Hello All,

I've owned since new a 2006 Honda Accord 2.4L (K24A8) sedan 180,000 highway mi., always Mobil 1 synthetic oil every 5-7K. Started excessive oil use around 70K, now using 2 Qt every 500 mi. The cam chain jumped several teeth at 160k and bent 4 intake valves. Had head professional rebuilt, new seals, bent valves replaced, all valves and seats reground, head checked and machined, valve clearances set to spec. After reassembly, oil use continued, thus planned to replace piston rings (assumed stuck or poor sealing oil control rings) in the Spring. Recently while traveling on the interstate the engine lost compression on #3. Pulled head and found 1 burnt exhaust valve, not sure why (approx. 20K on head rebuild). Recently pulled pistons (removed oil pan while still in vehicle), all rings appear to be free in their grooves, oil rings are expanded slightly beyond piston surface and can see light thru drain holes in oil grooves. Cylinder walls look fine and all bore gauge dimensions are well within service limits per Honda service manual. Pistons measure within service limits as well, though one is at the lower end. Black wear area on piston skirts have mid and lower areas worn thru but some of the black remains. (see images)

I'm hoping to get another 50-100K out of the car which will be used by my 15 year old daughter. To keep the budget down, I was thinking i'll thoroughly clean the pistons and re-ring with new NPR brand rings (Honda motors can go many hundreds of thousands without rebuild). I considered replacing the pistons with reasonably priced Evergreen brand made in Taiwan. However, thought I'd stay with my orig. Honda, new Honda too pricey. I'll leave the block as-is, Honda service manual states not to hone cylinder walls unless scratched. As for the head, I'll have the engine shop replace the burnt valve. The rod bearing seem to be in good shape, I'm considering re-using these.

Does anyone have any comments or insight on my plan of action or why the motor uses so much oil? Burnt valve? Reuse rod bearings?

Any sound advice for this shade-tree mechanic would be greatly appreciated.

 

Seat on that valve does not look like is has built up carbon. Cheap valves? I have seen several cases of high oil consumption burning valves as the carbon builds up and the valve can no longer seat.

Very likely if you are burning that much oil the catalytic converter has long ago melted and plugged up. Possible high EGTs lead to the burned valve.

How is the vehicle driven? Does it get the throttle mashed the floor often or is it a gentle never sees north of 3,000 rpm part throttle kind of ride?

 

Thank you for the reply. The exhaust valves are OEM Honda (original with the car). The engine shop who rebuilt the head is pretty reputable and looked things over pretty closely during the process. My research agrees with you, oil consumption can cause detonation and deposits, both can cause a burnt exhaust valve. The Catalytic Converter is not plugged presently the power seamed fine, no sulfur odor, however did recently throw a CEL code "...efficiency below threshold.." Oxycat added to fuel system cleared this briefly. I assume cat. is failing due to fouling and possibly heat. I will likely remove (not fun, torch rqd.) and based on appearance either attempt to clean, buy aftermarket or try a "test pipe" (honda gets over $1000 for new cats.)
The car was adult driven mostly highway miles, throttle to the floor only periodically for passing other vehicles, no teenage drivers.

As I look at the parts during cleaning, the excessive oil use issue still has me baffled. No stuck or broken rings, no cracked lands, no plugged oil drain holes in oil control ring grooves, cylinder bores look good. Valve seals replaced, head gasket replaced. PCV valve replaced, no external leaks. Having 180K miles I could rationalize using 1 qt. per 1000 mi. (Honda's official max. for "normal" oil consumption) but I'm seeing 5 times that number. At this time, I think I'll have to go with just poor sealing of piston rings to the cylinder wall.

I'm thinking my other issues are all symptoms of excessive oil use.

 

Measure the bores, guessing they are ovalized, oil control ring gaps, are they with in spec, were all oem parts used, including valve stem seals?

 

Looking at the piston you pictured, it does not look like oil is coming up from the bottom. Typically when oil is getting past the rings, you get the staining and build up between rings on the ring land part of the piston. The piston looks clean from the oil ring on up.

Do the other 3 pistons look the same? If so, I would believe your oil is coming from the head. Like, guide seals were forgotten to be installed before assembly sort of thing.