[glhs#116]

So.. I've been fooled before by a terrible sound that sounded a lot like rod knock. it was generally my torque converter bolts loosening up. But this doesn't seem to be that.

1971 455 HO with Edelbrock 87cc CNC heads. Crower 61919 "041" cam. Harland Sharp roller rockers.

So, the start of this whole thing was putting in a wicked custom cam that Jay had made for me. Slightly bigger cam. Rhoads VPro lifters. Long story short, it didn't make it through breakin. Shredded three lobes and lifters through my oil system. So I had to put the old cam and lifters back. I did keep track of what went where and lifters went in same places. Distributor gear was OK.

Anyway, when it was together again I had a hammering sound that (by its timing) seemed to be on one hole. It ramped up with load. Classic rod knock behaviour.

So, I ordered some new bearings and tore in. I was doing this all on my back in the car so after I decided #1 main looked OK I decided to just do the rods. All the rods had some scoring, of course, but journals were pretty good. None of the rods stood out at all, they were all similar. Replaced all.

Today I got it all back together and running. It sounded its old self all through the no load stuff. But when I went on a test drive I immediately had the same knocking on load. Ramps up with load. Since it sounds so much like it I didn't really push on it. I did have to complete the drive to the petrol station and back because there wasn't a good place to turn around. Big road. So, I noticed that it didn't get worse at all. So not like a lobe going flat. It also was absolutely fine with light load and cruise. The whole way. But if I had to pull away as soon as I lay in some throttle it sounded like a rod was trying to fall out of it.

So... I don't know. I can't think one journal suddenly went so away. They looked OK and similar. Bearings all new. Like I said, none of the old ones stood out from the others. So I'm a little sceptical about actual rod bearings. I just can't see how. Oil pressure good as ever. But it really ramps with load. So in my mind it has to be
* Exhaust related some how (but near a port -- either one port or the crossover on one side)
* Valvetrain related but pertaining to an exhaust valve. Can you get a collapsing lifter to sound like that?

It's really really rod knock like but I just don't see how it can be. Collapsing piston skirt? What do they sound like? Similar?

Really scratching my head. And got Street Weekend breathing down on me in like two weeks.

Sam

[steve25]

Well since you had so much crap from the failed cam and lifters go thru the motor then maybe there was still enough grit left in the blocks oil galleys and the oil passages in the crank to take out a new rod bearing when it got pumped in.




Try this.
Get the motor fully warmed up by light driving so as to get some oil temp taking place also .

Try to simulate the motor being under load.

With the motor at idle out of gear ramp
up the timing ( maybe a lot ! ) a long with cranking up the rpm by means of the idle speed screw and see if you can start to hear this knock take place.

If you can then pull one plug wire at a time to see if it goes away.

If this does not turn up anything then I would unbolt the converter, slide it back out of the way and look carefully for any cracks as you rotate the motor over little by little.

Failed flex plates can make some strange noises.

One thing I can tell you for certain is that once you hear a rod knock ( from a rod that’s going south) even under light load and low rpm you will never mistake it again for anything else.

If it’s a wrist pin going bad then that makes a double slap knock sound at TDC and BDC, kinda like a castinette .

[Jay S]

If you took it apart, and the rod bearings were ok, then replaced the rod bearings, and now still have the same noise. It doesn’t sound like that was ever creating the noise.

The crank can throw debre from the cam up into the pistons and make the wrist pins tight. But that should knock badly all the time, not just under load. Steve’s idea of pulling a plug wire to see if a dead cylinder changes the noise is a good next step.

[dataway]

How does it sound from under the hood while goosing it?

[glhs#116]

This is against the torque converter from inside the car

https://youtu.be/GsxemomD7Qs

And this is against the torque converter hood open from out the window

https://youtu.be/PpX4XphGIGU

Sam

[steve25]

Sam I know you have had this apart more than a few times.

That does not sound good in that video and sounds to me heavier then just a bad lifter would.

Was that with the motor warmed up or cold?

If it was cold then I would not run it anymore to even do the run & remove a plug wire test!

I guess get prepared to unfortunately pull it and tare it down before a big failure takes place.

How have you torqued up the rod bolts these last two times you had it apart and put it back together , with a torque wrench or a stretch gauge?

After 5 times I would have replaced the bolts and then got the rods checked annd resized if needed .

