Valve guide removal and refitting

[1NRO]

Hi Guy,

I have in mind to remove a set of guides from a head I'd like to have a tinker with and would like to ask for your advice and instruction please. Is this something I can DIY? I have access to presses and lathes to make tooling but know not a correct method to follow.

I have a set of new O/E guides for refitting and again would like to ask for direction. As an aside would "sharpening" the end that protrudes into the port be something worth doing? They look very blunt to me.

The head in question is a 16v Integrale.

Thanks,

Nik

[Guy Croft]

Nik, hi

not quite finished but article now up at:

http://guy-croft.com/viewtopic.php?t=949

As I say, not finished yet - but any interim queries re just post here.

GC

[Evodelta]

Nice guide (no pun intended) Guy,
How do you guage the depth or know when to stop pressing in the guides (correct depth)? A stop/spacer between the guide and the base of the press?

Martin.

[Guy Croft]

That's right Martin, some sort of 'stop' is needed.

I have put in some added info today on that subject.

GC

[1NRO]

Thanks Guy,

You really have surpassed yourself.

Some tooling is first on my list of tasks, namely the Flex-Hones and a digital micrometer. A jig to hold the head on the press will have to be made and this I'd like to ask about. I've measured the angle it needs held at as 23.5 degree but not with what I'd call great accuracy and I was somewhat hurried. I'd like to ask for confirmation. What materials should I be using for such a jig? Will an accurate wooden block suffice?

Thanks again,

Nik

[Guy Croft]

Thanks!

The angles are 23.5 inlet and 22 ex.
Your press jig needs to be solid steel or aluminium, I have a special rig for doing the 16v Lancia head that supports it via a thick round steel bar along the cam housings. The risk of sitting the head on the upper faces to remove guides is crushing all the cam cap locating dowels.

GC

[4v6]

Many thanks for that article Guy, its answered one or two outstanding queries that had been rolling around in my head for a while now.

One question though; Would it be prudent at all to warm the head to facilitate guide fitment, or is that simply not an issue using your methods?

Thank you again for an informative (as ever) and thoroughly enjoyable read.

[Guy Croft]

OK - re: heating/warming head, chilling/freezing guides.

If you follow my preparation regime to the letter you won't find a better way, I speak as one who has used 'every method known-to-man' to fit guides!

With brand-new heads and fully assured dimensions of everything (guides, bores etc) and only if the guides have a circlip or stop to prevent them dropping right thru the bore (I got my gloved finger trapped once, VERY frightening) then yes I am all in favour of heat/chill, but to be effective the head has to be fully heated to 120 -150 deg C and the guides have to be cooled (frozen actually) in liquid nitrogen. I say fully assured dimensions because with this method you are completely relying on engineering drawings to generate the necessary interference fit.

In the past where I have used -184 deg C nitrogen and 150 deg C heating on old heads (Abarth Gp 4) without bore-gauging the bores and the guides have gone in part way and got stuck halfway down the bores due to a tight spot that I would otherwise have noticed during cold pressing, I mean I would have seen the press gauge pressure rising too high. That heat/chill combo can induce a clearance of over 0.005" - you can visualise what I mean by stuck. To attempt to press them in could have split the head. I had to machine them out.

On old heads, with all the out-of-true they exhibit in valve guide bores I think you are well advised to avoid any application of non-ambient temperature and stick to the regime I use. There are others who prefer other methods, good luck to them. Even the 1st class (FER member) engine reconditioner I use asks me to his more difficult guide removal and fit sometimes.

GC

[4v6]

Ok Guy, thank you for the rapid and in depth response, i will endeavour to employ your method to the letter, as to me it seems to be a whole lot less trouble than warming the head and freezing guides only to get one stuck, not to mention the difficulties arising from handling hot heads and liquid nitrogen.

Thank you very much sir!