Epic Fiero Fail at 24 Hours of Lemons (Page 1/1)
billy bee OCT 05, 12:21 PM
Where to begin... Well, the car lasted less than 30 minutes in a 14.5-hour race. The short story is that the engine blew up. It was a "built" 3.4 with a cam. I have the build sheet and will upload that at some point. But for now, here are some pictures of the post-mortem on the engine:

Blown head gasket and damage around the crown of #3 piston:


Exhaust valve seat in #5 fell out of the head:


Valves in 2 and 4 (I think I have the numbers right) hit the pistons and bent in the head, bending the push rods:




Bent exhaust valves:


--bb

[This message has been edited by billy bee (edited 10-05-2022).]

Notorio OCT 06, 12:27 AM
Sorry to hear that your motor blew. I'm sure we'll all look forward to seeing the build sheet. With the bent valves I guess the timing chain broke??
cam-a-lot OCT 06, 06:58 AM
Bummer... hopefully it is covered under GM extended warranty.....
Spadesluck OCT 06, 08:55 AM
Did it overheat then blow the head gasket?
Raydar OCT 06, 09:01 AM
Holy crap! Sorry to hear about your misfortune.
Any idea what caused all the mayhem?
billy bee OCT 06, 11:02 AM
Hey guys:

Well, the car did overheat. My wife was driving at the time and probably did not watch the gauges. There is probably a high-lift cam in the engine. That may have led to the valves hitting the pistons. No idea why the valve seat fell out of the head. I am told it is not uncommon, although I have never seen that.

This is speculation, but I think more than one problem led to the failure: overheating, poor valve guide tolerances on the build, possible warped head to start (I have not place the heads on a surface plate to see if they are warped just yet). I cannot figure out what caused the deterioration of the piston. The only thing I can think is that the head was warped, allowing coolant past the gasket which accumulated in the cylinder and corroded the piston. Open to your thoughts...

The big question is on how to move forward. I am probably going to pick up a junkyard 3.4 and simply swap it in...but I'll probably reseal the engine first. Open to suggestions on that front, too.

--bb
Joseph Upson OCT 06, 03:10 PM

quote
Originally posted by billy bee:

Hey guys:

Well, the car did overheat. My wife was driving at the time and probably did not watch the gauges. There is probably a high-lift cam in the engine. That may have led to the valves hitting the pistons. No idea why the valve seat fell out of the head. I am told it is not uncommon, although I have never seen that.

This is speculation, but I think more than one problem led to the failure: overheating, poor valve guide tolerances on the build, possible warped head to start (I have not place the heads on a surface plate to see if they are warped just yet). I cannot figure out what caused the deterioration of the piston. The only thing I can think is that the head was warped, allowing coolant past the gasket which accumulated in the cylinder and corroded the piston. Open to your thoughts...

The big question is on how to move forward. I am probably going to pick up a junkyard 3.4 and simply swap it in...but I'll probably reseal the engine first. Open to suggestions on that front, too.

--bb



Without all of the details of the build, I suspect the cooling system couldn't keep up, the motor got really hot, spark knock probably caused the erosion on the piston edge (coolant leak into the cylinder usually cleans the piston like water/meth injection) and that combined with thin oil film/poor lubrication from the overheat possibly lead to a very hot and compromised timing chain that skipped a tooth or two allowing the piston to valve contact. Tight valve guide tolerances are a possibility as mentioned also, but having read of a similar failure of a stock 3.6L DOHC motor while being tracked has me suspecting the timing jumped at some point.