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I spent a very pleasant morning yesterday adjusting the valves on my wife’s 2005 Acura MDX. The service was due at 105,000, along with new spark plugs and a new timing belt. I intended to spread these three services out some, and did the new plugs at about 90,000 miles, did the timing belt just shy of 100,000 miles…but…never could seem to find time for the valve adjustment job. I’m just now getting around to it, at 128,000 miles. Fortunately, the valve lash was still fine (more on that in a minute).

I took a lot of pictures and did this write-up for a non-Acura forum I’m on. I thought you guys might be interested in it as well, for those who haven’t gone this far into the engine.

The upper intake plenum is a single cast aluminum unit, with a removable top cover that allows access to the fastening bolts and to the central chamber butterfly valve (which opens at 3,600 rpm to equalize the two plenum halves). It also delivers EGR to the engine, passed up from the lower intake manifold and delivered to each plenum half by an EGR pipe in the smaller top plenum chamber (the chamber nearest the throat of the plenum). There’s also a mass damper fastened to the bottom side of the plenum throat.







The upper plenum sits atop an aluminum spacer on the 3.5L engines destined for Honda’s vans and SUVs. This spacer lengthens the intake runners and adds low- and mid-range power to the curve. This is a somewhat common addition that owners of TLs and Accords make – those engines lack the spacer from the factory.



The seals are very high quality 3-layer metal seals that are reusable.



Interestingly, the lower intake manifold is actually two pieces – and bolts to the engine in halves. The small passage on the right side of the pictures next to the #6 intake passage is the EGR passage. Intake gasses are moving DOWN through the system in the first six passages and EGR gasses are moving UP through the system in that seventh passage.

Keihin is a fuel systems supplier to Honda, and their emblem or label is adorned on the fuel rails and on the upper intake plenum. Keihin is also the carburetor supplier for Honda on their small engines (found on equipment like lawn mowers and pressure washers).



In the picture above, you can begin to make out the fuel injector spray pattern – by the lack of deposits on the intake passages downstream of the fuel injector. As an aside, I have really begun to enjoy doing maintenance work like this, because I learn something about my vehicle or about engines in general every time I do it. This really drives home for me the challenge engineers face with direct injection, where fuel is injected directly into the combustion chamber and not into the intake manifold or cylinder head. I’ve heard of “deposit buildup” and the need for more frequent valve cleaning on some of those designs, and this engine has very clearly demonstrated that potential challenge faced by powertrain engineers.

The pictures below are a close-up of one of the intake passages. It’s incredibly clear where the fuel sprays – and where it doesn’t!





Everyone likes valvetrain pictures, right? I don’t have great ones here – if you want to see a Honda J-series valvetrain, there are a ton of pictures on the internet. But this is what this engine looks like. This oil, which is Peak Synthetic 0W-20, has about 3,000 miles on it. As you might expect from a transverse mounted V-6 engine, the front cylinder bank has a little more discoloration and varnish than the rear cylinder bank – the front bank gets that hot air blast from the radiator fans. This engine has had pretty consistent oil changes every 5,000 miles since new, and with everything from conventional Super Tech to synthetic Mobil 1.





Okay, to the real work – adjusting the valves. The hardest part of the entire job was getting the rear cylinder head cover off the engine from underneath that recalcitrant wiring harness draped across it. The front cover was easier to wiggle off the engine, but the rear one was a challenge. It took me about 5 minutes of fiddling with it to get it out. Once I had access to all the valves, the job was a breeze.

The spec is 0.22mm +/- 0.02mm for the intake valves and 0.30mm +/- 0.02mm for the exhaust valves. That converts roughly to 0.009” and 0.012” respectively. I found all of the intake valves to be either perfect or ever so slightly loose, so I didn’t touch ‘em…any of ‘em. The exhaust valves were all tight, and I expected this. I expected worse, though. The engine was silent like a church mouse, and I was afraid that the valves were…too…quiet. The exhaust valves were pretty consistently dragging about 0.009”, just like the intakes. They need to be 0.012”, so I re-set all of them. I don’t have the special Honda valve adjustment tool, and I find the screwdriver-and-wrench method sort of awkward, especially when you’re reaching across an engine of an SUV (with a taller front fascia).

I found the best method was to crack the lock nuts loose with a 10mm socket, and turn the adjustment screw with my finger and thumb until it just barely trapped the feeler gauge against the top of the valve. I’d then turn the lock nut until first contact, then cinch it down with the 10mm socket. This worked well – it turned the adjustment screw a little tighter and locked the whole works in one motion. The 0.012” feeler gauge would have just a little drag as I moved it. I feel that there’s plenty of room for error here, especially erring on the loose side. They’ll tend to get tight over time, and there’s still plenty of tolerance – anything from 0.010” to 0.014” is okay according to Honda. I actually might have been able to squeeze a 0.010” gauge through many of the exhaust valve gaps before I started, and they’d have barely been within spec. My only concern was making sure the lash wasn’t closed on any of them, and that was far from happening – great news.

