So finally fixed my noisy 445!

[Kirk Morgan]

That sounds just like a friends 426 Max Wedge. It would get more quiet as the engine warmed up. It was the piston to cylinder wall clearance.

Kirk

[CaptCobrajet]

Almost sounds like spark knock from here, but hard to tell.  I have heard similar "chatter" from timing/compression related issues.  You may have already ruled that out......

[Heo]

Kind of cold Diesel sound 

[My427stang]

I have had the timing all over the place and it really doesn't sound like that in person.  I am leaning toward the pistons yet again

They were at .0045, recommended clearance, Probe lists min .003 max .007, first build they were between .007 and .0075 but given it was my own and having run some very loose forged pistons, I figured I'd live with it.  If that is the issue, maybe I reshaped them the first time bouncing around

They are 2618 no pin offset.  I see wear on the both top and bottom (thrust, non-thrust) on every cylinder, surprising for so few miles.  I'll measure again and see what I find

[My427stang]

Not a whole lot found with measuring the pistons

4.075 across all 8 with the micrometer flush with the end of the skirt, at the .500 measuring point, all were 4.074, 40 degree garage temp

Zero'd my bore gauge, checked cylinder clearance all nothing wild, as garage warmed up, checked again, tightest is .0055 after a few hundred miles, no taper, loosest is under .0062, looser than I put it together, but well within spec for the pistons.  Could chalk it up to summer temps in the garage when measuring the pistons the first time plus break in, but nothing jumps out

Overall height of the piston at the skirt is 2.325 and compression height is 1.33, these numbers are not that important, but it does show a pretty short piston by FE standards, we'll see if other manufacturers use slightly longer skirts as I research

Here is what the base of a couple cylinders look like, I cannot feel these marks, and they don't measure with the bore gauge, but odd for only a few hundred miles, the last one isn't as "shiny"

[Joe-JDC]

I think you finally have the answer.  I would think those pistons needed closer to the .003" clearance instead of the .0062, and the skirts maybe need a fuller skirt with the longer stroke.  Joe-JDC

[My427stang]

I think you finally have the answer.  I would think those pistons needed closer to the .003" clearance instead of the .0062, and the skirts maybe need a fuller skirt with the longer stroke.  Joe-JDC

Joe, thanks you may be right.  I have never used a Probe piston before, but the 2618 alloy, plus an advertised "low drag skirt" could mean "narrow contact area" combined with the relatively small bore could be letting them flop around

Likely going to go with a 4032, talking to a couple manufacturers about skirt design for 445s, both length and barrel and I may even ask what the cost would be for a little bit of pin offset

[machoneman]

How about a few piston pics? The bottom wear pattern of those walls seems to flare out a tad and that's a bit odd. Usually the pattern is straight (like the pattern up the wall) all the way down the wall (could be the pic though).

I think Joe and you nailed it as short skirts + piston rock at BDC may have caused the sound. We though as an FYI ran a .007 minimum wall on new ForgeTrue 4.30 and up bores w/o any issues in the 70's but that's IIRC what they called for (maybe it was a .0065 minimum) and all were unmuffled race engines.

Who even knew if they clanked when cold!   

[My427stang]

How about a few piston pics? The bottom wear pattern of those walls seems to flare out a tad and that's a bit odd. Usually the pattern is straight (like the pattern up the wall) all the way down the wall (could be the pic though).

I think Joe and you nailed it as short skirts + piston rock at BDC may have caused the sound. We though as an FYI ran a .007 minimum wall on new ForgeTrue 4.30 and up bores w/o any issues in the 70's but that's IIRC what they called for (maybe it was a .0065 minimum) and all were unmuffled race engines.

Who even knew if they clanked when cold!   

Sure!  BTW, I have never feared loose pistons, in fact, I ran the old TRWs in my 433 at almost 10 thou!  However, they were longer and likely a different shape

Interesting when I took the pics, look at the wave-like shadow on the skirts.  Not sure what it means, but another "not normal" thing

[machoneman]

Yeah, they are clanking around until warm. I've never seen that weird wave pattern on a gas powered car but oh, yes, on blown race engines!

Before the nylon buttons were used on the lower skirts of pistons in blown alky and nitro engines, similar waves would appear. These on a aluminum Donovan 417 that Diamond Dave Miller ran on a R.E. TAD and on a 426 KB aluminum Hemi that John Sinibaldi ran on a R.E. T/F  dragster. Nobody gave a damn as clearances were IIRC .008+ on the Donovan and .009+ on the KB Hemi (man, my memory is good but that was a long time ago!) but I do think the numbers are close).

Anyway, crewing for both over time, the then kinda' new button pistons prevented rocking until the engine heated up. Still, the pistons didn't stay long (burnt, 'backsided', collapsed ring lands and worse!) but they did work. No waves on the button pistons but the pre-button pistons did look similar to yours on the skirts.

Btw, not suggesting at all that buttons are needed!     

[My427stang]

Thanks Bob, I am not in a hurry to get this one together.  So I have time to think about it, but likely will go with a set of 4032 Diamonds.  I'd like to see if it's possible to build a set of 4032 Racetecs with some pin offset too, if I am going to go big, may as well overdo it

Might just put the ported heads and intake on the bench build 390 and see how it does LOL

[turbohunter]

Loving this diagnostic work.

[machoneman]

Go big! That's the spirit! Hah!

[Joe-JDC]

Ross, would you mic those pistons laterally where that wave shows up?  It sure looks like they aren't round there.  I know the skirts are not round, but if you mic them in several places left to right laterally you may see a collapsed/flattened spot that causes the phenomenon.  What I am trying to suggest is twisting the piston in the micrometer to see if there is a low spot where the wave is located.   Joe-JDC

[HarleyJack17]

This may be a dumb question but is the mark inside the bores on one side of the wall? Inner side on each left and right bank, vice versa, or on both sides of the bore? Just curious and not sure it makes a difference. I would agree it is likely in the piston like everyone else and like Joe D-C said, I would like to know the measurement around it to see if there is a variance/flat spot. I would not think short skirts would be the absolute cause. Definitely some contact going on...