XC90 2.5t dead #3 cylinder

[69ragtop]

The intake side of the turbo is intact and free from any shavings or metal particals. The running clearance between the shaft and bronze bearing is good. My thoughts are possibly a thrust washer , or snap ring as you mentioned, broke apart and caused the damage. But it would still have to travel through the intercooler maze first, and the catalytic converter honeycomb after. There wasn't anything in either when I tore it down searching for something.

[mrbrian200]

Another thought: the throttle body. Two little screws hold the throttle plate to the linkage that extends into the electronic mechanism. If one of them worked loose the throttle plate might still hold together (run and drive). Those little screws seem about the right size/shape for the impact damage to the piston/head surfaces seen in your photos. And small enough to get past the intake valve.

I forgot about the intercooler, anything metallic from the turbo would most likely would drop to the bottom on the inlet side. Even if it did make it to across to the outlet side, would have to fight gravity to get pulled halfway back up the side of the thing to the outlet pipe. The air flow at the bottom on the outlet side would be from one or two horizontal channels out of many and not likely enough to pick up anything metallic heavier than air/larger than a grain of sand. I could be wrong (at WOT) but still seems unlikely.

[69ragtop]

Good catch, I'll check it out when I get back in the shop later today. I did remove the throttle body and gave it a cleaning when I did the service but didn't notice the screws missing nor did I check them for being snug.

[mrbrian200]

If the screws on the throttle plate are still where they belong, the next thing I might check would be the valve guides. I believe they're brass or steel inserts pressed into the aluminum head. Possibly one of them fractured and dropped a chunk of material down into the cylinder.

[mrbrian200]

Thinking about it, any harder metal bit that found it's way into the cylinder: you may never find it. The repeated extreme heat/cool cycling between intake and combustion temperatures would make it very brittle. Eventually it would fracture/break apart into smaller particles that would either oxidize/burn up or push out with exhaust gasses and (small enough) to push right through the catalyst honeycomb. May have only survived in there for a matter of minutes or hours, then the impact damage/pitting causes detonation that cascades damage further as you continue to drive it.

[69ragtop]

I was also thinking about the guides and valve seats possible fracturing and would like to disassemble the head further to check them out, first I want to get this engine swap finished and get this car back on the road. I did check the throttle plate screws and no smoking gun, they're both good and tight.

[siouxperXC]

Unfortunately, I encountered the same failure. I chronicled mine here and never got to the bottom of it... until recently.
viewtopic.php?f=10&t=74366

I've told folks that it 'idles like a diesel but runs well otherwise'.

I called a local independent shop that specializes in Volvo because I was betting that I only needed to replace the head as I expected it was an exhaust valve that had been damaged when something hard went through. The shop let me talk to the mechanic and he assured me that he knew exactly what it was. His theory was that the banjo bolt(hollow screw) on the intake side (PCV system) has a BB in it. This BB gets sucked into the intake and rattles around, hits the plug, and damages the exhaust valve before being ejected. He went on to tell me that he hasn't seen it make it to cylinder 3 before, it usually takes out cylinder 1 or 2. His fix? Replace the engine.

My son continued to drive it and I continued to debate the next step. Recently, my son's buddy's dad referred me to a Volvo mechanic that has done a bunch of work for him out of his garage. When I explained my story to him, just as I had to mechanic #1, he went to the exact same explanation - except he wasn't surprised it took out cylinder 3. Your pictures corroborate the hypothesis. It's crazy, really. Thanks for digging in and taking a look. Now, I'm curious, if you look at your banjo bolt, if it will be empty.

This week, I'm buying a used engine and mechanic #2 is going to swap them for me. We're going to do the usual preventative maintenance on it at this time too (timing belt, water pump, PCV system, plugs, serp, etc). Mechanic #2 believes that there was a design change along the way to the banjo bolt and he said that once they replace, they haven't had to do a second time.

[mrbrian200]

That ticking time bomb of a check ball in the banjo bolt. Grrr. I'm upset with myself now-- I've read about this before and meant to get the updated part put onto my own car... but kinda-sorta forgot about it.
I'm going to have to resort to using a spreadsheet to keep track of everything.

[69ragtop]

Siouxperxc, I have read your previous posts on having a smashed spark plug and losing a cylinder and was wondering if you had found an explanation, and how it turned out. Thank you for chiming in and sharing your experience, the BB from the check valve seems to be the most believable cause. Just to clarify, am I looking for a BB, or lack of one, in the banjo bolt or the fitting in the front left corner of the intake manifold? The next question would be if it's not there, do you just leave it out or is there a replacement for it that won't play Russian Roulette with your engine?

[69ragtop]

Mrbrian200, you might want to diffuse that ticking time bomb ASAP, I'm not as fast with the wrenches as I once was and I was proceeding cautiously, but even with a lift and shop full of tools it took me an honest 15-20 hours to get this engine out and stripped. Going back in took considerable less time, I'm sure an experienced Volvo mechanic can probably do it in a lot less time, but it's no day at the beach.