4V COBRA Rattle Noise

[Mystic1350]

Hey,

I have posted prior but wanted to give more exact diagnosis/description.
I have a 96 cobra. I just had substantial work done to my engine/car due to busted bearing…

I will get to the problem I am having in a sec but wanted to describe what was done to the rebuild(to rule out possibilities) and then the problem I am currently having

Rebuild-done at B&B performance in Rahway, NJ

Essentially all internals replaced with eagle rods/pistons
Kept stock crank and cams
Bored to 0.20
Cylinder heads were ported and had valve job
(we left stock lash adjusters/cam followers in-only 75k on pre-rebuilt motor)-potential problem
Entire timing chain, tensioner, guides were replaced in front
A bunch of exhaust goodies i.e LT, x-pipe, dumps
SCT pre-loaded custom tune to above noted mods (once problem is fixed I need to get fine tuned/dynoed)

PROBLEM I AM HAVING IS EXACT NOISE PER BELOW LINK
YouTube - Mustang Engine Sound
PROBLEM IS ALSO MOST NOTICABLE WHEN THROTTLE IS PUSHED INITIALLY AND UP UNTIL 3500 RPM RANGE (I assume oil pressure is getting up there making noise go away)

Just from the what I have read in the forums and due to what I have done, I have to rule out timing chain tensioner guide/wrist pin/spun bearing etc, especially since I have taken it easy on the the engine since I got it back regardless of what people say about break in period etc.. Which leads me to believe it’s a lash adjuster/cam follower
I have also tried all the oil weights as well as some mystery oil crap, etc..

What are your thoughts?

 

[oxfordgt]

Its way tofast to be part of the valvetrain. Sounds like bad wrist pins to me.

 

[Mystic1350]

rattle

i cant believe that is the issue with the internals being completely rebuilt/better parts being put inside and the fact that i havnt driven it for more than 500 miles

 

[stylin99]

Actually sounds similar to a recent 2v motor I heard. It had too much piston-to-wall clearance making it rattle back and forth in the cylinder. It will usually be worse when it's cold before the aluminum pistons expand outward to fill the PTW gap. Do you know what clearance the shop set the pistons at? That would be a crucial number to ask. Should be .003-.0035 depending on if it had coated skirts. Anything over .004 starts making noisey pistons.

It will eventually scuff the piston skirts and possibly destroy the rings, if left to go uncorrected too long. So better to fix it before putting any more major miles on it.

It may not be that, it could be something more simple, but that's definitely a symptom of a bottom end rattle if you ask me. It goes away at higher rpm because it pushes the piston outward against the cyl wall and it stops rattling for a moment.

 

[trinity_gt]

Hate to say it but it sounds like it's in the reciprocating assembly. I know it's all new, has good good components and low miles but the sound is pretty compelling.

Re: The "busted bearing" you spoke of: I'll assume means "spun" bearing.

- Was the cause of this ever determined?
- You kept the stock crank: Was it inspected for damage from the bearing failure?
- Was it ground or otherwise cleaned up to remove traces of damage from the journal?
- What bearings were used for the rebuild (mains and rods) and were they checked for clearance before assembly?
- Was bearing crush checked? (Inadequate crush can lead to spun bearings...)
- Was the oil pump disassembled and checked after the initial engine failure?

The engine was bored 0.020" (not 0.20) and was thus cleaned afterwards: What cleaning method was used after machining? Were all gallery plugs removed to allow proper cleaning of all oil galleries?

Did you assemble the rods to the pistons? What locks were used?

Like I said, it sounds reciprocating-assembly related to me. Age and mileage doesn't matter if there was a pre-existing fault (e.g. scored journal), a bad clearance, schmutz in the oil galleries or pump from the previous failure that made its way to another bearing and caused a failure...

 

[nancygrl]

I agree with trinity gt...it sounds like the something in the rotating assembly. A while back we had a circle track car and the motor spun a bearing twice (built by a local race engine shop, both times said the crank was ok) bullshi*!
1st instance #1 bearing spun.
2nd time #1 piston exploded during the race, taking out the entire cylinder because #1 spun bearing.
Got a different crank, and block, rebuit the motor ourselves and had no more bearing/engine issues. Our sound was a litte different than yours, but close. In any case, be it bearing, piston slap, wrist pins, whatever, it needs to get checked out...

Just 'cause a performance shop did the rebuild doesn't mean it's going to be 100% OK.

Good luck with the engine...Hope whatever the problem is, isn't terminal.