bebbetufs

I've posted on this same topic over in the turbo forum but not specifically to ask for help to track down the source of this engine knock. I am suspecting wrist pin slap, but I'm not very confient in my conclusion.

UPDATED with additional information.

The noise:
The knocking is at twice the crank speed.
The noise grows in intensity after startup. Immediately after startup it is inaudible, then it becomes more and more present. After 30 seconds it is audible and by 100 seconds it is easily identifiable, but not as loud as a knocking rod.
Shutting off and letting the engine sit for a minute or two causes the sound to diminish a bit immidiatly after startup, but it returns much quicker than when starting the enine from cold.
It does sound like a rod knock though, but there is no change in noise when pulling any spark plugs. The noise does not alter character when accelerating or decelerating.
It is loudest directly beneath cylinders 1 and 2 at about 7-8 o'clock.
Oil pump and front of block hums silently like a sowing machine, as does the rear.
The oil pan vibrates beneath these cylinders where it sounds like a relatively loud mechanical knock.
It seems do dissapear when the RPMs increase.
There is no direct noise from anywhere on the block only a faint knocking.
There is no direct noise from anywhere on the head or the cam.
I believe the knocking frequenzy is at crank speed.
Here is a mobile video of the engine after checking #2 rod bearing. The video shows a startup from cold (if you have an equalizer plugin cuttin all frequenzies and bumping 600Hz - 1kHz helps)
Here's an audio file taken directly from the front of the oil pan.

Troubleshooting effort:
I see no signs of contact anywhere on the rods or counter weights.
There are no marks in the oil pan.
I found no loose fasteners in the crank case.
Oil pressure at idle is 5, falls to 4.5 as oil heats up.
Rod bearing #2 and pin looked new apart from some slight shiny patches on the upper bearing shell backing and some very slight polishing of the coating immediately below the locating tang.
Removed DIY windage tray, but the noise stayed the same.
Since the windage tray is bolted to the scrapers I would expect the noise to change after removing the tray, hence I do not think the noise is from the scrapers.
I have yet to inspect the other rod bearings, but the symptoms do not point to rod bearings in my opinion.
Removed ALL belts - no change
Shorted one plug at a time - no change
Revving the engine increases frequency, but not the level or character of the knock.


Engine specs:
Rebuilt and completely blueprinted engine which has done 50kms.
20kms since oil change
New rings from LR. Gapped correctly,
Block: Brand new block from porsche. Perfect cyilnders. Windage ports have been machined between 1/2 and 3/4. The block was align-bored and align-honed to get rid of some out of round on the mains.
Piston to head clearance: I didn't have to but I used the thicker HG for safety.
Rod Bearings: ACL Racing coated Toyota Supra bearings. Clearances around 0.043mm on all pins. Bottom shells are 0.0100" thinner to get enough clearance.
Rods: Wössner. Honed and machined to accept the Supra bearings. about 0.15mm thrust clearance. Big end ID measured a tad on the tight side for the bearings.
Mains: Glyco bearings. Coated. I don't remember the clearances, but they were well withing spec.
Cranck: All journals on the minimum limit. Runout well within specs.
Pistons: Selected from several tolerance group 1 pistons based on weight and size. Balanced to 0.01g.
Wrist pins Lindsey Racing lightweight pins. Brand new. One rod and one piston needed honing to accept the new pins. All pins slid slowly through the piston bosses by their own weight when lightly oiled.
Balance shafts: Counterweights reduced axially to match weight reduction in rotating assembly in percent.
Oil control mods Ported oil passages around pump and filter bracket. Teflon crank scraper on up-stroke. Steel scraper on down stroke. Windage ports machined in block. Baffle system in sump. Ported oil return chutes from head/cam.

Van

Is it possible that the noise is happening at twice crankshaft speed... and it's coming from a balance shaft?

Did you use the right balance shaft bearings? There are early and late ones... Or, could your lightening the balance shafts be a contributing factor?

You could disconnect the balance shaft belt and see if the noise goes away.

bebbetufs

Thanks. I'll try removing the belt to be sure, but according to the stethoscope the shafts are close to silent.

Would wrist pin slap be heard from the top of the engine when using the stethoscope, or is there enough mass there to dampen it enough to make it seem loudest from the bottom, even if the noise is generated in the middle of the block?

Paulyy

Well you cannot put early bearings into late housing. Ask me how i know..

Make sense if you put late bearings into early cover.

