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Discussion Starter · #1 ·
Was driving around in my 2010 gtr today and while slowing down I hear what I would describe as a rod knock. Started while down shifting. I pulled the car into my shop and threw it up on the lift. Looked underneath and didn't find anything obvious. With the car running it sounds like the engine is knocking but when I'm under the car it's obviously not the engine making noise. Just to make sure I drained the engine oil and cut open the filter and everything in the engine is minty fresh.

The noise I am hearing is coming from between the engine and the bellhousing. I was thinking it might be a lose flex plate bolt or possibly a cracked flex plate. I checked the bellhousing for movement and there is a little but with the drive shaft removed completely there is almost no in and out play. The noise I am hearing is an actual knocking/tapping noise from directly inside the inspection panel on the bellhousing.

It was getting late so I left the car on the lift and headed home. Wanted to at least post what's going on to see if anyone else has had a similar failure. I've had bad bell housing bearings that typically rattle on and off in gear but this literally sounds like someone is tapping a ratchet on the bellhousing.

Tomorrow I'll drop the subframe and pull the bellhousing and see what's going on. I've only ever heard this kind of noise from a cracked flex plate or a loose flex plate. The engine just went in 700 miles ago so it's quite possible that it wiggled loose. Either way I just wanted to see if anyone has ever heard of or seen this issue.

Thanks.
 

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Discussion Starter · #2 ·
Pulled apart the car today at the shop when I had some down time. The bell housing had minimal play in and out and none side to side. It did make a distinct clunk noise when I pushed it in and out though.

After removing the down pipes and waste gates I pulled the bellhousing out which wasn't all that bad after I dropped the subframe enough and lift the engine a little bit. Once I got inside I removed the flex plate bolts and wiggled out the bellhousing. After doing that I inspected and found no issues with the flex plate. All bolts were tight and no cracks like I've seen on other cars. But now after removing the flex plate I find surprisingly bad pitting on the back side of the crank. The only time I've ever seen this kind of damage is when a flex plate/flywheel comes loose. The powder coating on the back of the flex plate was also equally pitted. I'll take a few pictures and post them up when I get a chance. I called boost logic to ask what they recommend and I'm waiting on their reply. The car has a 4.1 stroker in it and the car was running great.

I was slowing down off of the highway from about 85 to about 20 fairly quickly and I started to hear what sounded like a rod knock or bad u joint. I drove it another 1/8 mile to the shop and started taking it apart. The fact that it happened on decel is making me think it might just be a loose flywheel but all the bolts were tight. I used a 1/2'' impact to remove them. Any help would be greatly appreciated.

Thanks.
 

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Discussion Starter · #5 ·
The seal looks great around the crank and no oil leaks. Just put the bellhousing back in without the coupler to rule out the bell housing bearing and the noise is still there. I also smoothed out the back of the crank and the flywheel and reinstalled the arp 2000's back in with red loctite. On cold start I'm getting 90psi oil pressure. Going to let it run for a little bit and then I'll drain the oil out to see if I can find anything in the engine. It pretty much has to be an engine knock at this point. I can't think of anything else that would cause the noise I am hearing. It's weird that the noise is coming from the bellhousing though.
 

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Discussion Starter · #6 ·
Hmm looks like corrosion? No seal damage at all?
No corrosion unfortunately. It's actually damage going into the crankshaft itself. Similar to what you'd get if you were to hit it with an air hammer. I've seen this on cars that have flywheels go loose but again mine was tight. Not sure what to do now. Going to talk to my machine shop and see what they recommend.
 

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Discussion Starter · #7 ·
Tomorrow is fully booked but as soon as I finish my last appointment I'm going to push the car back in and start pulling the engine.

I'm running a sleeved 4.1 boost logic bblock, pnp'd heads, Tomei cams and all the fancy pants valvetrain and arp 2000 everything. Before I drop the engine and start pulling it apart can anyone think of something that isn't engine related that could be causing the noise that I'm hearing?

