Heads and Cylinders Off: Things could be worse

Rot 911 · 06:02 PM

Well I started my engine rebuild due to cylinder #5 having 60lbs of compression and a 100% leakdown with air escaping into the exhaust. I suspected at the least a problem with #5 exhaust valve. Well after my battle with the rocker arm and eating some lunch I attacked the heads and cylinders. With the exception of #5 all the valves looked like this:

And then here we have #5. See anything unusual?

But look at the cylinder, perfect condition. The cylinder still shows the factory hone marks after 133,000 miles!

The piston and rings looked ok too.

Sonic dB · Sonic dB's Garage

Wow. Its Pac Man. Looks like you did your rebuild at the right time, sorta preventative maintance in a way.

Rot 911 · 10-18-2003, 06:19 PM

Sonic I wasn't even going to do my rebuild for another 3-4 months. I just got the leakdown tester and thought I would give it a try. Who knows how much longer before that valve broke up and trashed the piston and cylinder!

makaio · 10-18-2003, 06:42 PM

Good catch Kurt! What would cause that, too tight of valve lash?

Elombard · 10-18-2003, 07:03 PM

I am curious, I have a similar situation on #6 in my SC motor. Did it run well? My car runs great.

kstylianos · 10-18-2003, 08:43 PM

Kurt,

How did the plug look on #5. Looks like it could have been caused by excessive heat from either 1) a very lean mix in that cylinder or 2) the valve not seating against its seat correctly thus not dissipating its heat into the head.

Good catch BTW!!

Rot 911 · 10-19-2003, 07:17 AM

Quote:

Originally posted by makaio
Good catch Kurt! What would cause that, too tight of valve lash?

In my case it was a very worn out valve guide. The valve is cooled by transferance of heat to the valve guide. When the guide is worn out the heat isn't transferred and the valve burns and cracks and ultimately breaks.

Rot 911 · 10-19-2003, 07:21 AM

Quote:

Originally posted by Elombard
I am curious, I have a similar situation on #6 in my SC motor. Did it run well? My car runs great.

Same here, my engine was running great, or so I thought. Good idle and accelleration. Last month I took it on a 1000 mile drive with no problem. Guess I was just lucky. Valve could have broken up and trashed a piston and cylinder!

Doug Zielke · 10-19-2003, 07:27 AM

Classic!!
I've been looking for that exact shot (burned valve) for the Mechanical Mayhem Files.
Thanx, Kurt.

rcwaldo · 10-19-2003, 07:32 AM

Good to see it didnt completely fail, trashing that cylinder. One little tip, as I noticed you labeled that head with a sharpie, make sure to engrave the cylinder number etc. since that sharpie marking will most likely be worn off with cleaning.

Are you gonna tear into the bottom end?

Chris

Rot 911 · 10-19-2003, 02:15 PM

Quote:

Originally posted by rcwaldo
Are you gonna tear into the bottom end?
Chris

Yep, this engine is going down to the bare case halves!

norustscott · norustscott's Garage

You have to love that little voice in the back if you head...no the other one that says, stop, do not pass go, tear down before it gets really expensive...great call.