So I just redid the motor with heads/cam/intake and all that... I was using stock length pushrods but they wouldnt take an adjustment
I called Crane and they said put some ink on the valve stem, turn the motor over, and see where it lands. So i took a magic marker on the valve stem, turned the motor over, and looked at where the wear was. I had to take about .200" off the stock length pushrod for it to fall into the center.

So I need a 7" hardened pushrod... I didnt see them in summit or jegs.. does anyone know where to find them?

 

Are you doing a roller cam in a flat tappet block? What exactly are you building? The most common length for the roller conversion is 7.2 inches. Are you using guide plates? roller rockers? If you're using guide plates you'll have to have hardened pushrods anyways. If no guide plates, then self aligning rockers.
Comp cams # 7608-16

 

You'll have to settle for 7.150 or 6.950, choose one that is the least of two evils so to speak.

http://store.summitracing.com/partde...5&autoview=sku

Actually Summit substitutes the above part number for the 6.950, that's kind of silly.

Scroll down through this PDF and it shows all the part numbers for each length...
http://www.compcams.com/technical/Ca...07/252-253.pdf

 

Do you have a checker spring installed? If not, the length will be wrong.

 

A checker spring? No, I measured it with the normal spring

The block is a 1990 van motor.. it came drilled for the roller cam but it came with a flat cam.. I simply installed all the roller hardware.

 

In order to get the length right, the factory springs must be removed(only 2 of them, 1 intake, 1 exhaust). Then a super light tension spring goes in its place. Jegs and Summit sell them for a few dollars a pair. Then do the sharpie trick and roll over the motor to check the length.

 

I really don't have time to take the head off to change the springs and I don't have a source of air strong enough to keep the valves up. Can I run the motor for a little while and then check it right away while the pressure is built up since I know more or less what length im going for anyway?

 

You can pick up a very inexpensive pushrod length checker and, using feeler gauges, determine the length you need. I believe Mr. Gasket sells it. Correction on that, it's Manley

A rule of thumb is it's always better to run pushrods that are a little too long than ones a little too short.

You can use the old "nylon rope in the spark plug hole" trick to keep the valves closed while changing springs.

Jake

 

if i use the length checker right after running the motor, the lifters shouldnt compress anyway right? i'd think that would be the fastest way to do it

 

There are quite a few tools on the market used for determining the correct pushrod length. They range from the relatively expensive to only a few dollars, like the Manley tool.

There are also several websites that show different ways to determine the correct length pushrod. Some of these sites disagree with each other.

For example, one site says to take into account the amount the lifter plunger is depressed after lifter preload is set. Other sites make no mention of that at all.

The main problem with running the incorrect length pushrod is the valve stem side loads the quide, which accelerates wear of the guide. You then end up with oil being sucked into the combustion chamber causing a smokey exhaust, oil consumption and a buildup on the back side of the valve head.

How quickly this occurs depends on how far off the length is and how long the engine is operated in that condtion. I'd never say it's "okay" to run the engine with the incorrect pushrod length, especially if you "know" the length is wrong. Your call though.

Without resorting to having a custom set made to the EXACT length you need, I'll bet the closest you can get is about .050 from what your measurements show. If that's the case, opt to go .050 longer, rather than .050 shorter.

Just my thoughts.

Jake

 

The main problem stemmed from the flutter im getting out of the tailpipes.. it's got a true dual setup so it's coming from both sides.
I was told that having the pushrod too long could cause teh flutter and have the valves open too long, does that sound right?

 

If you ask ten (10) people you'll get eleven (11) different opinions.

If I had to take a shot at it, I'd say what you were told is, to put it politely, HOG-WASH.

The BIG GUYS, like CompCams and Crane, etc., tend to agree on the correct movement of the roller tip of the rocker arm as it cycles the valve from closed to closed.

With the lifter on the base circle of the cam lobe, the centerline of the roller tip should sit slightly inboard (toward the intake manifold) on the valve stem. As the valve opens and reaches mid lift - the roller centerline should be centered over the center of the valve stem tip. As the valve continues to open to is fullest, the roller tip on the rocker arm should be slightly out-board (toward the header).

Then, as the valve begins to close, at the mid-point, the roller tip should, again, be centered over the valve stem. At the full closed position, the roller tip should be, again, slightly in-board.

In-board, centered, out-board, centered, in-board.

Jake

 

That's basically the same thing the guy that built my motor told me - he said that the line in the ink should be .060-.120" wide and right over the middle but if its closer to one side or the other it shouldnt make a difference. the best way to get that position short of using a solid lifter would be by checking it the second i shut the car off while it's still under pressure. my line is within that size BUT it starts and ends halfway down the exhaust side of the valve stem

 

Correct length push rods are usually determined during engine mock-up, long before the engine is ever installed in the car. So choosing the correct length rod doesn't require the engine to be run, shut down, etc.

The correct length pushrod is determined while the engine still bolted to the engine stand, even without an intake or starter installed. It's done by turning the engine over with a crank socket and ratchet, etc. I'm not sure why you're concerned about checking right after engine shut down.

You can get an idea of how different length pushrods effect the travel of the rocker arms' roller tip.

Exaggerate these movements just so you'll be able to see it visually.

Bump the engine until the lifter of the valve you've chosen to check is on the base circle of that lobe. Lifter on base circle.

Now remove or loosen the adjusting nut to allow you to move the in-board side of the rocker arm up and down.

Notice what happens when you raise the in-board side of the rocker - notice what it does to the roller tip as it sets on the valve stem tip.

Now lower the in-board side of the rocker arm and notice what that does to the roller tip.

Raising the in-board side of the rocker arm will cause the roller tip on the rocker arm to move inboard - this simulates a longer pushrod.

Lowering the inboard side of the rocker arm will do the opposite; that'll simulate a shorter pushrod. It'll move the rocker arm roller tip out-board.

If the witness mark you're seeing is more outboard, then you need a longer pushrod. The issue then becomes - How much longer??

As I said before, there are a lot of different checking tools in the market. For a street engine, the Manley tool works just fine. Simply bring one lifter to the base circle of the cam lobe, remove the rocker and slide on the Manley checking tool

If there's a gap between your pushrod and the Manley tool, your pushrod is too short. Use feel gauges to meaure how much too short they are.

If too long, a gap will be between the Manley took and the valve stem tip. Again, use feeler gauges, etc.,

All you now need to do is measure the length of your existing pushrods (one's enough) and add (for too short) or subtract (for too long) your feeler gauge measurements and you're good to go.

I haven't checked in a while, but the last time I did, pushrods were readily available in .050 increments, but not readily available in smaller increments than that.

You shouldn't have a problem finding a set to meet your need.

Hope this helps,

Jake

 

Are we talking about an LT1 here with 1.6 rockers, I assume we must be because L98 pushrods are much longer right?

If so 7.150 rods work real well, I've seen two instances now where that turned out to be the correct length. 7.200 would work but 7.150 puts the tip more centered. It might not be ABSOLUTE perfect but it's closer than stock.

 

The 7608-16 is just the most popular conversion, its off the shelf, so to speak. The correct measurement when you check it with a checker sping is about 7.10-7.15. The 7.2s work just fine. And the explanation of how to check was dead on, but long. The easiest way to remember it is, the roller tip should be AT THE CENTER OF ITS TRAVEL on the valve stem @ 50% OF THE LIFT.

 

I'm one of those cases Thank you again for helping me figure out my problem