The noise started while slowing down from about 100mph to 20mph rather quickly while down shifting. By about 30mph I could hear something and then the noise kind of continued. I was convinced it was coming from the bellhousing but after pulling it and finding nothing I'm now thinking it's bottom end near the back of the engine. The other possibility is it's from the top end though.

When I have the hood open I'm hearing it from the very back of the engine. It changes with rpms and to me sounds like a rod knock. The only reason I haven't said rod knock yet is I have 90psi oil pressure starting the car up in 90 degree weather and it was holding 30psi at idle when it started knocking. I also have no metal in the oil and the engine only has about 800 miles on it on it's 3rd oil change so I'd expect to see some glitter at least. The car was built to run about 50 psi and it was only running 12psi on the boost logic 15x turbo kit.

I've also reached out to boost logic and they are also reaching out to their machine shop to see what they think it might be. Unfortunately I might have to ship this thing back after only 800 miles of driving it :(

I plan on pulling the intake and valve covers first to make sure it's not something stupid up top but if you can think of anything else just lmk. Thanks!
 

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Did they build that engine with a used crankshaft? The reason I say that is because sometime the flywheel had came loose. That’s what causes the damage on the back of the crankshaft. That will definitely cause a knocking noise.
 

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Discussion Starter · #9 ·
Did they build that engine with a used crankshaft? The reason I say that is because sometime the flywheel had came loose. That’s what causes the damage on the back of the crankshaft. That will definitely cause a knocking noise.
As far as I know I paid for a new crank but unfortunately it was already assembled with the flywheel installed. I only installed the damper to the flexplate/flywheel. It honestly looks like it might be old damage. I've had flywheels come loose before and make noise but I'm not sure if it's the flywheel or something else because there aren't any highs on the crank, only lows and around the center there is about 3/4 inch of perfectly flat material with no markings at all and even after removing, cleaning and reinstalling it's making the same noise. Plus I checked break away torque on the bolts with my snap on digital and they were all within 2ftlbs of each other.
 

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Do you have a photo of the mating surface of that damaged crankshaft? I`m inclined to go with BSE here surely that was a used crankshaft?
Were all of the springs and retainers okay on the damper plate?
 

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As far as I know I paid for a new crank but unfortunately it was already assembled with the flywheel installed. I only installed the damper to the flexplate/flywheel. It honestly looks like it might be old damage. I've had flywheels come loose before and make noise but I'm not sure if it's the flywheel or something else because there aren't any highs on the crank, only lows and around the center there is about 3/4 inch of perfectly flat material with no markings at all and even after removing, cleaning and reinstalling it's making the same noise. Plus I checked break away torque on the bolts with my snap on digital and they were all within 2ftlbs of each other.
Make sure the bolts aren’t bottoming out in the crankshaft. Possibly to long.
 

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Discussion Starter · #12 ·
Checked the length and I have 1.5 mm of room for the bolts. and there is no wiggle on the flex plate itself. The crank was new when the engine shipped according to Boost logic. The damper is actually removed right now to verify it wasn't part of the issue.
 

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Checked the length and I have 1.5 mm of room for the bolts. and there is no wiggle on the flex plate itself. The crank was new when the engine shipped according to Boost logic. The damper is actually removed right now to verify it wasn't part of the issue.
If that’s was a new crankshaft 800 miles ago. That is your noise problem. The flywheel came loose and is making noise. Those two surfaces are going to need to be repaired.
 

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Discussion Starter · #15 ·
That's what I was originally thinking. Besides changing out the crank what else do you think I could do? I ran a straight edge over the crank and it doesn't stick out at all. It only dips into the back of the crank. I thought about welding in the low spots and then making a jig to machine it flat.
 

