What's the thinking about adjusting the vacuum advance? Also, it's plugged into ported vacuum on the carb, not manifold vac.

 

In your audio/video clip it sounds more like a leaking exhaust manifold gasket than a ping to me. If retarding the ignition timing doesn't lessen it, gasket is what I'd be checking.

 

Sound quality is a little off due to wind noise, but it isn't even close to any ehxaust leak I've ever heard.

 

Update - Got tired of fumbling around in the dark, so to speak, so I took it up to a local hot rod shop that specializes in older engines. They found no compression on #5. With compressed air through the plug hole, it leaks out the intake valve up through the carb. Looks like I'm pulling the head.

 

Let us know if it was the metal mites that ate the valve

 

Think I might've found the problem:


Just wish I'd inspected that spring more closely BEFORE I PULLED THE HEAD!!!! On a positive note, check out my pristine lifters:

Here's a shot of the chamber of the dead cylinder:

 

Think I'd be alright to just replace the spring & reinstall the head, or do i need to have a machine shop clean up the valve & seat?

 

It shouldn't need to have anything done as long as the valve is straight and the valve still seals. I'd change all of the springs.

 

Might as well; easy to do with the head off. Will stock springs be fine with my cam, or should I look at slightly heavier ones?

 

Byrd.Dog,
If you have both heads off consider bronze valve guides and yes new beefy valve springs
True the springs should match the cam so doo not go too overboard
That said My Boss motor was built with a Crane Blazer to start with that had .561" lift I believe and I was sold a triple springs kit for the cam
That cam was a bit much and I went back to a close to factory race grind
I still have the triple springs and the bronzewall guides and love it
All they are going to do is wear out over time like yours did
The triples mine are still okay 40 years later (built that momo in 1982)

 

A new stock spring should be able to handle that much lift with reasonable loads. If your engine has the rotators on the exhaust(needs a shorter spring) that might be getting pretty close. .040-.060 from coil bind is fine but only if you're able to check every spring.

 

Stock valve spring reach coil bind around .500 lift
Mellings list stock replacement spring VS820 with a installed height of 1.820 and coil bind at 1.330, that’s .490 lift
Mellings torque cam recommends valve spring VS280 with a installed height of 1.820 and coil bind at 1.260 or .560 lift
If they reused your stock springs that most likely explains the broken one
You need to get the correct springs for your cam

 

Springs break from fatigue not from being close to coil bind. In fact they actually last much longer the closer they're run to stacking. I'd take Melling's book numbers as sort of a worst case. Take 16 of their springs and pull them to coil bind on a spring tester. I doubt that there's less than .060 variance between them when it comes to coil bind height.

 

Springs break from a number of reasons, fatigue shouldn't have been a factor on the new springs I had break some years ago with less than a hours run time, 20+ minute break in plus 15 mile drive when the first one broke, second one broke at idle shortly after replacing the first one, they all got replaced after that.
We tested several springs from different brands and sizes of engine back in the 70's-early 80's, every stock production non performance engines valve spring we tested would reach coil bind in the area of .490-.510 lift, this was measured it the factory recommended installed height for each spring and then compressed until it reached coil bind
Reusing the original springs that had been running of a stock engine with .380-.430 valve lift and then subjecting them to a cam with .080-.100 more lift and having them compress to near or at coil bind could induce fatigue very quickly.
The Melling MTF-2 cams .486 intake lift is probably not causing a issue but there's not much margin left before coil bind, far less than the .040-.060 recommended above
The exhaust .512 lift is probably causing the lifter plunger to collapse .005-.020 farther down into the lifters bore, this would induce a temporary loose lash condition that would sound similar to a mechanical cam with it's .015-.025 lash clearance

I had a 79 F-150 4x4 with a 400 I rebuilt using a Cam Dynamics 272 .520 lift torque cam and their recommended springs, no issues with that engine
A cousin had a 78 F-250 with a 400 he rebuilt using a different makers .508 lift cam with stock springs, after bending push rods a second time he called me, after discussing his build I told him the stock springs were most likely binding and needed replaced, after he bent push rods a 3rd time he swapped in the same springs I was using and never had another issue

Here's my take: A engine was built using a Melling MTF-2 cam and stock springs, there's what appears to be valve train chatter and now a broken spring, rather than installing more stock springs that will only fix the broken spring issue, install the VS280 springs recommended for the MTF-2 cam that should provide .048-.074 clearance before binding and see if both problems go away.
If one doesn't want to use Melling springs get some from another mfg that has similar specs

 

I have a set of stock springs from a 400 here on file in my computer these are the ones with the rotators on the exhaust side. If I plug in the lifts of .486 and .508 I get average open loads of 246 on the intakes and also on the exhausts. the average distance to coil bind is .077 on the intakes and .071 on the exhaust side. The seat loads are 77 intake and 70 on the exhaust. Those loads sound about right to me and that's from a set of used springs. Am I missing something because this data is from an actual set of springs not a catalog.

The springs that I've recommended before and have had good results from in this sort of applications are the Qualcast 32-909-D. At 1.800 they would give a little over 90 on the seat and open loads of about 240 and 250. About .125 from coil bind too. But they are too tall for the exhaust side if you're using the rotators.