[Tigers] Stock 260 Engine Maximum Cam Lift

[Tom Witt]

>>>Even with the original 1.67" intake valves, a 0.010 deck height and a 0.040 thick head gasket, I don't comprehend where a 0.070" minimum valve to piston clearance is possible.<<<

I don’t know to what extent you are versed in the engine, but I’ll put this out there and use as you see needed (no insult to your knowledge intended in my comments).

The valves are recessed in the combustion chamber so the total of the deck height and the gasket in and of themselves do not determine the piston to valve clearance (if in fact that is what you assumed???). Probably the best way to determine the actual clearance is to:

A. If the head is not installed remove a larger intake valve spring. Set the head on a flat surface with the valve down, then set and zero a dial indicator on the valve stem tip. Push the valve up and measure the distance.   Add the stated deck and gasket thickness and that gives you the clearance. Unless you check them all there is a likelihood that not all will be the same. Casting accuracy and seat recession from wear or prior valve jobs can change the numbers. But, hopefully the others will be “close.”

B. If the head is installed you can bring the piston to TDC, remove the valve spring and do similar.  There is the likelihood that carbon build-up will give a lower number (but is the actual functional clearance). Also do not add in the deck height or the gasket thickness as they are already present. DO NOT crank the engine while doing this or you can drop or bend a valve. A narrow magnet may be required to pull the valve back up. Narrow rope can be fed into the chamber through the spark plug hole to support the valve while the spring is reinstalled. 

Remember this gives you the total distance until a valve hits a piston so the required clearance (0.070?) will have to be subtracted from the total number.  Also, Cams ramp up and down the lobe and may not be at its highest lift when the piston is at TDC.  Therefore it is possible that the cam lift can be greater than the minimal clearance because the piston is not at TDC (or near enough) when it occurs.

  People have used talc powder on clay on top of the piston then cycled the engine through a few revolutions, and measured (Calipers) the height of the clay. Thus getting an “active” rather than a theoretical valve clearance.  This requires assembly/unassembly to measure and a very light spring so as not to collapse the lifter (if hydraulic). Also consider that advancing/retarding the cam from the centerline will also alter these “active” clearances. Lastly, the valve stem to rocker tip clearance (mechanical lifter – if used) will create additional clearance.

I hope there is something you can glean from this and I haven’t created any confusion. 

From: Rob Hogan via Tigers 
Sent: Friday, April 22, 2016 9:17 PM
To: Tiger's List 
Subject: [Tigers] Stock 260 Engine Maximum Cam Lift

Does anyone have experience using a hydraulic lifter camshaft with a lift greater than 0.440 (Clymer book page 41 maximum) in the flat top piston stock 260 cu. in. engine?

Even with the original 1.67" intake valves, a 0.010 deck height and a 0.040 thick head gasket, I don't comprehend where a 0.070" minimum valve to piston clearance is possible.

 
Rob Hogan
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