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Darkbound

VR6 24V BDE Knock from Engine, everything is changed, its still there

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Hey guys, I've been trying to track down and solve the issue that I am having for almost 5 months now, everything so far was in vain.

There is a knock coming from the engine and I just can't figure out where is it coming from and what should I change to stop it!!!

It sounds like its coming from the bottom end, but that could very well be just acoustic playing tricks.

 

What has been changed so far:

- Crankshaft

- Conrods + pistons

- Crank + conrod bearings

- Camshafts

- Oil pump

- Chains + tensioners (changed by previous owner, timing is perfect)

- The knock is not from the lifters! I've bled them and they were ticking not knocking I could easily distinguish between the two sounds when I first started the engine

- Flywheel+clutch+pressure plate etc were also changed

 

I was not the one who did the repairs the first time (when crank, conrod, pistons etc were changed) and the only thing that I know for sure was measured is the journals on the new(second hand) crankshaft. I was also told that the cylinder walls are not worn out or elliptical, but I don't know the specific measurements that they got, so I can't say that at 100%.

 

Aside from all of that, the car runs great, I also had compression leak in one cylinder but after the rebuilt that was sorted out, all cylinders now have 11 bars compression when engine is fully cold.

 

Oil pressure is also fine now, well within specs, 2.4 bar when idling, reaching 6-7 bars when revving (5-6k rpm, in neutral not on road) and I think 4-4.5 bars (not sure) at 2k RPM again within specs.

 

What I am suspecting:

- The VVTs (dont know if its even possible at all that they can make such noise if faulty for some reason, but its one of the things that aws not checked at all)

- Intermediate shaft and/or its bearings/gears

- Axial play on the crankshaft maybe? Not sure if its there or if it can make such noise, as far as I am aware this was not measured

 

Also not sure if its related but I have vibrations at 1100-1200 RPM when reving in neutral and if I hold them steady, they can be felt everywhere, can't feel them when driving, I had them before and after the rebuilt.

 

 

Edited by Darkbound

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So I tried unplugging the coils one by one, and there was a difference in the knocking when I was unplugging cylinder 1 and 2, this is where I think the knock is the most loud. When I unplug cyl 1 it gets quieter, when I unplug cyl 2 it gets more violent

 

 

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Also you may notice that the knocking in the new video has much lower frequency, the first video was from before the rebuilt. I analysed the sound and determined that now the knock is occuring at exactly half of the crank RPM. So for 2 crank rotations, I get one knock

Edited by Darkbound

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Is no one able to even make a guess? I am really out of options at this point, I really like the car and I want to start working on improving performance and looks but I just cant move on to do anything until I sort this shitty knock first as I dont know what it is from :(

The things I know for certain:

- When listening on the top of the head, the knock is most noticeable above cylinder #2, confirmed with stethoscope

- When listening at the oil pan, the knock is again most noticeable bellow cylinder #2, riiight next to the oil temp/level(?) sensor, the sound is much more clear and louder than from above, again stethoscope

- The knock occurs once for every 2 revolutions of the crank, confirmed at idle 680 RPM on crank, 340 knocks, confirmed also at 1000 RPM, 500 knocks and at 1200 RPM 600 knocks

-- The previous owner had a spun bearing on cylinder 2, he did a rebuild, changed crankshaft and only conrod for cylinder 2 new conrod/main beaerings and everything else that has to be changed, I also changed crankshaft and ALL conrods/pistons with all new bearings...

- Last night I played a bit with my old crankshaft/conrods/pistons, I assembled them and there is no up/down play at all on the piston pins, axial (side) play on the conrods is between 0.15mm and 0.20 mm, wear limit is 0.40mm si thats not it either

 

Yes the knock is much louder and it sounds like u r right next to it when you are listening bellow the oil pan, but it doesnt make a sense, how could a knock coming from the crankshaft area will skip a crank and do it only once every 2 cranks? If the knock was from piston pin/bearing I would expect to get at least 2 knocks per revolution, or 1360 knocks per 680 rpm, instead they are 4 times less. The sound looses its "power" when the engine is fully hot, the sound also sometimes goes away if I let it idle for a couple of minutes..

