Bent Pushrod, Idle Miss

[IDave]

I've been in the process of chasing down an intermittent flapping sound over the last couple of months (it would happen for a half hour or so every two weeks, then stop just before I got it into my shop). I've gone down a couple of dead ends and am not yet sure I know what it is.

Anyway, I found that I had a slipped intake valve keeper on my #6 cylinder, which of course implied that the sound I heard may have been the valve hitting the rocker or the piston, who knows?

Now, having replaced the keeper, I realize that the pushrod for that valve is bent.

At the same time, having put things together, I have found I have a new problem.

There is a persistent miss/popping sound: kindof:

"PUH, PUH, PUH-PUH, PUH..."

...that speeds up and slows down with engine RPM. I hear it best at the tailpipe, and the tailpipe spits water with the sound.

I'm sending for a straight pushrod, of course.

But my question is, is it likely that the bent pushrod is causing my miss, or am I being deceived and should I be looking elsewhere?

I have fresh points, condenser, cap, rotor, plugs, wires, fuel filter.
Timing and dwell are right on, fuel level right on the mark in the site glass.

Vacuum is steady at 17 inches at idle, which is normal, and with the "miss", the vacuum drops only about 1/4 inch.

 

[Poser]

David-


You do not have another pushrod from another engine lying around there to install and see what changes?


I do not understand the correlation between the moisture coming out the tail pipe, unless the engine has not fully heat cycled the exhaust, and the moisture is condensation from multiple starts and stops of the engine running.

 

[IDave]

I have plenty of spare pushrods, Steve, but they are for the 68 and later engines. I actually haven't compared them side to side to see if they are the same length, but the early rods are definitely different, skinnier, than the rods from my FJ40 engines.

The bent rod still spins. In fact, although I should have rolled it on glass when I first saw the valve issue, I didn't, and it was only when I did a first startup last night that I could tell it was bent from watching it spin in the running engine. (I rolled it on a pane of glass this afternoon to confirm the bend).

You might be right about the condensation issue, but there's actually a pretty big puddle of water underneath the tailpipe.

I forgot to mention, 3 times during my 20 mile test run this morning I had a single small backfire through the carb when accelerating from a stop.

 

[Degnol]

I have plenty of spare pushrods, Steve, but they are for the 68 and later engines. I actually haven't compared them side to side to see if they are the same length, but the early rods are definitely different, skinnier, than the rods from my FJ40 engines.

The bent rod still spins. In fact, although I should have rolled it on glass when I first saw the valve issue, I didn't, and it was only when I did a first startup last night that I could tell it was bent from watching it spin in the running engine. (I rolled it on a pane of glass this afternoon to confirm the bend).

You might be right about the condensation issue, but there's actually a pretty big puddle of water underneath the tailpipe.

I forgot to mention, 3 times during my 20 mile test run this morning I had a single small backfire through the carb when accelerating from a stop.

Lipitor, Zetia, Metamucil........stat rampart Diet and exercise.

 

[IDave]

Lipitor, Zetia, Metamucil........stat rampart Diet and exercise.

As I recall, I'm not the one with the metamucil issue....

I just thought of something. Maybe I need to recheck my plug gaps. One might have gotten bumped.

 

[Pin_Head]

I wouldn't get too excited about the exhaust sound until you find out if you have a more serious issue with the valve, like a bent or burned valve that won't seat.

The tail pipe emission on mine has a kind of reggae beat, but the engine is smooth and steady. Yea mon.

 

[IDave]

I haven't seen the vacuum signs of a sticking valve yet, unless I missed an intermittent one. (One of two upgrades to both my trucks was a Poser-recommended in-cab vacuum gauge! The other is a tach.) Maybe that's what happened with the backfire.

I wouldn't have been excited about the exhaust sound except it was such a change. And it turns out....

















...it was a spark plug. The gap on the number 5 cylinder plug was about half of what it should be. I must have dinged it putting it back in. Re-gapping fixed the puh-puh, puh, the water sprinkling out of the exhaust, and the vacuum tic!

I'm still VERY worried about having bent the valve stem or slugged the head of the valve into the piston, obviously, but I hate to pull the head unless I have to...

 

[IDave]

I wonder if I was having a local overheating problem near the back of the head due to sludge in the waterjacket, causing the head gasket to burn and resulting in an intermittant locking of that valve as well as a transient head gasket leak resulting in temporary loss of power.

 

[Trollhole]

Have you run a compression check or a leak down test?

I'm betting on a bent valve.

Also you need to remove all that paint from under the rocker assembly, valve springs, head bolts, etc. Paint can screw up all your toque specs once it gets hot a squishes out. Especially if there happens to be a thick coat. I'd re-torque those head bolts just to be sure.

