Most of mine look like the one in the photo below... I'm assuming the benefits would be marginally greater valve opening since the material that's worn off the old ones would be replaced? Or do the hydraulic lifters account for that difference?

 

The rods are worn to the lifters and rockers. I would think just changing the rods would either wear the rod right back to what the old ones are quickly or wear the lifters and rockers further.

 

You're right that the lifters take up the difference, but only if the cam isn't worn out. I suspect if the rods are worn out that the cam, lifters, and rockers are also worn significantly. Those parts are all fairly easy to obtain and replace.

 

There's no benefit to replacing push rods unless you have a damaged pushrod, or if for some reason you need a different length pushrod. The hydraulic lifters will take up the valve lash within a certain range and it will not make any difference in terms of valve opening.

 

Cool! And what exactly are the symptoms of a lifter in need of replacement? The truck didn't make any odd noises before disassembly and ran nice and smooth, FWIW. It feels way more sluggish than the 2004, but I've always chocked that difference up to less displacement ¯\_(ツ)_/¯

 

The displacement makes a big difference. My 4.6 P38 has considerably more power than my 4.0 D2.

 

As long as it wasn't making any noise I wouldn't replace any lifters either. They're already mated to the cam and you're only putting things at risk if you replace lifters without a specific purpose.

 

Good thoughts. I'll leave those old boys be.

 

Perhaps it depends on how many miles you think you'll drive the beast. Shop manual says wear pattern at cam contact surface should be even and circular. If pitted or square wear pattern (i.e. lifter is not rotating properly) then replace the lifter. Likewise, if rod contact surface is pitted, then replace the lifter. The gap under a straight edge on the flat end of the lifter should be less than 3 thou, as I recall. New lifters are flat, so they contact the cam in a very specific way to help them spin in the bore. You won't be sorry installing new lifters and a new cam now, versus later wishing you'd done it. The cams and lifters are known to wear out in Rover V8s, so if you have the engine apart, it makes sense to renew those parts, if mileage is more than 80K or so. The good news is these parts are easy to get, and you'll save on gas down the road.

RPI Engineering (England) has very good write ups about what to look for with photos on line. They really know these engines. That's my two cents worth.

 

Keep in mind that it's the lifter is pitted, the cam will also be damaged. I would not put a new lifter on a used cam if I were replacing the lifter because of damage to the contact surface.