this is the area that looks suspect to me - could be glare from the scope light but the edge of the piston doesn't look right - and that oil on cylinder wall could be hanging on scrapes - i'm hoping i'm wrong though - try the chemical route - as stated above ..not going to hurt anything - good luck on this

 

It's going to sound stupid, but that's ok, cause I don't mind. For the aircraft Continental engine low compression diagnostic, they recommend running the engine at full rated power in flight for 45 minutes and check again.

Because - aircraft engines(like 928 engines) do not get regularly driven and this causes rings to stick and not expand onto the cyl wall properly. I have experienced an aircraft engine go from 29PSI leakdown cold to 71/80PSI after a spirited flight.

So - perform the 'Italian Tune-up' on the car before taking **** apart. Drive it until fully warm, get out on the road, and get on it hard for a while. Not sure it'll fix the issue, but it's fun anyway. Not going to do any harm unless you get ticketed. If you are stopped by Johnny Law, tell them Doc said it was ok, that you need to unstick your piston rings. I'm sure they'll understand.

Edit to add: Using any kind of upper cyl lubricant(MMO, etc) in moderation will not harm anything, and may help with a stuck ring.

 

Yeh - I've spoken to anybody who will listen to me and a few have pointed out that area. The black dot is a lump of something on the piston rather than a hole. I can see it "live" but haven't managed a good picture. I think the shiny bit is there.

I don't think I'm far away from pulling something apart to get a proper look.

 

Sorry.

I thought that the 2nd picture was the valve and valve seat.
I see, now, that it is of the piston.
That's worse.

Although the result is the same...forget chemicals.
Proceed to removing the engine.

 

Increasingly this reality is becoming apparent to me. Maybe next year I'll get to drive it :-P

 

Small update.... I got hold of some Sea Foam and chucked some in the cylinder. It's been in there a couple of days and I keep winding the engine over to move it around.

What surprised me is that it's still there. Given the circumstances, I expected it to escape past the rings. I'll syphon it out tomorrow and repeat the leak down test. I'm not really expecting a miracle.

 

Why did you do that?

 

Why not?

Unstick sticky rings??

 

It never ceases to amaze me what people do to these cars. With that said it will probably actually work, just because it makes no sense at all and should do absolutely nothing.

Skip through this video, then when you are ready jump to 6:00:


Never heard of sticky rings, but that doesn’t mean anything because I learn something new everyday! The only product that I’ve seen dissolve carbon by using it according to the directions is Liqui Moly Valve Cleaner. With the head off and just soaking Berryman’s ChemTool dissolves it in minutes.

 

I'm not expecting it to do anything, to be honest.

But the next step is the huge expense and hassle of extracting the engine and sorting it properly - whatever that turns out to be. As it's going to be my money and stress, I hope you'll excuse me for clutching at straws.....

 

No, I was serious. I’ve seen so many quirky things that people have done that shouldn’t work but somehow do that nothing surprises me anymore! Do your compression test.

If it doesn’t show improvement, or if it does but not enough, try the Liqui Moly products.

 

Liqui Moly flush should be coming today. If the 'in the cylinder' approach does nothing the flush is going in the oil and getting run. If that does nothing it's clearly something more serious and the spanners are coming out.

 

Attempting to "fix" this engine with chemicals isn't going to hurt anything.
However, the markings/oil on the cylinder wall, directly above the damage on the piston tell the entire story.
You've got broken rings/piston ring lands.
Super common on these engines.
Get those spanners warmed up.

 

I'm looking menacingly at the engine crane in the corner....

 

Are you sure it's not looking at you, instead?