Are wet cylinder liners' shims utterly neccessary?

Question

This old Skoda engine I'm rebuilding has wet cylinder liners, and uses thin copper shims in their seats. The manual talks about liners protrusion between 0.14 to 0.32 mm above the block, and available shims between 0.10 to 0.14 mm. When I inserted and homed the new liners I will install, I realized they already protrude above the block WITHOUT any shim on their seats. The old liners do have the shims, and even with them, they protrusion was almost in-existent. All the old liners got also silicone gasket maker in there as well.

I think I will use silicone gasket maker for the new liners too, since I guess the seats and the liners may not get a perfect fit. But my question is, well, if I get the liners protruding without shims...do I still need them? I'm concerned about the height shims + silicone gasket may add.

Edit: I found this in a Volvo trucks manual: "If the cylinder liner is installed without a shim, an even strand of jointing compound, approximately 0.8 mm thick, should be applied to the underside of the cylinder liner collar."

Edit: So I measured everything carefully today. The old liners:

• The overall height is the same
• The outside diameters are the same

BUT

• The height between the top and the seat bevel are different:
• Old is 94.6 mm and the new is 95 mm

So 0.4 mm is the difference. Curiously, the new liners protrusion against the block at top without shim is 0.4 mm. The manual says 0.15 to 0.2. Photo showing old and "new" liners.

The old shims are homemade.

The manual says right length between top and seat to be 95 mm, so the new ones are good. I wonder if the block got rectified its top surface...

Answer 1

Use a caliper gauge and measure the height of the new liners with the old ones and also the thickness of the shims from the old liner.

I would measure the new vs old liners. You may have needed to turn down the new ones (they can be generic and fit multiple Skoda engines) or they may be the wrong liners (Skoda engine with taller stroke).

Those "shims" are basically a crush washer to hold up against the high pressures of a power stroke. The steel liner is much too hard and will damage your head if its torqued down and probably not seal with the head gasket as well.

The protrusion is usually very small slightly bigger with new seals that have not been crushed.

If this is not a crush seal for the cylinder and made of higher strength steel then it may be fine if the new one sticks up some. This might mean the crush seal is part of the gasket.

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it sounds like the engine block was resurfaced 0.4 at some point. but this would mean the old cylinder liners are 0.4 shorter than the new. It could be that it the old liners seats were machined but depending on the block that bevel might not fit right. but then they needed a shim because they machined it too much. This is just a possibility.

either way it looks like you will need to machine down that seat by 0.225 (split the middle should work 0.15 to 0.2).

I would definitely use some high heat RTV on that seat.

Another thing to consider is the copper gives a little more than the steel liners and the block. You may want to machine the liners by 0.4 and find a copper shim that is 0.175 and 0.2 thick to act as a softer "cushion" against torquing down the head. still use plenty of RTV though. I always suggest using yamabond its pretty good for sealing surfaces together. I am not quite sure which one to get probably yamabond 4 is my guess but take a look at the reviews and the recommendations to pick the right one for that engine.

here's a link they are not cheap but they work really well.