Tools used were few – Honda engines are just so easy to service. All I needed was a 10mm socket (which took care of most of it), a 12mm socket (for the intake manifold and throttle body fasteners), a 6mm hex cap screw socket (for the coil pack cap screws), the two feeler gauge sizes, various ratchets and extensions, and pliers for the various vacuum hose clamps. I didn’t replace a single part or gasket during this job. The cylinder head cover seals are very pliable rubber seals – both on the perimeter and sealing the spark plug tubes. No replacement necessary. Likewise, the intake manifold spacer and plenum seals are 3-layer metal seals and it’s just not necessary to replace those. As I was after the timing belt job, I came away very impressed with the quality of material and design, here. Not once did I try to access a fastener to say, “well, THAT’s dumb – I can’t even get to it!” Not once did I break a cheap plastic clip or tear a vacuum line – the clips are durable and many of the “rubber” lines I had to touch are actually silicone in material – and seem to last forever.

Start-to-finish, it took about four working hours. It was a pleasant and enjoyable four hours. I learned a lot about the engine’s design and construction and gained an appreciation for how a lot of this stuff works. I put it all back together and it runs smooth and silent, just like it did before I started.

I look forward to doing all three services at once on our 2009 Ridgeline in the spring – it’s got 99,8xx miles at the moment, and I’ll schedule the plugs, the timing belt, and the valve adjustment for a fair weather Saturday in the spring some time. Parts for the whole service total about $500 from a discount Honda dealer online, and it’s a $1,500-2,000 job if you have a Honda dealer do all three.

Or a very relaxing Saturday out in the garage!
 

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Thank you for sharing this info here. I have an 03 touring package and also put up a post on this forum. My problem with the vehicle is losing power and I just don't know why. However, I was able to get some feedbacks from a mechanic here and he said I might need to do the valves clearance adjustment. My vehicle has 141+K right now, I bought it when it had 83K (plenty of power) but just recently I have noticed a very declined in pick up power. This is especially when the vehicle is at a complete stop, then when I stepped on the gas the car would just drag and takes a while to pick up speed. Very annoying, I was thinking about taking it to a dealership to have it checked out and see if that is the case or it might be something else. What is your take on this?
 

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I just did a valve adjustment today, too. While I was "in the area" I took out my starter, cleaned and lubed it to fix the dreaded "after-start screech". It was just that much easier to get to it with the intake manifold off, and the throttle body out of the way. I didn't have to pull the battery or any hoses - just unbolt the starter and cables, twist it around and pull it out. That would be a little harder with the intake manifold in place, but not at all impossible.

According to the previous owner, the valves and plugs probably hadn't been done previously, and I'm at 170,000 miles! I haven't actually driven anywhere yet, but the starter IS quiet (hooray!) and the engine seems to have a lot more "punch" when goosing the loud pedal.

The job was really fairly easy - didn't have to replace any gaskets because the nice folks at Honda know how to make gaskets! I was also easily able to turn the engine over to find the timing marks using the upper serpentine belt pulley bolt - I couldn't see the marks when I was cranking on the crankshaft pulley bolt. I ended up using a small inspection mirror and a flashlight to verify the cylinder I was on at any given time. I'd recommend doing the front half of the valve adjustment first, as practice for the rear half - a lot of what you do "back there" has to be by feel, and having just done it up front makes it all a lot easier.

Yesterday I swapped out both upsteam (top / pre-cat) O2 sensors (both were really crusty) and the PCV valve. I was getting only about 19mpg on the road, and no better than 14 or so around town, which I considered pretty bad. Hopefully this will give me a reasonable improvement (which would be nice, since I really only invested about five hours (including the starter) and a couple hundred bucks (most of which was for the O2 sensors). The only down side is I really won't be sure which "fixes" made the difference... (I can live with that).
 

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habbyguy, the dragging starter is the next thing on my list for this vehicle. That, and a pre-emptive radiator replacement, and I think it's good to go for another 130k miles. What were your exhaust valve clearances like at 170k miles? Close to no clearance, or did you still have a safe margin?

dali854, you could be down on power if your intake valve clearance is excessive. Too much valve clearance at the top of the valve mean it doesn't get opened as far as it should down in the combustion chamber. The intake valves tend to loosen with time (as the valvetrain wears). This same mechanism works on the exhaust valves, too, but they undergo the additional stress of having the hot exhaust gasses passing over them and the valve seats at the same time. This tends to counteract any valvetrain wear, and the exhaust valves tend to tighten some with use. You want to catch it before it becomes too bad -- if the exhaust valve lash becomes too tight, you can burn an exhaust valve. I suppose that could cause loss of power as well -- bad exhaust valves due to poor valve lash. Lots of variables here.
 

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Hokiefyd, most of my intake valves were at spec or pretty close to it, but virtually all of the exhaust valves were too tight - I'm not sure I could have gotten the 0.2mm feeler into any of them before I adjusted them, and a couple had NO lash at all (I couldn't move the rocker arm even a little). I'd say I was overdue!
 

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All of my exhaust valves were tight as well when I did mine at 157k. Personally, I think this is an important service that most people overlook, but really should be done on the same schedule as the timing belt (i.e., every ~100k miles). It's not that difficult (except for wrestling that rassin-frassin rear valve cover off), just time consuming, but if you take your time and get in the right frame of mind, as hokiefyd suggests, it can be pleasant.

Re: the position marks/cylinder number on the cam: I found lining up the position marks easy enough, but couldn't see the cylinder number, but after lining up the marks, I put my phone down there and snapped a pic of the cylinder number. Not only let me see quite clearly what cylinder I was, it also created a record of which ones I'd done.
 
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