 

Any guesses, crystal balls and whatsoever are welcome if they can provide at least a little logic :(:(

 

More recordings of the knock:

 

 

Edited by Darkbound

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Hi
I had a similar knock on my first vr6 aaa engine. It occurred after I used an engine flush kit. I had many people try to assess it and most mechanics told me it was probably the big end bearing which was causing it. On the vr6 this is obviously a total rebuild and I was advised that it was not worth doing the work. In the end I replaced the whole engine from a donor car ( actually only cost me £100 ) and a garage in Trowbridge swapped it out for 200.
One thing to check though is has it got the correct oil ? You might see an improvement by applying oil of a thicker viscosity as I was advised. I never did this however due to the swap out but maybe it would be worth a try. My old engine btw did not suffer in any way apart from the knocking noise
Regards
Mark

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6 hours ago, markhaywardbailey said:

Hi
I had a similar knock on my first vr6 aaa engine. It occurred after I used an engine flush kit. I had many people try to assess it and most mechanics told me it was probably the big end bearing which was causing it. On the vr6 this is obviously a total rebuild and I was advised that it was not worth doing the work. In the end I replaced the whole engine from a donor car ( actually only cost me £100 ) and a garage in Trowbridge swapped it out for 200.
One thing to check though is has it got the correct oil ? You might see an improvement by applying oil of a thicker viscosity as I was advised. I never did this however due to the swap out but maybe it would be worth a try. My old engine btw did not suffer in any way apart from the knocking noise
Regards
Mark

Thanks! The problem is that the engine was rebuilt twice already, and it still has it, once from the previous owner, he spun a bearing on Cylinder 2, when I bought the car it had the knock, then I rebuilt it (didnt have it spun, just did it cuz of the knock) and its STILL there..... the only thing that I notice is that the old bearings that I removed (new when previous owner did rebuilt) haev no more than 10k miles on them, and there were a few bearings that were almost worn out, not a single bearing came out with its cap, and not a single bearing fits and clicks into its cap, they stayed on the crankshaft. The patterns on the worn bearings points to insufficient oil on the specific cylinder, but i dont know which cylinder that bearing came from... The only thing that I can think of is that, some oil gallery probably for cyl 2 got clogged and cant provide sufficient oil. And somehow it stayed clogged after 2 rebuilts.. gonna drop the pan after 2 weeks and inspect the bearings..

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As for the oil, I am using the best oil that I could find, currently its 100% synthetic 5w30 bardahl with fullerine additive, the engine sounds amazin when the knock goes away, so silent... after the rebuilt I briefly used 10w40 durinjg the break in period it had almost no effect on the knock.

Edited by Darkbound

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Does the sound go away when it's up to temp? Been running a while
 


Sometimes, but the sound definitely loses its strenght when its warm.
I gave my old parts to a mechanic to inspect them and he said that he found play in the piston pins.
I am almost 100% ready to agree that this is the source of the knock, it makes sense.
What i cant figure out is why after tbe rebuild i still have it on the same cylinder? I got a whole set of rods and pistons from another engine its extremly unlikely that thet have the exact same issue and the bad pin will fall into the same cylinder.
There is some oyher underlying issue somewhere and the knock is nusy byproduct. Thats what i think..

Also worth mentioning that when we did the rebuild not a single bearing came out with its cap (rods) they all seem out of place when placed on the caps they stayed on the crankshaft. I cant find any information what this means. Also there were worn our bearings and thry have only 10k miles on them (old owner did a rebuild shortly before i bought the car)

These beaings are the onea that i think are most worn out
20170807_235535.jpg

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P.s. i said that it makes sense to be piston pin or possibly beqring, because i finally found logic about the knock skipping a revolution. 1 revolution there are open valves and no compression in the cylnder 2nd rev closed valves and pressure. One of these scenarious causes the knock. This explains why its half the crank rpm but it comes from the bottom. So its not in the alve train. Some guy told me that piston wrist pin knock occurs only during its "work stroke" so it really makes sense if this is true.

 

 

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So I just got my parts back and got the play measured, it really is there but its negligible... had all my old parts measured, crankshaft turned out ot be perfect, pistons are ok (I think, still looking for the correct dimensions for BDE pistons), the only problematic thing is that there is significant wear on the bearings, and the caps of the conrods dont align perfectly with their respective conrods, when you slide your finger on the inside you can feel a notch at the place where the cap and the conrod connects.... still looking.... gonna drop the pan next week and see how are my new bearings and if I Will find anything that may cause a knock..

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Allright, it is now confirmed, piston #2 is worn more than the allowed limit. They should be 80.925 - 80.965 mm, all pistons are 80.94 mm except piston #2 which is 80.89 mm measured by two different people. There is no apparant damage of any kind on the pistons, just the graphite(?) skirts seems a bit more worn on one side.... one of the guys that measured it, said that most likely I have elliptical cylinder wall on #2 cylinder and this is what is wearing the piston. It would also explain why the knock is still there, but I have no loss of compression/performance, its not burning oil, nothing... Shouldnt this be happening if there is problem with the cylinder walls? (I was not ther when they were measured during the rebuilt, they just told me that they are ok, supposedly they were checked by a specialist, but I can't be 100% sure that they really measured them correctly)

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