Drag Racing Online: The Magazine

Volume VIII, Issue 9, Page

Reher-Morrison Racing Engines' David Reher and Darin Morgan answer your questions about cylinder heads or anything else concerning your racing engine building problems. Remember who you're are dealing with so no soft-ball questions.



On a BBC head with stainless steel valves in SuperGas what valve stem clearance should I have with bronze guides?

Bill Trum


Valve stem clearance can range from .0006 to .0025 depending on the application and many other variables such as stem diameter, crank case vacuum, length of guide, guide material and thickness, head material and engine operating temperature to name just a few.

The type of metal the valve is made from will dictate the clearance requirements as well due to the fact that the coefficient of expansion of steal and titanium differ greatly. The bottom line here is that there is no set standard and every case must be studied closely in order to derive the proper clearance for that particular application. Knowing all this, I will try and give you an adequate answer to your question but in doing so I will have to assume a few things.

I will assume that your heads are made from aluminum and that the bronze guides you speak of are solid .500OD guides and not guide liners. With solid Bronze guides and steal valves at an operating temperature of 165°F-180°F in aluminum heads I would set the initial clearance on the intake guide at .0008 and the exhaust at .001. 

David Reher asked Darin Morgan to answer this question because it is his area of expertise.

Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
Visit our web site at http://www.rehermorrison.com

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