Bobs69BB

Just when I almost got my carb issues sorted out, I broke a pushrod!





Motor is an original 512 block stroked to 496 with all new internals. Engine was rebuilt by PO, and sat for about 4 years before I fired it up a few months ago. Only has a few hundred miles on it, and was running well until the last time I started it. The engine has not been reved over 4500, as I was not getting enough fuel to go any higher.

Sounded like a loose rocker, and I shut it down and removed the valve cover to find the #8 intake pushrod broken! I was suprised that it was not making a lot more noise and running a lot worse. I was able to fish the two pieces of the pushrod and the hydraulic lifter out with a magnet without removing the intake, so the lifter must have been thrown clear of the cam. The lifter would not compress, I took it apart, cleaned and reassembled and it compresses OK now. The pushrod was from Sealed Power, and hardened.

A few other items. I had valve noise about a month ago, and when I readjusted the valves, the #8 EXHAUST valve was quite loose, and it was loose again today, though the nut did not seem to have backed off. Could that also be a sticky lifter?

Also, the engine has been burning a lot of oil from day 1, 4 quarts in about 300-400 miles (odometer not working yet). I was initially assuming high oil use during break in, but anything else I should investigate?

I assume the stuck lifter caused the pushrod to break, probably debris from the rebuild causing the stuck lifter.

I am interested in opinions as what I should do next.

I am going to pull the intake to make sure there are not additional pieces of the pushrod lying around. Also drain the oil and replace the filter.

Definitely replace the intake lifter and pushrod. Since the engine sat for 4 years dry, should I go ahead and replace all the lifters out of caution?

Do I need to pull the head to see if the valves or piston was damaged? Is there an easier way to verify? I did hook my compressor to the cylinder and it is holding pressure, so I hope that is a good sign.

CA-Legal-Vette

Just a few thoughts until the BB experts chime in.

It's beyond me how you were able to fish ouT the bottom of the pushrod or he lifter without removinge intake.

I don't see how a stuck lifter would damage the pushrod. More likely to be caused by binding somewhere.

A broken pushrod should have no effect on the valves or pistons. No reason to pull the heads.

427Hotrod

Is that a 5/16" pushrod? They aren't all that stout if it is. I'm assuming the cam isn't too wild?

Usually the lifters comes apart after the breakage. The wire clip type don't like a lot of RPM or valve float and and they don't like being run loose at all. The plunger pushes on the clip and it can come out. I've seen several wasted engines when one of those clips found its way into the oil pump. You're lucky!

I'd pull the intake and look at the cam closely...especially that exhaust that kept getting loose.

JIM

larrywalk

Rocker arm nuts that are worn won't hold their position and will allow the valve train to become loose. Bad things then happen.

If you're sure the nuts haven't loosened, pull the pushrod from #8 exhaust and check for straightness. If it's bent, you most likely have something binding or insufficient clearance in the valve train, e.g. valve retainer to valve stem seal or valve guide, or valve spring bind at max lift. Also possible, valve to piston clearance may be inadequate especially if your cam has a tight lobe separation angle or you have milled heads.

OMF

On the one that keeps coming loose, you should measure valve lift and see if it's at spec for the cam. If it is, switch the nut with another and see if the problem moves also.

I had a pushrod bend and break into 4 pieces on a 440 Mopar i did for a guy. The roller lifter came out of the bore, and this should have killed the engine due to no oil pressure on the last main bearing. We couldn't figure out what the cause was, and concluded that it was a hard starting issue that was fixed at the same time.

Any hard starting issues for you?

Bobs69BB

No hard starting, no backfires, no high rpms. Pushrods are 5/16, 0.075 wall thickness. Cam is aggressive, Dema Elgin 240/244, 112 LSA. I checked the #8 exhaust pushrod, very slight bend, probably a few thousandths, can only tell by rolling on a granite counter. I did notice that the tip of the #8 exhaust valve score pattern is hourglass shaped rather than straight like on the intake. Does this mean anything?

