Compression Test - Blown Head Gasket?

The 7 piston is broke....not sure why 5 is bad

 

That's your issue. I was sure it wasn't a gasket issue. Response #1.

 

I wonder if the head can be repaired

 

That is the nice thing about aluminum heads, almost anything can be repaired. I made a few trips to the welder when I was running L88 diamond elkins heads, many moons ago.

 

What needs to be repaired? What am I missing? I see a few minor dents, looks like a .015 cut would clean them up...but I'm not saying that would be required.

The aluminum head on my Lumina--and the top of the piston--looked worse than that. The engine must have eaten a machine screw or something. Looked like the threads of the screw pounded little ridges in the aluminum. I cut the head because it was warped and the head-gasket fire-ring of one cylinder was about to let go from lack of being compressed, left the piston alone, and bolted it back together.

 

Are those forged pistons?

 

It's just my lack of experience...the pitting looked so deep that I automatically thought worst case scenario.

These are normal cast (non-hypereutectic) pistons

 

At this point you're looking at a full teardown and inspection. You may have a bent valve from the piston chunk floating around the chamber.

 

That's what they looked like.they are
020 over and you need to clean the bores up. I have a set of new hyper pistons .030 already on rods that are for sale that could make your rebuild easier

 

Time for a do-over, with forged pistons this time, and a close inspection of total timing when you are done. Make sure you calculate, or better yet, plan for the compression ratio you want for the fuel you want to use.

 

I was impressed with the eyeball measurement until I took another look at my pic and saw the 020 stamped on top of the piston lol

I appreciate the offer but am in the process of putting together a spreadsheet of options, and associated costs, ranging from the terrible idea of honing the cylinders & dropping new cast pistons in to the good idea of boring it 30 over with forged rods and pistons. The dream is to find a way to afford getting a 470 short block from TSP.

The CR was about 10:1 and even before the engine was rebuilt 10 years ago, never had anything less than 92 octane ran through it. The cam (TA284-88H; .460 lift; 223 in 230 ex) was pretty mild because it was for iron, non-stage I heads. The total timing was at 10 initial with all 32 degrees coming in at 2,800 rpm.

 

I would have expected more initial, about the same total, but "all in" at higher RPM--say 3K, 3,200.

What is happening with the vacuum advance?

 

3k was the goal, but having tried different combinations of springs, it was either 2,800 or 3,500. I would have bent the posts but since it didn't ping, 2800 seemed good. The MSD distributor I'm using doesn't have vacuum advance

 

That explains all the excess carbon on the pistons. You're throwing away power and throttle response.

 

I disagree. On a 10 year old, carbureted build like that, the carbon to me looks 100% normal. Heck, I've taken apart who knows how many modern, fuel-injected engines with piston tops that look like that, except the ones that were "stream-cleaned".

Matt, I think your distributor set-up is fine too, w/o vacuum advance. It's a hot-rod, not a new vehicle looking to meet CAFE or emissions regs. I think you'll be adding more potential problems w/ vacuum advance than what it's supposed to be good for.

 

Its not terribly uncommon for debri to get pushed out of a cylinder back into the intake and down a neighboring cylinder. I'd inspect that #5 cylinder very closely.

 

I'm embarrassed to admit this, but when the block work was done, I hadn't learned about quench yet. I asked the machine shop to just square up the deck, but didn't measure how far in the holes the pistons were. With higher compression from the smaller chamber and quicker cooling aluminum heads, I wonder if incomplete fuel burn also contributed to carbon build up on the piston tops.