Ask me how I know. Also. New to me and I'm assuming it's something on earlier valve springs but what are those covers on top of the spring? Are they used with the tool?

 

[Southeast Overland]

Ask me how I know.

How do you know?

 

[IDave]

Have you run a compression check or a leak down test?

I'm betting on a bent valve.

Also you need to remove all that paint from under the rocker assembly, valve springs, head bolts, etc. Paint can screw up all your toque specs once it gets hot a squishes out. Especially if there happens to be a thick coat. I'd re-torque those head bolts just to be sure.

Ask me how I know. Also. New to me and I'm assuming it's something on earlier valve springs but what are those covers on top of the spring? Are they used with the tool?

Those are good points. Whoever futzed with the head before did some things I wouldn't have. Those covers are covers. I have no idea whether or not the truck came with them. There's just not a lot about F135s. The FSM and Parts manual I have don't show them, but they seem to fit alright. And yes, the valve stem seals are in the wrong place (no longer).

When I pull the head, and it looks like I will, now, we'll get rid of the paint on those surfaces.

 

[IDave]

F135 pushrod left vs. later F engine pushrod on right.





Just to make things interesting: I was having some intermittent hesitation on acceleration and I checked the accelerator pump (fine) and then the timing. Took the truck out for a test drive and it seemed to be running well, 3 miles up and down hills. Parked in the barn and decided to rev it once to see how the vacuum looked (worn ring test) and heard a pop. Then coolant rained all over my floor from the back of the engine.

 

[Cruiser_Nerd]

Dave, as you figured out the valve assemblies aren't stock. Here's some info for the F135 valvetrain.

The valves and keepers have been changed, who knows on the springs, shroud may go with the valve and spring, and the seal should be under the keeper because you want that getting oiled. Anyhow, hopefully the same person wasn't in the rest of the motor.

Sounds like you lost a freeze plug last night........................happy day!

 

[IDave]

Thanks, Jim. Yep, there are a number of things that make me nervous about what's underneath, but I guess I'll be going in there sooner now, rather than later. Thanks for the pointers and the link!

 

[Trollhole]

How do you know?

When I painted the big gay I was careful not to paint anything under the valve cover my fear was that the paint could come off and block an oil passage or it would screw up the rocker stand tolerances. What ended up happening was I painted the area around the valve cover. Put the head on and torqued it down. No issues until I did the break in and the paint got hot an squished out from under the row of head bolts that were not under the valve cover. The tell tale sign was the hot stream of coolant squirting out the side of the block. Needless to say I removed all the head bolts after draining the block and stripped all the paint off the head and cleaned the bolts and torqued everything back. No issue since. Paint should never be used under something that requires a certain torque. Best to torque and then paint. Or not paint at all.

Those are good points. Whoever futzed with the head before did some things I wouldn't have. Those covers are covers. I have no idea whether or not the truck came with them. There's just not a lot about F135s. The FSM and Parts manual I have don't show them, but they seem to fit alright. And yes, the valve stem seals are in the wrong place (no longer).

When I pull the head, and it looks like I will, now, we'll get rid of the paint on those surfaces.

I didn't notice the valve stem seals on the top until you pointed them out. Crazy. I wonder if that is spring caps from an inline chevy motor.

F135 pushrod left vs. later F engine pushrod on right.

Yeah I'm thinking the head needs to come off and see what kind of crazy PO crap you are dealing with. It's looking crazy so far.

 

[Degnol]

Dave, you should source a nice '74 F-n-a-half to rebuild

 

[IDave]

Paint should never be used under something that requires a certain torque. Best to torque and then paint. Or not paint at all.

That would have been my plan.



I didn't notice the valve stem seals on the top until you pointed them out. Crazy. I wonder if that is spring caps from an inline chevy motor.

Yeah, I wondered that, too, once I saw that nobody else had them.

Yeah I'm thinking the head needs to come off and see what kind of crazy PO crap you are dealing with. It's looking crazy so far.

:biting nails: It's a wonder it's run as long as it has!

 

[IDave]

Dave, you should source a nice '74 F-n-a-half to rebuild

Trust me, Ed, the thought has never been far from my mind as these things keep happening. ;p

 

[IDave]

Piston Holes!

So, in addition to the rear engine freeze plug having been blown out, which was the final straw, I found 1/4 inch holes along the edge of both the #6 AND the #5 piston, blown out from below!

Any thoughts on how that could have happened? I mean, yeah, probably a broken ring, but two pistons at the same time?

 

[IDave]

And, no, the cylinder walls aren't scored.

Yes, it looks like those piston heads have been beaten on. Haven't found debris.