Acura/Honda 3.5

[ak diesel driver]

So I decided to start a thread on this engine in my wife's car. It's a 2004 Acura MDX. I originally paid $700 for it and had to fix the engine with a burned valve. That was about 3 years ago and 80-100k miles ago. Well here I am again with a burned valve, interestingly enough it's the same cylinder.
So part of the reason I'm posting this is I'm looking for ideas as to why the same cylinder. Someone suggested possibly a slightly out of spec injector, which has some merit in my mind. It would have to be pretty small difference to last 100k.
Also before I broke the head bolts loose I dropped the exhaust and about a cup of antifreeze came out of the pipe. Currently head is at a shop being pressure tested. No obvious cracks to be seen and it wasn't using antifreeze before either. Kind of a head scratcher for me.

 

[ak diesel driver]

So here's the original burned valve

 

[Rockabillyrat]

The 3.5 are somewhat common for the valves to become too tight and cause issues with burnt valves. Honda guys say to adjust them every 30k. I've had a few come in that needed adjustment to fix a misfire. But the fact that its on the same cylinder is kinda odd thought.

Honda builds great engines, and the 3.5 is another example of that. I hardly do anything to them other than timing belts and tune ups. I told my wife she could have any car she wanted as long as it was a Honda/Acura lol. In my opinion they are hands down the best cars out there.

 

[ak diesel driver]

I did check the lash just before and that cylinder was slightly tight but just barely. I wonder if that side tucked under the firewall runs hotter and needs more?

 

[MrMarty51]

When grinding the seat and getting a new valve ready to go.
Forcefully slam the valve into the seat then look at the black ring created on the seating area of the valve. Using a flatter stone, grind the outside of the seat just a little to narrow it down.
Wipe off the black ring and slam the valve into the seat some more:
Look at the black ring and see where it now is located.
Grind the outside of the seat until that black ring is over half way between the middle of the valve seating area and the very inside of the seating area.
That will keep more of the heat to a thicker portion of the valve seating area.

 

[ak diesel driver]

So here's the offending valve. I'm kinda wondering if there was some carbon build up between the valve and the seat. There was/is quite a bit more carbon in that cylinder. Hard to tell how much is from when it started running poorly though.
This picture of the valve seats was after I scraped it fairly clean

 

[ak diesel driver]

Here's the one next to it

 

[Will L.]

Lets see the cylinder wall...

 

[ak diesel driver]

Already showed that earlier. Looks okay

 

[Rockabillyrat]

How do the EGR ports look? I've seen all but one port clog up causing all the EGR to flow into one cylinder.

 

[ak diesel driver]

I'll have to check. Do you remember how many there are?

 

[Rockabillyrat]

If I remember correctly there is one for each cylinder built into the intake manifold.

 

[ak diesel driver]

So there is 6 holes on the top of the runners but as far as I can tell they're sealed by the lid and gasket.
At the throttle body end is where the EGR comes in and there's a diverter there that splits it in two, one for each side. It appears to just go into the main runners before breaking down to individual runners.

 

[Rockabillyrat]

They look clean in the picture. Always worth a check while you have it apart!

 

[ak diesel driver]

So I guess my system must be different than others. Watched a few vids and a lot of others had channels in the lid to direct flow into those holes my lid has none. Just a contained area with a gasket all the way around the holes so essentially a dead area.

 

[dbrannon79]

looking at the pitting on the other valve seating area, how are the other valves? wonder if this is from the ethanol that's in the gas nowadays. or something causing too hot of a burn like you mentioned, an injector not atomizing and squirting a stream of fuel directly to that area in the cylinder.

an easy test on the injectors you can leave them in the fuel rail, they should have a keeper to hold them in place. let the fuel pump run and then connect 12v + and touch the neg momentarily to make them pulse one by one watching the spray pattern.

 

[ak diesel driver]

So just an update , I was hoping to get my parts while I had a lull in my work schedule but not so. By the time I got my parts I was pretty busy. So only managed to get in a couple of hours at a time. Finished it up this evening, glad to have my hoist back for other maintenance items.