Don’t forget that the first time the bolts where torqued up was before you even bought them, so if you have had the rod caps off 4 times I would have gone for new bolts, or at least used a stretch gauge this passed time around .

This would have shown if a bolt was too elongated to pull up to torque fast as a good bolt should.

[400 Lemans]

Sometimes the spring under the fuel pump arm can break causing slop and makes that sound. Something easy enough to check.

[VCho455]

I would cut the oil filter open and inspect it to start.

Years ago I had a brand new flex plate that cracked just after breaking in the cam and made me think I had lost a rod bearing. I discovered it after pulling the engine.

[steve25]

Yes I have had the flex plate issue twice , but that being said do as stated above so you can hopefully feel better that it might not be a bearing issue, remove, cut open and inspect the oil filter.

[mgarblik]

That is a pesky noise for sure. Doesn't sound like valve train to me . Taking the engine out is a big job, so I would recommend eliminating EVERYTHING else before doing all that work. Eliminate the fuel pump as mentioned in other posts. Then remove one V-belt at a time to eliminate each accessory. Finally, unbolt the torque converter, move it back. After each individual test, if the noise is still present, the engine will unfortunately have to come out. Lets hope for the best.

[glhs#116]

So, today was a bit of a roller coaster.

Started the car and warmed it up in the garage. Let it run a good fifteen minutes or more. Totally warmed up. Tried to reproduce my hammering noise by driving it against the torque converter. Couldn't make it happen. Never mind. Good time to do a compression test.

Did compression test. Values are not too far away from the last one I did about a year ago. Put all the plugs and wires back in. Fire it up again. Now I can hear some real clatter from passenger side valve cover. Hmm, maybe something valve related. Ran it with the valve cover off. Number 6 intake is really loud. I can feel it feels not smooth like the others. I don't know, a little, like, mildly crunchy. Check the poly lock nut depth. It's in line with the others. Recheck the lash. It's about right but it is one of those lifters that compress really easily (unlike, for instance, the one next to it). I tried just dialing it down to almost no lash (just slightly up from the bottom instead of "plus 1/2 turn"). Seems quieter. Take off other valve cover. All the others feel smooth. Swapped number 6 intake and exhaust rockers to see if it is the rocker. Nope. the lack of smoothness stays with number 6 intake. Swap back. Relash again. Now, all is quiet again. All seem good. Hmm.. Maybe I just flushed something or whatever.

Anyway, now valvetrain is quiet. Won't knock against the torque converter. OK. I'm going to try a short drive. Pull out of my gate onto the road and bam! Instantly the moment I'm actually accelerating from low speed I'm hearing the knock. Now I have to go a ways before I can safely turn around so I play with it a little. No hammering at constant load even at higher revs. Less of a hammering if I apply the acceleration at higher revs. Anyway, I get turned around and drive back. Seems it is the same but the engine just needs to be totally totally warmed up through. I guess that means the clearance in <whatever> is only just slightly excessive. Anyway, park it in the garage and I'm dejected of course because I know I can't drive it like that. But then I realise the only chance I have to try pulling spark plug leads is now. So, given as it always sounded passenger side to me and like it was rearward, I try pulling number 8 lead. No knocking against torque converter. Pull number 6 and reinstall number 8 and I can make it hammer against torque converter. So it does seem to be number 8.

So from all of that I take it that I have some genuine trouble under load to do with number 8. Rod bearing? Hard for me to credit. I didn't see any obvious difference in its bearing from the others. And it was replaced with the others. And it was making this noise before and after the rod bearing replacements. Same with stretched rod bolts. They are ARP bolts and I tightened them to spec with the ARP lube. Yes, I know a stretch gauge would be better. But also none of them were slow to gain torque or felt off. But, I dunno. Maybe I collapsed a skirt. Maybe the big end is deformed from detonation or something and I just didn't notice. Whatever it is the obvious to me thing is that this car isn't going anywhere, least of all to Street Weekend in two weeks without a replacement piston/rod assembly with rings that I can just swap out.

I mean, pretty clear that I'm about at needing to rebuild the short block. but that's not something I can fund this year and it's not something that will get me running in two weeks.

Well, thanks for all the help, all. I'm thinking it can't be any of those other things if I can pull a spark plug lead and it goes away. So it seems exactly like rod bearings on number 8. Except that those bearings are new. Or stretched bolts. Except that they seemed fine. Or deformed rod. But how? That crank journal looked fine. Oh well. I guess I don't have all the answers. But number 8 does seem to be the problem.

