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Old 09-04-2009, 08:09 AM
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Valve Stem to Guide Clearance Question

I recently had a rebuild on a SBC that had less than 1000 miles on it. When the builder went thru the heads it was determined that (3) exhaust valve guides were borderline in spec (on the loose side). Well there were problems with the rebuild and needed to be tore down after 500 miles and now I was told the (3) guides that were borderline out of spec are now way out of spec and suggested they all be replaced (Aluminum heads) with the appropriate bronze replacement guides. Builder really don't know the cause but mentioned that the combination of the borderline out of spec, high spring pressure and previously breaking in the cam MAY of caused abnormal wear. Wondering if anybody can comment on this and also what is the typical Valve Stem to valve guide clearance ? Thanks.

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Old 09-04-2009, 09:45 AM
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Intake 0.0015" to 0.0016"
Exhaust 0.002" to 0.0025"
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Old 09-04-2009, 09:47 AM
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Intake 0.0015" to 0.0016"
Exhaust 0.002" to 0.0025"

Thanks !! Builder sized new exhaust guides to .002" (said exactly where likes them).
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Old 09-04-2009, 10:51 AM
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guides

The 2 killers of valve guides.

1. to much valve seat run-out.

2. Incorrect rocker geometry.

So if one or both of those issues still exist with your engine it will destroy the new guides also.

Keith
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Old 09-04-2009, 11:13 AM
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Quote:
Originally Posted by k-star
The 2 killers of valve guides.

1. to much valve seat run-out.

2. Incorrect rocker geometry.

So if one or both of those issues still exist with your engine it will destroy the new guides also.

Keith
Thanks for that info Keith. Are these typically checked by the engine builder/machinist when "going thru the heads" ? I believe the shop mentioned that along with resizing the valve guides they also reseated the valves, I am guessing that referrs to cutting or grinding the valve seats ? If that is the case I would assume they checked the runout (concentricity) with the proper gauge?

Last edited by y2k600f4; 09-04-2009 at 11:21 AM.
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