Inliners International Forums General Discussion Engines bending push rods

I have a 261 6 cyl. I think it is out of a 1958 chevy truck and I put it in a 1954 3/4 ton chevy I bought the engine from an inliner in Fort Worth, I have 15 miles on the engine and bent a push rod, the push rod is 11 1/4 inches with solid lifers, there is a crane cam in the motor and the valves are both set at 20 thousands, I replaced the push rod and insured the valves were all working, I drove 3 miles and bent another push rod, the engine sat previously for 2 years I would guess, but it ran fine for 15 miles I have 50 lbs of oil pressure and no valve chatter and the timing is good.
any suggestions on the issue?
john

Hi John . . .

I suggest taking the valve cover off and rotating the crank slowly. Examine closely the valves that are bending the the push rods (at max lift). It sounds like the valves are being lifted close to 'coil bind' . . . when things heat up the coils ARE binding and push rods bend.

There are a lot of variables here: cam lobe lift, deck machining (reducing block height) and head milling . . . not to mention shims under the valve springs (to adjust on seat height/pressure) . . .

regards,
stock49

Also piston to valve clearance ?

Indeed if that Crane cam is wild enough it may have the intake valves way off the seats at TDC during the exhaust stroke creating the possibility of valve to piston contact . . . lots of variables here . . .

My bet is something much easier to fix. How old is the gas you are running? I have fired engines that ran fine when last driven and then after sitting for a year and the gas will varnish up the valve stems and bend pushrods after a few minutes running.

Is it predominantly the intakes that are bending?

I have dumped the gas and then run a couple gallons of 2-cycle mix and then new gas and the problem clears up.

Dry valve guides? Dry enough to bend push rods? Never been here.

I've seen a few reports of that over on The HAMB.

The ones I recall had dry or nearly dry tanks, where the fresh fuel dissolved the old varnish and deposits in the tank, and they redeposit on the valve stems (elsewhere too I'm sure, but it doesn't seem to cause the acute problems except where it can cause something to lock up).

I had the same problem after mine was in storage, A couple of valves were sticking.I pulled the valve cover and lubed all the valves, added Marvel mystery oil to the fuel and the oil. No problem now.

We used to use Marvel Mystery Oil on large Radial aircraft engines when we had a coked up guide.

A gallon or two of MMO in the oil (30 gallon useable tank) made the sticking guide clean up almost immediately (it would clear up on ground run).

I've run low doses of it in old engines to clean them out (couple ounces per oil change, change the filter every 400-500 miles if you try it though ).

Not dry valves, rather, varnish seizing / sticking the valves. I had this happen a few times with older gas in the tank on both 216 and 235 motors.

thank you everyone, I did check the valves with the cover off and it looked like all the valves were moving properly when I replaced the push rod the first time but it bent again, I will pull the head and have the valves looked at, the engine was sitting for a year but did not have old gas,
thank you again I will let you know what I find.
john

Coil bind
Collar hitting the guide
Collar hitting the seal
Intake valve hitting the piston

Be sure to check for sufficient rocker arm-to-valve spring retainer clearance, rocker arm-to-stud boss/hex clearance, rocker slot-to-stud clearance, pushrod-to-head clearance, pushrod cup-to-pushrod tip clearance, oiling hole alignment, and for sufficient thread engagement of the adjusting nut. Of course do a piston-to-valve clearance check throughout the cam cycle too, and also check for rocker arm-to-valve cover clearance. Correct any clearance issues by machining.

You might want to check to see if the valve keeper are installed properly. If they are not, you will bend push-rods and even break rocker arms. I don't know how, but I did this on two intake valves and couldn't figure it out until I pulled the head off. Just one of those dumb thing. They didn't bend until the engine got up to running temp.

Had a similar situation but only on a cold start. Once it ran e-thing was OK till the next cold start. Would actually hammer the pushrods straight on a 2x4 and reinstall them. It was only the intakes. Dropped the tank, checked it, replaced it, pulled the head, did a backyard clean, lap, v-job reinstall and haven't had a problem since. All this due to the old nasty gas sitting for I don't know how long. Been running the 216 over 10yrs , it just won't quit. It was unreal how that bad gas lacquered those valves, when cold you couldn't move the valves with a 2 foot pipe. Sounds like you are having a problem with only one p-rod so you might want to check the guide clearance. If its too close, along with a slightly bent v-stem, a little heat and ........ good luck !

You also have to be concerned with using alcohol based gasoline in any engine, the alcohol washes the oil away from the valve stems and can cause valves to stick as well. In racing engines that soley use methanol, you have to use a top end lube additive or you will stick all the valves in just a few minutes of racing.

It's possible a valve hit the pistons but from the sounds of it I am not so sure. Those intake valves are not all that strong and once they kissed the piston, it would have bent the valve. Then the motor would have run like dog do. One way to check though is to do a compression check. If any of the cylinders comes up really low, you might have a bent valve. If the head is off, tilt the head on its side with the intake ports facing up and put some solvent, parts wash, in the intake port and if there is a bent valve, the fluid will leak past the closed valve. I think I am with the rest, either coil bind or stuck valve, lacquered or rusted up or possibly just poorly installed valve guides or inserts or something that is binding up the valve. The other thing i guess is really high spring pressure. You don't say, but are you running double springs? The reason I ask is that I had a 235 that I put a clifford cam in way back when I was young, stupid and thought a .512 lift cam in a 235 was a good idea, and the spring pressure was too much for the stock push rods, even the trw aftermarket and had to use chrome moly push rods. The chrome moly rods solved the push rods from bending but of course did not solve the issue of the motor running awful. I still have the cam to remind me that bigger is not always better.

The valves are sticking, same problem after mine set. i used marvel mystery in the fuel after a new tank was installed and squirted each valve and guide with the cover off. that varnish is hard like dry laquer or shellac it takes a while for it to soften.