Preload Adjustment method.....

[gulf blue rsr]

Hi,

Apart from my interest in Range rovers and v8's I also have an obsession for Porsche 911's.

I've been meaning to ask this question for a while so here goes,
whilst setting the preload on the rover valves why not use an alternative method suggested for 911 engines which usually get done in a similarly fiddly method as we use on the v8?

If someone could work out the rocker ratio you could then just use feeler gauges straight of the top of the valve using the same go/nogo method that you would with the go/nogo wire method in the lop of the lifter?

I'm not sure if I've explained very well so have a link to a thread in a Porsche forum that I use a lot.

I would guess that others may have suggested this method before, am I missing something here?

check out the link there is a picture on post 10 and a good description on post 8 by 2.7Racer

http://forums.pelicanparts.com/showthre ... adjustment

What do you think??

STEVE

Oops forgot to paste the link

[CastleMGBV8]

Steve,

The method you are describing is for solid lifter engines or as with the porche engine depicted, where the rocker acts directly on the over head cam and you have adjustable rockers so the gap can be set.

If you put a feeler gauge between the valve and rocker on a Rover with hydraulic lifters and fixed length pushrods, all you will do is increase the preload above what ever is currently present.

I suppose if you have adjustable pushrods or adjustable rockers and set t all the lifters to zero preload which is what I would do anyway, you could put an 14 thou feeler in and this would give just over 20 thou pre load but you would still have to adjust the rockers or pushrods anyway.

I've just done this job on a new engine and the method I used was to insert a 25thou piece of welding wire made into a shape that wont fall into the engine, between the lifter piston and the wire retainer, it will stay in place with the pressure of the lifter spring against the retainer clip.

I then adjust the pushrod to take up the slack and as soon as the wire moves lock off the adjustment nut on the pushrod, one down and 15 more to do, took me about two hours, with double checking to make sure I got it right. Not a job I want to do again soon.

All setting to be done with the lifter on the base circle of each cam lobe.

If you have standard fixed length pushrods you have to measure the preload on each one, average it out and then add shims to get the best average figure.

The standard rocker ratio of 1.6/1 should be used to establish shim thickness. ie if you need to reduce preload by say 24 thou then divide that figure by the rocker ratio of 1.6 and you get 15 thou shim required for all rocker pillars.

Modified engines with non standard components and those which have had machining done, will almost definately require shorter than standard pushrods whether adjustable or not, especially if the valve gear geometry has been optimised.

Hope that helps to clarify the situation.

Kevin.

[ChrisJC]

http://forums.pelicanparts.com/showthre ... adjustment

What do you think??

STEVE

Unless I'm missing something, that Porsche is completely different.

With the Porsche, you are simply measuring the rocker-cam clearance with std. feeler gauges, then scaling it by the rocker ratio to calculate the valve-rocker clearance.

With the Rover, there is no clearance between valve & rocker, in fact, it is pre-loaded by the hydraulic tappet. The checking process is to ensure that the preload is within limits, and is undertaken on the hydraulic tappet.

So with the Porsche, you're effectively adjusting the tappets in the traditional sense, whereas with the Rover you're adjusting something completely different in the valvetrain.

Chris.