Forum

[Ginetta lad]

Thanks so far I like the sleeve idea and will see if the engineers can make them so the guides can be used. Easier to turn than full guides I'd guess. What spec would the interference fit need to be to prevent them coming loose when hot? H

[Dennis C]

On that size guide I would go 2 thou heat the head to around 150c put the guides in the freezer and drive them in as fast as you can before heat transfers.

[PeteF]

"drive them in as fast as you can"
Yes, but with a correctly sized shouldered drift. This helps to keep it straight and prevents any chance of it breaking if you need to clout it harder than you thought.

[Dennis C]

You are of course correct Pete, sometimes I forget to point out things I think are obvious, which it may not be to others. A valve guide punch can be purchased quite cheaply or easy to make on a lathe.

[papasmurf]

Given the different coefficients of linear expansion involved I should point out no heavy hitting should be needed.

[Dennis C]

Papa, too many long words!!!, but yes at 2 thou and those temperatures they should just be a firmish sliding fit if done very quickly.

[PeteF]

No it shouldn't Papa, in an ideal world, but if you end up with an extra thou (quite possible if you're making them up) then the drift is a good idea.

[papasmurf]

I agree about using a drift, it is the belting with large hammer that worries me. A few taps with a hammer.
As someone who turned the chrome plate off of a 8ft long 2ft diameter printing roller on knackered lathe with the result being parallel and size, I don't do a thou out.

[Dennis C]

If a couldn't turn them to the exact 2 thou oversize I would throw my lathe in the bin.

[PeteF]

You must have a big bin Dennis
OK, understood chaps but unless you have some way to accurately measure the bore (and the tools to correct it) then the odd thou can go adrift when working in the average shed. They do in mine anyway.
And I wasn't advocating "belting it with a big hammer" Papa but there are times when a bit more coaxing than expected is required.