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Discussion Starter · #16 ·
You would have thought that there would have been a lot of metal filings visible with that much wear?
It looks like the powder coating on the back of the flywheel kind of gummed it all up. I'm just surprised how deep they got. I'm planning on running the engine up to temperature while monitoring oil pressure and then immediately pull off the bell housing and flywheel to weld into the low spots and then we are going to use a jib we made to grind it back flat. I haven't had any of my machinist buddies suggest anything better. Worst case scenario I just have to swap out the crank and bearings but that's not too bad. I'm wanting to at least see if I can make the noise change. If it doesn't change at all after all of that then it's gotta be a bearing, wrist pin or connecting rod doing something weird. Possibly something in the valve train but it definitely sounds more like a bottom end/rear of the engine noise.
 

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It`s a tricky business welding shafts so as not to warp them, it`s easily done. You may get a problem with leakage from the oil seal as well.

I did have a crankshaft thermally spray welded on the diameter(under the flywheel) and then reground to size many years ago at my place of work, that turned out well.
The welding was done in place then the crankshaft was removed and sent to another company for finishing. This was a crankshaft from a recip compressor, however.

I still can`t understand the marks on the crank the hollows have a similar pattern on the bottom, start roughly at the same point middle of the bolt holes, and spread outwards. Nothing towards the center? If there was >90% contact between the two surfaces how can this possibly occur?
Just so I understand you said that there was 1,5mm to spare on bolt length is that with the bolts in the holes or bolts measured and the depth of the holes measured?
 

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Discussion Starter · #18 ·
It`s a tricky business welding shafts so as not to warp them, it`s easily done. You may get a problem with leakage from the oil seal as well.

I did have a crankshaft thermally spray welded on the diameter(under the flywheel) and then reground to size many years ago at my place of work, that turned out well.
The welding was done in place then the crankshaft was removed and sent to another company for finishing. This was a crankshaft from a recip compressor, however.

I still can`t understand the marks on the crank the hollows have a similar pattern on the bottom, start roughly at the same point middle of the bolt holes, and spread outwards. Nothing towards the center? If there was >90% contact between the two surfaces how can this possibly occur?
Just so I understand you said that there was 1,5mm to spare on bolt length is that with the bolts in the holes or bolts measured and the depth of the holes measured?
I figured a nice hot tac while the crank is already preheated up to operating temps would be the best case scenario. I can even to 2 or 3 at a time and wait for it to cool slightly. After that I'm thinking about just grinding it back flat with a straight edge jig I made that bolts to the back of the engine.

And about the marking on the crank, that's what was confusing me. The center section from the inside diameter of the bolts to the center had perfect contact. It was only from 1/2 the diameter of the bolt holes outward that had marks and had surprisingly bad marks. Keep in mind the car went from driving normal to that in less than 2 minutes of run time. The back of the flywheel was mirrored. Now I'm wondering if there is supposed to be a spacer between the crank and the flywheel or on the outside of the flywheel to the bolts because from what I can see the powder coating kind of got pushed out from between the crank and the flywheel.

Also, measuring the depth of the crank holes from the center of the hold. The bolts have a very slight taper to them and I used a paint pen to see if it was touching and it was definitely not since no paint transferred. It's just weird that it can go from perfectly fine to tap tap tap tap like it did. But the fact that I was slowing down, primarily engine breaking is leading more towards a flywheel issue after all.

I wasn't able to get my car back inside the shop because all my guys had left for the day and I was busy with customers so it'll have to wait til after the holiday weekend.

One last question to anyone. Have you ever had an engine knock/rod knock where you have great oil pressure? Whenever I have bearing issues it's usually as a result of low oil pressure and it gets progressively worse. At this point it still looks great. I might have to just start tearing it apart to find what's making the noise. Want to rule out any valve train issues first even though it sounds likes it's too low and towards the back of the engine to be anything valve train related.
 

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Discussion Starter · #19 ·
Another guy on here started a thread that had a similar issue and someone else mentioned the cicio crank/flywheel washer. I'm going to order one of those bad boys, weld and machine the crank and throw it back together and see what's what.
 
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