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#1
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Whats wrong with my lift?!
Hey, I'm trying to figure out a ballpark figure on the lift of the cam currently in my engine and check piston to valve clearence so I can figure out if the cam I want will clear. I rigged up a dial indicator(with range of 1") onto the valve spring retainer and turned the engine over(by hand) and I got about .365" of lift!! Whats going on! Am I doing it wrong? When I checked the piston to valve clearence it was only a bit more than the lift. This has to be wrong.
Please help, it's very frustrating Thanks |
#2
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You do have a hydraulic cam, don't you? If that's the case, then propably while testing the lifter plunger compresses to the bottom and that affects the lift. Lifter ratio also may have an effect on this.
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#3
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Use a single solid liffter and correct pushrod to figure it out. Its also good to have for setting up the cam.
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#4
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To measure valve to piston clearance, it is soo much easier to put plasterseen on the piston and drop the head and valvetrain on. I'm thinking of how to do it with the engine together and in the car. But there is a wide range of motion where the valve is open. And the piston is moving. I don't think there is a good accurate way. I have measured cams with them out of the engine but going off the valve is best.
I know when measuring the cam out of the engine you have to times the lift by rocker ratio. Its weird that you don't have much valve to piston clearance and it shows such a small lift. You need around .100 valve to piston clearance. |
#5
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I dont know if you have the intake pulled or not so everything is easily accesable but if you can remove the lifter and replace it with a solid, use Rumblefish's idea, he is right with going with a solid lifter and correct pushrod length to get the true reading. There is another way to get a reading that is not as true as Rumblefish's but better than how you checked it. It doesnt take into consideration the ratio but at least you can check your cam lift fairly close. Remove the rocker shaft and arms. Set up your indicator so the travel is parallel with the pushrod travel. when you turn your engine over without the force pushing down against an unpumped lifter, it wont colapse and your reading will be more accurate. Not perfect but much closer to what it is. Then take that number times the stated rocker ratio and your in the ball park. LIke I said, its not perfect but it removes 1 variable that you had with the collaped lifter. I did this while I was waiting for my solid lifter and adjustable pushrod from Hughes just to test it out and I was within .004 between the 2. Rocker ratios will vary though and what you have or think you have will then determine the final outcome. I had to go thru 3 sets of Roller rockers just to get 1 good set because they varied so much.......good luck.......dj
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#6
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If you want a cheap easy way to verify piston clearance with the engine assembled you could try this old trick.
Install feeler gauges between the rocker arms and the pushrod, stack them together to come up with the needed clearance.... .100 on the exhaust side is normal. Slowly turn the engine over by HAND 2 complete revolutions. If it turns over without any binding, your good to go. Make sure and do it on at LEAST one intake, and one exhaust rocker. I did this on my last engine, it worked slick. Later, Jeff C. |
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