I have decided to just replace the exhaust guides, the Inlet are not so bad and can stay for another day, I assume the inlets have a bit more lubrication from the fuel.
Note Inlet valves are 8mm diameter and exhaust 9mm diameter!!
I have an old head so I practised removing and refitting the guides first as I have not done this before, I had a few problems particularly with galling of the thread but that may have been low quality threaded bar.
The normal method, so I have read, is to tap the guide then using a long bolt or threaded bar and a tube spacer wind it out. Easier said than done, I found if you didn't tap right through the bolt hits the end of the thread and then starts expanding the guide which stops it moving, I snapped a bolt doing this so I moved to tapping right through not sure if it's the best way but it's what worked for me.
There are problems with tapping right through in that the tap is not long enough so I counter bored 20mm from both ends and just tapped the middle section.
Counter bore from top was 10mm followed by 11mm drill, counter bore from valve side was just 10mm
P1060362 by
Paul_Barr, on Flickr
I used M8 studding carefully slid through the inlet valve guide acts as a good guide to drilling and tapping square, vacuum cleaner to reduce the amount of swarf left.
P1060383 by
Paul_Barr, on Flickr
Keep pulling the drill out to check it's drilling square and evenly
P1060387 by
Paul_Barr, on Flickr
then drill from valve side
P1060390 by
Paul_Barr, on Flickr
using two M10 tap sizes, first runs through easy the second is a bit harder, never going to get in there with a tap wrench so used a battery drill on slow, and kept going forwards and backwards, used grease.
P1060395 by
Paul_Barr, on Flickr
P1060396 by
Paul_Barr, on Flickr
Checked the studding threaded through easily
P1060399 by
Paul_Barr, on Flickr
spacer tube and washer two nuts locked off on the end, a hardened bolt would be better I think
P1060400 by
Paul_Barr, on Flickr
wind it out
P1060401 by
Paul_Barr, on Flickr
P1060403 by
Paul_Barr, on Flickr
clean holes out removed as much swarf as possible with a rag first then washed it all down with paraffin
P1060404 by
Paul_Barr, on Flickr
P1060405 by
Paul_Barr, on Flickr
P1060406 by
Paul_Barr, on Flickr