Symphony of destruction

[Sandy]

WOW!!! And that seemed to be running really strong. I guess the old adage that they run best just before they blow is true. Does remind me of my previous life though "Pi$$ed 'n Broke".

[Tom MLC]

Dude!

[Kris V]

That is damage from something beating the living sh!t out of piston and head! looks like the weld job that the guy did not adhere to the head and it came off during the ride. Look at the piston, those marks are from impact NOT detonation, they are sharp not melted!

[mighty13d]

That is damage from something beating the living sh!t out of piston and head! looks like the weld job that the guy did not adhere to the head and it came off during the ride. Look at the piston, those marks are from impact NOT detonation, they are sharp not melted!

do you think that the excessive heat from detonation caused the weld to fail, causing the whole issue? You can tell that it got REALLY hot too....

[49er]

Sorry to see this again Bill.

I'm with Ray on this one, but it may not be your timing. By the look of your 3rd and 4th pics, it appears that most of the heat and destruction is on the inlet side of the chambers. The 3rd one isn't clear enough, but it appears that you have may had a head gasket leak adjacent to the inlet valves. If that is true, the damage will be from detonation through an over lean condition. If you were already running on the lean side, an air leak through the gasket will lean it out even more. The pic showing the top of the bore, shows that the most heat was on the inlet side during the initial meltdown. Did you check the surface across the block at the last re-build? It could be warped.

Did you have the chambers in the head repair welded. If so, the distortion will have bowed the head surface. If your machinist resurfaced the repaired section, your #2 & #3 chambers will have a smaller volume than the outer pots. Your CR on those inner pots could be significantly higher than the outer ones. Did you CC all your chambers after the repair welding was resurfaced?

Cliff may be right, perhaps a nice docile little 850 with stock .............. fitted might be the answer.

[chef1366]

No head gasket leaks.
I did not check the compression on the inside cylinders. Just got it together in time for a Rally.
You may have something with the higher CR. I'm ditching this head and cylinder. Getting a new cylinder cut, got two pistons, send a different head out and do this one more time.
I'll start with a larger main jet and richer needle. Tired of this song and dance.

[mighty13d]

If you lived in New England I would bring over my spare 850 engine for you to throw in it until you got yours back together. Holy heart ache.

[chef1366]

If you lived in New England I would bring over my spare 850 engine for you to throw in it until you got yours back together. Holy heart ache.

Thanks but this is a 16 valve chain drive.

[salty_monk]

Really bad luck Bill... more patience with that engine than me! Not sure I can do anything to help but let me know if I can......

Dan

[mighty13d]

Thanks but this is a 16 valve chain drive.

OHHH I saw "L" and thought "GL" I'm surprised you are able to type without smashing the keyboard. I probably would be out kicking things till I wore myself out or hurt myself.

[salty_monk]

Damn L models

[49er]

Damn L models

No, damn CV's and pods

[Steve]

This brings to mind a philosophy that a friend had about the older air-cooled Volkwagen engines.

"They are spring-loaded in the blow-apart position. The more your hop it up, the tighter you wind the spring."

It's amazing to see how dead reliable the stock engines are and how much they can be built up,
but this is a very good example of how you really need to watch the details when you do it.

.

[Don-lo]

Owwwww, it hurts to see the pics.

Which 2 cylinders was it?

[Dave8338]

Bill do you have an oil temp gauge on that bike? It sure looks like the damage to the piston is from something letting go and not limited to detonation alone. One thing with welding cast aluminum...the porosity of the weld rarely if ever matches the original casting and as a result will expand at a different rate than the surrounding cast material.

As temps increase, so does the effect of this expansion difference. Add to that the vibration and stress of an engine, internal heat temps of the combustion chamber and compression and it is no surprise that things let go.

Also...do you know if the shop preheated the head to 500-700 degrees first and brought the temps back down slowly to promote penetration and bonding?