TDC lift on advanced (or retarded) cams.

[838]

Is there a conversion formula to calculate the TDC lift changes that occur when advancing or retarding cams? +/- 4 ond +/-2?

[Ohio HD]

There's no way to accurately determine TDC lift changes when advancing or retarding a cam without actually measuring. The shape of the lobe plays a huge part in what the lift is changing to.

That being said, this will only estimate the lift change.

(TDC Lift / Intake Close) x (Intake Close + Advance degrees)


Also don't make the mistake most do, advancing the cam increased intake TDC lift but decreases exhaust TDC lift.

[kd]

If it was me, I think it would be a degree wheel, dial indicators, clay and a Trock valve travel checker tool.  As Ohio said, it's too hard to adjust for unknown variables just using theoretic numbers.  Depending on the cam and valve size the Trock tool will also help confirm valve pocket eyebrow and valve to valve clearance.  Kinda fail safe and evidence based.

[Don D]

Maximum lift at overlap does not happen at tdc. It is higher at 10 deg either side

[kd]

   Good information Don and another good reason for guys like me to use the Trock tool when using close tolerance cams and valves.

[838]

Maximum lift at overlap does not happen at tdc. It is higher at 10 deg either side

Thanks. So would you check clearances for TDC and at +/- 10*? Would this effect valve to piston clearance any? Or just valve to valve?

[Don D]

Too close is too close. Check it. Different cams have different lobe geometry.
Are you going to put a degree wheel on and determine true tdc? If not all the discussion becomes just empty bandwidth. You can determine lobe lift at the various points and decide for yourself. No trock tool is needed but the springs need to be off. The rest is math. Valve drop method has had quite a bit of discussion before. Dykem can determine valve edge for radial clearance measurements. Checking springs and dial indicator is used.

[Don D]

There is a good video here:
https://youtu.be/PXzO9u93-n8

[mike jesse]

Something else that needs to be brought up is retainer to valve seal clearance.
Easy to check while doing your V/P clearance routine.

You Tube has a few videos put out from Reher&Morrison Racing Engines that go into
great detail on valvetrain checking procedures.
Worth a look.

T Man also has an adjustable cam sprocket for the TC engine that works quite well if a person wants to spend
the time to degree in the cams. Part #216025.

[jsachs1]

Retainer to seal clearance, less valve springs, should be checked, and measured, before the final assembly of the heads. Seal OD to inner valve spring ID, needs to be checked also. 1 reason the MoCo released their "Bend Me Over"  expensive black viton seals.
John