astro.domine

https://youtu.be/v2PrCewfMHE

Sounds kinda like a metallic clack/buzz, that only happens at ~1-3k RPM. It seems like the obvious culprit would be a noisy lifter, but I've bled my lifters many, many times and they all look to be in good condition. Noise becomes softer/quieter when warm.

Engine has been rebuilt with Wiseco pistons, Eagle rods, but I think it made this noise even before that. Subie 550cc injectors, Jim Wolf S3 cams, S15 turbo.

This doesn't sound like bottom-end noise, right? Could it be I need to re-shim the valves?

Kingtal0n

The way it gets quieter when you rev usually means rod bearing or wrist pin failure


I admit it sounds like a top end noise but there aren't many types of load-based engine noises and bearing/piston is the most common

I really hope it isn't for you

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burnsauto

piston slap? How does the noise relate to engine temp? Does it change at all?

Either way, that engine isn't staying together for too long, either because you take it apart, or it takes itself apart.

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astro.domine

That would be truly disappointing. Thanks for the info though.
The pistons & wrist pins are new, and all the bearings are new, with clearances under .002".

Could it be piston slap if it has 160psi+ compression though?
The noise becomes much softer & almost disappears after it warms up.

Kingtal0n

New as in Forged aluminum low silicone alloy?

I've heard those pistons make a similar sort of noise. yes, 'piston slap' because the pistons need to warm up when they are set to manufacturer recommended piston to wall clearance.

But,
1. I've never heard it that loud before
2. If it really is cold piston slap, that noise is the pistons gradually wearing the bore into an oval shape (it will have scuff marks down the lateral sides of each bore)
3. Engines built with forged aluminum pistons and massive piston-wall clearances are not intended for cold start or to be operated while the oil is cold. They require oil temp minimum of around 170-185*F Before you can load the engine, otherwise, loading the loose piston from the top will create additional force which will further accelerate the bore wear.

generally, forged are not good pistons for daily drivers or street cars unless a low expansion aluminum specific alloy and closer piston-to-wall is used.

Now all of that said, if you told me those pistons are new but they are cast aluminum, I would suggest you have the wrong size pistons, improper machine work, something like that. It shouldn't rattle with a cast piston.
Also when you make a thread asking what this noise is it would be very helpful if you had mentioned that all of the bottom end parts are new, or the engine was just rebuilt, etc... Because in the video I and from the post I assumed it was a 200,000 miles high mileage beat up ruined sr20 engine and there is no way to tell any difference.

burnsauto

yeah it could still be piston slap with good compression. Over time, the compression could go down as the rings wear more, but since it's a fresh rebuild you could still be getting good compression due to the freshness of the engine.

Try doing a leak down test to further check on things if you don't want to go elbow deep into the engine just yet, just know it's inevitable. Hopefully there is some sort of warranty from your engine builder if that winds up being the case.

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