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Sorry it took so long. My machinist wanted to be there on tear down. Any insight would be appreciated.
same thing happened, rings started to seize into the pistons again, but I caught it at the beginning stages. We took rings out of 2 pistons and checked the bores, does not look like the ring ends touched. Gap was 16 top-18 bottom on the ones we checked, but just like last time we had failure, and debris in the ring lands which caused them to stick. Will need to rehone bore. I’m still at a loss, will be re-ringing, new pistons (old out of a 99), rehone, and trying one more time. We will use Mazda rings like the last go round. Any ideas??
There is a lot of carbon on the piston crown. Is there a chance your running so rich that raw fuel is washing the oil off of the piston skirt/bore. There is too much wear on the piston skirts. How does the crank look? What about the oil?
There is a lot of carbon on the piston crown. Is there a chance your running so rich that raw fuel is washing the oil off of the piston skirt/bore. There is too much wear on the piston skirts. How does the crank look? What about the oil?
Good point. I still maintain it’s something in the tune, not the physical build of the short block.
I am entertaining tune, but I ran 500 or so miles before failure but I’m questioning everything now so I’m not sure. I also was thinking maybe blow by would cause excessive carbon. I know enough to feel comfortable with my tuning ability to keep it right enough to get miles on before I brought it to a tuner I trusted. Failure also came as I introduced boost. I did go expected slightly rich in boost cells, then pulled it down, but not anything excessive.
crank is fine, bearings fine, not perfect, but useable, oil was as expected with the wear on rings.
I am entertaining tune, but I ran 500 or so miles before failure but I’m questioning everything now so I’m not sure. I also was thinking maybe blow by would cause excessive carbon. I know enough to feel comfortable with my tuning ability to keep it right enough to get miles on before I brought it to a tuner I trusted. Failure also came as I introduced boost. I did go expected slightly rich in boost cells, then pulled it down, but not anything excessive.
crank is fine, bearings fine, not perfect, but useable, oil was as expected with the wear on rings.
Well I guess I should have specified; something wrong with the boost tune, since that’s always when things go belly up.
How did you determine this build was failing, eg low compression, knocking etc? On this build what components did you reuse from the first? Did you measure the bores on the first build after it failed?
New block on that motor, honed. Rods, bearings I reused as they were fair, and they are still usable, but may replace at this point. Pistons were out of a ‘99. New rings. Pic below of that build.
low compression after seeing slight smoke on a short ride, figured it out quick as been here before. Also afr’s started to get jumpy on idle, seen that before, so instead of working on tune I checked mechanical.
Vapor honed, after the same issue with my forged pistons, I ran out of money. It is what it is. I’m not looking to replace my 2560, no need to go forged.
I don't believe the rings were the root cause. The first build could have been caused by oil wash down and oil dilution combined with too small of a piston to wall clearance. The second eng looks like it was from contamination and oil wash down. Vapor honing is bead blasting. The oil wash down is a tuning issue. The contamination is mostly likely from parts that were reused and in an accelerated state of failure.
I have seen people reuse heads without cleaning out the oil galleries. The result was the head started to wear quickly which sent a substantial amount of metal through out the system. The same can happen with the oil pump. The oil contamination shows on the piston skirts early since they get a fair amount of unfiltered oil from the sump via windage. The pressurized oiled components receive filtered oil and can fair better then the others . The oil pump is a special case which is lubed by dirty oil and that is why an oil pump from a failure should never be reused. The pistons could have been cleaned up with a nylon brush and soapy water by hand. I will often use a wire brush on the crowns if the carbon is very hard.
I am entertaining tune, but I ran 500 or so miles before failure but I’m questioning everything now so I’m not sure. I also was thinking maybe blow by would cause excessive carbon. I know enough to feel comfortable with my tuning ability to keep it right enough to get miles on before I brought it to a tuner I trusted. Failure also came as I introduced boost. I did go expected slightly rich in boost cells, then pulled it down, but not anything excessive.
It might be helpful for you to quantify the AFR statement (give actual values or post a log). Also, what was the procedure you used to verify or calibrate the AFR readings. Qualitative information does not give people anything to really evaluate.
Here is my tune. . . don't beat me up to bad, it was on it's way to the tuner this last motor, but fail . . . I thought I was confident enough to get miles on it before the tuner had his way, but alas I can't build a motor that will stay together so I'll take the abuse.. . . lol.
This map is when my idle afr’s started to fluctuate because of ring failure. Before that idle wanted to stay at 13-13.5 afr. My weakness has always been tuning. I know enough to get me by, but not near enough.
Did you install the pistons wet or dry? I doubt a dry install would be the cause of a failure, but I'm curious. I agree with LeoNA with all his points. That looks the engine was being flooded with fuel and washed the cylinders. I suggest never getting into boost until after you have it tuned or you at least have tuned a nearly perfect NA tune yourself.
We typically put a small amount of oil on the skirts. From my research and experience both ways are acceptable or practiced. I’ll def be looking at tune on startup and bring it back to a tuner for boost. Thanks all.
It might be helpful for you to quantify the AFR statement (give actual values or post a log). Also, what was the procedure you used to verify or calibrate the AFR readings. Qualitative information does not give people anything to really evaluate.
DNM
The above question remains unanswered. If you are tuning to a mis-calibrated AFR reading, then no amount of tuning, even if done well, will give good results.
Actually, I don't need an answer, I'm just suggesting you consider the question.
I would also suggest you put your over-boost safety cut to about 105kPa, rather than 205kPa; just to be certain you don't repeat.
I did put a new sensor in before I put the new head in. It registered about .5 off vs mspnp. I adjusted my ms map to confirm as I couldn’t figure out how to calibrate it. I’ll do some research on making sure It’s calibrated and reading properly again.
I’ll get going on getting it together, then turn my attention to tune. It seems everything is pointing to my lack of understanding with tuning. I’ll have to spend some effort there.
10-27-2020, 05:35 PM
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