kman0066

History first. I lost a pushrod 100 miles back, it came off and I replaced it with the lifter. Worked fine. 100 miles later I went to the drag strip and while I was about to shift to third, I started to have a problem the car started stuttering. I pulled the valve cover at the strip, but since it was so dark I didn't notice the bentass pushrod. Well, the second from the back on the drivers side pushrod is bent like crazy(Is this exhaust or intake?)

Now to the fixing. Why could this happen? The motor is running fine besides. No spun bearings, lost rod caps, etc. The motor has around 1500 miles on it now.

My thoughts.

1.) I have LT4 valve springs from the LT4 hot cam kit. I am allowing the engine to hit 6400rpms. Is it possible that I had valve float enough to allow the piston to hit the valve and bend the pushrod?

2.) I am using Impala gaskets with shaved LT1 heads. No, in my cheap motor build I didn't check poopie for clearances. I'm not really sure on clearance issues but I don't think the heads were machined much and the pistons I am using are low compression pistons with a huge valve relief(12.5cc). Could too long a pushrod cause one to bend? Hard to believe since the SAME pushrod messed up twice.

3.) Cheap pushrods and lifters. I bought both from Autozone. Melling I think is the brand. Are these not good enough for my motor? It's not that great, maybe 425-450 flywheel/hp at a max though I haven't dyno'd it yet.

4.) Do I need pushrod guideplates? Never really understood these. Always thought the were just safety devices to prevent the pushrod from flopping around once it has come off or are they meant to actually hold the pushrod in place while it is running fine? Could this be my problem since the Impala gaskets don't have the guide holes like the '93 Vette gaskets did?

rsafier

Well did you lose the pushrod because a rocker came loose? That would be my first question. I lost mine reving to about 6600 rpm at an Autocross 2 weeks ago. Luckly it was the intake valve so no real damage. Was able to get it back tighened up, no damage to the rocker or pushrod. I had only had the car 5 days, and didn't realize the dude has programmed the computer rev limiter WAY to high.

I would think if it wasn't misadjusted rockers perhaps you have the wrong pushrods, or just reving too high.

If your not using the HOTCAM, just a stock LT1 or LT4 cam, you aren't making any more power above 6K so no point in reving any higher.

You don't use guideplates with self-adjusting rocker arms like the LT4 hotcam kit ones.

Sure others with more experaince with this stuff will chime in. But seems like you probably damaged the pushrod the first time, just didn't noticed it at the time.

kman0066

Using the LT4 hotcam from GM, so it should be going to 6400rpm from what I understand.


From what I am thinking, I am going to go pruchase a single pushrod of the same type I was using and redo all the valve lash and see what happens. That it unless someone chimes in and tells me otherwise.

Does someone have a guide to checking what length pushrod you need? I'd like to check to make sure mine aren't too long.

cprgmr

I just got done doing the top end on my LT-1 and one of the things I learned real quick is that it is imperative that you have the correct valve train geometry.

I don't think the lift on the hot cam is great enough to cause a valve to make contact with the top of your piston. I think if this did happen, you'd have more problems than just a bent pushrod.

When I put the valve train back together, I used CompCams hardened pushrods. At first I used CC hardened guideplates, but these were not giving me the correct geometry so I switched to a GM guideplate. When you use non-self aligning rocker arms, you have to use the quideplates to keep your geometry correct.

You can purchase an adjustible pushrod length checker from many places. I picked up a CC Hi-Tech unit. Check out http://www.compcams.com/Technical/Cu...g/HTML/293.asp for more info...

Good luck! :cheers:

JAKE

You have a valvetrain geometry problem, so just throwing new parts at the problem isn't going to cause it to go away.

Melling is a major player so their pushrods don't just bend on their own; there's a problem with the geometry that's causing this.

You must have either self-aligning rocker arms or guide plates - one or the other.

You need to grab a pushrod length checker to verify that the pushrods you're running are the correct length. I suspect they aren't because of the thinner head gasket and shaved heads.

You need to check for valve spring coil bind at max valve lift and make sure you have at least .060 clearance between each coil at max valve lift.

Check ALL the pushrods for signs of them contacting the head; you should see signs of wear along their length if they've experienced interference.

After two incidents you can be sure this condition will continue until you locate the cause and fix it.

Jake

kman0066

Alright, I'll go pick up a pushrod length checker. Hopefully it comes with instructions. If not, how do you know when it is at the correct length? Are you just making sure they are not contacting anything or is there a measurement to taken besides the pushrod length?

VetNutJim

Actually you have now. You've used the 'Self Checking' feature of your engine two times.
It's told you twice there's a clearance that isn't correct.
It may tell you with more authority next time.

