The Stovebolt Site Forums The Shop Area Engine Shop Replace all pushrods?

I recently got a 20 year old field sitter up and running but could not get it running smoothly. After doing a valve inspection I noticed 3 pushrods broke or bent. Should I replace all the pushrods or just the ones that are obviously damaged. What else should I look for?
Thanks in advance

'Ya know,

"common wisdom" always says, "be sure to keep pushrods mated to their original positions when rebuilding an engine". I've also heard "replace one, replace them all".

I've never really understood either one of these. If the pushrods are correct for the engine, and you adjust the valve clearance properly, what's the difference?!

I say, check 'em all carefully, both ends, check that oil is getting down to the tappets, replace just what needs replacing, adjust them all (warm), and re-check 'em after running it a few times.

I guess the bigger question is, "why are 3 bent or broken?!"

Have you done a compression test? Are you confident all the valves are moving? Seems like a bent or broken pushrod spells a stuck valve (or jumped timing?)

Someone far wiser than me will correct me soon, I'm sure . . .

-Michael

I had a 1946 truck with many bent push rods in a six cylinder motor. The engine ran on five and six cylinders until I fixed the problem. I straightened all the push rods and reassembled as needed. Each rocker arm is adjusted by itself no need for pairs or the like.

I believe the reason for the bent push rods was due to too many hight RPM's

My engine runs smooth and sweet. These old engines were nothing like the hight tech we see in todays motors.

smokejumper,

Welcome to the Stovebolt. There is no reason you can't just replace the damaged ones, but keep an eye peeled for any obvious reason those bent ones failed. Valves that get gunked up and stick in the guide are the usual cause of this, and it might be especially true of a rig that sat for a long time.

If you spend some time fiddling around, it's possible to get a bent one straight enough that it won't turn into a pretzel again provided the valve is free.

Stuart

Ive always used this tip I was taught from a fella that was way beyond me in yrs. and wisdom especially on the older motors.
lay a pc. of flat glass on your bench and roll your pushrods on it if ya see any amount of wobble it is time to replace.
just a tip.
Tim

The usual reason a pushrod bends is because there is a valve that doesn't want to move.

As I am turning the engine over by hand to adjust the valves a stuck valve should reveal itself, right?

Thanks for all the advice gentlemen, I need all I can get.
If there is a stuck valve that is causing the bent pushrods, is there a way to "unfreeze" it with the head in place or do I need to remove the head it and take it to a machine shop?

Smokejumper,

I think the general consensus is where 'varnish' is involved, the only way to solve the problem properly is to remove the head and have it rebuilt. Turning the engine by hand won't always show a problem. The 'varnish' tends to become gummy as the engine warms up and this is when it will freeze a valve.

I would replace any bent pushrod, clean the engine up a bit changing the oil and dealing with any old, stale gasoline and see how it works. I have fiddled with these old rigs for many moons and have personally never encountered the 'varnish monster'.

Stuart

In addition to what was mentioned above, I broke 3 rocker arms and bent 3 or 4 pushrods on my 248 due to that old gas gumming up the valve stems.

I pulled the rocker assembly off and cleaned it up. Then using wd40 I ran a sledge down the row of valves, tapping and spraying, repeat, etc. It took awhile but all of them work fine now. Once that was done, I reassembled the rocker assembly and bumped the starter over slowly, so I could see if any valves still stuck.

Its slow work, but well worth the time.

Jeff

It's been my experience that push rods are cheaper per rod as a set then when bought individually. If you think you may end up replacing more down the line,I'd opt for a set.

I had about 4 valves stuck on my 57 235 and got them moving with a lot of tapping with a ball peen hammer and Kroil spray penetrant. One was stuck down and I rolled the engine by hand and pushed it back up w/piston. It popped up and I just kept working it. Got a few bent push rods that I will replace this week. I have always followed the don't fix it if it ain't broke thinking. Why change out a good push rod? I know the valves were stuck and that is what bent mine when I pulled it to try to roll the motor over.

In a pinch, the pushrods can be straightened carefully and reused. Have done this with old tractors, both diesel and gas with good results making sure that no oil flow is restricted. Worked well for me.
dg

Bent pushrods could be a number of things.
Valves adjusted too tight, pushrod bends.
New built engine has coil bind, bends pushrod.
Valve stuck closed, pushrod bends.
Valve stuck open, valve hits piston and bends valve-bent valve gets shoved into guide and gets stuck harder and bends the pushrod.
Timing chain breaks or cuts loose-valve hits piston, bends valve, sticks valve tighter when bent valve rammed into the valve guide, and bends pushrod.
I think the rule of matching the used valve components is because the parts wear into each other creating different clearances between the parts. Yes, if you place them in various order, odds are that it will work OK, but you will accelerate the initial wear to get them to wear (fit) together again. Also, when dealing with a sphere (like the end of a pushrod) the pushrod sphere wears smaller as time goes on, and the socket gets bigger, creating less surface contact, and a sloppier fit. That in turn creates more lbs. per sq. inches, which in turn promotes faster wear and failure.

Builder,

Well stated - thanks. The "bent Valve" scenario makes me shudder to even think about.

Not to side-track the thread, but the timing gear model always seemed superior to me than the timing Chain model. Am I wrong? Seems like the gears would be less likely to slip, or wear. Manufacturers must know better than me, since I think the timing "chain" is more prevalent?

-Michael