Timing jumped?

Yesterday, I was driving home on the freeway, and I heard something break from under the hood. Immediately, I experienced a loss of power, with the pedal all the way to the floor, and was getting very meager acceleration.

I was stopped at a light, and the car just stalled out. I was able to get it started again, and drove it home. So today, a friend and I pulled off the valve covers and found that the rocker shaft over cylinders 1-4 had snapped in two! Strangely, did a compression test, and found that the cylinders on the same side as the snapped rocker shaft were reading fine, minus cylinder 1, which wasn't firing. On the other side, three cylinders were not firing, but there doesn't appear to be any major issue there.

Could this be a sign that the car jumped timing?

Ummmmmmm WOW! I am not sure that jumping timing would cause the rocker shaft to snap...... The fact that you were able to get it running again makes me think that if it jumped it only maybe jumped 1 tooth. If it is firing on all but 1 cylinder that is not indicative of jumped timing but of a bad wire, cap, etc (assuming that you are checking fire by trying to jump spark to ground). I would say you have something else going on there bud.... Your problem may be the snapped shaft itself rather than something else.

Keith/Bumble

i second bumblebee......timing could not have jumped and only 1 tooth..usually on these engines if the timing jumps its either the chain snapped or the actual sprocket broke apart...seems that you have other problems....give it a more in detph inspection

Do the three cylinders on the other side still have good compression? Do the electrode tips still look good on the spark plugs? No sign of something hitting them, shiny spots are anything?
If you have any evidence of spark plug damage you could of had either a valve head break off or a screw fall out of the carb or something like that happen? Once loose a piece can travel from cylinder to cylinder creating havoc.

Scott...

Originally Posted by one37tudor

Do the three cylinders on the other side still have good compression? Do the electrode tips still look good on the spark plugs? No sign of something hitting them, shiny spots are anything?
If you have any evidence of spark plug damage you could of had either a valve head break off or a screw fall out of the carb or something like that happen? Once loose a piece can travel from cylinder to cylinder creating havoc.

Scott...

I had this happen to me years ago. If you got a 390 or 352 engine, the rocker arm shaft used to break over the 2-3 or 3-4 division stand. Found that the boss the stand was to mount on to was elevated just a bit. Once the holding bolts get torqued into place they sort of distort the shaft. Check with a steel straight edge. Can only be fixed via removal and machine work.

Watch out for any bent pushrods too. I bent two on other side of engine. Low compression there made me open up that side initially. Extra gasket made me open up other side then.

Now, how did that break?
This ain't going to be just a couple hour fix.

Wm.

Not a whole lot of chances that the engine jumped time. The broken shaft can explain all your issues for the most part.

How long have you had this engine? Do you know for sure the compression was good on all the cylinders BEFORE this incident?

Originally Posted by FEandGoingBroke

Not a whole lot of chances that the engine jumped time. The broken shaft can explain all your issues for the most part.
How long have you had this engine? Do you know for sure the compression was good on all the cylinders BEFORE this incident?

The engine is the original 352 that came with the car when it was brand new.

The compression wasn't always good, in fact, it had a miss in two cylinders at idle, but now, four cylinders are not firing. It's strange though, because on the side that had the original problem with the rough idle, the valve action seems to be fine, despite one bent pushrod. I'm lead to believe that there's a good chance that some of the valves on the drivers side have probably become bent overtime.

On the passenger side (the side with the broken rocker shaft), we had two broken pushrods, but 3 cylinders were still firing fine during the compression test. It's the strangest thing ever.

We're going to replace the rocker arm, and the pushrods, then maybe we'll pull off the timing cover and make sure the timing chain didn't break or anything like that. It'll probably still run like crap, but at least we'll be in a position to where we can get the heads rebuilt.

Bent valved get bent all at once. Not over a period of time. Car's don't sometimes run ok then not run ok with bent valves, they run crappy the entire time....

Replace the shafts and pushrods, but take the heads off and get a valve job first, because I am POSITIVE that you have a lot of exhaust valve recession that needs to be dealt with before a new shaft and timing chain will fix anything.

I had a 400 that would bend pushrods at about 4500 rpm...motor was shot, but wouldnt die- apparently had been overheated severely in its past,valve springs were way too soft.
I'm guessin on the highway were you passing someone or getting on a onramp? if it kicked down and revved, valve float can tear stuff up quick
I also had a 396 chevy that would float at 5500- limped home on 5 cylinders one day after getting on a onramp, found a bunch of rockers with the little fulcrum ball segment area pulled right thru or broken in half. if the valves float its like little jackhammer on all the parts when they meet back up going opposite directions

not familiar with FEs, but from the pics ive seen the shafts look pretty substantial- but still after 40+ years of service, you never know. good luck- hopefully damage is all topend- but in any event may be a good time to tear into it before something terminal fails.
I checked the timing chain on ours by just pulling the fuel pump- get a finger in there and see how sloppy the chain feels, maybe even a light/mirror to try to peek at the nylon teeth(or are FEs all metal?). if you got any pieces missing(chipped our pushrods/rockers/pedestals, would suggest tearing it down sooner rather than later- I found little rocker arm bits in the relief valve on the 396...pickup screens are big mesh, and ahead of the filter...pump was grooved up, relief stuck. weirdest thing I found was timing geat plastic bits clogging crossdrilled crank holes- wether filter bypassed because of clogging with plastic bits or what, somehow the oil passage was full of plastic

Originally Posted by ford4v429

I had a 400 that would bend pushrods at about 4500 rpm...motor was shot, but wouldnt die- apparently had been overheated severely in its past,valve springs were way too soft.
I'm guessin on the highway were you passing someone or getting on a onramp? if it kicked down and revved, valve float can tear stuff up quick
I also had a 396 chevy that would float at 5500- limped home on 5 cylinders one day after getting on a onramp, found a bunch of rockers with the little fulcrum ball segment area pulled right thru or broken in half. if the valves float its like little jackhammer on all the parts when they meet back up going opposite directions

not familiar with FEs, but from the pics ive seen the shafts look pretty substantial- but still after 40+ years of service, you never know. good luck- hopefully damage is all topend- but in any event may be a good time to tear into it before something terminal fails.
I checked the timing chain on ours by just pulling the fuel pump- get a finger in there and see how sloppy the chain feels, maybe even a light/mirror to try to peek at the nylon teeth(or are FEs all metal?). if you got any pieces missing(chipped our pushrods/rockers/pedestals, would suggest tearing it down sooner rather than later- I found little rocker arm bits in the relief valve on the 396...pickup screens are big mesh, and ahead of the filter...pump was grooved up, relief stuck. weirdest thing I found was timing geat plastic bits clogging crossdrilled crank holes- wether filter bypassed because of clogging with plastic bits or what, somehow the oil passage was full of plastic

Many-many years ago, had a 410 Merc. in my 1959 Edsel. It had a miss, and took it to college to see why using their scope. Before, instructor would even let us connect it in, he wanted us the remove valve covers and measure stroke to each push rod. Upon removing them, found two completely broken in half pushrods and one bent. I see why now of his concern. Then without doing too much more, we got a few off old engine sitting out back. Replaced them, and then noticed that number one and five only moved a very small amount. Instructor came by any mentioned he worked on the Mercury assembly line even earlier, and their flame hardeners for camshafts often went bad. Before anyone would notice, there was like a good dozen or two camsahfts that had soft lobes. Which is what happened to our 410, for there essentially were no lobes on one and five.

One by one we got the engine to fire off on all eight.

Wm.