On my way home from San Francisco last night, I noticed my motor started missing. Uh, mis-firing... Then about 30 miles down the road I heard a light ticking noise and smoke out the driver side exhaust. I pulled off the road into a shopping center to investigate. I took the oil fill cap off the driver's valve cover and saw the #3 intake rocker arm sitting 90 deg to where it should have been . Pulled the valve cover and pulled this pushrod out, luckily still in one piece. Also noticed the rocker stud had a groove, ground half way through the stud. Assuming this was caused from the rocker arm being pushed to the side. Any ideas as to what might have happened? Thanks. I should have some better and more detailed pics up later, maybe tonight.
Are you running self aligning rocker arms with guideplates? Looks like the push rod bent/broke where it locates on a guide plate.
i had a customers used motor do the same thing.we installed 1987 and up self aligning rockers and it fixed the problem.we found that the factory pushrod alignment hole was worn allowing the rocker to move off center. give that a try. -danny
I had this happen one time on a 283. The problem was that the cam wiped and wore the lifter clean through to the hollow part inside. I kept it as a souvenir for years. Paul '56 Nomad
i vote lock nut. if it has been running like a champ and this just popped up then i would fix the culprit and double check the valve lash on the rest and drive it some more.
several reasons could have caused it --- seen it to many times in the dealership life of repairs most common was a worn out rocker
Thanks guys for all the responses. I finally got some rest after I got home from work last night. I'll see if I can find an hour or so tonight to pull the intake off and start there. I'll check the lifter 1st, then see if I can see anything wrong with the cam lobe. The motor has @ 2000 miles on it. The rockers look like stock replacements, though they do have a "C" on them; Comp Cams? There are no guide plates and the rockers are not the newer self-aligning type. Putting self-aligning rockers on it does sound like a great idea, along with guide plates. I still have to deal with the pressed in rocker stud having a groove worn into it... Sinister - I wish I would've been hotroddin' it when it happened. Then I'd at least know why and have someone to blame...haha. The valve spring looks ok, from what I can tell. I guess it would be possible to have a broken spring stay in the retainer? The lock nut on the rocker arm didn't look like it had backed off any. There is @ 4 threads showing on the top of the rocker stud, It looks the same as the others.
it would have CC on it if it were Comp Cams, might be Crane but my Rollers have the full name on them.
Check the head of your valve make sure that it is flat and not worn off to one side also check the valve guide for side to side movement.By all means replace the stud they make a screw in stud.And Some of those studs do go into your water port's so drain your water out be for pulling it out.I used to have some of those screw in studs I'll look to night. Let Me know If I can be of any help I think that I still have the tool for pulling the stud out.I'll check on that as well. Don
check to see if the studs are all the same height. had a press in stud pull out on my 327 did the same thing. changed them to screw in no more problems
my stroker did the same thing but to12 or the 16 push rods!!! had a cam in it that was not what the box said it was. it was snapping the z-28 coils inners and outters then breaking all the push rods put guide plates and manley valves rockers and springs and rods in it and now its fine
Buy a quality set of pushrods, those look like reused stockers so there's no saying if the rod was bent when it went in and failed under the pressure of new springs. Get welded ends, if you're not spending +$40, you're probably not getting good enough pushrods. Good luck
May want to make sure the valve isnt stuck, or the valve guide toast. Normally if the guide is bad enough to wear a grove in the side of the stud you have a spring full of carbon from exhaust coming up through the guide. I don't know if it is the exhaust valve but it seems the exhaust valves are the ones that give the most trouble. Pioneer makes a screw in stud to replace the pressed in stud if the stud drives in to easy. It's threaded with a little shoulder instead of a hex. If you do tap the threads make sure you go through with a 3/8 drill first. The stud hole is a little under 3/8 and taps like a bitch without drilling. Hope this helps. Jeff
Well, here's some more pics... I see several problems now. Valve train geometry? Incorrect valve springs possibly? I couldn't get a decent pic, but the #7 exh valve is open and to me the spring sure looks like it may be close, if not already binding. This motor is supposed to only have a couple thousand miles on it. Which it does look pretty fresh... 1st pic - You can see where the pushrod had worn a half moon shaped groove in the pushrod hole. 2nd pic - Look how offset this rocker sits on the valve tip... It is also starting to wear a half moon groove in the pushrod hole. 3rd pic - The top threads on all the rocker studs are stripped or really close to it... Also, the valve retainer is not centered over the spring. Could that be a positive ID that the valve guide is worn? Looking through the pushrod hole and a hole next to it with a flash light, it looks like the lifter that the broken pushrod was on is destroyed... Won't know absolutely till I pull the intake off, but it sure doesn't look right. I guess I need to bone up on some valve train geometry lessons as well... Have thought about and even read a little about it before, but never had to deal with it until now...
