Valve guides

[Mike / Linganbo]

A lot has been said about valve guides both bronze and cast iron. Please accept my first comments to the group.
The inlet valve is seldom a problem, it is cooled by the incoming charge of cold vapour but it is vital to transfer the heat away from the exhaust valve. Phosphor Bronze is what is normal used and conducts heat better than iron and aluminium conducts heat better than bronze, so a bronze guide in an alloy head makes sense. There is no heat transfer benefit from using a bronze guide in an iron head. In bar form, bronze is further handicapped by not possessing any inherent lubricity properties, whereas cast iron contains about 5 percent free graphite which benefits sliding contact. However, I concede that sintered bronze could very well be composed to include solid lubricant particles like molybdenum disulphide, for instance. Colsibro seems to be a beryllium copper alloy, which does have better inherent lubricity.
I spent 40 years working in oil and gas industry and we had a lot of stainless steel galling problems. These were almost always with 316 against itself or similar chrome content or hardness. If you can make one part soft and the mating part harder the problems are reduced. I can see how small clearance between a valve stem and guide could lead to seizures but that would be by thermal expansion issues. I have never seen galling between bronze and stainless steel when designed properly.
Sent from my iPhone

[jerry atric]

Thanks for the extra info, its reduced my confusion very slightly🙂

[Andrew Nahum]

Nice summary thanks - but I thought phosphor bronze, at least,  is considered to have some self-lubricating properties? 

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[John O Regan]

Hi Guys,

Mike, 

Colisbro is a very good hard wearing material for valve guides, however it must have lubrication, which in the case of an iron head open valve spring Guzzi is marginal to say the least!

Somewhere I have a 316 SS bolt that looks as though it had "woodworm" , I took it as a souvenir from a probably 1 ton  box of scrap SS fasteners, when I was working at a power station on the coast.. The bolts on the saltwater intake filters  had to be changed at frequent intervals due to  galvanic corrosion.

Andrew, 

Again there are hundreds of different recipes for "phosphor bronze"  

The grades that have a degree of lubricity usually contain a higher % of lead and are comparatively soft, Colisbro is hard and it's very difficult to ream the guides, honing is the preferred way to size the guides.

John

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[bobka...@verizon.net]

Hi Folks,  Does anyone out there own or know somebody who owns a Daytona.  If so, please contact me at bobka...@verizon.net.  I have some parts to give them.  Bob Andren

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