bbc clearances

Alan Roehrich · 11-18-2015, 09:59 PM

The quench is too tight. I can't get away with closer than 0.042" on a 4.165" bore with 0.0055" clearance. That's with a light piston, a light Crower rod, and a really good wrist pin. I'm near touching at that.

For a bracket engine, the valve clearance is too tight for comfort, too.

Tom Goldman · 11-19-2015, 12:19 AM

Like Alan said ,Piston is gonna kiss the head a little . I'd use a.050 or .055 " Cometic gasket .
I'm assuming it's the exhaust thats tight on the radial clearance , you can cheat a little and shift the head with offset dowels and avoid having to cut the pocket.
I did that more than a few times back in the old TRW piston days.
I've run valves that tight myself,but i wouldn't recommend it . they will kiss the piston .

11-18-2015, 09:59 PM	#1
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,118 Likes: 1,576 Liked 1,837 Times in 417 Posts	Re: bbc clearances The quench is too tight. I can't get away with closer than 0.042" on a 4.165" bore with 0.0055" clearance. That's with a light piston, a light Crower rod, and a really good wrist pin. I'm near touching at that. For a bracket engine, the valve clearance is too tight for comfort, too. __________________ Alan Roehrich 212A G/S

11-19-2015, 12:19 AM	#2
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,477 Likes: 892 Liked 883 Times in 237 Posts	Re: bbc clearances Like Alan said ,Piston is gonna kiss the head a little . I'd use a.050 or .055 " Cometic gasket . I'm assuming it's the exhaust thats tight on the radial clearance , you can cheat a little and shift the head with offset dowels and avoid having to cut the pocket. I did that more than a few times back in the old TRW piston days. I've run valves that tight myself,but i wouldn't recommend it . they will kiss the piston . __________________ Tom Goldman 1500 SG , 1506 STK