Rocker geometry
Turbo Mini Forums

Hi,
I've seen rocker post spacers to restore geometry when cylinder head have been skimmed a lot.
When a thick gasket (0.090")is used, would machining the rocker post have the same effect instead of using longer push rods ?
Sorry if it's a stupid question...

Rocker geometry is not massively affected by skimming the head. If it was right before the skim, rocker spacers are not the right fix.

The right fix to compensate for a skim is shorter push rods.

But unless it was optimised before, has skimming made it better or worse?

Edited by wil_h on 27th Nov, 2016.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

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I'm looking at restore to standard geometry if I use a thick head gasket that would raise the head of around 0.06" comparing to standard if that would make a difference.

I understand that the right fix would be longer rods but they don't seem to be available

You'd just set the valve clearances properly, that's what the adjustment is there for, to compensate for wear and uneven pushrod lengths, valve stem lengths etc. Personally, I would not worry about it.
Alternatively, skim the rocker posts and the top ofnthe valve stems by the added thickness of the gasket, but I doubt you would gain anything by doing this, and may alter the hardness of the valves where the rockers contact them.

Think about what you're changing, and how the thickness of the had affects it.

You should only be altering the rocker height if it was already wrong. A head skim won't affect the relationship of the rocker to the top of the valve.

I think minispares sell pushrods that can be any length.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

In a highly developed engine such as mine, we use rocker post shims to correct the geometry. If the shaft isnt the correct height it does alter the ratio. I have 35 thou shims in mine to optimise the ratio after the block height and head face were machined.

I seriously doubt it!

Thanks for your answers.
I'll give it a try and check if it 's out or not using the adjusting screws

I'm not sure your clear on what needs changing if anything,

rocker shaft spacers are to correct the sweep of the rocker acros the valve, maximising lift and minimising sideloading on the stem, below is a good illustration of this. normally you should be able to ignore this unless the top of the head has been skimmed, or the seats have been cut deeper therefore moving the valve stem. ( or any other effect that causes this)



in terms of skimming the head gaske face, if this is skimmed, then adjustment is taken back on the screw, what you would need to counter this is a shorter pushrod, but tbh I dont think it is worth the bother unless somthing is binding.

That makes things clearer.