Checking for Pushrod length

-
DartVadar

DartVadar

Well-Known Member
Joined
Apr 3, 2013
Messages
1,293
Reaction score
41
Location
Alberta
So it turns out my 360s push-rods are too long, I must have measured something wrong originally...

What is the correct procedure to check for correct push-rod length? And because its a hydraulic lifter how do you take into account correct lifter pre-load? And while I'm at it I may as well check for correct rocker arm geometry. Any particular way I should do this?

I have an adjustable push-rod and I roughly determined the correct length, and kept about a thread and a half of the adjuster sticking out as I understand that is what is needed for proper oiling of the ball and cup.

Engine is a LA 360 with adjustable shaft mount rocker arms. Hydraulic cam, block was decked as well.
 
Thanks! those were exactly what I was looking for. But what is a good pre-load for the lifters? A half turn after setting zero lash?

And when measuring for pushrod length do I take into account the turning after zero lash?
 
Half to a full turn, or about .020"-.060" preload.

Measure the pushrods without any preload, but make sure to wind up all the rockers so that their adjuster nuts are fully seated (wound all the way up). Then use your pushrod checker to measure every lifter/rocker combo and write down the number on a piece of paper until you have measured all 16 pushrod lengths.

There will be a small variance in length for each measured pushrod, so take the shortest measured pushrod, and that will be the length for all of them.

Measure twice, order once!

With a hydraulic cam, you should measure the pushrod with the rocker fully seated and adjust your checking rod so that it is just touching the lifter with no preload. The idea is that most roller rockers are designed to work with the adjuster nut about half to 1 1/2 turns out (maximum two turns out) to ensure correct oiling to the pushrod cup or ball. By measuring with no preload, once all the pushrods are installed you'll find that some of them sit snug (touching both ends), while others will be a little loose. The snug pushrods get half a turn of preload and they're done. With the looser pushrods, you take up the slack first - until the pushrod is just touching both the rocker and lifter without depressing the lifter plunger - and then add another half turn.


If you want to check for correct geometry at the same time, install a checking spring on the rocker/lifter combo with the shortest pushrod. Then ink the top of the valve stem and rotate the rocker through its full arc. If the hydraulic lifter is fully bled down, then the plunger may depress while you do this and give you slightly shorter travel (less lift). You can push down on the valve end of the rocker at max lift until you see the plunger pop back out, and that will be your true lift (once the lifter is fully pumped up, the plunger won't move, and will give you full lift).

Check the pattern on the valve stem tip. If you need to use rocker shaft spacers or lash caps to correct your geometry, then you'll obviously need to measure your pushrods again (or just add/subtract the difference to your measured totals - but I'd still check a couple of pushrods just to make sure).
 
Okay good.

But as I'm turning the motor over with what I think is a good pushrod length I'm noticing that the wear pattern on the valve is closer to the valley of the motor, indicating the pushrods are too short. Would this be due to me improperly measuring or that the lifters just aren't pumping up?

Was writing as you were posting. So to accurately check for geometry I'll have to install a checking spring? Because I don't currently have one is there any way I can measure at full lift?
 
Just for the heck of it I tested for rocker arm geometry with the stock springs. So the pattern is biased towards the valley because the lifters are bled down as already stated?

Think it would be good if they were pumped up? I still want to try and find a check spring to actually check though.
 

Attachments

  • photo.JPG
    33.1 KB · Views: 584
This is where an adjustable push rod helps. As for pre load,I usually pull apart a old lifter,shim it with washers. Get you're pattern right,add some push rod length on the ones you order for pre load.
 
You're real close... This is an adjustable push rod. I would shim the lifter solid,or get the settings at 0 pre load.Either way will work.
 

Attachments

  • IMG_20140522_152226.jpg
    32.9 KB · Views: 513
I have the old lifters that originally came out of the engine before I rebuilt it, so I think I'll pull one apart and put washers in like you mentioned.

But will getting full lift theoretically make my geometry good? I kinda thought that the push rod on a shaft system doesn't effect it.

Or in my case will it just give the rocker full travel and ultimately even out the pattern on the valve, because it's pretty close to being in the center.
 
Yup I have one of those. And am I close enough to be able to have correct geometry without shims do you think?
 
OK,you are a shaft system still.(didn't know). Are they 273 adjustables,or stock stamped rockers?
 
