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Sunday, April 24, 2016

Camshaft Clearance Adjustment and Check for an RB26DETT Engine

Super Taikyu R34 N1 with NISMO built engine. Altia R34 as ran in World Challenge in the USA. 
Setting valve or tappet clearance in an RB26 engine. The RB26DETT engine is a shim under bucket, twin cam, 24 valve engine.   The stock cams are a 32 mm base circle. There are some aftermarket cams that are a 30 mm base circle.  These smaller base circle cams require a taller bucket, custom shims, or custom valve stem clearancing.

  • Camshafts
    • Intake 8.58 240 duration 113 deg Lobe Center -R34N1 117 deg Lobe Center
    • Exhaust 8.28 236 duration 125 deg Lobe Center-R33N1 120 deg Lobe Center - R34N1 121 deg

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Stock exhaust cam in an RB26 head
The exhaust valve clearance is tighter than the intake side, as the exhaust valves are sodium filled from the factory. If you change intake or exhaust valves, check with your parts manufacturer for recommended tolerances.  Too tight, or too loose are both bad things, that can rob you of horsepower.


  1. The RB26 has a long camshaft. If you are not careful when loosening or tightening it, you can snap it in half. 
  2. Shim under bucket means the camshaft will be in and out of the head a few times to get the clearance correct
  3. If you are using aftermarket parts, try and use them as a set. Camshaft, springs, buckets, retainers. Mixing and matching is a recipe for disaster. 
  4. More than around 9.15 mm of lift needs cam lobe clearance. The head needs to come off, and it has to be ground to clear for a tall lobe, UNLESS its a 30 mm base circle cam, and under about 11.15 lift. 
  5. Small base circle cams NEED taller buckets, or custom shims. 

Valve clearance Intake cold - 0.45 mm +/- 0.03 mm
Valve clearance Exhaust cold - 0.38 mm +/- 0.03 mm

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