, and with the belt on, we think this was enough to be constantly trying to move the crank forwards and backwards, wearing the thrust faces out well beyond where they should have been. We think that is the reason for the lower crankcase 'rattly' noise when it was warmed up; the crank was just whacking back and forth on the thrust faces. Rod bearings looked pretty good.

Main journal and rod journal wear look to be .0005-.001" so should be good with just a polish. We might try to find some .001 undersize bearings.

Pistons not worn much at all but bores worn about .004-.005 at the tops. Oil rings are very worn and jammed with varnish; explains the occasional sudden use of oil. Plugs would look good one time, then a few would look oily at another time. A .020 over bore and some moly rings will makes things all good.

Sludge? I think this is some sort of record! See photos of lifter gallery, pan, and screen below. The granular stuff in the pan is all sludge bits and exceeded 1/4' deep in places! The screen looks to actually be sucked in and has just one clear opening. So, my engine cleaning got a start but there was just waaaaay to much for a simple cleaning. And all the sludge bits in the pan explains why recently the oil light would come sometimes when stopping at the bottom of a steep hill; all that crap was sliding to the front of the pan and plugging the screen for a moment....wow!

Varnish is soooper thick everywhere. As we worked with this engine, we kept adjusting the valves and they would 'loosen up'; however the adjusters were not backing out. Come to find that the varnish was .010' or more thick on some of the cam lobe heels, and as we tightened the lash, it would simple wear down the varnish on the cam lobe heels and appear to loosen... wow, never have seen any real varnish on the cam lobes. But it seemed like the valves were never, ever adjusted in this car. Had to gently beat the lifters out of their bores with 10-20 gentle whacks on each one with a wood dowel; the varnish ring halfway down the lifter bores was thiiiick. Cam wear on the toes and lifter face wear looked good.

So, all in all, this engine really needed to come apart for the sludge and varnish; no way to just clean that level of crap out in the car. Except for the #3 main/thrust bearing, general wear condition is resonable. Water jacket needs a good session with some muiratic acid. We're glad to be going down this road.

Thanks for everyone who commented and made recommendations. Those who said main bearing and thrust bearing can reach around and pat themsleves on the back... LOL

Regards, Mark B.
 

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Glad you found the problems. A p.o. had not been changing the oil regularly.

I think the "pushed in" screen look is correct. At least my slant looked like that (not as much junk), and I recall my 273 and 383 engines do also.
 
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