VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 Engine Knock Solved...!

You may recall the many "posts" over the past year about the "engine knock" I've had for years and was unable to solve...

As I had written before, the "knock" was fairly loud...Sounded like a ball-peen hammer on steel, but slightly duller...And only at idle, about once every second...Would not go away if you pulled a plug wire, so I had ruled out a "rod knock" long ago...

So, here's what I found...With the engine running I removed the "rocker-arm" cover and low and behold the very last valve push-rod was slightly bent...With a total side-to-side run-out of just under a 1/8 of an inch...I grabbed a hold of it and pulled to the side and "viola"...No more knock..! Let go and it comes back...!

I've read other "posts" about engine "knock" mysteries, maybe this discovery will help others...

Now, the question is the what is the easiest way to resolve the problem...Replace the one..? Replace them all...? (I count about 3 others that run-out slightly) or should I place the offending push rod between "centers" (on my lathe) and using a dial-indicator, straighten it...?

Remove the push rod and straighten it.

I vote for a new set my friend...
Although it must be a great day solving the probem have on me

If you treat the problem, then straightening on a lathe is the approved solution and the offending pushrod only.

Thank you, gentlemen...I'll get on it...Now, I count 3 or 4 others that I can see that are just a tiny bit bent...Should I have a "go" at them as well...?

Another question is, if the bending was caused by "over-reving" at some time in the past...?

Most common cause is a valve stuck. It is not uncommon to find one or two that wobbles, even when the cars were new.

Now I can only imagine what's been going on with the engine before I acquired this car...
I've got the push-rod out and someone has attempted to straighten it before...I see hammer marks...And it's bent in more than one place...Good thing I love a challenge...

Stuck valves...! That's right....!I'll bet someone tried to start this car with bad gas, before...That's why the tank had the Redkote Tank Liner in it, that has caused me so much grief...Thanks, Gene...

So kevin what is your thoughts for the rest of the rods??

Well, like Gene says, it's not uncommon to have a few that are a tiny bit wavy...And as long as they're spinning and otherwise behaving themselves, there's not much to worry about...

Now, that I have this push-rod out, there's more of a bend to it than there appeared to be while in the motor. The two spots with the bends are down about 1/4 & 1/3 of the way from the bottom, so I couldn't see how bad it was before...And the bends are in different directions...Making the total run-out approx. a 1/4 inch...I can see where it was rubbing in two different spots...I still don't understand how that translates to a "CLOCK"-ing sound...But I'll be relieved when it's gone...Man, was that noise ever embarrassing...!

This one of the 1st repairs the had to do when I purchased the in 85...I love it now but when I think back,I should have looked around a bit harder

Which was that...? The gas tank or the push-rods...?

Usually when you by an old clunker like ours, at first you pretty much not know what your getting in to. That idiot that sold it was just trying to get out from underneath it...And we didn't possess the knowledge we should have to have any business buying such an "investment"...If we only knew now what we should've know then, huh...?

I had good gas flow but also had a nice engine knock...You know that well...I am glad we have both solved the problem

Would have been glader if you would have told me you had the same problem, a year ago..hahaha

I would not replace any more push rods than necessary unless I could find NOS Genuine Chevrolet push rods. Most of the items like push rods, camshafts, and lifters that are made today are inferior to the originals and I avoid using them. Some are not even made in this country.
Back in "the day" we sold very few push rods because they just did not wareout. Most that were replaced were bent due to valve problems and not the fault of the push rod.

I straightened the offending push-rod, today. Holding the last two inches from the top (of the push-rod) in the lathe chuck, I would "indicate" the amount of run-out about 3/4 of an inch out from the chuck. Tap it "true" with a brass bar...Loosen the chuck and slide it in 3/4 of an inch and repeat...Run-out at any given spot averaged +/-.003 when done...Plenty good enough...I could roll it across a surface plate with little noticeable lope. I don't believe it will give me any more trouble...Since the other few bend ones spin almost as quickly as the straight ones and make no noise...I will let them go for now...

Replace push-rods...? Sorry, that costs money...

like Gene said most bent push rods are from a valve stem sticking in the guide, either from sitting for years or months without proper lubrication...or what has happened here is the machine shops will set the valve guide clearance too tight, using modetn specs. when the car is run several hours the valve will stick closed and the pushrod bends.
Before I start a six with solid lifters I will tap on the valve side of the rocker to make sure the valve isn't stuck in the guide. a stuck valve will go THUD solid and a valve not stuck will bounce back up.

Good Advise...While looking at my valve stems today, I noticed they appear to have some type of guide seal...It's large and black...Almost as tall as it is wide...(?)

Lord,then, what would you do if a "visor" came up for sale????

I found the same problem with the engine in my 48. When I bought the car, I knew the idle speed was set way too high, but, I couldn't get her to idle any slower without stalling. I fixed a bunch of vacuum leaks, and, then adjusted down the idle. Then the "knock" showed up. I pulled the valve cover and found a badly bent pushrod. Then I noticed that some of the rocker arm tips weren't even hitting the entire top of the valve stems. Somebody had used incorrect rocker arms in some of the positions. I bought an entire rocker assembly and 12 pushrods, and, put everything back together by the book. Not only was the idle speed knock gone, but, my old 216 now makes more power. I set my valve clearances loose - at the top of the tolerance because I do a fair amount of interstate running with the car - so- she clicks happily at idle, but, the loud knocking is gone. You might check the numbers on your rocker arms to make sure they're correct in all positions. The shop manual tells you which of the 4 different rocker arms should be in each position.

Regards:
Oldengineer

Okay...! Sounds a lot like the trouble I'm experiencing...I have to "set" the idle higher than it should be...And, when I do lower the idle it really runs rough, and it stalls often when I let off on the gas quickly...I was able to get it to idle smoother by "retarding" the timing, but then I lose too much power...

I'm going out to re-install the straightened push-rod, today. I've checked the engine point-gap, it's good...I'll re-set the timing, too...Along with the carburetor idle...And get back in a few to tell of the results...

Thanks for your help...

I'm awaiting my latest acquisition ( my 4th visor ) as we speak...Unfortunately, I am now so poor it will be "Beanie-Weenies" on the menu again, tonight.

When are going to put one of these visors on your 47???And did you gat a new camera for Xmas,we need some pics of these jewels..I would like to know what I am missing

FWIW, I know nothing! That said, I well recall the days when these ol' stove bolt 6's were still common ('40s & 50s). Most folks said, including good mechanics, "If you can't hear the valves on a Chey, you can bet on getting burned valves". I still think they were right. So, I'm glad if mine click a bit.

Gaither,I hope this is somewhat tue,"the purr of a 216"

What a difference...! The engine is much quieter and smoother...I installed the straightened push-rod...Point gap's at .014 thousands and retarded the timing 4 or 5 degrees...Idles smoother, idles lower, I can feel more power...Running smoother at 2,000 PRM's plus as well...Hey, it even seems to start easy without fooling with the throttle. Found the generator belt a bit loose as well, tightened it.

I'm having a good day...