I will check valve lift next, later this week.

gkull

Kind of like Jim indicated the thin wall small diameter push rods. I would recommend at least .080 wall chromemoly or better 3/8th

cv67

X 3

Ironcross

A 5/16 push rod is for stock 396/427`s with hydraulic lifters....performance types are either 3/8 or 7/16 th...... but the guide plates must be changed to accept the larger push rods.....You may have adjusted the valves that are loose incorrectly by mistake and not on the heel of the cam

hugie82

You need long slot rocker arms with cam lifts over .500
I learned that the hard way. It ran fine until I wound it out and cracked all the rockers....

Bobs69BB

Am getting ready to check valve lift to see if my cam is ok. Is there accurate way to do this with hydraulic lifters from the valve or pushrod? I would think the compressed lifter height is not fixed, wouldn't that throw off the measurement? Or to be accurate do I need to take off the intake and measure from the lifter body, which is a fixed distance to the camshaft?

gkull

Lifters have a spring in them. dial indicators have very little internal resistance to turning a little dial. It is not like fighting 130 seat pressure of a valve spring

Bobs69BB

I was questioning the stack up tolerance of the piston, disk and spring of the lifter shown above. But your answer got me to measure the compressed height with and without the lifter spring. Dimension is the same, which says the compressed spring height does not factor in. Looking more closely at the lifter design, there is a machined ledge in the barrel that contacts the bottom of the piston, this determines the compressed lifter height. As you said, it is a weak spring.

So my conclusion is that measuring off the top of the valve spring should be reasonably accurate.

gkull

What I said was: With the intake off you slip the lifter into the lifter bore and with a magnetic base dial indicator riding in the center of the lifter you rotate the motor over zeroing it on the low or even highest point and measure the lobe lift.

then you get a calculator out and multiply that number by the rocker ratio. which is probably 1.6 or 1.7

So a cam lift of .400 inches X 1.7 = .680 inches of valve lift

larrywalk

Or, much easier, leave the intake manifold in place; remove the rocker and put the tip of the dial indicator plunger into the hole in the end of the pushrod. With a hydraulic lifter, its internal spring will fully expand the lifter with no load on the pushrod - this spring is considerably stronger than the spring in the dial indicator, so the lifter will be fully expanded while measurements are taken.

larrywalk

I don't think this is a good way - see my above post. The only what this would work is if you zero lashed the hyd lifter from its fully compressed position so that it couldn't compress any farther, but that would be additional work compared to measuring off the tip of the pushrod with the lifter fully expanded.

cardo0

If your newly rebuilt engine rebuilt by someone else was making lifter noise a month before the p-rod was destroyed - its more than likely whoever adjusted the lifters/vlvs did so incorrectly. Someone hacked the vlv adjustment.
Did u look on the bottom of that lifter for convex surface? I would pull the intake and inspect each lifter/cam lobe now.

cardo0

Bobs69BB

Didn't need to measure anything. Once I pulled the intake, it was clear that the #8 exhaust lobe was wiped, the lifter was completely dished :-(

Now the next question. How far do I need to go to clean everything out before installing a new cam? Can I leave the engine in, or should I pull it? Can you replace the cam with the engine in if the radiator is removed?

cardo0

Well that is big decision for u to make. The safest is to dissemble the block inspect and hot tank then reassemble. But unlees u want to spend the bucks and time to do so then just change oil and filter and maybe flush a couple of times - with the new cam. Like how much do u have to lose now? U may have metal scrapes on the crank & rod journals or maybe not. On a corvette with good oil pan access if u really want to u can roll out the old bearings and roll in new. U will have to remove the oil pan anyways so u may want to pop the main caps for a look - replace the rear main seal while there too.

Min, new cam and lifters.
Heck cam shopping is always fun,
cardo0

mirage2991

did anyone mentioned checking valve spring for bind?