Composite gaskets

Preedster

New Member
Evening All, I recently bought an engine rebuild kit for my late r reg v8 p6 the kit was described as being for the 3.5 engine with the 9.35 compression ratio which mine is ,however the kit contains composite head and valley gaskets which I have been informed may not be suitable for the p6.Any thoughts please thanks as always
 
Compsite gasket will lower your compression by about 0.6. On a 10.5:1 engine this may not be such a bad thing and allow you to use 95 fuel.

On your car you have three options. Live with a very low compression and loss of power. Skim the head by 20thou. And by far the best of all find some 10 bolt heads from the Discovery or P38 which this gasket is designed for and enjoy 16% more gas flow and proper oil seals while maintaining the compresson as it is now.

As you are putting the effort to rebuild it, I'd swap the heads. If not find a tin gasket, they are cheap enough and work fine given everything in good condition.

What you must do when you put everything back together is do the pre-load on the lifters (the shim kit for the rockers). You can use the composite valley gasket regardless of which head gasket you have.
 
Thanks for the advice Peter illI probably go with the standard tin gaskets for now never knew about the pre load for the liftersl either so Will be looking that up as well thanks once again
 
If I want to fit my carb inlet to a 3.9 with composite head gaskets, is it safe to assume the inlet will line up and seal OK on a composite valley gasket?
thanks
 
If you dry fit the valley gasket and bolt it down with the end clamps and then press it onto the heads you will get an idea of how the fit is around the inlet ports, then you can decide if you want to take a little out of the gasket or not.
I use a long nose die grinder with a 6mm diameter tungsten carbide cutter to trim the gasket, clamping the gasket in a vice and going very slowly.

There should be negligible difference between tin and composite valley gaskets.
 
Last edited:
If checking lifter pre-load is necessary, why did the factory never use shims on the rocker pedestals? I have never seen any shims in there. Or are the lifters not to spec now? Questionable quality?
 
The lifters used by Rover and later by Land Rover for the Rover V8 engines were manufactured for the entire time in the United States by the Diesel Equipment Co, Grand Rapids, Michigan.

There is a degree of tolerance with all measurable components, nothing is perfect, indeed there is no such thing as perfect in terms of measurement. Accordingly, if using the standard factory fitted equipment, there is no need to use shims as the allowable variations do not exceed the minimum that would require their fitment.

Ron.
 
Ron, Using currently available lifters , whose origin might be unknown, mean we should at least check the pre-load?
 
Skimming the heads or the block deck can possibly have an influence on the lifter pre-load. To be honest, I don't think it would be necessary if you cannot be certain of the origins of your engine's lifters assuming all else remains as per original specifications. The pre load is a result of changes elsewhere and that is what you are looking for.
V8Wizard
Ron.
 
That link talks of a range from 40-60 thou being OK, where others talk of 20-60 thou...??? (RPI give 20-50) Also, can somebody explain how the rocker ratio is relevant to the pre-load? In my head the valve end of the rocker is being held on the valve stem by spring pressure inside the lifter, so there is no clearance anywhere in the chain of parts. Since the lifter spring is much weaker than the valve spring, its the one that compresses. If say there is a preload of 80 thou, we have some options (for the sake of argument) - shorten pushrod by 40 thou, OR, relieve the valve stem by 64thou (because that will lift the pushrod end by 40 thou, since the ratio is 1.6:1. If we pack the pedestal by 40 thou.....why will the pushrod end rise 64thou? The end on the valve stem is fixed as regards height, so that end is effectively the pivot point of the rocker if we move the pedestal.
Having trouble visualizing the movement at the rocker end.
Edit - just measured a rocker, and did the trig....40 thou at the pedestal moves the pushrod end very close to 1.6 ( I got 1.594)...lets just move on. based on my measurements (shaft centre to pushrod centre 22mm, centre to valve stem centre 37mm) the ratio is 1.68.
 
Last edited:
The whole point of Hydraulic lifters is to remove the need for adjustment. They are particularly useful in Aluminium engines as the metal expands quite a lot more than iron, requiring rather large rocker to valve clearences when cold which causes solid lifter valvetrains to tick till the engine warms up. They consist of a small piston inside the lifter with a spring to keep the valvetrain tight when the engine isn't running and some holes and valves for the engine oil in the same space. When the cam begins to lift the lifter, the oil flow is shut off and the inner piston moves as a solid lifter pushing the other valve train components. The preload is there to ensure the inner piston is somewhere in its very wide (several MM) working range and not going to bottom out or hit the retaining circlip at the top (particularly as the valve train wears).

Shimming of the pedestals is for a different purpose; the rocker tip scrapes across the top of the valve as it moves up and down. It is important to ensure the contact point is in the correct place on the valve top for its entire period of travel. Lifting or lowering the pedestal moves the contact arc across the valve hence making the adjustment. Checking preload is just a final step in case the inner piston of the lifter has moved to a position outside its safe operating range (which given the amount of movement available in a Rover pedestal is highly unlikely.

M
 
Back
Top