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Ask Anything - April 2014

Lash Tactics

Ron Nelson; Sonora, CA: I have a 2,000-pound T-bucket with a 350ci small-block Chevy. I installed a solid lifter cam that has 256 degrees of intake and 264 degrees of exhaust duration with 0.506 lift and a 105-degree lobe-separation angle. The camshaft to lifter clearance is intake 0.026 and exhaust 0.028.

Is there a way to set the lifter clearance with a cold engine? I have the degree tape on the harmonic balancer, so I can set each cylinder to TDC. Would the cold setting valve gap be less at a higher engine temp? Would the valve gap on both the intake and exhaust be set at a single spot on the degree tape? Adjusting the valves on a running, warm/hot engine requires parking in the center of a Walmart parking lot at 1 a.m. and wearing a wet suit because everything gets covered with oil. Any light you could shine on this will help greatly.

Jeff Smith: You're right, Ron, that setting lash on a running engine with the valve covers off is a messy affair—but there's a much better way. A long time ago, I learned how to set lash on a static engine that doesn't require memorizing the firing order or using a timing tape. It's a really simple process, and all you have to remember is "Exhaust Opening and Intake Closing" or E-O-I-C.

The process goes like this: Warm the engine up, pull all the spark plugs (so it's easier to turn the engine), and remove the valve covers. Let's start with No. 1 cylinder. You can start anywhere, but this is convenient. No. 1 on a small-block Chevy is the front cylinder on the driver side. Slowly turn the engine clockwise until the exhaust rocker has opened the valve roughly a quarter of the way. At this point, the intake lobe on this cylinder is on its base circle, which allows you to set the intake lash. In your case, the intake lash figure is 0.026 inch for a warm engine, so set that clearance between the valve tip and the rocker arm. Once that's completed, turn the engine until the intake valve is roughly halfway closed. Now the exhaust lifter is on the base circle of its lobe, which will allow you to set the lash at the 0.028-inch clearance. You've now completed both valves for that cylinder, so you can move to the adjacent cylinder. I do it this way because of the simplicity, since I can just run right down the line of valves doing each pair of valves per cylinder. For the rookies who have not tried this before, you can set the intake first and then the exhaust; the order isn't important as long as you follow the order of lashing the intake when the exhaust is opening and lashing the exhaust when the intake is closing. The key is making sure the valve you are setting is actually on the base circle of the lobe.

The one drawback to this procedure is that you have to turn the engine over a couple of more times than you would if you set the lash according to the engine's firing order. Once you become adept at setting lash this way, you will discover you can do it on any four-stroke engine of any design—a V2, flat-four, inline-four, V6, V8, or V12, it doesn't matter. All you need to remember is Exhaust Opening and Intake Closing (EOIC). If you get the letters confused, just turn the engine over and watch the valves operate. You will quickly realize that trying to set intake lash with exhaust closing won't work because the intake valve is also opening and because the cam is in its overlap phase. The beauty of this procedure is that even if you forget the sequence of the letters, the engine will remind you. This procedure is also the same for preloading hydraulic lifters. The only difference is you set hydraulic lifters with a specified amount of preload instead of clearance. For most performance situations, I like to use a quarter turn of preload rather than a full turn or more, but there is evidence ("8,500 RPM!" Feb. '14) that preloading a high-quality hydraulic lifter to about a turn and a quarter will improve performance.

You also asked about setting lash on a cold engine, and you are correct in assuming the lash changes between a hot and cold engine because of something called linear thermal expansion. This simply means that as an engine comes up to operating temperature, the metals expand. We won't get into the metallurgy, except to say that aluminum expands roughly twice as much as cast iron, so changing the lash specs from the published hot specs to a cold engine will depend upon whether the engine has aluminum or cast-iron parts. Crane has published a handy little chart that we've reproduced that gives you a starting point. To use your engine as an example, we'll assume for our first example that the engine is a cast-iron block with iron heads. With a hot intake lash of 0.026 inch, to set the lash on a cold engine you would add 0.002 inch for a total of 0.028 inch. As the engine warms up, the lash will tighten up, but you should still recheck it to ensure that the clearance is what you desire.

For an engine with an iron block and aluminum heads, Crane's spec changes to subtracting 0.006 of lash from the hot setting for a cold engine. If the engine is all aluminum, then you would subtract 0.012 inch from the hot lash for a cold setting. Again, these are merely recommendations to start a cold engine, and you should recheck the lash once the engine is at operating temperature.

I will also take this opportunity to dive into one of my pet peeves around setting lash. It seems that a wives' tale still persists that you must constantly reset lash on any mechanical lifter street engine. I've heard guys say they have to reset lash as much as once a week on a daily driven street engine with a mechanical lifter camshaft. If the engine's lash is in fact changing, my contention is that it's likely due to those stock-type locking rocker stud nuts that are allowing the clearance to loosen. Those stock pinch nuts are only good for perhaps one setting. After that, they begin to lose their built-in tension. After several settings, they are probably no better than a regular fine-thread nut. In that case, pitch those things and buy a set of poly locks. Now that the adjusting nut is truly locked in place with an Allen set screw, the lash should not change. Think about it: If while using poly locks the lash changes within a short number of miles of driving, the only reasonable explanation is that something is either bending or wearing very rapidly. As an example, the 420ci small-block Chevy in my '65 Chevelle uses a mechanical roller camshaft that's been in the engine since 1991. In that time, it has been raced unmercifully at multiple drag races, hillclimbs, road-course events, and even two 90-mile WOT Pony Express Open Road Races. Within that time, I have checked the lash dozens of times, and it has never appreciably changed. The valvetrain is very stable; the springs probably should be replaced because they are so old, but nothing is wearing—so the lash has not changed.

More Info

Automotive Racing Products; 800/826-3045;
Comp Cams; 800/999-0853;
Crane Cams; 866/388-5120;

CC Quickies

The color for our '71 Demon project car is called '69 Chrysler Blue Fire. Look for it next month.

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