Dang, Dang, Dang!!!!!!!

[dave from mesa]

Karl ran his car this weekend and heard a tapping noise.
Help us figure it out. This car has fought us all the way.
Click on the pic.

Spark plug


Notice on the piston #6, 3rd from the right, there's a nick at the top.


Head




Notice how clean looking #2, on the right, cylinder head looks.


Gonna pull the engine on thur.

the fun starts again.

[CHANMADD]

Something went down the carb or the top of the piston broke. I made a mistake once of reusing the rod, which had the big end journal slightly ovalated. I trusted the machine shop who who had promised me he had inspected the rod and I then had him assemble the short block..........
That rod broke at 5k and destroyed everything below the heads...Oh the valves also needed to be replaced. The ring gap on pistons with a high top ring land needs to be larger than the manufacturers say because the ring gets hot , expands and breaks a piece of the top land out and the result............not nice.
You gotta get all the sharp edges out of the combustion chamber to prevent future pre-ignition ,if you re-use the heads.
Good Luck...

[xlr8or]

What are the odds of that loose chunk hitting the end of the spark plug???

Just how far does that plug extend into the cylinder?

[dave from mesa]

Am pretty sure the heads will be replaced ( I'm not the owner tho). Heads, pistons, other stuff.
Have no idea about the plug. Will check this out when we get the engine out.
Ain't gonna be fun. Thought we are close after 2 1/2 yrs.

[Hotfingrs]

Looking at the tops of the pistons, sure looks like detonation. Detonation broke a piece of the piston.

[Danr55]

Did Ratboy get anywhere close to the engine?

[CHANMADD]

What make and type of pistons are they?

[vettestr]

Karlos,
Whatever it ate got several holes. I see impact marks on other pistons too. It is amazing how it can go from cylinder to cylinder. If it didn't go out the exhaust you may find IT in one of the holes on the left bank when you pull that head. The plugs' electrode ceramic seems to be missing and could account for some of the damage.

I have seen damage from the damndest things, from screws falling out of the carb body or a little chunk of the head casting broken loose when new guides were installed. It does not take much to crush ring lands down on a piston or bend valves. Let me know if I can help in any way. Jeff C

[mikiec]

Dan, my first thoughts...

Karl, I guess you will not be making the run this Sunday. Get it fixed quickly.

Mike

[Hotfingrs]

It is amazing how it can go from cylinder to cylinder.

It didn't go from one cylinder to another. It was detonation and the spark bouncing around the top of the piston. Here is what a piston suffering from detonation looks like and notice a piece missing.

[CHANMADD]

The most likely cause of that ,imho, would still be the ring ends expanding into each othervthen cracking the piece of land out. Many motors where assembled with incorrect top ring gaps on pistons with high top lands. The problem will only manifest itself when the motor starts to be used aggressively, and as we know a lot of these cars never experiencence really tough use. There has been a lot written in regards to this problem. This manifested with the newer long rod applications and the resulting raising of the rings on the pistons.

[FWB]

Originally Posted by Hotfingrs

Looking at the tops of the pistons, sure looks like detonation. Detonation broke a piece of the piston.

i agree....looks like little pieces of piston welded to the head.

whats the CR? looks sooty too so doesn't seem to be running lean.

if the pieces of piston weren't there and you kissed the plug i would venture to say it was over-reved. maybe a little of both....

[CHANMADD]

ergo...... If its rich how is it going to get so hot as to do that?

[lovehamr]

Originally Posted by CHANMADD

ergo...... If its rich how is it going to get so hot as to do that?

To much ignition advance for the fuel used? To much compression for the fuel used? A combo of both? Any of that could lead to pre-ignition with crappy fuel.

[Hotfingrs]

Looking at the tops of the pistons, that's more burnt oil, than a rich condition.

[CHANMADD]

Pre-ignition does not select certain cylinders only, it would effect them all the same. Mostly it looks like that motor runs a little rich.Maybe the plugs porceline broke off, I have seen that before.

[Hotfingrs]

That piston came out of my engine and NOT all the pistons looked like that. Show me a carbed intake that flows equally to all cylinders. Rich WOULD be a different color black on the piston top, that color black is oil, either from the guides or past the rings.

[CHANMADD]

How did you determine what broke the piston? From that pic it looks like the ring gap is right at the crack.....that is where it expands...It does look like some oil burning too. What was the ring gap at assembly?

[jhv48]

Dave, did you run it by Gordon Levy yet?

That is one of his engines, isn't it?

[dave from mesa]

Not my engine. 4 of us have been working on Karl's car for 2 1/2 years. Finally got it back on the road and now this. We didn't do anything to the engine except change the oil. Had less than 100 miles on it when this happened.