Valve guide replacement

[Peter Naulls]

I'm building up a replacement block for the Ruby including replacing worn valve guides. Should I warm the block first, given that it's not got much above freezing today? 

The worn guides have been shortened at the top, presumably to improve gas flow. Is this modification worthwhile? and what about any mods that facilitate removal of the cam followers if necessary? I don't want to make work for myself, just wondering about the pros and cons.

Thanks in advance.

["Slack Alice" Simon]

Shortening the guides to improve flow is a mod suggested by the Bill Williams' book.

Presumably it also shortens the guide's life a bit.

I have always just tapped the guides out, without heat.   Warming the block a bit, in this weather, is probably a good idea.

These days, having acquired a lathe, I would probably make a drift with a lead on it.

Before, I think the tool was the t-bar from a box spanner.

The guides can be brittle, and break off the tops, if over tight.   Still come out, though.

[Chris KC]

Gentle warming can do no harm and may help a little - just bring it up gradually, don't subject an ice-cold block to rapid localised heating. I think this strategy is more useful though for things like flywheel ring gears which are on in 30 seconds. By the time you've got the valve guide in it will most likely be the same temperature as the block. 

Sometimes I tap them in, lots of little taps rather than one big one. Try to pick a drift which won't chew up the end, but you'll still need to run a reamer through after. Support the block properly on a wooden workbench.
I'm always a little nervous of cracking something though and would recommend making a simple puller from suitably sized nuts, bolts and washers.

Rather then shortening the guides I simply insert them so the top is ever so slightly proud of the floor of the manifold - just so I can see they're in properly - and let the rest stick out below. Haven't yet encountered a problem doing so. Perhaps different if you have stepped guides or a fancy cam.

[Andy Bennett]

I put my guides in the freezer and the block in the oven (for fitting to a naked block). They were still a decent interference fit needing a drift to get in and a ream back to correct size.
But, for removal, the expansion coefficient of brass is higher than cast iron, so I guess that if heated as a complete assembly the guides will actually tighten in the block. The reverse would thern be true so cooling will make them 'looser' and so aid removal

[Peter Naulls]

That's very helpful one and all. Many thanks.

[Howard Wright]

Hi Peter

I’ve used an old valve with an old guide on the stem to gentle tap new guides in.

Regarding cam followers. If you’ve had these (or/and the cam itself) reground you need to take a bit off the top of the follower guides otherwise the tappet nuts foul the top of the cam guides.

Cheers

Howard

[Peter Naulls]

Yes, thanks Howard, I've had to do that on another block. This one has been done previously.

The old guides are out, new ones will go in tomorrow if I get time.

[Peter Naulls]

I knocked the new guides in this afternoon (utilising a stepped drift which I turned on the lathe) and reamed them. As I was out all morning I left the block beside the gas boiler and stuck the guides in the freezer; if nothing else it kept my hands warm!