Checking piston to valve clearance with 0 lifter preload.
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Checking piston to valve clearance with 0 lifter preload. I recently went to a comp cams 232/234 112 +2, and milled a set of stock valved 241's .040. I flycut .090 reliefs into the pistons. Im using .060 GM MLS gaskets. My calculations say im going to have .011 more lifter preload using 7.400 pushrods using both the pushrod calc excell spreadsheet, as well as my calculations by hand.
Now im checking piston to valve clearance. I used my old lifters and some low tension checker springs and mocked up the head.
1. When I torque rockers down, the test springs dont have enough tension to give me any lifter preload, so the valves open even opposite the cam lobe when they should be closed. When i get to the cam lobe the valves hit the piston and i cant turn the motor.
2. When I only tighten the rockers down enough to set 0 preload (just resting snugly on the pushrod and valvestem, then the motor turns over fine and I maintain much better than .125 piston to valve clearance throughout the rotation of the motor. Its probably closer to .200 clearance, but I only had a .125 spark plug gapper to check with. I tested atleas every 2 degrees from 15 degrees before to 15 degrees past TDC.
I assume the second way is the correct way to test using the low tension test springs. I just wanted to verify that it was correct here on tech. I can only assume that I have a large ammount of lifter preload, however like i said above, its only .011 more than stock.
Now im checking piston to valve clearance. I used my old lifters and some low tension checker springs and mocked up the head.
1. When I torque rockers down, the test springs dont have enough tension to give me any lifter preload, so the valves open even opposite the cam lobe when they should be closed. When i get to the cam lobe the valves hit the piston and i cant turn the motor.
2. When I only tighten the rockers down enough to set 0 preload (just resting snugly on the pushrod and valvestem, then the motor turns over fine and I maintain much better than .125 piston to valve clearance throughout the rotation of the motor. Its probably closer to .200 clearance, but I only had a .125 spark plug gapper to check with. I tested atleas every 2 degrees from 15 degrees before to 15 degrees past TDC.
I assume the second way is the correct way to test using the low tension test springs. I just wanted to verify that it was correct here on tech. I can only assume that I have a large ammount of lifter preload, however like i said above, its only .011 more than stock.
The 2nd way is the way to do it but you really need to invest in a dial indicator to be accurate. Can you tell if the lifters are being preloaded when the vale is open? They shouldn't be with the soft springs. The measurement you get is actually the minimum clearance since the lifter will add to that once the engine is running and the preload is in play. That's to bad you went with such thick head gaskets and valve reliefs. You could have really tightend up the quench with thinner gaskets, but then you would have needed shorter pushrods too. Oh well. 
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Yeah, I know im leaving a bit on the table with the thick head gaskets, but I had them, and i couldnt get others on such short notice (and i didnt want to spend the rediculous cash on cometics). The car is my daily driver and its been down for a couple weeks as it is.
I also do have a dial indicator, but i dont have the right stand to check. Regardless, Im positive ive got more than enough clearance on the second way. And no, i dont have any lifter preload with the test springs. I could barely push in the lifter plunger with my finger.
Thanks for the reply. Im in new terratory thats only existed on paper before this...
I also do have a dial indicator, but i dont have the right stand to check. Regardless, Im positive ive got more than enough clearance on the second way. And no, i dont have any lifter preload with the test springs. I could barely push in the lifter plunger with my finger.
Thanks for the reply. Im in new terratory thats only existed on paper before this...
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Originally Posted by slow trap
use some clay or play dough and you'll know exatly how much clearance you have.
I guess i could leave the rockers loose and set to 0 preload, but thats effectively what i did with the sparkplug gapper. Im confident ive got a ton of room. TSP says they mill .015 with this cam. I milled .040. But I put in .090 flycuts, so i should have plenty. .125 is a good safe minimum, and my test shows that I had atleast that much.
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Thanks for the reples all, but at this point the heads are on and shes well on her way to going back togather. Ill keep it in mind for the next job though. Thanks again!
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Verdad Gallardo You can still check with the heads on if you want, but you will need an adjustable pushrod, dial indicator and a method of slowly turning the crank a couple of degrees at a time.
another way you can check witht he engine assembled is to get an in-car spring tester. what it does is hook onto the rocker arm and it has a handle to compress the spring (using the rocker to open the valve). you can get a good idea of how much clearance you have by turning the engine over and using the tool to open the valve a little farther.
moroso makes them and i beieve summit or jegs has them.
moroso makes them and i beieve summit or jegs has them.
