sounds like a slight rod knock

[m3boost]

I'm in need of some input... This is for my e30 s50 turbo m3..I rebuilt the engine cause it was starting to smoke. I bought 86.5 mm JE pistons with eagle rods. So the engine had to be slightly bored. I used new main and rod bearings all stock. Everything was plastic gauged and tolerance was basically in the middle of what its allowed. The car at first start up, had a loud ticking noise in the valve train.. I removed lifters and found two that were completely squashed, so I replaced them. To make a long story short, I replaced all of them. The engine is now quiet with the exception of what sounds like rod knock. You really can hear it unless you really know what you're listening for. If I accelerate to 2000 rpm, it's heard a little louder. But if I start driving it, then it can be heard with ease. I can not seem to pin point where its coming from even with a stethoscope. I can point to the general area which is around rod 5,6 and transmission housing..

Things I've done so far,
1) I removed the engine to plastic gauge everything again and it's with in specs.
2) Since it's an s50 in a e30, it requires the oil pan from a e34 with it's built-in tray. I didn't have an issue before when it was stock, but I went ahead and remove that tray and placed the oem tray for the s50 on the block.
3) with the car at 2000 rpms, I disconnected one coil at a time to see if the knock would null on a particular coil, and there was no change in the sound.
4) Also, forgot to mentioned that I placed new oil squirters
5) today I finally installed an oil pressure gauge. It reads 60 psi at idle on cold start, and reduces to 22psi once it's warm. It increases as the rpm's go higher.
6) it also has a brand new s52 flywheel, clutch, pressure plate, throwout bearing, and pilot bearing..
7) made sure spark plugs were tight.
8) At cold start, the noise is not heard or atleast I can't hear it. Only as it gets warm

I have basically have ran out of options. The head is from a 93 325i with my m3 cams and trays.
So any input would be greatly appreciated. Thanks

[vollosso]

Piston slap?


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[jakermac]

You said S52 flywheel. Is it single mass or dual? If single, it could be the Getrag (don’t know if ZF does this too) gear rattle.

[vollosso]

Both pistons and gears would be more pronounced warm.

That oil is a bit high.. not a worry just a note.

Tell us more, is it turbo? What injectors or tune?


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[rajicase]

Do a compression test. If a rod is tweaked , compression in that cylinder will be low. It'd be best if you had a baseline test to compare it to.

Also keep in mind rod knock gets worse as you increase rpm. If you're not hearing it get worse, and worse the more you increase rpm it likely isn't rod knock.

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[m3boost]

You said S52 flywheel. Is it single mass or dual? If single, it could be the Getrag (don’t know if ZF does this too) gear rattle.

dual mass with zf trans

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Piston slap?


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I keep thinking that may be it. But then again wouldn't it be louder at first start up and be less as it warmed up?

[m3boost]

Both pistons and gears would be more pronounced warm.

That oil is a bit high.. not a worry just a note.

Tell us more, is it turbo? What injectors or tune?


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gt35r, 80lbs and tec3r.. before the rebuilt, car ran fine with this setup and even started within 5 seconds on first start up after rebuilt.

[m3boost]

Do a compression test. If a rod is tweaked , compression in that cylinder will be low. It'd be best if you had a baseline test to compare it to.

Also keep in mind rod knock gets worse as you increase rpm. If you're not hearing it get worse, and worse the more you increase rpm it likely isn't rod knock.

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A little more info..I've been working on this issue for about a year already. I don't get a chance to work on it often. But, I did do a compression test at the beginning when I first heard this issue. I can't recall but I think it was at around 175 all across..but again I don't recall. I do know that they were all the same. these are low compression pistons.

[beeasy]

Try running it without the drive belt on. Make sure its not an accessory making noise. I had a loose water pump pulley sound like rod knock.

[chikinhed]

Did you check both bearing halves of each rod? The rod side is usually the one that will show the damage. If the piston to wall clearance isn’t totally way out to lunch piston slap should go away once the engine is up to temp. It sounds a bit like it’s a diesel with some aftermarket piston installs.

[m3boost]

Did you check both bearing halves of each rod? The rod side is usually the one that will show the damage. If the piston to wall clearance isn’t totally way out to lunch piston slap should go away once the engine is up to temp. It sounds a bit like it’s a diesel with some aftermarket piston installs.

