wheelsmithy GRM+ Memberand SuperDork
11/24/19 6:32 p.m.

So, I've got a crappy QR 25 engine out of a 2003 Nissan Altima. It ate its catalytic converter.

This is a problem for these cars, Sentra SE-Rs, MR2s (MRSs), and I'm sure others. The cats come apart, and are sucked into the combustion chambers where they wreak havoc on rings, and I imagine, everything else.

The pink stuff above is ATF I was soaking the cylinders in since the bastidge locked up on me. It was free, but my guess is the moisture in the air seized it tighter than the proverbial drum.

So, questions: assuming I can knock the pistons out, I figure a bore is highly likely. How about the valves? Can I grind them, and make it work? Does platinum ingestion mean everything is junk? How about the oil pump? Does a thorough cleaning get me out of the woods? Cams? Lifters? Timing chain? The hope is to do this on the cheap, and I don't mind labor.

I could find nothing on this topic in my first Googling, and I thought GRM might have answers. 

Has anyone rebuilt an engine lunched by its close coupled Cat?

dculberson MegaDork
11/24/19 7:35 p.m.

Spoolpigeon tried to rebuild my mr-s engine that had eaten its catalyst and it was toast. I don't think he was able to use anything but maybe he'll chime in with a more definitive answer. Just remember that it's ceramic and far harder than most of the wear surfaces in an engine. 

TurnerX19 Dork
11/24/19 7:58 p.m.

The biggest variable here is how long it ran after cat ingestion. Open up the oil filter. If it is full of cat debris it ran a few miles or more after failure. Take it all the way apart. Turn the block upside down and remove the crankshaft completely first. Then remove the pistons and rods. You may  have to chop the siezed piston(s) out of their bores. Then start measuring things. the block can probably be bored. The crank may even be perfect as is. If the crank is damaged throw it all away and try again with another unit.  From your photos the thing that worries me most is the cavity between the right intake valve and the right exhaust valve. Valve seats can be replaced and the head welded at that cavity, but the expense is probably much greater than another head. All the machine work and new parts will go over challenge budget.

Streetwiseguy MegaDork
11/24/19 8:29 p.m.

That seems like catastrophic damage for cat inhalation.  I thought they just brought little bits in, and scored the cylinders.  That looks like a water/rust/detonation load of destruction. What melted the hole in the head?

If it is the cat, that's spectacular. I'd go find a far less damaged engine and freshen it if need be.

buzzboy HalfDork
11/24/19 8:38 p.m.

Forgive my stupidity, but how does the cat get into the combustion chambers?

759NRNG UltraDork
11/24/19 8:42 p.m.
buzzboy said:

Forgive my stupidity, but how does the cat get into the combustion chambers?

yeah me too...............

Streetwiseguy MegaDork
11/24/19 8:44 p.m.

In reply to buzzboy :

Exhaust reversion.   Nissan shifts the cam timing to draw a bit of exhaust back into the cylinder on the  intake stroke instead of using egr, and the cats are part of the exhaust manifold, so ceramic particles can come back as well, if the cat is damaged somehow.

TurnerX19 Dork
11/25/19 7:21 a.m.

In reply to 759NRNG :

This happens on the over run. High cylinder vacuum and valve timing overlap. 

TurnerX19 Dork
11/25/19 7:24 a.m.

I will add that the corrosion appears to be the big issue here, especially as the engine did turn over when purchased. That cavity in the head might be more shadow than real damage, can't tell until it is clean.

11/25/19 8:04 a.m.

 Seems ro be a common thing with new engines parking the car right at the exhaust ports. Mazda 3 engines do the same thing with some regularity.



dculberson MegaDork
11/25/19 10:13 a.m.

Another way catalyst bits get into the engine is that the cat breaks apart and plugs the downstream cat some so pressure will build up in the downpipe. Then when you turn off the engine, chunks of the broken up pre-cat get blown into whichever cylinder still has its exhaust valve open as the downpipe relieves that pressure. Then you start it up and it breaks up the chunks and spreads them all through the engine and oiling system.

How much is that engine worth to you? It seems like an Altima 2.5 would be much, much cheaper to just replace with a low mile junkyard motor.

wheelsmithy GRM+ Memberand SuperDork
11/25/19 2:27 p.m.

Thanks for the responses, everyone.

I'll retort:

Cutting apart the oil filter is a really good idea. I should have thought of that. Oil that came out was very black, bordering sludgy, but no discernable bits of stuff in there.