Sam

[steve25]

Sam I am sorry to hear this.

I know all too well what it's like to have a fun event planned to take the car to and then there's a mechanical issue that derail's that fun.

Sam are these still factory Pistons in this motor ?

What services do you have near you?

In other words how hard would it be to get #8 rod to someone to check and resize if need be?

Also if if does need to get resized new bolts should be installed first.

I know you have rebuild this motor before in some major difficult conditions and yet got it done, do you at least have a big enough garage space this time around and a engine crane?

[glhs#116]

So, I woke up this morning with, I think, a clearer head. I have a pretty good guess at a cause that fits all the evidence. I think I have some trash in an oil passage.

Hear me out. What if the old rod bearing knock was rod bearing knock (like it sounds) but the bearing wasn't really damaged yet? I mean, I've never given it much throttle after I hear the noise. I was thinking knock because the bearing is already pounded (like detonation) but what if it is knock because LOCALLY I don't have enough oil pressure. Because THAT PARTICULAR pressurised oil feed is weak from partial blockage. There would still be some supply. But weak. I would only hammer it under load. As soon as I do I stop and I haven't done it much so the bearing looks OK (because it mostly still is). I put in new bearings and it still knocks because the supply is still weak. The clearance is fine but the oil pressure for that rod bearing isn't?

What do you think?

I've been pondering on

(from my shop manual)


I could be starving (partially) some of this passage from oil galley to #5 main. Main probably won't care as much with other mains fully pressurised. Or it could be in the crank from main to that rod bearing (although those are bigger passages so I kinda doubt that part).

Anyway, that's my current best theory. Rods and bolts and rod bearings look OK because the are. I do have great oil pressure. 60psi at hot idle with 5W-30 oil so I'm not surprised if a partial blockage doesn't have much symptoms until more load is applied.

Well, if I were right I'd definitely need to pull the whole engine. Would need to lift the crank out and can't do that in the car.

I have a garage but not an engine hoist. I can rent one. But the garage has a pit. Now I thought that was a great feature until I found that it is always flooding and you have to be a midget to stand in it. What it mainly does is make jacking the car a pain in the arse because the boards can't take a lot of direct pressure. But I'm pretty sure I could wheel an engine hoist in there. Just trying to think through the minimum I would need.
* Rent hoist
* Gaskets
* Rod bearings again
* New rod bolts if I'm smart
* More oil
* More coolant

By the way, checking the oil on this car is now hilarious. With iike three oil changes in a row in a few hundred miles the oil is basically invisible on the dipstick. My engine may be undriveable but it is the cleanest undriveable Pontiac 455 on God's green Earth.

What do you think? Not sure I can get this all done in time but also maybe I can..

Sam

[steve25]

Any sound stemming from an out of round rod big end or an oil restriction, or a combination of both is going to show up as distress in the rod bearing there’s no two ways about it.

Once you get it apart you could also plasti gauge that rod journal and see how that checks out.

Also God forbid that the crank is flexing from an internal crack and is on its way south!

So it’s time to cover all of the bases with this issue and get the crank Magnaflux tested also .

I don’t want to see you loosing that block and possibly one or both heads .

[Jay S]

Could you have some fillings stuck in a lifter on the number 8 cylinder? It sounds like possibly a valve terrain noise yet, it doesn’t sound like rattle in the video. It if was a lifter noise, and you pull the engine, you will take the engine apart, put it back together and it will still have that noise. The oil galley which feeds the number 8 lifters is the end of the galley and also where sludge and filings ends up. I think it should have been obvious if it was a rod bearing when you replaced them, a collapsed skirt on the pistons is extremely unlikely. A tight wrist pin will loosen when warm. I am still not sure it is an issue in the rotating assemble. I would hate to so you go thru all the work of pulling it and not find the smoking gun.

[BB70]

I've had a loose wrist pin mimic a bad rod bearing noise before.

[Tim Corcoran]

Do you think you may have an out of round rod?

[glhs#116]

Good to see the forum back.

I have a hoist, some new rod bearings and gaskets. I'm ready to pull engine if I need to but been doing a little chatting with Jay offline whilst the forum was down and I'm not so convinced it really can be the red ends. Well, it's hard to see how anyway. So I'm doing as much diagnostics before I pull the engine as I can.

