Topic: CB400f Minimum Piston to Valve Clearance

[Tom R]

Hi all.
I’m assembling a 400f motor I’m hoping to run in AHRMA vintage superbike lightweight…
Carrillo Rods, hd studs, CR26 carbs, ported head…
Kibblewhite valves and springs (new)… +1mm on the intake.
Megacycle race cam and custom Weisco pistons.

I installed the cam pretty close to straight up
The tightest I'm seeing is .058” on the intake, and .060” on the exhaust.
Too tight? What’s a safe redline on a build like this? 12k? 13k? [/img]

[MRieck]

I'd run about 65lbs of spring....Those clearances should be OK. Depending on your race schedule I'd change those springs out every 2 seasons....I have seen them lose a good amount of pressure. Brent Waller and others can testify to that too.

[Tom R]

Thanks Mike.
From memory, the kibblewhite springs are around 45lb?
Shims? 
 -Tom

[MRieck]

Thanks Mike.
From memory, the kibblewhite springs are around 45lb?
Shims? 
 -Tom

Yes Tom. You will need to use the OEM spring bases. The large shim is .060 thick if I remember correctly. 2 of those (which is all you can fit secondary to the height of the guide) and 2 or 3 small, inner shims. That should work unless the valves were sunk a lot during a valve job.