The hope for this engine is, indeed for the challenge. I am considering buying a junkyard engine as a replacement. The concern there is ending up in the same place, as this is what kills these engines. I believe a buddy has a bore scope I could borrow.

The head doesn't have any surprise holes. That's just a trick of the photography. I have indeed torn it down, save for the pistons. They are soaking in PB blaster. 

This is the worst main bearing:

Honestly, the crank, cams, etc look really good. 

The thing is I can get a Re-ring kit for $107. That includes either standard, or twenty over pistons, rings, main and con rod bearings, gaskets (including mains, head, intake, and more, but perhaps not complete). The same buddy can maybe get me a deal on the bore, and crank polish. The timing chain and guides show very little, if any wear.

So, This is on the borderline for doing within my challenge budget. I'm about $770 in right now, with a free X1/9 body, a $250 Altima donor, $250 in wheels, and $270ish in MR2 suspension. It will be tight, but my thought is to have an engine that I've been over with a fine toothed comb, or another junkyard gamble. 

z31maniac MegaDork
11/25/19 2:57 p.m.

Wouldn't it be much cheaper and easier to just find a junkyard 2.5 to swap in?

I just can't imagine the scenario where rebuilding that engine will be worth it.

TurnerX19 Dork
11/25/19 3:26 p.m.

I have rebuilt a couple of seriously rust siezed engines, and, after chopping the pistons out, the bores cleaned up within the .020 oversize you have cheaply available. One of the engines had been rusted tight for years, the other was only stuck for a few months. Damage substantially similar.

The0retical UberDork
11/25/19 3:44 p.m.

Well I was dragging my feet on replacing the wifes X-Terra cat due to a P0430.... I guess Thanksgiving weekend is now spoken for.

wheelsmithy GRM+ Memberand SuperDork
11/27/19 1:41 p.m.
The0retical said:

Well I was dragging my feet on replacing the wifes X-Terra cat due to a P0430.... I guess Thanksgiving weekend is now spoken for.

Maybe not a bad idea.

At this point, this thread is more for posterity than anything. I may still knock the pistons out, hone, and measure, but my gut strongly tells me this engine is junk. A "new" Pull-a-Part long block runs $125, and This anchor likely deserves no better fate than as a core.

My research tells me that the years of this engine affected are 1999-2015. Gulp. I thought they came out in '02 or '03

TurnerX19 Dork
11/27/19 1:43 p.m.

In reply to wheelsmithy :

That is a seriously long production run!

noddaz GRM+ Memberand SuperDork
11/27/19 2:28 p.m.

You will have a hard time finding a good used engine.  Up to two years ago I worked at a Nissan dealer.  Altimas came in all the time burning oil because of this issue.  Used engines were not to be found, at least in the Maryland area.  But good luck.

Floating Doc
Floating Doc GRM+ Memberand SuperDork
11/27/19 3:48 p.m.

In reply to noddaz :

Engines with a fatal flaw can be really hard to find used.

wheelsmithy GRM+ Memberand SuperDork
11/27/19 5:12 p.m.

In reply to noddaz :

That is exactly the reason I am considering rebuilding this lump. I'd be cool with a rebuildable block, but yeah, I'm very concerned that's asking a lot.

May be time to find a different donor.

Indy-Guy PowerDork
11/27/19 8:13 p.m.
wheelsmithy said:



May be time to find a different donor.

This.  Buy a running driving donor, and one without this fatal flaw.

GameboyRMH GRM+ Memberand MegaDork
11/28/19 9:49 a.m.

Since this is for a Challenge car I'd say you should gamble on another junkyard engine, the budget hit of rebuilding this engine isn't worth it.

codrus GRM+ Memberand UberDork
11/28/19 11:11 a.m.

Room in your budget for a VQ35 swap? :)


wheelsmithy GRM+ Memberand SuperDork
11/29/19 5:38 p.m.
codrus said:

Room in your budget for a VQ35 swap? :)


Yes, possibly, or a great many other types. I'll try to keep an open mind, but This lump was going to require extensive frame surgery, and now this has me a micron from jumping ship. I'm out 265 bucks and a header. That doesn't go to challenge budget, and can be largely recouped by scrapping what I've got, and maybe selling a bit (airbags, transmission, axles).

One caveat: this car must be a stick shift, unless I can make it electric, and within challenge budget, that's dreaming.

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