787 engine failure diagnosis

[THUNDERPIMP]

MAG piston has a nice big seize for it's entire length. ugly.

the big end of the rod is discolored like i tgot REAL hot.

i can't tell the difference between water damage, and lack of lube, one of which would be my guess....

what makes the rod cook itself like that? lack of lube? when my oil pump feed went, i had only a light seize... ( i shut down immediately and didn't run again, these guys kept running it till it wouldn't run again...)

anyway i'd like to figure out why it died before i rebuild it. i think that's a good idea:)

greg

[ February 20, 2003, 08:14 AM: Message edited by: Technical Support ]

[Technical Support]

Seeing the other sides and the underside, along with the bearings would help in diagnosys.

[Bill O'Neal]

Most likely, one of two or three things happened here.

Either there is a problem with the oil feed to that clyinder or the clyinder just ran too lean.

Check the oil lines for cracks and check the injector for a stuck check valve that wouldn't let oil past it.

If you do not find anything wrong with the oil injection, start looking at the carbs. A siezure like this can be caused by a clogged up internal fuel filter. Actually it would be foolish to rebuild this motor without checking the carbs anyway.
Another possible culprit is an air leak. Check the manifold for cracks. Check to see if all the bolts are tight on the carbs and rotary valve cover. Check the RV cover oring to see if it was pinched.

The rod got hot because the piston got hot enough to melt aluminum, which is totally normal when a piston is siezed badly. You need to get a rebuilt crankshaft.

If it were damaged from water injestion, it would have vertical lines on the skirt and show no signs of overheating. The rod would not be blued from heat.

[THUNDERPIMP]

bill,

are the check valves on the orifices that are pressed into the intake manifold?

how can i test the oil pump?

i will certainly go through the carbs, and everything else.

greg

[THUNDERPIMP]

PS techsupport or whoever, thanks for importing that photo.

this forum is slick.

greg

[Bill O'Neal]

Yes, those brass things in the intake manifold are the injector nozzels and it has a check valve that should pop open if you put 1.5psi pressure into the line.
To check an oil injector, run it in a drill in reverse rotation. Small dribbles of oil should come from both of the brass oil line fittings on the pump. Make sure the pump is primed, bled and has oil going to it.
I'd check the carbs first. You may just have a very commonly clogged up internal filter or a stuck needle and seat......

[ February 20, 2003, 08:37 PM: Message edited by: Bill O'Neal ]