Quote:
Originally Posted by tortuga
I wonder if anyone knows the answer? Scenario; Windsor iron block aluminum heads, as the motor goes form ambient to what 180+ degrees F, I would submit that the heads would get taller and wider (a minuscule amount)?
Resulting in the intake (which also gets wider) being “pinched” in the valley tighter?
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I don't know the answer regarding intakes, but I have listened to and studied my iron block/aluminum headed mill for almost 15 years and the fact that it has a solid, flat tappet cam and the clatter that it makes, or doesn't make, depending on the time and temperature after start up. I gap my valves at .018" COLD and I have aluminum roller rockers. The cam maker calls for a lash of .025" HOT. The classic answer to the difference between cold and hot lash on an iron block/aluminum headed engine is .007", give or take. When I first start my engine up COLD, there is virtually
no valve clatter at all. When I then take her out and she begins to warm up, as measured by the
coolant temperature, the valve clatter will be at its loudest and sharpest when the coolant becomes hot but the
oil is not. I presume that the aluminum heads and rockers have now had a chance to heat up, and expand, but the iron block has not. As the
oil temperature reaches the same temperature as the coolant, the valve clatter reduces down to a "normal" level of clatter. I presume this is because the temperature of the iron, and the expansion of the block, has now had a chance to catch up with the temperature, and the expansion, of the heads. A few years ago we had a thread over on the FE forum about the difference between cold and hot lash on iron block/aluminum headed FEs with SFT cams. A couple of guys took it on themselves to go out to the garage, check their lash while cold, then they drove the car until the coolant showed it had warmed up, pulled back in the garage, checked their lash again, and proclaimed the difference to be .011" to .013" difference! That was quite a change from the standard answer. Of course they did not run their engines until the block was at the same temperature as the heads, just until the coolant got hot. When I run my engine, the lash starts out as .018" and the valve train is quiet as a mouse, the lash then grows to .030" or more for a short while (when the heads have expanded but the block has not), and the valve train has a really nice, pronounced clatter to it. Then the lash shrinks down to .024" or so and has a "normal" clatter to it. It actually took me years to figure this out.
Hope this helps.