Van

If you load the video file into a movie editor, you might be able to measure the time interval between the peaks of the knocking and know exactly what speed it's occurring.

Out of curiosity, have you done a leakdown test?

bebbetufs

I did attempt to do that, but I'm unable to single out the knocking from the other noises.

I haven't done a leak down because the rings have not seated completely.

Van

I think it's worthwhile to do... especially if it's warm. If one cylinder is low, it might be a valve seat problem. You're not using solid lifters, are you?

bebbetufs

Thank you for helping.

The engine is idling at normal speed around 900 rpm. I'm guessing the sound is at crank speed, but this could of course be two things knocking to give a double count.

I took a break today to hopefully regain some motivation to pursue this. Tomorrow I'll do the leakdown test, and rule out the balance shafts, but would not the sound from a bad valve seat be evident on top of the engine? Apart from the injectors the top is really quiet. The intake is dead quiet. The noise is only really evident from the bottom end, and is easy to pin it to to the shallow end of the oil pan. This area of the oil pan is much sharper and crisper than any other on the engine.

The sound is weak where the pan attaches to the oil pump. Immediately aft of the pump it grows to a clear crisp knock in the sthetoscope, only to diminish when getting close to the sump.

Moving the stethocsope probe from the oil pan to the block causes the the level to drop sharply to the point where one would be inclined to say that there is no serious problem. Moving up along the passenger side of the block only has a distant muffled knock.

The are around the RMS has only a faint distant knocking noise.

951Tom

Not sure if this will help much, but one time I thought I had a rod knock. Turned out to be the serpentine pulley bolts had come loose from the balance shaft drive gear. It was in the same area and had me stumped for awhile until I found it.

bebbetufs

Did some more troubleshooting today. I'm throwing in the towel on this for now. After 4 years of work on this engine on and off, including every moment of this summer there simply is no more energy left to continue. I'm putting the car in storage. Anyway, this is what I did today.

I removed the balance shaft belt, alternator belt and PS pump belts.
I made a funnel for the mic on the phone so I could block out ambient sounds and get the sounds internal to the oil pan only.

Analyzing the audio track the knock happens at twice the crank speed. The engine was idling at 1180 according to the tachometer. The wave file shows 2280 KPM (knocks per minute ) which gives a crank speed of 1140 which is close enough to seem right. This the audio recoring made: https://dl.dropboxusercontent.com/u/...03rd%20try.wav

Van

So, it's making the noise at twice engine speed *with* the balance shaft belt removed...

I'm just thinking out loud here... but if it were wrist pin or connecting rod, wouldn't you think it would happen every other stroke... because of the parts pushing together on the power stroke?

Did you say anything about your deck height and or head gasket type? I'm wondering if the sound is made by both the #1 and #2 cylinders... since they're out of phase.

Have you done an oil analysis? if there is play between the cylinders and pistons, that should show up as aluminum and silicon.

bebbetufs

Thanks Van. It's helpful to consider all possible causes. I measured the stick-out of the pistons carefully and concluded it would be best to use the thicker HG. I saw no signs of piston to head clearance in the bore scope. If the pistons where touching the head I would expect the sound to be clearly audible from the top, but it's quiet.

The piston to bore clearance is on the tight side of the allowed.

I haven't done an oil analysis. Since the oil has only done about 15kms I'm not sure I will find anything.

Could it be two piston pins? Or could one pin be knocking both at the top and bottom of the stroke?

Tiger03447

I don't know what viscosity oil you are running, perhaps going to a heavier weight might help some. When you pulled the bearing cap on #2 rod, were the oil passages lined up OK with the hole in the crank? I can't remember when we did my engine, if the bearings could be installed backwards or not (in relation to the oil hole in the crank). If so, you might be starving the rod bearing for oil. Just a thought.

Tiger03447

Van..if the wrist pin was too loose,wouldn't you get a sound at both ends of the stroke, I would think? 1 knock when the piston goes up in the bore and the rod reverses, and also at the bottom of the stroke when it reverses again, giving knock #2. Sounds like the bushing on the wrist pin end of the rod might be worn or have too much clearance. just wondering out loud too.

Van

That does make logical sense... But you said the wrist pins fit the connecting rods well? Unless something has broken apart, it shouldn't have changed.

Did this noise start immediately after the engine rebuild, or after a few miles (kilometers) of driving (presumably under load and boost)?

I had another thought... could the whole rod be shifting fore/aft (due to the too much clearance on the piston end)? Meaning the rod might be moving to the point where one of the crank counter weights is nicking it...