I did do a visual inspection of both halves the last time I removed the engine. Then plastic gauge everything again. It doesn't hurt to try, but I'll remove the the belt tomorrow and try it..But I really can't run it for too long or it will overheat without the belt. And this noise is more noticeable when it's warm..It is rpm depended. If it's still there, I'll remove the transmission including the clutch and pressure plate and then try it again.

It doesn't bother me if I have to tear everything down as long as I find out exactly what it is..

[vollosso]

You should definitely post on the fb groups. They might could solve it.




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[m3boost]

You should definitely post on the fb groups. They might could solve it.




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lol..those groups still don't know about the waterpump plastic impellers

[pbonsalb]

The Facebook guy boring out his m52 intake manifold might come up with an explanation you have not thought of.

[DunDunSkeert]

Do a compression test. If a rod is tweaked , compression in that cylinder will be low. It'd be best if you had a baseline test to compare it to.

Also keep in mind rod knock gets worse as you increase rpm. If you're not hearing it get worse, and worse the more you increase rpm it likely isn't rod knock.

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That's not always true about rod knock. I've heard several engines with bad rod bearings that only knock at certain RPM. Most of these get pretty loud around 3000rpm then quiet down when you go higher. I'd speculate the raised oil pressure dampens it.

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OP post a video so we can hear!!!

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Just saw you have a DMF. I'd check it to make sure it's not bad since the noise is coming from the back of your motor.

[Robocop]

my rod knock only happens when the engine is cold mostly at idle, then it just goes away.

[vollosso]

my rod knock only happens when the engine is cold mostly at idle, then it just goes away.

More likely, Too much ptw.. piston slap.


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[m3boost]

Here's a video i took of the sound.. There's slight valve train noise since I took the cams out to check all lifters and timing...The noise I'm concern is heard at the bottom end. oil pressure at idle when fully warm is 10 psi and will rise to 40psi at 3000 rpms...

https://youtu.be/npMAknQTPgg

[M3turboE36]

Here's a video i took of the sound.. There's slight valve train noise since I took the cams out to check all lifters and timing...The noise I'm concern is heard at the bottom end. oil pressure at idle when fully warm is 10 psi and will rise to 40psi at 3000 rpms...

https://youtu.be/npMAknQTPgg

Crankshaft bearing failure?

[Yother]

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I keep thinking that may be it. But then again wouldn't it be louder at first start up and be less as it warmed up?

Yes, it would be louder at start up and quiet down as it gets hot and the piston expands. That's why you give it more clearance than a pressure cast piston, it grows. Built an engine for a customer and he was there at first start up and I heard what I thought was a rod knock and totally red in the face until it warmed up and the noise went away.

Sounds more like lifters to me. Hydraulic or solid? Easy to pull the pan? Debris in the oil?

[m3boost]

No debris in oil pan... during this rebuilt, i did use another head and its from a 93 325i... the springs are straight and not tapered like the 95+... im using my same s50 cams,cam trays, and lifters.. i don’t know if that would make a difference..


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[Yother]

With no debris in the pan it's unlikely it's a rod knock. Filter clean too I suspect? The bee hive springs shouldn't make any difference. Lifters would be the only thing or an accessory. Hydraulic or solid lifters?

If you can start it without the accessory belt on see if that makes a difference. Of course don't run it that way for more than a minute.

[m3boost]

With no debris in the pan it's unlikely it's a rod knock. Filter clean too I suspect? The bee hive springs shouldn't make any difference. Lifters would be the only thing or an accessory. Hydraulic or solid lifters?

If you can start it without the accessory belt on see if that makes a difference. Of course don't run it that way for more than a minute.

I tried with out the belt, but I can't leave it on long enough for the knock to be heard.. I would have to leave it on for atleast 5 to 10 minutes for it to be heard..The compression is same all across. Even though it's new rods and pistons, I'm leaning towards wrist pin knock.. It doesn't sound solid enough for it to be rod knock..I have to tear it apart again regardless. I'll update on what I find..

[Yother]

Think you had a keeper come out? I've had that happen before. No knock but gouged the cylinder walls.

[vollosso]

Piston slap?


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