Alright, I finally got the subframe off (after a lengthy battle with a seized bolt), the oil pan off and the affected pistons out. Definitely some sludge in the oil pan.



Not easy stuff to get off. It even put up a pretty good fight against a pressure washer. I'll definitely be spending a bit of time getting as much of this stuff out as I can, and then do few extra oil changes once she's back together. Any advice on ridding the engine of this stuff would be more than welcomed.

The no-compression issue did turn out to be the rings. For 7, 8 and 9, they were all seized into their slots, flush with the side of the piston.



Here is piston 10, for reference, which had all rings moving freely:



The pistons themselves show some pretty good wear along the side next to the exhaust ports.



This side of the piston was right next to the exhaust ports, so obviously this scoring is from the cat pieces being sucked back through.

I pulled the rings off 10 and tried them in 7, 8 and 9. They moved around decently, but the scoring on the side of the piston cause a burr to form which grabbed the ring a bit.

All and all I'd say I am pretty fortunate. I'll need to ball hone the sleeves, clean up (hopefully) the piston heads (or otherwise replace them), get some now rings, and clean up some sludge. Then there's the cats. I've decided to pull all four primary cats. I'll basically just cut open the side, remove the brick and weld it back up. I haven't decided on a method of tricking the ECU, but there's a quick an easy potential option putting spark plug non-foulers on the downstream sensors.

Side note for anyone curious: the O2 sensors feed the ECU data showing lots of voltage spikes for upstream sensors, and a much more even voltage after the cat. If the downstream sensor shows lots of voltage spikes, it triggers your check engine light because your cat is either ineffective, or gone entirely. However, if you add some spacers to the O2 sensor, it removes the sensor from the direct path of the gases to show a more consistent voltage, and, in theory, tells the ECU not to worry.

I'm also probably in need of a rear cat. Most of the primary cat ended up running downstream and a lot of it got pushed into the rear cat cells. After slamming it on the ground, pressure washing it, spraying it out with compressed air, slamming it more, soaking it in vinegar, slamming it and spraying it, I'd say it's a little more than 50% clear.

Well, that's about it for now. The earliest I'm free to work on the car again is mid-December, so I'll be spending the next month sourcing the parts. Again, if anyone has any tips or tricks to removing engine sludge, please let me know. Otherwise, I'll resurrect this thread in a month or so with some updates.

 

should probably be mic-ing the diameters of cylinder bores and pistons, just in case they are undersized (pistons) or oversized (cylinders) due to the excessive wear. if the pistons are appreciably undersized and the cylinders are oversized, you might find it necessary to purchase a few new oversized pistons. ...hope not.

 

FWIW, the pistons/rings are the same as the duratec 3.0 six cylinder ford motors (think taurus/escape). as are the valves/rockers, rods/rod bearings. As these parts are practically free in the world of AM they are worth thinking about swapping out.

I went ford stock on my rebuild. And the new rods have the new design bearing to improve lubrication. They come out the bottom which is trivial with the motor out of the mounts, but I'm not sure with the subframe in the way...

In any event, really well done getting this far!

Best
Larry

 

Bob, very interesting thread, and kudos to you for saving this engine!

This is why it's very important to pay attention to any check engine lights -- if it's from misfires, this is what can happen.

 

61mga: good thinking. I plan to bore hone the cylinders and I'll make sure to confirm they are within spec. I've gotten reliable info that the pistons will need replacing, so that will alleviate concern of them being undersized.

AM4884: thanks, I've read your rebuild thread several times now. A great source of info, so thank you for that! I'll be honest, I'm keeping my expenditures to a minimum on the car until I can confirm I can get her back on the road. The previous owner was anything but responsible, so I'd like to figure out exactly what I'm into here before I start replacing everything. I've got the engine pretty under control, but there's still a lot that could be in disrepair.

Speedraser: I appreciate that, thank you. After investigating this issue first-hand, I'm fully intending to gut the primary cats to prevent it ever happening again. This is just not something that's easy to prevent, even if you know what to look for.

 

It looks like you are making progress Bob and we all hope that you get this beast on the road again.

I am sure you already knew this, but if not, there is an alternative parts list at the top section for Aston Martin on Pistonheads and the Aston Martin DIY Facebook page.

 

Thanks MAUMAU, I hadn't seen the Facebook one. That's a nice and tidy list they've put together.

 

I'll be watching this thread. Good luck on the rebuild. I'm going to get rid of my OEM Headers and go with VelocityAP headers because of this primary Cat issue.

Jim

 

anybody know if a similar problem with the cats applies to either the 4.3 or 4.7 V8?

 

I fully support anyone wanting to get rid of the primaries. Cat ingestion is not fun a mess to clean up, assuming it doesn't totally destroy your engine. Keep in mind you'll also have to have them do an ECU remap.

 

In all my research, I didn't hear/see any reference to the V8's. Of course, that doesn't mean it hasn't/can't happen.

 

According to Mike at Bamford Rose, this is just a V12 issue.

 

Also, from the reliable source that you introduced me to, "No, it's not a problem on the V8s, only the V12. It's because on the V12 the primary cats are so close to the cylinder head and exhaust cams have a large amount of overlap.

 

Hello everyone. I'm the former Aston Martin technician that is being referred to in this thread (although I did do test driving for a few years at Gaydon, my primary role was electronics, software and sometimes major rectification). I just thought that I would join this forum and post, so that I might be able to add any additional information if i can and so that I can keep track of the progress. Mike at Bamford Rose is a former Aston Martin powertrain engineer and so, as you would expect, has explained the problem in his video very eloquently. This problem only affects the naturally aspirated V12 engines in the VH-platform cars. Again, as previously mentioned, it is essentially a design error and is caused by the combination of long exhaust camshaft overlap, with the primary catalytic converters being so close to the exhaust ports. As I previously mentioned to the original poster in our messages, once the powdered remnants of the catalyst get into the engine oil, they get pumped around the engine and act like a grinding paste. Thus, the entire engine oil system needs to be closely inspected and meticulously cleaned to remove all traces.

 

Thanks for chiming in and taking the time to help!