My truck, a work in progress
Monday, February 25, 2002
  02-25-02, Part 10: More drama

Well, it seems that not everything was happy in turboville. The headgasket melted (!!) between the #1 and #2 cylinders, and this caused a chain of events that ultimately resulted in a detonated piston. Miraculously, the broken piston left the combustion chamber without damaging a valve or a cylinder wall; it made a clean escape. Unfortunately, it lodged itself in a narrow part of the turbine housing, killing both my turbine wheel and turbine housing:



That part on the bottom half of the turbine blades that looks all chewed up? Well, it shouldn't...


The upshot is that the motor is down again for a rebuild while we replace the broken piston. I guess this is an opportunity to correct a few things I didn't get right in the initial build up...but that doesn't make it feel a whole lot better. While the motor is down this time, I will be doing the following:

  • installing a set of Eagle 4340 steel rods.

  • reshaping the combustion chamber to bring the compression ratio down to a more boost-friendly 8.1:1. This will let me run more boost AND more timing, both of which are good things.

  • relocating the O2 sensor bung from the mid-pipe to the down pipe.

  • changing the wastegate spring to a much lower value (3-5 psi) so the electronic boost controller will have more control.

  • resurfacing the flywheel and changing to a stronger clutch, as the current combo showed signed of slippage.

    I'm trying to remain philosophical about this, but it sure ain't fun spending a ton of money and putting in a year of effort only to have parts fail. Unfortunately, I don't think this is unusual when you try to get double the stock power output. Every single detail becomes important, and the smallest detail can trip you up. Financially, I am poorer for the experience, but I am otherwise undeterred: I will solve these problems, the motor will go back together, etc. But it does suck to be in this position yet again.

    On the morning when things went bad, I made an adjustment to my BOV to get it to open at a lower threshold. I don't think this adjustment had anything to do with what followed, except for the fact that it may have masked some of the other things that were going on.

    After making this adjustment, I was feeling good about how the motor was running. In low boost situations, the BOV was now opening when I closed the throttle plate; previously, I needed 6 or more pounds of boost present to get the BOV to crack open, so this was definitely an improvement. Driving to work that morning, it seemed like things were running really well: upshifts were crisp and the motor was accelerating a little better than usual. I attributed this to the BOV adjustment, but I now believe it was due to an exhaust leak between the mid pipe and the exhaust pipe.

    I was on the freeway on my way home from work when things went bad. I always scan my gauges when I drive, and I distinctly remember that the EGT was no higher than normal. My water temp gauge had been running a little odd, intermittently reading just a few degrees higher than normal, but it was reading fine when I suddenly noticed that the motor was pinging *a lot.* I had the music up and wasn't paying attention, so I didn't catch this immediately. By the time I pulled over, the motor was running like crap. No changes to the temp gauges, no white smoke, but something was clearly wrong. I didn't see anything obvious but didn't want to chance it, so I shut the motor down and called for a tow (gotta love AAA "Membership Plus" towing privileges :-).

    When I got home, I had a chance to go over the engine more thoroughly. The first thing I noticed was that I had lost some downpipe flange bolts, and my mid-pipe was only attached to the down pipe by a single bolt -- there was a big 1/2" gap between the two pipes. I then pulled the plugs, and saw right away that #1 plug was physically damaged: the ground electrode was bent and pushed to the side of the insulator nose, and the insulator itself was cracked. U-g-l-y.

    Next, I did as compression test, followed by a leakdown test. The compression and LD test revealed that the #1 & #2 cylinders were Siamesed, as were cylinders #3 & #4. Hmmm...

    At this point, I called my engine builder (Tim J.) and discussed the situation. Since it seemed clear that "something bad had happened," we decided that it would be best to pull the motor and ship it to him for a tear down inspection and rebuild. At worst, I would be out the effort of pulling the motor and the cost of shipping the motor (plus a couple hundred bucks in rebuild supplies). But since I was certain something more severe had happened, I wanted to be as thorough as possible. I could have torn the motor down in my garage, but since this motor is something of a rolling advertisement for Tim's services, Tim wanted to take ownership of the tear down/rebuild, which was fine with me.

    What Tim found when he pulled the head was that the headgasket had melted away between #1 and #2 and also between #3 and #4. Neither the head nor the block was scored or otherwise damaged by this!!! Wild, huh? Tim said he had never seen anything like it, and neither have I...but it is as I've described it. Additionally, a big chunk of the top ring land was missing from the #1 piston, as was the entire top ring. Tim described it as missing roughly 25% of the top ring, from about the 3:00 to the 6:00 position, as viewed from the front of the engine. Much to our surprise, the missing piston piece did *NO* damage to either the head, valves, or the cylinder wall, but as I mentioned, it did manage to damage an expensive turbine wheel. I am actually very lucky, because it could have wreaked considerably more havoc in the block and still taken out the turbine. Not exactly the kind of luck you want to take to Vegas, but I guess it's better than it could have been.

    So that's what I know at this time. The piston damage was obviously caused by detonation, but the headgasket probably failed over a longer period of time. My supposition at this point is that the headgasket became damaged during one of the tuning sessions, and the detonation occurred when the computer corrected the A/F to compensate for the exhaust leak, and this finally put things over the edge.

    Anyway, I'll post more when I know more, but that's what I know now. A big motor making big boost is going to chew up some parts, and I guess mine is still teething. Grrrrrrrrr. 


  • The ongoing saga of my 1986 Toyota 4x4 truck and its much-modified 22RTE turbo engine.

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