URQ quirqiness

[E. Roy Wendell IV]

On May 2, 2006, at 12:00 PM, quattro-request at audifans.com wrote:

> Well the head is off and the verdict is in.
> Cylinder's 4 & 5 had a huge breach between them. Not only was the   
> gasket
> burned through, the head has a valley burned through about a 1/2"   
> wide and
> almost an 1/8" deep. Cylinder 5 is clean as a whistle, and the  
> breach  is shiny
> aluminum.
> I can't see how this could happen in 3 miles. The car ran fine  
> until the
> last 3 miles, and it hadn't been run hard for some time! The head  
> is  ruined. It
> would probably be prudent to deck the block to be certain of a  
> good  seal
> before installing another head?
> I've never seen anything like this. This looks more like an  
> endurance  race-
> many laps at red line type of failure!
>
>
>
> Dennis
> Denver

I had an identical failure on my turbo kitted MR2. Too lean and too  
much timing advance caused detonation and one day it went from  
running fine to running on two cylinders in the space of a quarter  
mile of high power driving. Stupidity was partly to blame as I didn't  
have a wideband O2 sensor installed but in my defense the piggyback  
fuel computer said it was doing it's thing and the previous owner  
told me it was good to go. I now know for certain the difference in  
sound between detonation and a loose manifold heat shield.

In any case, I found the exact same thing as you when I pulled off  
the head. Gasket fire ring missing between #3 and #4 cylinders and a  
1/8" deep by 1/4" wide groove worn in the head. I had the welder at  
the aircraft shop I worked at at the time fill the gap in the head.  
He took out a little more metal so that he had a clean surface, built  
up the gap with filler rod, and filed it flat by hand. Worked just  
fine for a couple of years until the piston rings/lands gave up. I  
didn't do anything special to the block other than use a gasket  
scraper to clean off the remains of the old gasket. No sign of any  
damage to the area between the cylinders.

The blown gasket isn't a surprise. The gasket is the weakest link at  
detonation pressures. If you look carefully I'll bet the fire ring is  
distorted elsewhere. Not that the gasket is to blame as the real  
problem is the detonation. What I am at a loss to explain is the  
metal missing out of the head. All I can think is that the  
combination of heat and high velocity just vaporizes the metal as the  
combustion gasses shoot back and forth between the two cylinders.

E. Roy Wendell IV
erwendell at mac.com
Too many type 44 tq
A pair of MR2s