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The installed pistons were after market Sealed Power.
Where did you buy them from? If eBay, good chance you bought garbage counterfeits.
I've even read of shady things from major parts suppliers when it comes to Chinese knock-offs.
The installed pistons were after market Sealed Power.
They list the minimum spec as .001, the shop did the measurements and installed the core plugs and oil galley plugs.
The shop cleaned the bores and lightly oiled them ready for piston install.
So I wiped them down and then oiled the cylinders as part of the piston install.
I did check that the pistons moved freely on the wrist pins. No binding.
I called Federal-Mogul and they said it was caused by either a;
1 - Dirty build, the shop confirmed they washed the bores down with hot soapy water.
2 - Tolerance to tight, I don't have the right bore gauges to check, and it may be to late with the wear right now. Maybe I need to buy a bore gauge set. Any recommendations?
3 - Bore out of round, again the shop measured and I done have a accurate enough tool.
4 - Running to rich and fuel washing down the cylinders. It didn't feel like it was running rich. O2 and computer controlled, also did not smell rich at all. I don't think it is this.
I am starting to think about removing a variable or two and going to a different shop and getting some bore gauges and doing my own verification of clean cylinders.
Ken
Unfortunately, the area where you need to measure the piston size is now destroyed. You will not be able to ever determine the piston to wall clearance, when it was assembled, at this point in time.
The undamaged bore in that one cylinder looks very well done. Textbook cross hatch and appearance.
Is the damage worse on the rear most cylinder and the least on the front cylinder?
How about a picture of the piston skirt....might be more clues there.
I figured the part I needed to measure was now destroyed.
The front #1 cylinder has the most damage. The 6 and then maybe 4. A little bit on 2 and #3 looks almost perfect. 5 is just barely scratched.
I'll attach a picture of the #1 piston when I pull the motor and get pulled apart.
Pictures would be nice. Do measure the cylinder and piston being less scratched. I strongly believe the piston to cylinder clearance was too tight.
Åke
So I got it apart and found that piston 1 wrist pin it tight and not moving well. That is part of the problem for cylinder 1. It was lubed and felt free before assembly. I checked them all.
There were even a few chunks out of the rt side skirt.
The other troubling problem is that almost all of the pistons had scoring or spots on the skirt sides.
Piston 2 left side, right side was similar.
Piston 3
Piston 4
Piston 5
Piston 6
The shop assembled the rods to the pistons.
So is this from not cleaning the bores prior to assembly, the shop said they cleaned the bores and it was ready to build.
In a way this is useful. Measure the bores and piston dimensions of the cylinders that show light scoring. It is likely that the same problem exists across the board, IMHO, although it may vary in extent from cylinder to cylinder, so these measurements should reveal improper clearances if that is the case. Again, IMHO, this has nothing to do with contamination - foreign matter in the cylinder - but massive overheating caused by too tight tolerances (or possibly a lubrication problem - I have seen a large number of air-cooled motorcycle piston seizures that look like #1 caused by bad or no oil), as a number of folks have already opined. If that is the case, of course, the next questions are how and why.
I have seen folks get tripped up because piston to wall clearances were specified such that you have to multiply the stated clearance by the diameter of the piston. Just a thought.
Had a 944 Turbo that scored the walls like this. Found the builder had actually put in a little smaller pistons because he thought a little more gap would be freer revving. Never got hot. Noticed the scoring when tore it down because improper head fastener torquing let the head lift and burn a hole in the O-ringed head gasket at 4000 miles.
Well, the engine is up and running again. It probably only has around 300 miles on it so far.
And of course this is on a Jeep 4.0 engine, but the lessons I learned here should apply to any engine rebuild. I have been looking at some Cayennes that may have a similar scoring issue. But that is probably from being to tight.
The consensus of opinion and what I believed to be the potential causes were tolerances to tight and or cylinder walls being dirty.
I did buy a micrometer and bore dial gauge to verify piston to wall clearances.
Before the last shop work, I checked the clearances. The cylinders and pistons did have some wear on them that probably affected the measurements. I measured based on what the piston size should have been. The pistons should have measured from 3.9134 - 3.914, The most worn piston was at 3.9 in. The others were all real close to spec. I am also very new to using a bore gauge and there may be a little bit of an art to it. But I was getting repeatable results.
The piston manufacturer specs for clearance was .001 to .0015. Even on the scored cylinder walls, I was getting some readings that were less than the .001 spec. The smallest reading I got was .0004, but only one or two and in line with the wrist pin.
I went back to the same shop and told them I did have some tight clearances and that I wanted it bored a little to the big side. To go to the .0015 end of the spec.
When we got it back the clearance went from a low of .0011 to .002, so not exactly what I wanted but not too tight.
Next, I had probably not cleaned the cylinders well enough. The shop did not seem to think that I needed to clean the cylinders, they cleaned the block before I picked it up.
So this time we washed the cylinders down with hot soapy water to start and then started to check with ATF wipedowns to see if the bore was clean. We were coming away with dirt (grinding abrasives or cylinder material?) so we continued to clean until nothing was coming away on cloths.
It is running good right now so we are hoping that buy cleaning the cylinders and the pistons prior to assembly ourselves, and having the tolerances a little on the loose side will have this motor running for > 100,000 miles.
Well, the engine is up and running again. It probably only has around 300 miles on it so far.
And of course this is on a Jeep 4.0 engine, but the lessons I learned here should apply to any engine rebuild. I have been looking at some Cayennes that may have a similar scoring issue. But that is probably from being to tight.
The consensus of opinion and what I believed to be the potential causes were tolerances to tight and or cylinder walls being dirty.
I did buy a micrometer and bore dial gauge to verify piston to wall clearances.
Before the last shop work, I checked the clearances. The cylinders and pistons did have some wear on them that probably affected the measurements. I measured based on what the piston size should have been. The pistons should have measured from 3.9134 - 3.914, The most worn piston was at 3.9 in. The others were all real close to spec. I am also very new to using a bore gauge and there may be a little bit of an art to it. But I was getting repeatable results.
The piston manufacturer specs for clearance was .001 to .0015. Even on the scored cylinder walls, I was getting some readings that were less than the .001 spec. The smallest reading I got was .0004, but only one or two and in line with the wrist pin.
I went back to the same shop and told them I did have some tight clearances and that I wanted it bored a little to the big side. To go to the .0015 end of the spec.
When we got it back the clearance went from a low of .0011 to .002, so not exactly what I wanted but not too tight.
Next, I had probably not cleaned the cylinders well enough. The shop did not seem to think that I needed to clean the cylinders, they cleaned the block before I picked it up.
So this time we washed the cylinders down with hot soapy water to start and then started to check with ATF wipedowns to see if the bore was clean. We were coming away with dirt (grinding abrasives or cylinder material?) so we continued to clean until nothing was coming away on cloths.
It is running good right now so we are hoping that buy cleaning the cylinders and the pistons prior to assembly ourselves, and having the tolerances a little on the loose side will have this motor running for > 100,000 miles.
Ken
89 GT
Ken, thanks for closing the loop. I was really interested to understand the cause of your scoring problem, as I suspect I will soon have to perform a similar repair on my wife's Celica (and was hoping to avoid the same fate).
02-20-2017, 09:03 PM
