weaz4200

So here's the 411. Working on a 383. In process of measuring for pushrods and am hitting a wall and not sure what to think or do next. This is my first build and I'm in need of help. Here's what I've done so far....

1) Checked the lobe lift on the cam and it comes out to what the cam is supposed to be. In this case, .353 lobe lift. So I know the cam card and cam are correct as far as specs.

2) Mocked up check springs and used a comp cams adjustable pushrod. I used the solid lifters that were included with the degree kit... At the time of using these lifters I did not check to see lift at the valve, I was just checking to see what witness mark I ended up with... I was getting something like 7.950" for length. Mistake on my part... The solid check lifter and the hydraulic roller lifter I have are different sizes (length wise)

3) So I decided to use the hydro lifter I got, along with the check springs... Now it's more like it... Getting a length of between 7.300 - 7.350... So I'm thinking I'm good. Witness mark looked good but also noticed the lifter bleeding down when I had a dial indicator on the valve retainer...

4) It just so happens there were 2 7.350 pushrod's laying around the shop. Installed them and checked the witness mark.. It looked relatively good, but still somewhat biased towards the exhaust side of the valve tip.

5) Put a dial indicator on the retainer and proceeded to check what the geometry looked like at mid lift... but before checking mid lift I decided to check max lift... and now here's where I'm stuck.

I have 1.6 rockers and the mock up 7.350 pushrods... I am supposed to have a .565 lift with these rockers... Yet once I achieved max lift as per the indicator it only registered .395!

WHAT?! What am I doing wrong here?

So I figured the difference from what it should be, .565 and what the indicator said, .395... THat's .170 less....I can't see the loss would be on the valve side... So I calculate backwards... .170 divided by 1.6 is .106...

SO I'm not sure if the lifter is preloaded .106 or it's a combination of lifter preload and pushrod length making me lose the lift.

I'd like to hear opinions.

1 FMF

iTrader: (1)

when the rocker rocks it's tip will swipe across the valve stem because the motion of the rocker tip is a circular arc. so with the lifter on the base circle of the cam and having the correct preload on the lifter and rocker tightened the rocker tip should be a little biased on the outside of the valve stem. then when the rocker rocks the tip will swipe across the middle of the stem face to the inside, then back to the outside. this swipe pattern that happens you want centered across the valve stem, and choosing the correct pushrod length accomplishes this. when checking this during the build process you have to account for lifter preload and bleed down, so you need to pressurize the oil system then rotate the crank to get the valve your checking at max lift. As long as your check spring has same installed height as the springs you're going to use, then your measurements will be valid and represent what's happening when the engine is running. if you have no oil in the lifter and your just compressing the lifter plunger till it bottoms out then I think that's around 0.060" of travel, or you can measure it on one of the lifters. 0.060 x 1.6 = 0.096" so not the complete amount your off but quite a bit. so it sounds like when you're checking valve lift you have the lifter plunger bottoming out and loosing some distance which results in less valve lift. to check max lift i would verify the lifter is full of oil, pressurize the oil system with a drill & prime tool and rotate the crank a few times then put a valve on max lift. measure the compressed height of your valve spring to see what your valve lift is then. hope that helps.