You don't include preload when measuring for correct pushrod length. You simply get the adjuster the couple threads out and lengthen the pushrod until all the slop is gone and JUST before you start to give the plunger preload. Also, the lifters are spring loaded. The plungers should be all the way to the top of their travel, regardless of whether they are full of oil or not. If for some reason they are not, there is a problem with the lifter(s). The pattern you have on that valve stem looks good to me.
 
Abodybomber said:
OK,you are a shaft system still.(didn't know). Are they 273 adjustables,or stock stamped rockers?
Click to expand...

Yup still runnin the old shaft system, kinda wish I woulda went with a magnum 360, roller cam and stud mounted rockers...next time I guess!

And they are some PRW adjustable roller rockers.
 
RustyRatRod said:
You don't include preload when measuring for correct pushrod length. You simply get the adjuster the couple threads out and lengthen the pushrod until all the slop is gone and JUST before you start to give the plunger preload. Also, the lifters are spring loaded. The plungers should be all the way to the top of their travel, regardless of whether they are full of oil or not. If for some reason they are not, there is a problem with the lifter(s). The pattern you have on that valve stem looks good to me.
Click to expand...

Okay that makes sense, I was adding some pre-load when measuring, I'll re-do the measurements then, kinda makes more sense that way anyways.

And the lifters are all at the top, what I mean is when I turn the motor over by hand the spring depresses. So the pattern looks good? Maybe the geometry is good then.
 
RustyRatRod said:
The plungers should be all the way to the top of their travel, regardless of whether they are full of oil or not. If for some reason they are not, there is a problem with the lifter(s). The pattern you have on that valve stem looks good to me.
Click to expand...

What I meant was, when you turn the engine over, and the lifter has no oil in it, the plunger will depress, losing lift at the valve. The spring in the plunger is usually weaker than the checking spring, so unless you use a solid lifter - or give the rocker a gentle push on the valve end to decompress the plunger - then you will see anywhere from .020" or more lift missing at the valve.

That valve-tip pattern looks fine to me, too. Pushrod length will not affect geometry on a shaft rocker system - you need either spacers on the shaft or lash caps on the valve (or short or longer valves) to adjust the pattern.
 
DartVadar said:
Yup still runnin the old shaft system, kinda wish I woulda went with a magnum 360, roller cam and stud mounted rockers...next time I guess!

And they are some PRW adjustable roller rockers.
Click to expand...
If they are PRW adjustable rockers, you will need to seat the adjuster nuts before measuring the pushrods (as explained above).

And shaft rocker systems are much more stable than stud-mounted rockers - IMO, that's one advantage to LA engines over Magnums.
 
Aussie Charger said:
If they are PRW adjustable rockers, you will need to seat the adjuster nuts before measuring the pushrods (as explained above).

And shaft rocker systems are much more stable than stud-mounted rockers - IMO, that's one advantage to LA engines over Magnums.
Click to expand...

No quibbles there,use what you have. Had shaft rockers on my 408,nice setup.
 
Aussie Charger said:
If they are PRW adjustable rockers, you will need to seat the adjuster nuts before measuring the pushrods (as explained above).

And shaft rocker systems are much more stable than stud-mounted rockers - IMO, that's one advantage to LA engines over Magnums.
Click to expand...

I was re-reading the posts, and what do you mean by seating the adjuster nuts? I know you want to leave a few threads for correct oiling but doesn't the lock nut just keep it in place? Or is there a reason for it to be tightened down with the adjuster nut as well?

And really? Didn't know that, I always thought that stud systems were what people preferred. All I know is they are the biggest pain to put together when you have to take the middle rocker out for whatever reason :p
 
Abodybomber said:
Everyone has a different way,whatever works. Go get it....
Click to expand...

That's right. The only one reason "I" do it with no preload is because it's easier (for me) to get them all even. If I include preload when measuring for length, there's no way for me to assure myself that each lifter is preloaded the exact same amount......if that makes sense. Just a personal preference and what works best for me. Opinions vary as they say. lol
 
DartVadar said:
I was re-reading the posts, and what do you mean by seating the adjuster nuts? I know you want to leave a few threads for correct oiling but doesn't the lock nut just keep it in place? Or is there a reason for it to be tightened down with the adjuster nut as well?
Click to expand...
The rockers oil best with about one turn out from the seated position (more than two turns out can cover up the oiling hole inside the thread). One turn out is known as the "initial position". The "seated position" is with the adjuster nut fully recessed, or turned all the way in - in other words, loosen the lock nut, and wind the adjuster nut anti-clockwise as far as it will go so that it is "seated" and there are few or no adjuster threads showing below.

