Cylinder Block height

[Roger]

I am having to machine a badly damaged top face between No. 2 & 3 cylinders, I guess the gasket was burnt away and then some of the metal from the top face. Does anyone know the height between the piston crown and the cylinder top face on an original unmachined block?
The original block height was 4.800” before I started and is now 4.780” (0.020” lower).
The original paper gasket is 0.010” thick so do I need to worry about the difference in height?
I am able to laser cut a spacer but not sure whether I will then make the block too high.
If I use one of the silicone gasket what thickness will this end up when compressed?
This block is sleeved and standard size and the best I have so would like to use it.

Roger

[Ruairidh Dunford]

David Cochrane and John Barlow make shims to go under the block, especially to overcome this issue.

[Alan]

Can’t answer your question exactly, but you ought to be setting the piston height anyway. With a standard gasket, and new crankshaft I aim to have the pistons level with the top of the bores. You can skim the tops of the pistons to achieve this, but remember it’s good if they all still weigh the same. With old cranks that whip a lot at high revs you might want to be as much as 20 thou below block height.

[Roger]

Alan, 
Thanks for your reply unfortunately my working engine in the car is in running order so I cannot measure the piston height so not sure where my starting point is.
I just hoped someone might know piston to block top face measurement.
As I do not know the shim thickness of the ones supplied I was not sure how much metal to remove, I took as little as possible off to clear the damaged part, with two joints and a spacer the block may be too high now.
 
Ruairidh,
Thanks I knew they were available but not what thickness they were, so that I knew how much to machine off without then being too high.

Roger

[Ruairidh Dunford]

I was able to buy various thicknesses - speak to the suppliers and they will let you know.

I opted not to use the silicone gaskets in conjunction with the shim.

[Roger]

Ruairidh,

Thanks will ring them tomorrow.

Roger

[Chris KC]

I agree with the above comments.

I would not rely on a compressible joint to give me the required block height - use whatever aluminium shims it takes to give you the clearances Alan suggests (n.b. some say this is only needed for 2-brg shafts but I say what happens if your C/M bearing fails?) then use a goo sealant and tighten the nuts while it is soft. This effectively gives you a sealed metal-to-metal joint. Just take care goo doesn't squish out into the interior of the engine where bits may migrate into your oil pump pick-up.

By all means check measurements Roger but I think this is one of those things which is better done empirically - do a dry assembly run and see where the piston crowns end up, shim accordingly. Even then I found the finished result was a few thou out. Too high is better than too low!

[Roger]

Chris,

Thanks for reply It did not occur to me to only use the shim, that will maintain the original height if I use a 0.020” shim.
I guess the ally will be soft enough to compress a little and fit any irregularities in the surface under the block.
I will not be fitting this till the winter weather arrives so just wanted to make sure it was all sorted in advance.

Roger

[Chris KC]

To be more precise Roger I meant put a smear of sealant between each layer, when you tighten up this will squish out until the high spots on the metal parts are in contact. It won't compress much more after that.

[spannerman]

What you take of the block
Take of top of pistons job done ?
Have done this a lot of engines and never
Had any problems even engine running
12to1 compression no shims to forget to fit!