What am I overlooking on 302 SBF

[1320 BOWTIE]

Did a complete rebuild on a small block Ford. Broke in on Superflow dyno for 1/2 hour at 2000 RPM. Everything fine great oil pressure, etc. Let it sit overnight. Got heavy noise at idle that went away when oil warmed up to about 160 degrees (Joe Gibbs Break -in oil) Cut open filter found nothing wrong. First thought was of piston problem. Disassembled engine. No marks what-so-ever on skirts. Bore was on the money. Because the noise went away when warm we changed pistons anyway. Didn't make any difference, noise still there. Bearings looked fine. All clearances were fine. Using stethoscope, the noise is along main line. Engine runs fine. Stock rebuild with a flat tappet Comp FS XE250H-10 cam. Engine timed at 8 degrees advanced at idle with vacuum advanced plugged. The block has been squared and heads resurfaced. Pistons are .016 -.018 in the hole. No marks visable on block or rotating assembly.
We taken it apart a number of times. What have I missed? Anyone experience this before? H-E-L-P

[SupStk]

Welcome.

I'm wondering if you are hearing harmonics from the dyno drive?

[mag2555]

With motor cold and idling if you pull off plug wires one at a time does the noise subside?
When cold does bring up the rpm make the noise more pronounced?
Does the noise follow rpm at 1/2 Crank speed?
If you back the timing down when cold by 4 degrees at idle does the noise subside?

[jprod]

Um... bore size finished vs. piston skirt size ...what are your numbers for clearance ??? Typically that cold knock sound is excessive piston clearance on a forged piston that mellows once the temperature gets to it . That's an old problem.. used to happen all the time with the old TRW slugs that really varied in skirt size one next to the other !! It was not caught because of shoddy machine work or over looking the measuring process while machining , you had to assign a piston to a specific cylinder . It can also be a weird cam cut on a piston skirt ( they're not round ) that causes it to "rattle" ...we had a big block like this once , different piston ..it quieted down . Nowadays they're consistent from one to another on size and weight ( within a gram and a couple of tenths usually!) ...but if the shape is awkward (CAD design) ..they'll all be the same...all wrong .. unusual , but it could happen . J.H.

[Carnut1]

XE lobes are a bit noisy, I would double check lifter preload and rocker clearances to be sure that is not from valve train.

[BILL-C]

Can you describe noise a little better?

[DaveMcLain]

Welcome.

I'm wondering if you are hearing harmonics from the dyno drive?

I think I'd be leaning toward that too. I've had that before where the dyno drive plate would make noise at idle on an engine just about like what a jet boat will do. It might be easy enough to unhook it and then start the engine cold to see if it still makes the noise.

[travis]

Harmonic balancer torqued to spec, and not an excessively loose fit? Stock crank/balancer I assume? Any evidence of distress on the woodruff key?

Any sign of excessive vibration at idle/low speeds?

[1320 BOWTIE]

I've got the noise when it was not hooked to the dyno. There is no vibration. Engine runs fine. The balancer is torqued and looks fine. Same balancer that was on the engine before the build. We changed the crank. It originally had a rear main leak. The crank had been turned .040. We checked line bore and it was good. We balanced the assembly. We are going to take it apart Saturday afternoon.

[1320 BOWTIE]

Bill C of Carlquist Competition Engines, Thanks for you input.
It is a heavy metallic sound when the oil is cold. When it warms up the noise goes away. At first the noise seemed most audible along the block from the sides and front along the pan line mostly just above idle. This last time after changing the rotating assembly over to a 302 Crank, rods & pistons we still heard the noise. That assembly was also balanced. We didn't run it long enough to let it get warm. The bearing look great, skirts are unmarked, however the pump showed signs of wear where it didn't previously. We used a high volume pump.

[DaveMcLain]

What about the cam/thrust plate area of the engine. Maybe somebody made some changes that could possibly cause trouble. Does it have the correct thrust plate that's thicker than the one used on the 351C, 400, 460 etc? I was just wondering if the cam couldn't be moving back and forth and making a racket when the pump is working hard and pulling it back too far. Then once the oil warms up the sound goes away.

[1320 BOWTIE]

David,
We are working with the cam plate that was on the block when it was removed from the vehicle. We'll look that over closely when we disassemble the engine, hopefully tomorrow. I want to thank everyone who contributed to my problem. We have never experienced this before. What was thought to be a quick basically stock rebuild has turned into so much more.

[BILL-C]

Crank counterweight hitting oil pump? Counterweight hitting bottom of piston at BDC?

[1320 BOWTIE]

Bill C,
We have looked for that each time we've taken it apart and saw no evidence of it as of yet. We'll be looking again for interference.

[Steve.k]

I know you said down near centerline but I did have a engine where we added cam and rocker was just catching baffle in cover? Only 1 on 1 side not sure if cover was not 100% square. Made a thud type sound till the underneath of covers were well oiled then quietened up. Never noticed where it was till valve set. Was just barely touching.Maynot be your issue though.