5.3l Valve Seat

steve summers · February 10, 2008

Thought I would post this up for an opinion.

I have an'05 GMC Sierra with 66K miles on it. A week ago it popped a flashing CEL while driving on the highway. It would alternate between flashing and steady depending on engine load. Based on the manual information it sounded like it may have been bad gas since I had just filled up. I checked the gas cap, and continued to drive the truck as it was running just fine and the manual lead me to believe it may be gas related. later in the week it started running very rough at idle but still seemd to run OK at normal speeds. I took the truck to a trusted independent shop for diagnosis. They said it showed cylinders 1 and 3 misfire. They checked the coil packs, plugs and injectors, all were fine, then they ran a compression test on cylinder 1, it was good, then cylinder 3, no compression.....

They pulled the vavle cover to see what they might find, nothing noticable, then they pulled the rocker arms and found the intake valve for cylinder 3 is sitting higher than the other vavles. They did a pressure test on #3 and it held air, then they put the rocker back on and it didn't. Their diagnosis is that the valve seat has pulled into the head. At this point I had them button it back up, I called GM Customer Sat, and took the truck to a GMC Dealer. They are going to tear it down and inspect the damage.

So in my mind I think this is a manufacturing flaw as I can see no reason the valve seat would pull into the head like that unless it wasn't installed properly in the first place. I've searched and this doesn't seem to be a known problem with these motors. Have any of you techs seen this before? Is there anything else that could have caused this?

Thanks

jefferias · February 10, 2008

i'd say either bad seat nest in cylinder casting or the seat itself was flawed. i work in a head shop and its hard to put a valve seat in wrong. could be non-concentric mating surfaces of where the valve face actaully contacts the seat face and slow wear cause vavle to stick or wedge in. just my 2 cents

steve summers · February 12, 2008

i'd say either bad seat nest in cylinder casting or the seat itself was flawed. i work in a head shop and its hard to put a valve seat in wrong. could be non-concentric mating surfaces of where the valve face actaully contacts the seat face and slow wear cause vavle to stick or wedge in. just my 2 cents

Thanks, just an update the GMC Dealer took the head off and confirmed the diagnosis, it seems the valve seat has "dropped".

It's going to be interesting to see how this plays out, in my mind this should all be on GM for the repair, I suspect my expectations won't be met.

KB06YUKONXL · February 12, 2008

Sounds like a casting flaw to me. They should replace the cyl head to be certain. If the seat were flawed it still shouldn't be able to drop if the cyl head is at spec.

steve summers · February 15, 2008

They have confirmed that there is an issue with the valve seat. Their solution is to send the head out to a machine shop for repairs. I'm a little concerned that I have no idea if I have at least 2-7 other seats to do the same thing at a minimum, and the other head could be suspect as well. At this time the dealer is offering a 50/50 split which is better than nothing, but my expectation would be 0 out of pocket for a manufacturing defect.

We will see how it plays out.