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Old 09-15-2019, 06:13 PM   #325
John V
No more BMWs
 
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Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
Those of you that have been to my house know that this was challenging. Only two inches on each side of the trailer fenders going to the upper garage. But it was better than pushing the car up that hill



Starting the teardown.



Ring lands aren't supposed to look like that.



Whoops.



So what happened?

Here is my theory. The engine had low compression before Nationals, and the turbo spool was extremely slow. That led me to believe it had cracked rings. Why did the rings crack? A few theories. First, I overheated the engine early on. It had cooling system problems... too small of a radiator, an insufficient fan, and a coolant temp sensor with the wrong calibration (thanks, Haltech). It didn't overheat badly enough to compromise the head gasket, but it probably fatigued the ring pack. Second, it overboosted quite badly when I was setting up the closed-loop boost control. It overscaled my MAP sensor, but my guess based on the turbo efficiency is roughly 30psi. The engine didn't have enough fuel to run up there, but it probably created some pretty crazy cylinder pressures. Third, with all the fuel system problems that took me forever to sort out, the thing had a lot of events of very lean mixtures. E85 is pretty knock tolerant, but even so that's violent.

But why the spun bearings? Well when the compression got worse and worse, eventually the ring land material (Aluminum) got into the oil pan and clogged the pick up screen and the oil filter. Also when you pressurize the crank case, the oil has to go somewhere and it typically stays in the cylinder head. That makes sense, the car had good oil pressure until my very last run on course where it gradually went down to zero.

Tomorrow I'm stopping by my local salvage yard. They have fifteen 2.5L Duratec motors, and five of them are under 20,000 miles, so they should be good candidates for rebuilding. I'm doing the most basic of engine builds.

1) New forged pistons (stock are cast) with a point more compression: 10.7:1 versus 9.7:1. Should help with turbo spool.
2) New forged H-beam rods. The stock rods are very strong, but I want to turn this motor to 8,000 RPM and the stock ones are marginal at the 7,400 I was spinning it to this year
3) ARP head studs. The stock bolts are very strong, but studs will improve clamping and ensure I should never have any issues lifting the head off the block.

Other upgrades for the winter are also coming but that'll have to wait for another post.
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