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Discussion Starter · #1 ·
Hi all, I just picked myself up a gorgeous 2007 MDX elite project with 174k on it very inexpensively as it has engine problems. The story with this vehicle is that it first blew out a spark plug. The dealer retapped and helicoiled the head, and the car was great for a couple of months but then started what almost sounds like a bad valve rattle/clatter coming from the head or front/top of engine. It happens all the time and varies with engine speed. The mechanic told them it would cost as much to tear down the engine to explore the problem as replace the engine with a used one, about 5 grand. Insane. Anyway I could replace the engine for less than 2g, but I really doubt I have to go that route.
When I check online I find a lot of videos where people show a similar clatter, but no explanation. It's not the usual injector noise complaint, suspension or exhaust rattle. Its definitely coming from the engine. I doubt it's failing timing belt system but I won't know until I take covers off.

Is there a known issue with these engines or heads that can cause what sounds like a bad valve clatter?
If nothing else I'm very glad it's coming from the front head and not the rear one!
 

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I’d think you would be able to check the valve gaps with a feeler gauge, from the lifter. This could be it, but obviously I don’t have a way to know without a tear down. At least you could check them from the front, and not the rear, which makes it easier!
 

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Bad valve trains. Replaced the headers.
First: No. Not enough information has been provided for a diagnosis, so it is counter-productive for you to make blanket statements such as "bad valve trains [sic]"

Second: The statement "Replace the headers" actually made me laugh audibly. The MDX doesn't have "headers" in the sense of what that word usually means. The equivalent would be exhaust manifolds -- but even then they likely wouldn't fix OPs problem.

Perhaps you meant "heads"? However, that is unlikely to be good advice, either. Certainly not enough information has been provided to make that diagnosis! And even if there is an issue in the valve train, it is unlikely that the entire head needs to be replaced.
 

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Have you personally checked to see if the spark plug is loose? This kind of sound is emitted sometimes when spark plugs come loose. It's been known to happen on these engines.

I'm wondering if it's on either #5 or #2 cylinder.

http://www.mdxers.org/forums/74-sec...e-spark-plug-thread-p1717-p0305-77-p0401.html

You should also question the quality of work when it was helicoiled and see if it was done properly.
 

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Discussion Starter · #8 ·
Do the valves cause problems with this vehicle? It does sound like bad valve clatter. But it's also possible the spark plug fix failed. But I can get a new replacement head for under $500, which is way cheaper than an engine. These cars sell for 12-14g around here so either way I'm miles ahead in the game.
I pick up the car today and I'll get a closer look. One thing that's suspicious to me is that I felt a lot of heat beside the head near the first spark plug, the one that was fixed. Running my hand along the head after it was first started, it was cool, cool, cool, hot, right beside that plug. Made me wonder if the exhaust gasket was blown in that area, as leaking exhaust gaskets can cause all kinds of weird metallic noises. But if the spark plug fix failed, that could cause it I suppose. Worse case is if the helicoil fell into the engine.
 

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Worse case is if the helicoil fell into the engine.
Pieces of metal may have fallen into the combustion chamber from the original failure. There could be a gaping hole in the top of a piston. No joke. Compression check should be first thing. And maybe borescope inspection. No sense messing with valve train and cylinder heads if you need a short block ( or more likely a donor engine for transplant ).
 

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Discussion Starter · #11 ·
Got the beast home. I'm too lazy to go take a further look at it tonight, but further info is that again I find it leaks hot air, but more specifically, the region of the middle plug, not the one fixed. Anyone want to bet its another loose plug?

Oh hell, I guess I should just do it. I'm dying to know. Bets?
 

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Discussion Starter · #13 ·
Interesting. Turns out it did have a loose plug. Also a loose battery ground. And I had a bad jumper cable. After getting all that taken care of it sounds better but still a valve lash noise. When it was cold and first "pumped up" the noise went away for a few seconds then came back. You could hear things moving and tightening up and loosening.

The noise is definitely in sync with the forward cam. To me it sounds like a bad lifter on the first or second cylinder. The cylinder isn't bad because pulling the coil results in marked RPM loss.

Those heads look crazy complicated, especially for SOC. Anything I should know before I pull the rocker cover?

This is what it sounds likeNote, forum won't let me post links. Interesting. Turns out it did have a loose plug. Also a loose battery ground. And I had a bad jumper cable. After getting all that taken care of it sounds better but still a valve lash noise. When it was cold and first "pumped up" the noise went away for a few seconds then came back. You could hear things moving and tightening up and loosening.

The noise is definitely in sync with the forward cam. To me it sounds like a bad lifter on the first or second cylinder. The cylinder isn't bad because pulling the coil results in marked RPM loss.

Those heads look crazy complicated, especially for SOC. Anything I should know before I pull the rocker cover?

This is what it sounds like. youtu.be/0pjCcSVb9_o

That's not the sound of needing a replacement engine IMO.

That's not the sound of needing a replacement engine IMO.
 

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Helping with the link:

 

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Do you have any service records on the vehicle? When was the last valve adjustment done?

I'd start with checking the valve lash.
 

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The valve train employs solid lifters and can become loose rarely due to wear. I checked my 03 MDX at 200K miles and found only two exhaust valves on rear head slightly tight (< than spec). Overly tight valves can lead to valve damage due to leaking and missing (fairly common on J35 engines).

I don't know how plugs become loose but would suspect improper installation initially. Suggest checking all plugs.

good luck
 

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The heads are pretty simple. The rocker setup is straightforward. On the front head it would be nothing to pull the vc and give the cam lobes and rollers a good look, you could also adjust the valves while ur in there.

Just loosen the adjusting screws completely before removing the rocker rails, and keep the fasteners in the rails to hold all the rockers in place, watch out for the vtec pistons falling out of the intake rockers when you remove the rail.
 

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Discussion Starter · #19 ·
Everything under there looks fine in terms of noting broken or badly worn, but the valves are miles off, especially the exhaust valves. Like 3X spec, over 0.8 mm instead of the 0.3 they're supposed to be. Intakes far closer to what they should be. I need to pick up a feeler gauge (who adjusts valves anymore?) and bring it into spec to see if that quietens it down. I had it running with valve cover off and everything seemed to work okay, no sticking valves or anything.

That would be something if a tech told them they need a replacement engine when all it needed was a valve adjustment.
 
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