XJ XJ8 / XJR ( X308 ) 1997 - 2003

Rough running engine

Old 11-30-2010, 10:27 PM
Join Date: May 2010
Location: Lockhart, Texas
Posts: 48
Received 1 Like on 1 Post
Default Rough running motor

Ok. Well, I had put some chemical into the intake and the motor actually sort of smoothed out enough to idle. Rough idle, but not like it was. I drove it around and, without the A/C going, wasn't too bad, but wasn't real good either. With A/C going, fa-get-aboud-it! Anyway, I decided to take it to Autozone to get the codes read. On the way there, it quit on me and wouldn't run again. Got it back home and removed the spark plugs. One of them was trashed.

An intake valve broke and trashed the head and the piston. (Probably the rod and bearings, too, but don't really know about that)

Got the head off and found out that the reason the other valves that were not seating were because the intake valve seats were floated. Ever heard of the valve seats coming loose? My speculation is that the valve seat on the trashed valve floated enough to hammer the piston, which in turn started bending the valve stem, which broke, and the stem punched holes in the head and the piston before being embedded into the head (at the wrong place).

I recently found a long block for not a whole lot of money, so I am going to put in this engine. I have checked the pistons with the bore scope and have found no irregular (to me) marks on the pistons, but I may just pull the heads off, anyway and have them refurbished, especially after seeing the floated valve seats on the engine in the car. It is a 1998, but I am hoping it will swap right in, despite the position of the VVT(?) sensors being in the front of the head instead of the top.
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