Engine Missing a Pushrod

Lanse · Oct 6, 2015

Hey everyone!

Quick question - why would an engine have a pushrod intentionally removed, and what affect would this have on how a V8 (chevy small block) would
run/perform?

Im working on aforementioned engine and noticed some red silicone on the valve cover gaskets. Out of curiosity, I opened it up and noticed it was missing
the pushrod for the intake on cylinder 2. Im thinking theres a problem with a cylinder and they just tried to "turn it off". Thoughts? I believe the engine ran
like this for quite some time.

dhermesc · Oct 6, 2015

Is the piston rod still connected to the crank on that cylinder (or even a piston in that cylinder)? That or a hasty repair that the mechanic forgot to install the pushrod. I had an engine "rebuilt" and the "mechanic" (I use both words quite loosely) installed different length push rods resulting in the pushrods being bent and the intake valve not opening on two cylinders. If someone would screw that up forgetting to install a pushrod isn't to far fetched either.

old · Oct 6, 2015

There could be a few reason for that.
#1 a bad rod bearing and that keep that cylinder from firing and less likely to throw a rod.
#2 bad rings or a hole in a piston
#3 a stuck valve so the push rod bent so they pulled it out not wanting to deal with the problem
Plus maybe a few more reasons

LAA · Oct 6, 2015

The engine would miss, may not have been intentional, someone may have been adjusting a lifter or something and removed the push rod and forgot to put it back, I have seen that before.

Goose · Oct 6, 2015

I had an experience once with an SBC engine where the pushrod wore through the rocker arm on an intake valve. Same effect as no pushrod. When the engine turned past that cylinder the compression blew back through the carburetor. And obviously didn't fire on that cylinder.

Steve@Advance · Oct 6, 2015

A flat cam lobe on the exhaust of that cylinder. The intake pushrod removed to stop the popping back through the intake. Flat cams were a common problem on small blocks, especially if they were idled.

Den N Ms · Oct 6, 2015

Lanse .A missing push rod would cause a bad miss, dead cylinder.I have seen a push rod get bent and fall under the intake manifold of a small block chevy and just lay in the valley and some one just replaced the bent push rod.The engine ran on all 8 before tear down for a rebuild.No telling how long the bent push rod was in there.So you might try a new push rod in the engine and see how it runs.

Bob · Oct 6, 2015

Steve, I'm gonna go with your theory on this one. Have seen that happen more than once, and without the intake valve opening, there's non "backfire" of combustion products back into the intake because they can't escape through the non-functioning exhaust valve.

Tom in TN · Oct 6, 2015

Lanse,

I'm going to take an "off-the-wall" approach here. Back during the gasoline crisis in the 1970's someone was marketing a kit for improving gas milage of V-8 engines. The "kit" consisted of two pushrods that actually had springs embedded in the so they wouldn't operate the rocker arm / valve. You were supposed to put them into two of the cylinders on the intake valves. I don't remember which cylinders they specified to put them into.

A friend of mine installed the "kit" and ran his car for a couple of years with it installed. It idled rough, but according to him, it improved gas mileage.

I don't know.

Tom in TN

Janicholson · Oct 6, 2015

As others have said. To see if a worn cam is involved, (either intake or exhaust can go bad, my dad's car had three cams replaced in 4 years) measure the distance moved on a working cylinder or two and compare that to the valve with the pushrod's movement. If different, that is it, Cam and lifter time. If it seems normal, or within 1/16th, put a pushrod in the hole (make sure you are on the lifter) and try that valves motion. If it is normal, it may have just dropped a pushrod from a temporarily stuck valve, The valve lifter will be fully extended, so adjustment might take a bit of effort. Jim

K Effective · Oct 6, 2015

My Grandpa used to tell about the Model T days- if a cylinder or piston went bad, the driver often removed it, sometimes replacing with a block of wood, and ran her on three. He sold a car to some of the seasonal migrant labor, knowing that it would never make the state line 20 miles away. He got the post card from Arkansas within a week...

Ozlander · Oct 6, 2015

'72 Chevy van sb 350. Broke a exhaust rocker arm on a trip, was out in the country at night. Couldn't get much above idle because of backfiring thru the carb, really ran bad.
Had to take the valve cover off and bent the intake pushrod to get it out. Ran good enough to go 90 miles to get home.

Traditional Farmer · Oct 6, 2015

Back in the 70's during the 1st gasoline shortage there used to be directions around on turning
8 cylinder engines into 4 cylinders by disabling 4 cylinders didn't run that bad but not much power

J.Wondergem · Oct 6, 2015

I've seen that done before at the races. Motor starts pumping oil on one cylinder and just disable it and run it on seven cylinders. Don't have the power and eventually it last, but can run until then.

GarryinNC · Oct 6, 2015

Sounds like you may be in for a tear down and inspection.

T.R.K. · Oct 6, 2015

Did you remove the intake manifold and see if the pushrod is in there or in the oil pan? Its not totally unheard of for pushrod to bend if it can't open the valve for some reason, then fall down into engine.

At least I have seen it happen twice in small engines in the last 8 years. . . . One time engine sump had to be removed to retrieve the pushrod. And the engine still ran on the other cylinder.

tractorguy2 · Oct 6, 2015

Could be a number of things. Could be bend or broken in the intake. Could have had a problem on that cylinder and the tight wad farmer fixed it by removing the push rod.

A friend of mine bought a 74 IH pickup. The rear brakes didn't work very well. I removed the left drum to find it was missing everything.No Shoes,wheel cylinders,or springs. The brake line had been pinched off.Right side was the same way!

I also knew the former owner. He told me he priced shoes and was so shocked at the price he removed the rear brakes!!

People will do anything to save a dollar.

01gentdc · Oct 6, 2015

lanse , that red silicone gives me a clue of idiots inaction ,,., think about the recent service history and the previous owners ,, if they are lackimn in common sense skills ,and never had anyone to teach them anything ,.. it is highly likely they removed the bent pushrod and stuk it back together ,,. people these days do a lot of very stupid things ...

Tim in OR · Oct 6, 2015

When I was a kid, I encountered a SB chev with the intake pushrods missing on 2 adjacent cylinders. upon pulling the head, I found the block burned out between those 2 cylinders (also signs of recient work). That smokin deal turned out smokin in a different way.
Tim in OR

Deutz Lover · Oct 6, 2015

I don't remember the GM make. It could have been a Chevy station wagon or a Pontiac back in circa 1982. The car was probably a about a 1975-77. A grad student did not know which cylinder was misfiring or which bank so I selectively removed each plug wire and replaced it. I told him which bank (left) and which cylinder.

The stamped rocker had slipped off the valve tip and had rounded it at a slant so it would not stay on. It could also have been a bent push rod or loose stud or even stuck valve. He had to pull the head and replace the valve. I did not follow up as to the cause. Up to that time I had never seen an engine that had no rocker arm shaft.

:?:

Engine Missing a Pushrod

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