Push rod length 101?

[goingballistic]

OK here goes............I'm stumped and feeling pretty stupid at this point. I'm trying to measure the length of the push rods I need in the 388 I'm building. I bought an adjustable rod from Lunati and tried that. I'm missing something as it's not doing what I thought it would do.

Does anyone have a "dummies guide" for push rod measuring?

I've tried rotating the assembly with the rod in place and don't seem to get the valve at full open....assuming that the rod is too short. Everything I've read states that I need a solid lifter in place, the "right size" rod ( if I knew that, I'd be all set) and the rockers in place.

Anyone got a full step by step on how to do this, I don't have any solid lifters, only hydraulic. There has to be a no brainer way of doing this, I'm thinking I'm turning this into a rocket science project when it's really a find Waldo thing.

 

[L48]

With a hydraulic lifter you will never get full open when the engine is not running. The lifter will compress down - hydraulic lifters rely on oil pressure to stay pumped up. (please ignore if you already know this)

If you need to measure, buy one solid lifter and use it to measure only.

What makes you think that you need a pushrod that is any different than the stock length? Do you have some special heads?

 

[goingballistic]

Thanks yea I am aware of the hydraulic lifter issue but before I go out and buy a solid I wanted to know step by step how to do this so if there is other stuff i need I get it all at the same time, this is holding up my rebuid.

Yes I have new heads, they are AFR 195's, the deck is cleared to zero and a new cam. I am concerned about getting the exact height of the rods correct. I have read horror stories of not doing this the right way and after sinking this kind of cash into the motor.............my wife will hang me ad if I blow this up.

This is the last piece of info I need to finish the block for the dyno.

 

[L48]

I looked through my Chevy performance books and found a section on valvetrain geometry in a great book I called "Smokey Yunick's Chevy Engine Guide". I highly recommend this book.

It was quite a lengthy section - over a page and a half, so I'll give you some key parts:

"The only way to inspect the geometry is to assemble the actual valvetrain and visually check the operation of the rocker arm."

"Turn the crank by hand - activating the valvetrain - and get down close to the rockerarm so you can see the interaction between it and the tip of the valvestem as you move through a complete cycle. Observe carefully as the roller on the valve end of the rocker (he assumes roller rockers are used) sweeps back and forth across the tip of the valve."

"The point of contact should never move closer than .020" to the edge of the stem butt. Ideally the point-of-contact should be slightly inboard of the valvestem axis when the rockerarm is in the lashed position (closed).

As the cam lobe begins to activate the rockerarm and puch the valve open, the point-of-contact whould initially move outboard, away from the rockerarm pivot. At about the midpoint of valve lift the point of contact should stop moving outboard, and during the final stages of lift it should sweep back inboard toward the rockerarm pivot.

Actually, the most critical thing is to make certain that the point-of-contact does not move too near or ride off the edge of the stem butt. If it does you are going to have a lot of trouble."

He goes on to say that he would only use the adjustable pushrod to determine what length was needed, then order a set of that length.

I couldn't find any sections on stopping your wife from hanging you if it blows up :L

 

[goingballistic]

L48, thanks for the info.......and looking out for the wife part !!!!

I made a solid lifter last night by taking apart an old hydraulic and making the lifter end so it can't move. I then inserted the rod into the engine and rotated it. The rocker ( yes they are rollers) does move from just behind the center line of the valve stem toward the center line, acutally just past it and then back toward the inboard side. From the geometry part it "looks" like it's doing what it's supposed to. The confusing part is that the adjustable rod is measuring shorter than the stock rod. The AFR heads are actually higher than a stock head, with a higher lift cam, which it is, I would now think that the "new" rods would be as long if not longer than the stock rod, hence my confusion.

I sent a note to AFR last night asking them about this and am waiting for a reply. What I don't know is the actual valve travel spec, basically I don't know if I'm pushing the valve open enough. The stock rod pushed further but is that too much? AFR, in their install instructions say that the stock rod or 0.100 longer should work.......we'll see what they say. I'm also concerned that the rocker is not set to the right height....ie valve lash adjustment.

I've kind of got a chicken and egg thing going. I can't check the valve lash without the right rod and I can't find the right rod without the valve in place.......this is more than likely why people charge so much for this work, the knowledge base is invaluable........

Cheers.

 

[JohnZ]

Manley and Moroso both make "Pushrod Length Checkers" that slide down over the rocker stud; when it touches the valve stem, you set your adjustable checking pushrod for contact at the pushrod end of the "checker", and order pushrods that length.

 

[AKRAY4PLAY]

this is what you need, it'll make life much better. http://store.summitracing.com/partdetail.asp?part=PRO%2D66789&N=4294925139+4294925138+4294859056&autoview=sku

 

[goingballistic]

Alrighty then........it appears that I've figured out the push rod length, it all relates to the roll across the tip of the valve..........I was making this out to be a rocket science project and it's actually fairly straightforward. I am overly concerned about frying this engine ( actually I'm afraid of my wife )

link here if you're interested-->http://carcraft.com/techarticles/116_0401_push/

Fairly good detail about how to measure the pushrod length and was the most helpful of everything I read. The plastic "thingies" I was cautioned to stay away from as they produce inaccurate measurements/results. As you more than likley know, the rod length is not overly critical but saves a lot of wear and tear if it's done right. With $1300 heads, I don't want a melt down ( see above statement about wife).


Next problem is the valve lash. Anyone have any experience on doing this. I've read several articles on this and it seems pretty easy to do.........is there anything I need to watch out for???

Signed "Dyno bound in July"..........Thanks to all the help on the CAC !!!!

Thanks.