Blown engine Post mortem
As I mentioned in a previous post i managed to seize up my engine on the track in a none spectacular fashion. I’m not sure how this happened but will try to do a quick summary of events,pics observations prior, during and after the failure.
- I did a lot of tuning the days before the trackday as the maf scaling was off on idle and lower cruise with erratic AFR readings (on the rich side). It turned out there was a boost leak trough the IAT sensor.
- After fixing the boost leak I upped the boost from 10psi to 12psi with no problems and a very healthy boost in power. Logs looked good so I upped the boost to my goal of 15 psi. The car felt superfast and was running without hesitation to redline for the 2 first tuning sessions. After that it developed a small hesitation about midrange which felt very much like spark blowout. AFR where also climbing to 13:1 as the fuel pump could not keep up. Both problems disappeared when going back to 12 psi. I could not get a new fuel pump in time for the trackday but decided to run anyway and keep a close eye on the AFR’r
At the track:
- Ran 20 ish laps in the rain with no problems at 12 psi. Logged AFR 12.5:1
- Track started to dry up. Some hesitation above 10 psi on the main straight but not as much as before. Ran like this for about 5 laps.
- Car started to feel slower in the upper rev range. Eased off the throttle and noticed that there was no power in the midrange. Engine wanted to stall.
- Parked the car. Tried to start it again after 20 mins without luck. Engine was cranking but it would not fire.
- No oil leaks or sign of damage under the hood. Datalog showed normal AFRs during cranking.
- Car was transported back on a trailer the next day after sitting for 30 hours.
- I had to tow the car the last 4 miles and very stupidly tried to start the car in gear while beeing towed.
- Large bang with parts flying around inside the block. Oil was leaking. It turns out the engine had seized during the 30 hours of cooldown.
- Since everything went FUBAR and the engine started on 3 cyl I drove the car the last 20m into the garage instead of pushing it.
- Face palmed and lesson learned
Some pics and comments from the engine tear down.
Sparkplugs looked fine. A little red from the E85. New one to the right for comparison
<div class="separator" style="clear: both; text-align: center;">
</div>
Spent a lot of money on a engine hoist which I hopefully will use once…
<div class="separator" style="clear: both; text-align: center;">
</div>
Made a flywheel lock out of wire
<div class="separator" style="clear: both; text-align: center;">
</div>
Oil smelled very much of E85 and had a slightly red discoloration.
<div class="separator" style="clear: both; text-align: center;">
</div><div class="separator" style="clear: both; text-align: center;">
</div> I was certain that I had a hole in the block with a rod sticking out since the oil leak under the car was massive. It turns out I only slightly dented the block and cracked the oilpan. Notice the FoMoCo markings on the MX5 oil pan.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
Number 4 rod had snapped and cracked the girdle, put a pice of the rod into the block wall and broken the oilpan.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
Locked the crank BFH style to be able to remove crank pulley, rodbolts and crank
<div class="separator" style="clear: both; text-align: center;">
</div>
Timing gear looked good. Timing marks lined up ok. No slipping of the friction washers or interference going on.
<div class="separator" style="clear: both; text-align: center;">
</div><div class="separator" style="clear: both; text-align: center;">
</div>The number 4 piston looks like it has hit the valves after the rod broke and spinning in the bore.
It was stuck in the bore but it was not a problem hammering it out with a rubber hammer.
<div class="separator" style="clear: both; text-align: center;">
</div>
The rest of the pistons looks fine except for the red deposits from E85. Head gasket was ok. No sign of leakage/coolant.
<div class="separator" style="clear: both; text-align: center;">
</div>
Pistons has a lot of red sludge from E85 on the piston rings. Number 4 was the worst which might indicate that is related. Stock pistons has coating on the skirts which is nice. I’m not sure how to identify a failed piston ring. All looked the same to me. No scratches or uneven wear.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
The number 4 piston obviously had a hard time having multiple marks and missing parts on the skirts. Looks like this have happend after the rod broke since the bore is smooth.
<div class="separator" style="clear: both; text-align: center;">
</div>
Piston bores are all smooth including number 4 where the rod snapped. This has me puzzled as I was expecting marks in the cylinder wall if a piston has seized. The marks on the first pic is just sludge.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
Crank bearings has som marks on them but the crank is mirror smooth. I wonder why there are som 10mm circular marks on bearing nr. 1. Some of the scratches might have happened after it started with the rod parts flying around.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
Broken rod.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
Piston pin moves freely in the piston. Oil channels seems to be ok. The rod and pin are pressfit together with no circlips at the ends.
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
What happend ?
I don’t know. The second incident might have masked over some of the clues of the initial problem as well. I find it strange that piston 4. has been stuck without leaving some permanent marks in the bore. The rod bearing and pin looks ok as well in case they were stuck and bent the rod.
My only guess would be that the oil have been diluted by E85 and degraded the oil to the point where the bores/rings could not be sufficiently lubricated . It could also be worsened by E85 crap/red dye/deposits clogging the oil ring. Feel free to leave a comment if the pics points out something obvious. I’m
What now ?
Since the block is FUBAR I need a new engine. Most likely a 2.5 Duratec/MZR from the US as these can be had for 1500-$2000 in good condition. It is a real bummer that the oil pan was ruined as this must be moved over to the new engine. The 2.5 with cams would most likely be the same as the 1.8l with 12psi on the FMSC. 2.5l with stock cams + FMSC maybe closer to a safe 280-300whp @ 12 psi on GOOD OLD FASHION 98 RON GASOLINE but with crazy torque.
Comments