Timing: chain tension

[Vincent 911]

I am currently rebuilding the top end of my 3.0L

Current step: canshafts timing.
I follow Waynes book.
Here is my question: I set the timing overlap at 0.1mm at 1.26 mm (964 cams) with high tension in the chain. After that I put my brand new Carrera tensionner (with oil in it per Wayne's procedure) in the chain housing: I have 0.1mm of diffrence in the timing overlap. That puts my timing out of the range (1.26 +/- 0.1mm).

1- Have you already experienced that?

2- Tonight my left camshaft is set for 1.25 mm WITH the Carrera tensionner. Should I keep this adjustment or redo it with full tension in the chain?

Thank you

High tension in chain: 1.16mm


Carrera tensioner tension in chain: 1.25 mm

[john walker's workshop]

i would replace the chains. look how extended the tensioner piston is. timing should be done with normal tension on the chains in my opinion. stretching everything real tight will give a reading different than what the engine would normally run at, so why do that?

[911pcars]

I concur with John, but here's another thought:

A rebuilt engine sometimes offers the appearance of chain stretch even with new chains. This is because the cams are sitting closer to the crank due to remachining material from the case, cylinders and cylinder heads in the course of making all surfaces parallel and consistent and to adjust deck height and compression ratio. If that's the case, one way to increase the clearance between the idler pulley arm and the chain box wall is to use a larger gear on the idler arm.

Sherwood