4.6 Rover V8 Raising compression

[bedbug]

Skimming Rover V8 Heads



Rover recommend both the 10 bolt 28cc Composite Gasket and the 14 bolt 36cc tin gasket heads are not skimmed beyond 0.5mm when used with their relative gaskets. Since this mainly about stopping the valves mashing with the pistons, any skimming of the block decks needs also to be taken into consideration.


How to work our what has already been done to your heads. 

There are datums areas at the end of the cylinder heads that look like the obvious place you would clamp a head down, if you wanted to machine it. The heads are taller on the inlet side.



The 36cc 4.0 / 4.6 engine heads that use composite gasket the dimensions of a head without any machining are

22.94mm and 62.56mm.



The 28cc 3.5/3.9/4.2 engines using the metal shim gasket the dimensions are: 23.9mm and 63.5mm.


Will your inlet manifold still fit? 
If, you remove any material from either the head of the block deck faces you will reduce the size of the valley the inlet manifold sits in. Either you have to remove the same sum total amount from the inlet manifold on the inlet manifold faces on the cylinder heads. If the manifold bolts don't screw in easily, something is definitely amiss.

[garrycol]

This is great information thanks - any idea about the block?

Both my 4.6 heads and block have probably been decked twice so I am now concerned about valve to piston clearance particularly with the cam I am using. Inlet valve lift is .3966" and exhaust .4082" and I have standard lifters, push rods and rockers.

I really do not feel like putting everything together to do a plasticine test of valve clearances if I don't really have to.

Thanks

Cheers

Garry

[bedbug]

You could use a micrometer to measure the thickness blocks at the ends of the heads and determine whats been removed, from the standard numbers that are mentioned in here somewhere. You could use a DTI gauge in a bridge to determine how far down the hole the piston is.

I have seen a spreadsheet that Does the maths but what if it's wrong?

Whilst the lifts not that wild ; the combination of the revised duration and the lift, could cause a problem.

The best way must be to measure it. I've only just got a pair of heads back for the 3.5. So the 4.6 is waiting.

[bedbug]

Garry,
To measure how much your block was skimmed by you're either have to use a bridge and a DTI or you'd have to measure deck height from the crank centre line.

If it hasn't been skimmed at all, your original factory serial number and compression numbers will still be stamped into the face.

A steve

[garrycol]

Sept 29, 2014 5:04:07 GMT bedbug said:

If it hasn't been skimmed at all, your original factory serial number and compression numbers will still be stamped into the face.

A steve

These are long gone.