I think Jake heard your engine talking.

cprgmr

Take the rocker off and blacken the top of the valve stem with a felt tip marker. Reinstall the rocker and find zero lash + 1/4 turn (make sure you're on the base circle of the cam when you do this). Rotate the engine a few times and remove the rocker arm. If the pushrods are the correct length, you should see a thin scribe mark at about the halfway mark on the valve tip. If the mark is more toward the exhaust side of the head, it's too long. If it's on the intake side of the halfway point, it's too short.

You may have to repeat the above procedure several times until you get the scribe mark just right.

This is where your adjustible pushrod length checker will come into play. With the one I used, each turn was 0.50 so it was relatively easy to determine what the exact length to use. Good luck, and let us know how it turns out. :cheers:

JAKE

There are several different pushrod length checkers out there. The least expensive one, I believe, is made by Mr. Gasket.

It's blue, plastic. You simply bump the engine until the lifter is on the base circle of the camshaft lobe, remove the rocker arm, slide the checking tool down on the rocker stud with the pushrod still installed.

If the pushrod length is correct, one end of the checking tool should touch the valve stem tip AT THE SAME TIME that the other end touches the pushrod.

If there is a gap at either end, you measure the gap with feeler gauges, then measure the pushrod length and add or subtract the difference.

If the valve stem tip touches first, leaving a gap between the checking tool and the pushrod, then your pushrod is too short; measure the gap and order a longer set that comes closest to the exact length you need.

If the pushrod end of the checking tool touches first, then there will be a gap between the checking tool and the valve stem tip. You'll need a set of pushrods that are shorter by the amount of the gap you measure.

Unless you order a set of custom made pushrods to give you the EXACT length you need, you'll need to order a set of off the shelf pushrods. They come in .050 incremental lengths. So finding a set of pushrods that are the EXACT length you measure isn't probable.

Remember, it's always better to have a set of pushrods that are a little too long than a little too short.

Check the underside of the rockers arms for any sign of wear, where the rockers could be touching the valve spring retainer. This usually occurs when the valve is closed.

Look for signs of the pushrod touching any spot where it goes though the cylinder head into the lifter valley.

Check that the rocker isn't hitting the underside of the valve cover or any baffle(s) in the valve cover.

Check that the valve spring retainer isn't touching the valve stem seal at full valve lift. You'll need a bright light to shine in there in order to see. At full valve length, use a feeler gauge to check the clearance between the underside of the retainer and the valve stem seal.

Check that the rocker arm tip is riding on the center of the valve stem using the procedure that someone else posted.

The tip of the rocker should be slightly inboard at closed valve position, move to the center of the valve stem tip at mid valve lift, continue on to be slighty outboard at full valve lift and return to center then inboard as the valve closes.

Are you running retro-fit roller lifters? Could you have installed them backwards?

Are you running guide plates OR self-aligning rocker arms? You must have one or the other, but NOT both.

You've been really lucky so far, but you CAN lose the engine from this problem.

Hope this helps.

Jake

kman0066

I have the 1.6 ratio self-aligning GMPP roller rockers. They worked fine on the old motor, but this one has the addition of shaved heads and a thinner head gasket. Just from looking at them, they appear to be too long now. I'll be checking the actual clearances this weekend.

I guess it's not helping that the Melling rods came in 7.2 and the stock size is 7.188. pretty close, but that probably adds up with the head and gasket reduction.

As to the roller lifters, no. They are not-retrofits. They are the normal ones for a hyd. roller SBC from Melling.

JAKE

The difference between 7.188 and 7.200 is only .012, so that, alone, isn't enough to be concerned about.

But, you're right, when you factor in the thinner head gasket and the amount the heads were cut, the pushrods could be much too long now.

I wouldn't just stop there though; there are a few other possible causes for this problem. I'd check out all of them.

How much was cut from the heads and what's the difference in thickness between the previous and current head gaskets?

Jake

65Z01

If you were getting valve float you would hear your engine suddenly go flat with a distinct change in tone. If they floated long enough the spring damage would bring on float at a lower RPM the next time.

Indeed use the felt tip marker to check roller tip motion; it will tell you if you need to get the pushrod checker.

Also, check the springs for seal clearance and coil bind at full valve open position.

kman0066

Alright, no coil bind. Nothing is hitting anything there. However, I found a couple of pushrods with small nicks in them, not the one that got bent, but others do.

I marked the top of the valve to check pushrod length and with 1/2 turn past zero, the line it created is about 2mm wide and the top of that line is in the center. So, it's about 1mm off the centerline of the valve. This is towards the outboard side. So, I do have too long of pushrods, I just need to find what size I need.

It so relieving to find the problem(or at least one of them). I have 7.2" pushrods. The next 4 down are 7.195", 7.188", 7.150" and 7.100"

Thanks guys, I appreciate all your help.


[Modified by kman0066, 8:29 PM 5/1/2004]