Valve guides

Hello Ian

Stay with the standard cast iron guides. There is no advantage in using bronze guides for everyday use. Bronze guides only come into play when you want the best heat transfer to keep the valve as cool as possible as in used in a racing engine. Cast iron will wear better anyway!

When renewing valve guides avoid anyone who knocks out the old guides, even if they heat the head first. The old guides should be machined out using a counter boring bit that will leave a thin shell of the old guide that will collapse inwards slightly allowing the guide to then be removed. Heating the head as well. The new guides can be fitted by freezing them with CO2 or pipe freeze or Liquid nitrogen. Take all suitable precautions with these very low temperature liquids. Just as deadly as hot stuff!    

Doing it this way stops the old guide galling and tearing chunks of alloy from the head (this is why so many cylinder heads have loose guides as they have been butchered in the past)      

Get the old guides relined, no risk of the new guides going cocked or galling in the head and then the seat being ruined or worn out by over cutting before the valve is even inserted.

Known as K liners.

https://www.hthoward.co.uk/engine-machining-services/how-do-ht-howard-ensure-the-best-for-your-cylinder-head/bronze-valve-guide-sleeving/

Colsibro is not for road bikes. If you buy Colsibro guides, fit them and the valves drop straight in then you have been ripped off. 

Hi Ian

Nothing wrong with Colsibro in a road bike or car, certainly my own and many others material of choice. Any cooling advantage in an air cooled engine is well worth pursuing, road or race. An engine can get just as hot stuck in summer traffic as out on track.

I had my old RH4 head fitted with bespoke Colsibro guides. Reamed to suit each valve so they fit with minimal wobble by BLR in Surrey. 
Don,t buy off the shelf ones (apart from Kibblewhite USA which still need reaming)

Ashley, Fullauto heads look to have Colsibro guides as standard if I,m not mistaken. Are you replacing yours with cast iron then?

Colsibro is used to reduce the clearance to the valve stem, so would need reaming to ensure the benefit of using it is obtained. It is hard wearing, but not as good as the latest bronze materials used in auto applications where long life is needed, if it was, the likes of Aston Martin and BMW would use it.

Most owners these days would not do the mileage to wear out guides no matter what they are made of.

Surprisingly, many top engine builders either side of the Atlantic do not use Colsibro, but the more modern alternatives out there. 

Which is 'metal matrix composite'.

Basically the guides are made by squashing lots of fine particles of the required materials together into the required shape. As a result they have all the properties required for their function. Extremely long life, very good dimensional stability, good machinability and of course reasonably low cost. (They cost more per piece than cast iron, but needing much less machining balances this out). 

The same technology is used for valve seat inserts as well.

The G&S valves web site has information on compatibility between stem and guide materials. Problem is that it is not always clear in ther catalogue what materials are used for each valve type so we rely on our retailers.

Colsibro is, it seems not strictly a bronze. Bronze is copper plus tin, and brass is copper plus zinc. Colsibro is copper plus silicon.  Bronze is not favoured at all, or so it would seem.

Some guide materials need to take chrome plated stems and some need other materials. It looks like a minefield but you cannot generalise and say which guide material is best unless you know the material of the valve stem and if it is plated or not. Our retailers don't usually quote the valve material and certainly do not list compatible guide materials for the valves they sell.

Check out G&S valves web site...