Last week my 2004 D2 with 168k miles developed a #6 misfire and a rattling noise. Took it to my LR shop and they checked spark/fuel which was all good. 2 compression tests showed good values except for #6. They think that it's the rings on #6. The shop indicated that they would have to pull the motor to re-ring #6 which puzzled me. They even suggested replacing the motor which seems a bit severe although I do have access to two low mileage motors in great shape if needed.

Wouldn't an alternative approach to be to pull the valve covers/inspect, then pull the heads/inspect and then pull the piston (after unbolting the oil pan and connecting rods) through the top and then work on or replace the piston? I don't have this kind of engine experience so I'm asking you all if my "in the truck" piston repair/replace approach is doable and if there are any pitfalls doing it this way.

Thanks as always for your great advice and help.

 

It's probably got a flat cam lobe.

 

Thank you for the feedback. How does a flat cam lobe happen?

 

good news is you can replace the cam with the motor in. not pretty but very doable. ac condenser is the biggest hurdle to carefully bend out of the way.

 

I agree much more likely a valve train issue. You need a different mechanic. A good mechanic would have run a leakdown test which would have identified whether the lack of compression was from ring leakage, intake valve, exhaust valve, or none. Bad cam lobe is a common thing, usually due to stuck lifter or an oil pressure issue. Valve train or cam lobe issue can be diagnosed with removal of the upper intake and valve cover.

 

Thank you for all of your responses. My shop did perform 2 leakdown tests and concluded that it was a piston ring issue as Extinct pointed out.

My question is, can't the piston be re-ringed with the motor in the truck as I outlined in my original post?

Honestly, my concern is that this project could become a slippery slope and I might be better off installing the late 03 motor with 92k miles that I can obtain.

 

Not sure what shop you are at but most won’t do what you are asking if they will warranty the work or for insurance reasons. How does the cylinder wall look on #6? There also could be more damage hiding in other areas. Your best bet might be to install a known good engine as you
mentioned.

 

You make a good point regarding "discovering" other issues beyond the #6 piston. We don't want to back into a rebuild. Working on details regarding the 03 motor with 92k miles to verify service history, etc.

 

I tend to agree with the others. If a leakdown test was performed and it was a blowby past the piston issue on #6 I doubt it is only a piston ring, it likely has damaged the cylinder liner as well. It is possible to borescope the cylinder and you might be able to see something but maybe not. You can do a re-ring with the engine in the truck but my concern woudl be you pay to have them remove the heads and then you find out the cylinder is knackered. Not sure of the cost of the 92k 03 motor, but if the cylinder is not bad on the existing motor a quick re-ring and bearing job with new HG should be only about 4-8 hrs once the engine is out.

 

Everyone's feedback has been very helpful. My gut tells me that, while anything can be fixed, trying to make the current motor work is probably wasted effort.

The 03 motor is in a front end damaged truck that has ben written off by the dealer and I only need to pay for the transport to my shop. Seems like it might be the most cost efficient way to go at this point.

I'll keep you updated as we carefully proceed.