Sleeving Valve Guides

Stephen Hill said:

Just read a twenty year old Classic Bike mag which recommends sleeving valve guides with phosphor bronze inserts as an alternative to replacing guides. (March 1992).

I think of this as an idea that has come and gone.

At the same time, when I hear about how driving valve guides in and out of the head can wreck the guide bores, perhaps it is a valid option.

Are inserts a recommended option?

I found a few older references to guide liners but wonder what the collective wisdom is at present.

Stephen Hill

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lcrken said:

I've never tried putting liners in Norton guides, but it's clearly possible. The only negative I can think of off hand is that adding another material interface reduces heat transfer from valve to guide to head. I don't know how significant that is. It's not that complicated to replace the guides properly, so that's always been my choice. Heat the head, remove the guide, measure everything, machine if needed, chill the new guides, heat the head, and install. I've never had a problem with doing that on a number of 750 and 850 heads. If the old guides are loose, there are oversize guides available, although that requires reaming the heads to size to do it properly. But if the guides are loose, putting liners in isn't going to work so well anyhow. As far as I can tell, the only real problem heads are the RH4 850 heads. If they aren't already cracked, you need to fit the new guides carefully (or just send the head to comnoz!). The only other ones I've had difficulty with are race heads that have had the port roof raised during the porting process. That reduces the width of the area supporting the guide at the rear of the head, and it's impossible to keep the guides tight for very long. Not impossible to deal with in a race engine, but a recipe for disaster in a street bike that gets a lot of use. I have a head like that, and I'm looking for some way to positively retain it, like some sort of threaded retainer, pins, etc. Haven't figured that one out yet. The guides are a custom design, so I can't just buy replacements, but have to make them from bar stock. In the past I just kept making new oversize guides, but I'd like a more permanent solution. So many projects, so little time.

Ken

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