I have the VVT unit(s) tapping on my XJ8 4.0L. It starts about 10seconds after cold start and continues until the engine warms up when it goes off completely. I believe the problem to be sludge build up in the VVT unit internals and have given the engine 2 flushes with engine flush and oil/filter changes (5W30 semi synthetic)~no success.
I read somewhere a while back that someone had pressure cleaned VVT units in situ by removing the solenoids and blowing a cleaning agent thro under pressure.
Does anyone have any experience of this? Any help appreciated. Charlie.
Are you sure it is the vvt unit? Rattle on startup is also associated with tensioner failure in 4.0 ‘s
What makes me think its VVT is that the noise appears after 10 secs and continues until the engine is fully warmed up then goes off. Thought that if it was tensioners the noise would persist. However have it in mind to change the top tensioners anyway. Rgds
If the tensioners have not been replaced I would do it immediately and then worry about the vvt if the noise is still there. Ihad a tensioner go on an s=type and it is NOT PRETTY. It will destroy the engine. My understanding is that a rattle on startup is pretty common with tensioners but mine had no warning signs at all.
Just about getting round to taking the VC’s off and checking. What happened in your case then? Did the engine simply go bang as you were going down the Motorway?. Rgds.
If the tensioners go the valves are no longer timed. The jag v8 is an interference engine so you get a lot of banging and crashing and bent valves and damaged pistons. Requires a total rebuild. There was no warning with mine. It just self destructed.
There is no point responding to this thread until it is determined if the engine is AJ26 or AJ27!
They are VERY different engines and we can ‘maybe-this-or-maybe-that’ until the end of time!!!
(I hate mystery cars)
Car first registered Jan 2000. Engine no
LC0001140450. Believe it to be an LC27. Hope i’m right.
Should be AJ27…Typo.