Replacing valve guide suggestions

[Novelo]

So I need to replace the exhaust valve guide on the vertical cylinder and need a couple of suggestions on the procedure. Upon trying to order a new valve guide I noticed that they come in three sizes .03,.06,.09. I understand that there is supposed to be a clearance but not sure on how to measure for this clearance. The service manual also has an odd procedure on how to change the valve guide. Heat the cylinder head up to 180c or 360f in an oven and soak the valve guide in dry ice, then use a Dow to drive the guide in. Is this correct, will the extreme temperature cause stress cracking in the guide? Any special care that should be taken for this procedure. Also it says to replace the valve at the same time what is the reason for this.

[Howie]

You select the outside diameter removing the old guide.  Measure the hole it fits into and select the size you need for the interference fit specified in your manual.  You are looking for an interference fit, not a clearance.  If you have clearance the guide will not stay in the head.  You do need clearance between the calve and the valve guide though.

The guide is an interference fit, in other words, the guide is bigger than the hole in the head it fits into.  Heat the head, cool the valve guide and you can easily drive the guide into the head.  Head cools, guide warms and all is good.  Installing without doing this can result in cracking.  At least cool the guide in dry ice.

[ducpainter]

Don't forget that the valve seat will need to be cut after guide replacement.

[64duc]

  Replacing the valve is necessary because the old valve has been rattling around in a guide that was worn. The valve will have wear on it also.

[Howie]

The seat will definitely have to be cut.  The guide also needs to be reamed to size.  If the valve stem measures within limits and you do not have excessive guide to vale clearance you can reuse it, though a new valve is a good idea.

[Novelo]

Thanks for the replies, the guide needs to be replaced because it was damaged not because of excess wear. The fit should be similar to that of bearings and not shift around. Think liquid nitrogen would be to much for the guide? I can get my hands on some of that if need be. Anything else I should know before preceeding? 

[scott_araujo]

Some grocery store near you probably has dry ice for sale.

Scott

[woppini]

Liquid nitro could shatter the guide. I wouldnt even try it. All you really have to do is stick them in the freezer over night. We did this all the time when replacing guides for mercedes.

[monsta]

make sure before you drift out the guide that you remove any carbon from around the guide, you can also put a bit of oil around where the guide proyrudes into port so as you dont score the bore when guide comes.

Measure the guide hole with some telescopic guages
http://cgi.ebay.com.au/MITUTOYO-155-903-TELESCOPING-GAGES-GAUGE-TELESCOPIC-AW_W0QQitemZ300353382557QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item45ee74e89d&_trksid=p3286.c0.m14
and a micrometer.

Make sure the hole isn't out of round or tapered, if more than .03 you should get em rebored.
Aim for an interference of .03 - .05 when getting the guide or it need turning to size.

You should make a drift to fit the guide that will fit up the guide hole and have a shoulder that drives against the protrusion at the top of the guide.
I just cool the guide in the freezer as mentioned previous. You'll have to work reasonably fast fitting it so as the guid dosn't warm up.

When fitted,  after cutting seats, ream guide for clearence on the valve, about .03-.04 for exhaust  (.02-.03 for inlet)
you can measure with some small bore guages,
http://cgi.ebay.com.au/RDGTOOLS-4PC-SET-OF-SMALL-HOLE-BORE-GAUGES-FOR-LATHE_W0QQitemZ370256356286QQcmdZViewItemQQptZUK_Home_Garden_PowerTools_SM?hash=item5634ffa3be&_trksid=p3286.c0.m14
and a micrometer.