Then measure your pushrods like this with no preload.

With the correct length pushrod, all the adjuster nuts should then sit about 1/2 to 1 1/2 turns out from the seated position - or 1/2 turn in or out from the "initial position" (which - remember - is one full turn out) - after you have added 1/2 turn of preload. This ensures correct oiling.

It also ensures correct geometry: the further out (more threads showing) the adjuster nut is, the more lift you lose at the valve, as this will slightly exacerbate the 59-degree angle between the lifter and pushrod on LA (and Magnum) engines.

If you can find a set of instructions for your rockers, then have a look - all that I have explained should be in there.

DartVadar said:
And really? Didn't know that, I always thought that stud systems were what people preferred. All I know is they are the biggest pain to put together when you have to take the middle rocker out for whatever reason :p
Click to expand...
Have a look at the best Jesel or T&D rocker systems for Chevs and Fords - they are all shaft systems. Shafts are inherently stronger and more stable than studs. The downside is, you can't use cheap Chev-style stud rockers. Which is no great loss, IMO.

http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Board=QuestionAnswer&Number=7774337
 
I'll try to make this as simple as I can :)

Seat the rockers when measuring the pushrods and do not add any preload.

Once the new pushrods are installed, there will be zero preload with the rockers fully seated. Once you have taken up the slack with the adjuster nuts and added 1/2 a turn of preload, then the adjuster nuts will all sit about 1/2 - 1 1/2 turns out (with about one thread showing). That is the correct place for them.

There are other ways of measuring pushrods with a hydraulic cam, but this is the simplest way to ensure your pushrods are the correct length, and that the adjuster nuts are not too far out once you have added your preload. This method works best with 1/2-1 turn of preload.
 
Aussie Charger said:
I'll try to make this as simple as I can :)

Seat the rockers when measuring the pushrods and do not add any preload.

Once the new pushrods are installed, there will be zero preload with the rockers fully seated. Once you have taken up the slack with the adjuster nuts and added 1/2 a turn of preload, then the adjuster nuts will all sit about 1/2 - 1 1/2 turns out (with about one thread showing). That is the correct place for them.

There are other ways of measuring pushrods with a hydraulic cam, but this is the simplest way to ensure your pushrods are the correct length, and that the adjuster nuts are not too far out once you have added your preload. This method works best with 1/2-1 turn of preload.
Click to expand...

Thanks! that makes sense.

The only problem is that I can completely screw the adjuster nut out the top of the rocker...so I can't really seat them. But from what I understand seating them essentially means turning the adjuster out until all the threads are in the rocker arm.

Because If I do that and there will be about a thread showing once the pre-load is taken into consideration.

And about the contact patch on the valve stem. What is better, completely centered or narrow? In other words is it okay if the contact patch on the valve is slightly off center but quite narrow?
 
That's correct. I'm talking about the adjuster screw with the ball/cup that the pushrod goes into - not the lock nut that tightens and holds the adjusters in place. (Sorry, I kept referring to it as an adjuster "nut", so I hope I didn't confuse you!) You don't want too much of it hanging out of the rocker or you will restrict oil flow and affect your pushrod geometry. However, if you have a set of instructions that came with the rockers, they will be the final word, as I'm not familiar with the PRWs.

http://www.jegs.com/images/photos/200/249/249-1321S-1.jpg

Depending on the rocker design, your adjuster thread may look something like this. The hole between the threads is fed pressurised oil from the rocker shaft through the rocker and goes down the inside of the thread to oil the top of the pushrod. You can't see it in this photo, but there is a hole in the middle of the cup on the left. Even if your rockers do not oil in this way (many ball designs), you still want to get the pushrod as close to the rocker as you can to improve your pushrod geometry and to ensure maximum strength. If the adjuster thread hangs too far out, it becomes the weak part of the rocker.

As for the contact patch, you basically want it in the middle third of the valve stem: if it is narrow and slightly off-centre, that's OK as long as it does not go outside the middle third towards the edge of the stem.
 
You must log in or register to reply here.
-

Back
Top