Oil consumption - Keith Black Hypereutectic Piston

[MGD72Monte]

I ran with Keith Black hyper pistons and didn't like them. They have rings situated higher than usual, and require big ring gaps. My machinist thought he knew better than to read the instructions, and gapped them as normal...they tore up my cylinder walls. Even after a re-hone and re-ring job, they were poor at oil control.

 

My new engine has Mahle pistons with low friction rings, which were recommended as an upgrade by my builder. They weren't cheap, but good for 40hp with the same compression ratio. It's hard to find 40hp with any single upgrade. A bonus is better mileage and quicker reving with the low friction rings and lighter pistons. I have no complaints.

 

I saw the above in a separate thread which sparked my interest so I stole it to explore further.

 

I put in Keith Black pistons as well and had oil consumption issues. After a couple of thousand miles I took the engine apart, thinking I had messed up. I found nothing wrong but for good measure I had a different machine shop look at the bore work and re-hone. I added a better baffle to the valve cover, changed valve guide seals from umbrella type to the stock GM seals, put new rings in, and had a tune up done on a tuning dyno. I still have the same consumption issue (approx. 1 QT/800 miles). The only time I actually see smoke seems to be after acceleration, when I take my foot off the throttle, and mostly from the pax side exhaust. I`ve thought of doing tests (leak down, pressure, etc...) but after a double rebuild I have not been overly motivated to dig into it further and it works fine other than that.

 

Anyone else with Keith Blacks with this problem? Any other thoughts? Thanks

[Mike 57]

Higher oil consumption is normal on a rebuild until the rings fully seat. What ring package are you running? Are they 5/64, 1/16 molly faced, cast or gapless? I hope you are running standard tension oil rings. Do you know if the block was honed with torque plates, what stones were used for the hone, and was it plateau honed?

I have done a couple of engines with the KB pistons and had no issues.

[MGD72Monte]

Thanks Mike, I know oil consumption is higher initially and on the first build it was about 1 QT every 100 miles then went down to what I have now (1 QT/800 miles) and after a few thousand miles on both builds, there is no furher improvement.

 

I don't have access to my records here, what I do remember is that the block was honed with torque plates and it was decked (0.010 I believe), the rings on the first build were molly rings gapped to the recommendations that came with the KB pistons. I think we went with cast the second time to see if that would make a difference but I'll have to check. Oil rings are standard type.

 

Complicating factor: the problem may be due to the carb running way rich until I got it on the tuning dyno only after the second build and realized I had to drop the main jets down but by then the motor had run for a few miles during break in and driving to the garage. Some have said that that was enough for the rings not to break in properly and it might burn oil for the rest of its life, not sure. I just don't feel like trying a third rebuild so thought it might be nice to have someone say that this is normal with KBs.

 

Thanks