Failed piston coating?

City
reno
State
nv
#1
Blueprinted 4.6 stroker built 7 years ago. Recently a serious and random tap tap tap from somewhere inside. Compression test shows very bad on cyl 5 & 6. Oil analysis shows high level of aluminum and babbit material. So..... out she comes. Ugh. Major kluster eff. Anyone ever hear of Teflon coated pistons fail due to coating wear off?
 

cbford

Legacy Registered User
City
CLT
State
NC
#2
Yes, that is a thing. Usually it is heat that causes the problem. Skirt rubs, teflon gone, galls up piston and cylinder wall. Most common with oiling problem. Also can come from a slightly out of round bore job, or an slightly over-clearance rod journal.
Did they use long or short rods in your stroker? Makes a difference in side load on pistons.....
 

mysunnshine

Legacy Registered User
City
Phoenix
State
AZ
#3
I'd vote for initial piston to cylinder wall clearance issues combined with the long stroke rocking the piston in the bore.
 
City
reno
State
nv
#4
Long rods from the failed original 258. 96 4.0 donor. 258 grind. The old blue smoker lasted a long time then stab in a new modern (lament OBD 1limitations) $dd mill then .....it takes a dive. FML.
Suffered blow by out oil filler and around dizzy.
Then just before on rubicon suffered a broken frame. These flimsy frames must be from harbor freight, lol.
Grinding then welding up in the rain at observation point.
 

Attachments

City
reno
State
nv
#6
Oiling problem? School me here please. It’s always run with correct pressure, regular changes and no leaks. There are some things I know and others no clue. This issue is the latter.

Tnx in advance.
 

93_Fummins

CJ-8 Member
CJ-8.com Member
City
Edmond
State
OK
#7
I'm not familiar enough with the 4.0/4.2 oil paths to say one way or another, but bearing failure and piston galling are generally an oil issue in my experience. Sensor pressure is tricky because it just means there is enough restriction in the galley you are plumbed to for the pump to float the regulator. However, the regulator can mask slight loss in a pathway if the loss is still less than the difference in pump volume and regulator setpoint. The flip side is blockage; the regulator and pressure sensor will generally not give you any sign that a galley is blocked if it's on the downstream side of the sensor port. For example, if your sensor is in the middle of your oil galley (assuming all branches parallel) and the 5 and 6 main/rod journal paths are blocked and not receiving nor losing oil, the sensor will still show perfect pressure, if not slightly higher pressure due to overall leakage being less than normal. Not saying this was the case in your instance, but excessive bearing material in oil is either poor oiling or significant trash in the system. Tolerances of bearings during assembly could be culprit too, but I'm going to assume it was built correctly for argument sake. Galling of pistons is generally poor fitment (either because of heat, or causing heat) or lack of lubrication. Teflon helps, but it only reduces friction and doesn't necessarily help the heat cycle expansion tolerance which could be the greater issue if not fitted properly.

Take all of this with a grain of salt because I am NOT an engine builder; just a snotty kid with a Mech Eng degree who thinks he knows everything. The only way to really know what happened is to tear it down and do proper root cause analysis. I just like to speculate in the meantime to see if I still have any brain wrinkles.
 
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