intermitant lifter tapping

[V8 Mini]

on my 3.5 RV8 if i drive at speed before the engine is fully warmed up i would get a noisy tappet/lifter, would last about 10-20 secs then stop again.
last weekend i went to MITP at santa pod, all was well going there, but coming back i would get this noisy lifter about 1/2 dozen times for no reason. this is the first time it has been driven on a long run (45 mile each way) the easiest way i found to stop it was dip cluctch and rev it up so pressure went over 3 bar.
oil is new, halfords 20/50, new filter, pressure is good, 2 bar + when cruising and its not running hot.
whats the most likely cause, might i have not shimmed the lifter preload right? or could it be a failing lifter. this engine has only done just over 800 miles from rebuild, new cam and lifters ect

[ChrisJC]

Probably not enough tappet preload.

I have the same on my 4.6, and I believe it is because the valve stem heights are all different, so there's no rocker shaft shim that puts all eight valves within preload spec.

Chris.

[V8 Mini]

so it might be worth just dropping down to the next size shim, and see what happens.
if there is too much preload what might happen that end? i assume you could get to valves not closing properly in extrame cases

[ChrisJC]

The danger as you say is that a valve may not close properly. Which might give interesting backfires into the inlet manifold, or exhaust, and burned valves.

But it would be an easy test to do I guess.

Chris.

[CastleMGBV8]

If your running a standard cam it should be safe to use the next shims down, if you have a cam with more lift you need to check that the valve spring has enough clearance at full lift or it could cause an expensive problem.

Kevin.

[mgbv8]

If you are going to the trouble of re shimming, why not pull the manifold off and check the pre loads?
what cam are you using?

[V8 Mini]

i'm using a Hurricane cam, i might take manifold off any way to take a look at the cam, make sure i've not done any damage.

when checking the preload, will i have to bleed the lifters first?

is it likely to be anything else causing this, would a better oil help i am planning on going for Valvoline VR20/50 on the next change

[mgbv8]

I drain my lifters everytime I refit them so I can check the pre load.

[john 215]

Hi
Worse case, you may have to go adjustable push rods does seam strange only does it on a run or is it when it gets warm,ie.if you left it ticking over on the drive? What condition are your rockers and shafts in,pad wear on a rocker
Cheers John.