Engine Rattle

[flat 39]

This is a long shot but here goes.

I have a 8BA in a '39 coupe. Scat 4" crank, .060" oversize pistons. 2 Holley 94s, Schneider F 260 cam.

The engine makes a light rattle noise that starts at about 1800 RPM. The noise occurs under light load conditions such as cruise down the road. The noise sound like if you took a PCV valve and shook it real fast.

If you take you foot off the gas, the noise goes away. I don't here it when accelerating but it may being drowned out by the exhaust noise. It happens in any gear but I don't hear it when in neutral sitting in the garage. I suspect
there is not enough load on the engine.

I've check that the exhaust piped are not hitting the frame. I found some loose Sheetmetal / trim pieces and tighten them up. no effect. I removed the PCV valve, no effect.

The engine has about 40,000miles on it and the noise has been going on for about a year but does not seam to be getting any worse.

Has anybody experience this before? What was your cause?

Thanks.

[philipswanson]

With mine, it turned out to be a timing issue. It was advanced too far and pinging.

[flat 39]

Phill,
I did have pinging issues before. I had to limit the amount of Vac advance in the MSD distributor. The rattle is not as sharp as a ping.

[19Fordy]

flat 39: Does the "rattle" sound "tinny" like a marble inside a tin can?

Does it sound like a rod knock?

Does it sound like piston slap?

Any way you can post the sound?
Does it sound like it's coming from the top of the engine,
the oil pan or does it sound like an internal sound inside the heart of the engine?

I bet one of the engine oil baffles in the valley of the block has come loose and is 'rattling" against the lifter or valve springs or just loosely rattling around in the valley. Baffle looks like this:
https://www.ebay.com/p/1323085877?ii...SABEgLgr_D_BwE

[alanwoodieman]

stick a scope down the oil fill pipe and remove the fuel pump stand and do the same, this will tell if it is something loose and rattling around the valves and while you have the stand off look for loose fuel pump arm

[1931 flamingo]

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Pull the fan belt(s) off and see if noise disappears...................
Paul in CT

[flat 39]

I will do the scope and fan belt thing tomorrow.

[flatjack9]

Originally Posted by flat 39

Phill,
I did have pinging issues before. I had to limit the amount of Vac advance in the MSD distributor. The rattle is not as sharp as a ping.

Most of these aftermarket distributors do no have a flathead favorable advance curve. They all usually have more advance than is needed. Have you checked the advance curve?

[flat 39]

Flatjack,
I changed the advance stop and put in lighter springs. I get about 22 deg advance at 2000RPM.