Built Z6 @ 10psi, (~250whp), eagle rods, ACL bearings, 59300, Crower valvetrain.

I took the car out for a few pulls, and it started making a weird noise when I got off of the highway. When I rev it up to about 3-4k, the second I let off of it I hear a knocking type noise. I cant hear it at idle at all. Only when I rev it up and let off. Any ideas? I'm thinking either loose valve train, or a rod bearing starting to go.

 

is it a knocking or a ticking? how many miles are on the motor. with the proper tune and your power level you should not have any problems at all.

does the sound come from your head or the block?


platinum.

 

I couldnt tell completely yet. The noise comes from the back of the engine, not sure if it's head or block, but almost sounds more block. But that cam has a lot of valve noise, so it's kind of hard to tell.

There is less than 7k on the engine since it's build. And it's more of a knocking. I'll look more this week, but I guess it could be something loose and vibrating. I have polyurethane inserts on tops and bottoms.

 

I played with the car a little today.

- The plugs are all normal.
- Nothing out of the ordinary with the valve specs.

I did realize though that the knocking gets louder with RPMs. You cant hear it at idle, you can hear it a bit in neutral when you rev it, but you can hear it the best under a load, and in higher rpms.

 

Get a stethoscope to pinpoint the noise. If you dont have access to one, you will be suprised how much noise a long 1/4 extension will carry

If it's in the block, it's best to tear it down now before serious damage happens costing $$$

You can always drop your pan and rotate the motor by hand to see where the knock is coming from.

platinum.

 

i would say rod bearing.. you put acl's in but did you check clearances at all? there is your problem.

 

Slowmotion Motorsports did the build and assembly. All the clearances were spot on.

 

Any chances it could be coming from your clutch area? I had a problem once with my SOHC back in the day and it was knocking from the clutch area. From what I remember the throwout bearing and pressure plate had messed up creating a knocking noise.

 

what psitons did u use??? maybe the c clip came loose some how?

 

Clip came loose on my Wisecos that I have in my car and it def made a knocking noise once the wristpin moved out of one side on the piston.

 

With the engine running pull the plug wires one at a time and see if the noise changes. If it's one of the pistons the noise will stop when you pull the wire.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1992Si &raquo;</TD></TR><TR><TD CLASS="quote">With the engine running pull the plug wires one at a time and see if the noise changes. If it's one of the pistons the noise will stop when you pull the wire.</TD></TR></TABLE>

If its one of the pistons? That method is good for checking to see if a bearing has spun since it takes a load off the piston instead of having combustion. When my clip fell out pulling the plug wires did nothing for it, the noise was still there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rota92 &raquo;</TD></TR><TR><TD CLASS="quote">Throwout bearing going?

My daily made lots of noise under load because of it.

Push clutch in and see if it goes away. just a though of something simple for ya!</TD></TR></TABLE>

Same here, thats like the problem i had along time ago

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1992Si &raquo;</TD></TR><TR><TD CLASS="quote">With the engine running pull the plug wires one at a time and see if the noise changes. If it's one of the pistons the noise will stop when you pull the wire.</TD></TR></TABLE>

It would be hard to do this, because you cant hear it at idle.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rota92 &raquo;</TD></TR><TR><TD CLASS="quote">Throwout bearing going?

My daily made lots of noise under load because of it.

Push clutch in and see if it goes away. just a though of something simple for ya!</TD></TR></TABLE>

Ryan, was it a knocking noise, or the hissing/fizzing noise that the throwout makes when it's on its way out? This noise is def. some sort of knock. It almost sounds like you've got a really bad cam in there.

 

If it sounds like a wooden clack clack noise, it's probably a rod bearing. Drain the oil and look for the goldfish food flakes and glitter in the oil. That will determine whether it's a damaged rod bearing or not.

Chances are that it hasn't spun yet. The crank and bearings will eventually eat each other to death.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TurboGoKart &raquo;</TD></TR><TR><TD CLASS="quote">Slowmotion Motorsports did the build and assembly. All the clearances were spot on.</TD></TR></TABLE>

call slomo and tell them. they will help you out

platinum.

 

I'd call them up too, since its their butt that's going to get ripped if it goes. Not that it may be their fault, but thats always how it seems to go.

Back when I fixed the coupe I got with a $100 block (short term), I thought it was the spare head I used (zex cam) that made all the noise - I thought I was tightening the rockers wrong. To make a long story short, the knocking (noticable on rev, sometimes changed tune, sometimes absent while cold, sounded like metal pounding on wood) was really rod #2, which got ejected out of the block. The main diff here is that yours was built, mine just came from k_motor & his brother, supposedly fine they said, but knocking from day 1.