Valves staying open

[BlueyXJ99]

1999 XJ. New head, new valve train, new timing gears and chain. My problem is at TDC (compression stroke) both of the valves are open. It almost seem like when I torque the rockers down 19ft lbs., the valves tend to stay open. Almost like the lifter(cam followers) are not compressing. I've cycled through each cylinder and used a borescope on each one. None of them are fully closing. What could be the issue. Maybe I'm doing the timing gear wrong. Lined up the two marks on TDC Cylinder 1. Anyone have steps on installing the timing gear correctly? New to XJs. TIA

 

[techno]

Check the timing again. You may have the camshaft timing off by 180* or you are checking the wrong cylinder. At a certain position close to TDC both the intake and exhaust valves are open especially on larger cams that have huge overlap. These are the cams that don't like low RPM idle.

 

[Anak]

Certainly sounds like the cam is not timed correctly.

I would degree it. That would be the surest path.

 

[ChillyB]

YouTube guy had same problem. Was a defective cam. Did you put in a new cam?

Most likely is improper timing but if that checks out then might want to find that video. Look up Dex XJ videos.

 

[techno]

To be sure the cam timing is correct, you need to remove the valve cover and rotate the engine in the normal direction of rotation.
While doing this, look at the valves for both cylinder #@1 and #6.
When the timing mark on the vibration damper begin to come into alignment with the marks on the timing cover one of the two cylinders mentioned will have both valves closed.

This cylinder will be on the compression stroke and ready to fire at TDC (Top Dead Center) plus or minus a few degrees.

The other cylinder will have both intake and exhaust valves rocking/moving. This indicates this cylinder is on the verge of completing the exhaust stroke and at the same time beginning the induction down-stroke.

At this point, the distributor should be inserted with the rotor pointed to the corresponding cylinder on the cap. I am assuming you have a distributor like my 1996 XJ.

These cylinders move up and down together based on the crankshaft profile. 1 and 6; 2 and 5; 3 and 4. what that means is when 1 of these cylinders in on the power stroke TDC, the corresponding cylinder will be completing the exhaust stroke and beginning the intake stroke.

The crankshaft in degrees during which time both valves are open is based on the camshaft profile AKA valve overlap.

 

[techno]

1999 XJ. New head, new valve train, new timing gears and chain. My problem is at TDC (compression stroke) both of the valves are open. It almost seem like when I torque the rockers down 19ft lbs., the valves tend to stay open. Almost like the lifter(cam followers) are not compressing. I've cycled through each cylinder and used a borescope on each one. None of them are fully closing. What could be the issue. Maybe I'm doing the timing gear wrong. Lined up the two marks on TDC Cylinder 1. Anyone have steps on installing the timing gear correctly? New to XJs. TIA

Reading your post again, I begin to wonder is you have installed solid lifters if such a thing exists for the 4.0L. I have not done any head or valve work on my XJ so cannot help you there. The deepest I have dug into my XJ was to replace the timing chain and gears.

Post up some more information, someone will be able to help you.

 

[75SV1]

I'd look at push rod lengths. If you take the push rods out, do the valves remain closed?