Thread: top hat liner

Top hat liners look like upside down top hats, hence the name.

The flange part of the liner sits in a groove machined in the block. This prevents the liner from moving downwards and the head prevents the liner from moving upwards.

It requires complete engine dismantling to retrofit the liners, so it isn't something you would do unless you had to pull the engine out and rebuild it anyway.

You can see the flange here:

Thanks guys that was what I thought, and you have cleared it up completely.

Definitely only when the engine gets rebuilt

Sorry to hijack the thread ...but it is relevant: ...I thought I read a reference "somewhere" that the blocks of later 4.0 /4.6 engines had been either cast or machined with a step in the bottom of the bore with the liner inserted from the top such that it sat on the step... is this true and if so is there any info as to which VIN signalled the changeover?

Second question: how do the engine builders actually heat the block evenly to remove/replace the liners...just wondering... do they heat it in oil, use an oven...?

I think it's in the Des Hammill book, but at any rate the step didn't make any difference. The liners were apparently not always pressed down to the step so they can come loose anyway. Top hatting has become the only proven guarantee that liners won't move, and there's no other fix that's easier . . . or cheaper. Which means I'll have both my V8s top-hatted by about the middle of this century!

Oh, I forgot your second question.

It would seem (pardon the vagueness but I haven't actually talked to one of these joints) that the old liners are machined out, then the block is machined for the top hats, and then the block is heated (I'm guessing in an oven) and the liners are pressed in. I read somewhere on here that a Perth company was pressing the liners into a cold block, which just sounds lazy to me. The idea of heating up the block is so it can cool and contract onto the liners.

[QUOTE=Hoges;1610994]Sorry to hijack the thread ...but it is relevant: ...QUOTE]

No hijack at all

Another question: what causes them to slip? I assume overheating would be one of or the most common cause - steel and aluminium expand at different temperature and speeds. What sort of temperatures are we talking?

If one does slip what is the potential damage?