Engine rebuild part 1: Tear down and damage assessment
I have started disassembling the engine to find out exactly how broke I’ll be after the rebuild.
After testing the compression all I knew was that cylinder one had 0 psi which is not good.
Getting the engine out of the car went a lot faster this time. For some reason I’m getting good at this…
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Stripping down the engine
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The oilpan contained some interesting new parts:
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Aluminium gunk in the pan. Parts of broken piston rings.
The head looked fine except the chamber and valves on cyl 1 was full of soot and oily deposits.
Gasket was fine.
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I removed the rods and crank and tried to be PRO by indexing the parts:
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Rod bearings had some debris from the carnage embedded into the bearings. Rod #1 was fine though.
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#1 crank bearing had the same damage:
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Crank needs some work on the #1 main journal and #1 crank journal. The other ones was fine. I hope this can be fixed without grinding so I can use the same size for the new bearings.
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I checked the oil filter for debris but found none. Since the bearings are damaged my theory is that they went trough the oil filter bypass valve during high RPM on the track. Running with too much oil might also have forced the bypass open due to very high crank case pressure.
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And finally , the pistons. Or more spesific piston #1:
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I don’t fully understand what’s been going on here. The ring land between the first and second compression ring has collapsed. This has again destroyed the ring lands below this area including the edge of the piston below the piston pin.
But what I found a bit strange is that there is no sign of detonation or damage to the upper ring land or piston crown.
The best information on piston failure that I have found online is this:
http://www.boosttown.com/engine/piston_damage.pdf
Page 36 covers “Ring land fractures”. From the pdf:
<blockquote class="tr_bq">Possible causes for the damageKnocking combustion on gasoline/petrol engines
• Use of a fuel without suitable anti-knock properties. The fuel quality must correspond to the compression ratio of the engine, i.e. the octane rating of the fuel must cover the
octane requirements of the engine under all operating conditions.
• Diesel fuel in the petrol, which lowers the octane rating of the fuel.
• Oil in the combustion chamber as a result of high oil consumption at the piston rings or valve guides lowers the antiknock properties of the fuel.
• Excessively high compression ratio caused by combustion residue on the piston crowns and cylinder head or excessive machining of the cylinder block surface and cylinder
head surface for engine overhaul or tuning purposes.
• Ignition timing too advanced.
• Mixture too lean, resulting in higher combustion temperatures.</blockquote>My guess is either detonation or oil in the combustion chamber. Or a combination.
The other pistons looked fine except some wear on the coated skirts:
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This could also be related to debris from #1 piston .
Thanks to me being clumsy during removal of piston #3 it fell on the floor, 30cm drop, and that was enough that ring land between the top and second ring actually broke off. Seems very brittle:
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I’m pretty sure it wasn’t broke before it fell to the floor as the surface was not contaminated by oil.
The block needs work on cylinder line #1. It’s not very deep but can be felt with the nail.
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#2-4 looked fine to me visually and while scratching with the nail. Pic from cylinder #2:
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I’ll have an engine shop look at both the crank and block. I hope honing and polish is enough. If not I’m looking at a full rebuild. I’ll buy new pistons anyway since two are already fubar.
Summary:
- Ring land on cylinder #1 has failed due to detonation / oil in cylinder. Parts of piston in the oil.
- Damage to cylinder liner #1. Honing of #1 or full re-bore of all.
- Two of the crank journals has scratches. Polish or grinding.
I’ll make another post once the shop has taken a look at the crank/block.
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