First, Jay suggested I see what other lifters are really easy to compress (like number 6 intake was). So I did that first. I backed them all off the same amount and then wound the poly locks all back the same amount (1.5 turns). I then did lash again (half turn preload) on all the rockers paying particular attention to which lifters were really soft. This time I only found one and it was over on the "quiet" bank. Number 3 intake was really soft. Number 8 exhaust was a little soft. All the others were totally normal. I'm going to guess some crud was in number 6 lifter and has since found the exit. None of the lashes had changed based on how much I had to turn the locks back in after adjusting.

After this I ran the car in the garage and warmed it up again. The rattle is pretty loud cold. Here's a video of passenger side where it is worst

https://youtu.be/PbOx_bFU8f8

Here's a little sort of side to side so you can see that it is in that back passenger corner

https://youtu.be/yWk-zz-ahAw

Warmed up it is fairly quiet

https://youtu.be/45m7n8hyBC8

Once it was all warmed up I put on the parking brake hard and gave it a bit of throttle in drive. I could just about get it making some noise which again sounded passenger side rear just before the parking brake was about to give up.

So, I started thinking what else could cause a knock noise around number 8 under load and I remembered the intake bolt hole I had to helicoil. I didn't have the distributor cap on all the way at one point and I remember worrying about any conductive shavings making their way to the magnetic pickup. Since I have this great balancer that has markings at 90, 180 and 270 also I was able to verify with the timing light that none of the 8 sparks are at all advanced or retarded from where number 1 is. So I feel I ruled that out.

Since I felt I was probably looking at piston noise rather than rod big end noise I fired up the engine again and did some runs against the torque converter with me holding the footbrake so I could load it a lot more. I found that when I got to a bit of a hammering noise I could push a little harder and it would actually tail off a little. A lot of rain outside made me avoid another test drive on the street. Looking for more clues I kept it running quite a bit while I thought about things. I revved it pretty high in neutral. 4.5k to 5k. Sounds great, to be honest. It really doesn't seem to make much noise or any from just speed (no load). I ran it quite a while. Left it running, sat inside, tuned the stereo equaliser just right. Cranked some Beach Boys and some David Lee Roth. I figure if it isn't rod bearings it is probably something that needs to flush out so more running is good.

Anyway, last thing I did was get some video of running against the converter with me on the footbrake. I did this by sticking the phone on the chest freezer against my tea mug. I pushed pretty hard as you can see from the car movement. What noise there is seems a lot quieter than before to me. It's reverse first, then drive.

https://youtu.be/Nn0bpHXjWNg

So. What do you think? I'm thinking not to pull the motor yet. Maybe I'll try a test drive again tonight if it is dry enough. I'm thinking maybe it just needs to run a bit more. I mean, I'll pull it if I have to. What do you think all?

Sam

[steve25]

Man I don’t know at this point Sam so I am glad you looked around more Corners for possibly’s.

That being said here’s one other possibility.
Does the motor have a factory Windage tray ?

They have been known to crack and split and then as they vibrate Rod (s) can strike them.
Please at least cut open your filter and see what you might find.

[Schurkey]

Originally Posted by steve25

If you can then pull one plug wire at a time to see if it goes away.

NEVER "pull" a plug wire to kill a cylinder.

"Pulling" a plug wire drives the secondary voltage sky-high, can damage the insulation of the ignition system including INSIDE the ignition coil.

You are ENORMOUSLY better-off to GROUND the spark. I have used small nails, blunt the ends on a stone. Lightly lube with silicone dielectric grease, and SLIDE them BETWEEN the plug wire and the plug wire boot (do not puncture the insulation) at the distributor cap until you can feel the metal end of the plug wire. See attached photo of Chevy TBI distributor as an example.

Then you can ground an INCANDESCENT (Not LED, not fluorescent, not neon) test light or a jumper wire, and touch each nail in turn to kill the spark to that cylinder.

Originally Posted by steve25

Does the motor have a factory Windage tray ?...
...Please at least cut open your filter and see what you might find.

Agreed.



I don't know why a windage tray, a lifter, or a fuel pump would change the intensity of the knocking based on throttle position. The speed of the knocking...sure. The loudness? Not so much. Possible, I guess, but it seems REALLY unlikely.

How rich does this thing run? Carbon buildup in the combustion chambers?