pushrod length?

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73dartneedswork

73dartneedswork

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I'm trying to determine if I have the correct length pushrod. The intake is closed and the exhaust is just starting to open. The pushrod just barely spins. There is no up and down movement. Does this sound like it's the correct length?
 
You really need to measure how much lifter preload (I assume you have hydraulic lifters) you have with a dial indicator to tell for sure.
 
Things we need.

What engine?
What machine work?
Heads milled?
Block decked?
Adjustable or non adjustable rockers?
What kind of rockers? Stock? Aftermarket?
Solid or hydraulic lifters?

You might as well have asked us what you look like because there is just as much chance of us knowing that as knowing the answer to your question.

It's along the lines of "I need help. My car is red."
 
It's a hydraulic roller with stock magnum rockers.

I have some valve train noise after a cam swap. I bought an adjustable push-rod tool so I could measure and see if my noise was being caused by to short of pushrod.

I've never measured pushrod length before and I'm trying to get this figured out.
This is how I was told to check the pushrod length
1. Run engine for a few minutes to make sure the lifters were pumped up.
2. Put the #1 cylinder on top dead center
3. Remove the rocker, pull the pushrod.
4. Collapse the adjustable pushrod so that it is shorter than the
pushrod that was removed. Install the pushrod and Re install and torque the the rocker
to 22 foot pounds.
5. Extend and twist the adjustable pushrod so that is in the socket of the lifter and rocker.
As soon as you feel the pushrod start to drag, lock down the adjustable pushrod.
5. Remove and measure the pushrod.
6. To know the correct pushrod length you need to add .050 to account for pre-load.

After getting on top dead center, I thought I would check to see how tight my push rods were. Well they spin, but don't move up and down. According to the method I was told this would mean that I need pushrods that are .05 longer than what I have. My current pushrods are the stock length.

Am I on the right path?
 
Again, what engine? LA with Magnum heads? Magnum? There's a reason I asked you all those questions. Is there any particular reason you didn't answer them other than the fact you obviously are making it very difficult to help you? I am at a loss for words, really.
 
73dartneedswork said:
I didn't see your post.
It's a Magnum with Engine Quest Heads and a Howards cam
Click to expand...

Thanks. My advice is simple. Put adjustable rockers on it. It's a performance engine. It needs them to assure consistent lifter preload across the board. Then measure for the correct pushrod length.
 
RustyRatRod said:
Thanks. My advice is simple. Put adjustable rockers on it. It's a performance engine. It needs them to assure consistent lifter preload across the board. Then measure for the correct pushrod length.[/QUOT
X2! !!! Went through this, same bolt on combination. (every combination, is different) I did the Crane conversion, with the Hughes 1110 spring/retainer combination. (Used a Howards retro fit LA hydraulic roller, and matching Comp Cams 1.5 ratio Chevy roller rockers.) Use an adjustable pushrod, for final length, check for sweep on the valve tip. (Hughes engines ,has a sweet conversion kit,. It's pricey, but nice...)
Click to expand...
 
I agree with what's been said. I will add that .005" either way won't make or break it with hydraulic lifters (assuming the current ones are within the operating preload range of the lifters).
 
Your method of measuring is correct but if the block hasn't been square decked you could see differences of up to .020" from one corner/side to the next (factory machining is shoddy at best) rendering your measurement ok for one part of the engine but inaccurate on other quadrants. Factory parts are so mild they can get away with more variance than performance parts so I agree with Rusty that adjustable rockers are the way to go. If your block was square decked properly you can get away with measuring like you did.

Even when you run the engine to pump up the lifters the lifters automatically self adjust so what you saw with the pushrod being able to be spun by hand is common but doesn't tell you anything about how much preload you actually have, just that it has some preload and isn't bottomed out in the lifter. When you installed the adjustable pushrod and adjusted it so you had .050 preload did you take it out and measure it and if so how did the length compare to your current pushrods?

BTW: where did you get that you need .050" preload? I'm not familiar with stock magnum lifters so I don't know what they require so I'm just asking
 
I have some valve train noise after a cam swap. I bought an adjustable push-rod tool so I could measure and see if my noise was being caused by to short of pushrod.
Click to expand...
with your original pushrods in there I would get the dampener slit on TDC then either work with cyl #1 or #6 whichever one is on compression. get a small thin steel scale 6" ruler & make a magic marker ink mark on one side of it & set it across the valve cover rails & slide it over FAST till it touches the pushrod & makes an ink witness mark on it before it dries. then unbolt the rocker arm pedestal bolt till the pushrod JUST stops moving upward (but does not get loose & move sideays which skews your test) & make another ink witness mark then remove the pushrod(s) (doesnt hurt to do in & ex) & measure the distance between the two witness marks for your preload amount. Post what you get. Using the adjustable pushrod (1) decide how much preload you want (ie .020") (2) on base circle go CCW to lenghten it till you JUST get to zero up & down clearance with your thumb/forefinger (dont rely on feel cuz friction skews that). (3) depending on how many threads per inch the adjuster pushrod has, lengthen it that amount from zero clearance till you get your preload amount & carefully lock the pushrod locknut in place & remove it. ie 3/8-24 is 24 threads per inch. 24 into 1000 = 41.6 so a half turn is 20.8 (.021" preload). As said check the wipe pattern with light springs
 
73dartneedswork said:
I'm trying to determine if I have the correct length pushrod. The intake is closed and the exhaust is just starting to open. The pushrod just barely spins. There is no up and down movement. Does this sound like it's the correct length?
Click to expand...

Don't worry about the spinning deal. All you want to do is adjust the pushrod until it JUST removes any free play from the valve train .Than add in your desired 0.050 preload. You don't want to keep winding it down to the point where it starts pushing the lifter plunger down.
So if the pushrod measures 7.000 inch when you remove the free play , then you would order a 7.050 long pushrod. You can check all 4 corners of the engine if you like, if your worried about head and block surface machining being out of whack.
As far as checking the rocker to valve tip wipe pattern, well unless you have some way of adjusting your rocker height, then it's just a waste of time, because you won't be able to change it anyway.
 
flat shim(s) under the square pedestal to raise it. Purchase a spare pedestal & trim some stock off of it then mockup/shim it back up a bit at a time & see if you can improve the wipe pattern. keep tabs on preload and pushrod to head clearance in the tunnell
 
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