Early 3-1 Valve guide threaded on both intake and exhaust

[OzWildman]

Hoping to get advice on valve guide replacement for my early 3-1(1934 I think, serial# 10539 with water cooled injector). I was expecting a threaded guide on the exhaust and a press fit on the inlet and that is what was in there BUT the inlet valve guide recess is ALSO threaded. Now I am left wondering if threaded valve guides should be in both. I see the guides have a different design(apart from the thread, the "nose" of the stem at the valve face end is longer and has a larger diameter bore at its tip, presumably to accomodate buildup of fouling on the valve stem without jamming). The manual for the CS' suggests the guides are different.

Do I just press fit another "intake" guide into the threaded recess or do I put threaded guides in both?

Thanks for all the amazing knowledge on this forum. I've been reading a lot! This is only my second post. One for each lister I have. This one is new to me last week. Absolutely in awe of how this thing is built. Such a different experience to work on. I got hooked on my recent rebuild of a 76 ST1 coupled to a 4KVA Dunlite.

[mihit]

Sorry man, can't find my manual on the PC, and can't find pics of when I had the head off the 3-1.

If it was running good before, then I would be inclined to replace like-for-like until I could get a better answer, though both threaded wouldn't do you any harm and since they're not under a lot of pressure to move...

[38ac]

It's been a while since I have had the guides out of a CS head  as I repair the old ones in place. That being said I do believe that both bores are threaded  as the valves switch positions on the number 2 side of a twin. I have two older 10/2 with wet injectors in the line for rebuild but it will be a few months before they get in the shop. You are correct that the longer couterbored guide is used to prevent sticking of the exhaust valve.  Replace the guides as they are now. 

[listard-jp2]

That being said I do believe that both bores are threaded  as the valves switch positions on the number 2 side of a twin.

That would correct for a 5/1, 6/1, or 8/1 cylinder head, but the 3/1 cylinder head is unique to the 3/1 and 3.5/1 engines, in that the valves guides are closer together (so that they fit within the confines of the 3.3/4" cylinder bore).

The only reason I can think for this is that Lister's had the same production process for all CS cylinder heads (even though in this case it incorporated some surplus machining activities).

[OzWildman]

Thanks for the great replies. I'll replace with interference fit for intake and threaded for exhaust as it was then.

Head and barrel sand blasted and painted, bore honed, big end white metal bearing shimmed and scraped to 3 thou. New valves and guides ready to go in. Lots of other goodies to give her a birthday.

Thanks again for the awesome knowledge here.