The last picture shows the pushrod at the bottom of the slot. Did you install 1.6 rockers? If you did the the pushrods are binding in the slots. I suggest you pull the heads and have a machine shop pull all your studs and machine the heads for studs with integral nuts. Tell them to open up the pushrod slots and either use guideplates and hardened pushrods or use self-aligning rockers.
The pushrods are not supposed to rub on the hole. As mentioned this is pretty typical for an sbc. Those of us in the garage business saw lots of it. I have seen the pushrods poked through the rocker, the ball part wore out and pushed off, nuts backed off, studs pulled. Basically the mass production factory valve train is pretty junky.
Like everyone else says, you've got geometry issues there that shouldn't be happening for the hardware you're running. You've got an inherent problem there that won't be fixed by a guideplate, only worsened First thing, look up the head numbers and make sure they're not late models that require self aligning rockers. Early and late heads need different rockers. Second thing, grab a pair of calipers or a machinist's rule and measure the center to center distance on the rocker studs, also compare them along a straightedge. Bent rocker studs will do a similar thing. Also throw the straightedge on top and check for those pressed studs pulling out. Third thing, measure your pushrods to be sure they're actually stock length and not something goofy that found it's way in. Fourth thing, thrown an old stock GM-manufactured rocker on there and see if the geometry mysteriously clears up. Fifth thing- Tape yer damn motor off man! All that overspray is now flowing with your oil and valvetrain shavings. Not good. good luck
They are 1.6 rockers. Look where the pushrod cup is moved closer to the stud. You need to pull the heads and install studs and guide plates. You could try pulling all the studs, installing new studs, and 1.5 long slot rockers but you'll hate life. Bummer Jeff
Yeah, you need to take it to a machine shop at this point and see what they say....and then start pricing some alternative heads if the estimate is out of control,
I just bought this car a couple weeks ago. I don't know any specs or have seen (as of yet, working on it) any paperwork on who built the motor. Maybe the guy I bought the car from installed the rockers, push rods etc. I just need to repair what I've got. I will be pulling the heads within the next day or so and take them to a machine shop. I'll have screw in studs and guide plates installed and buy some good ol' made in the USA aftermarket rockers. Talking with a couple guys at work, the rocker arm suggestion did come up. If they did have long slots, we're thinking that might have cleared up the pushrod rubbing against the hole... Even if they are 1.6 rockers, correct? The heads are 041, so earlier model heads. Though I have not looked at the date code on the heads, the block is out of a 1971 Chevelle 4 speed car. I'm assuming the block and heads have never been separated, only for the "rebuild". It's got great oil pressure @ 30 lbs idle, 65 - 70 lbs on the freeway. So, I do believe it has been rebuilt recently, not just repainted... Had I been the guy that painted the motor, it would've been taped off or at least had an old set of covers on it... I'll update more as I dig further...
If you have 1.6 rockers You probably need at least .100 longer pushrods than stock to correct the geometry. I'm guessing the guy put the 1.6 rockers on with a stock length pushrod by the looks of it. You probably don't need long slot rockers unless you have a pretty radical lift cam. If you are buying new rockers I'd get self aligning ones and ditch the guide plates altogether. I'd also recomend upgrading to poly locks and good name brand pushrods. Stay away from anything that says proform or summit brand They are junk.
Looks like from your pictures that you have early heads that don't require guide plates or hardened pushrods. If that is indeed the case, I suspect you simply wiped a cam lobe and that resulted in all the carnage topside. You mentioned you had around 2000 miles on the motor which also leads me to believe a wiped cam lobe (the voice of experience there with a similar SBC with big valve heads (202 intakes) that started "ticking" about 5-600 miles and totally lost a cam lobe by 2500). In my case, a fresh cam and lifters with a healthy dose of GM EOS for break in were all that was required to get back up and running (I didn't bend or break any pushrods) and no exotic or non Chevrolet parts were needed. When you get the intake off you'll figure it out, good luck. A great deal of information on cam failures and the relationship to zink reduction in modern oils has flowed through a lot of HAMB threads recently, enough to make it definitely worth dittling the search button. On a lighter note, although you didn't directly say so, if the 50 Plymouth is the current home of the SBC, all your troubles might be stemming from transplant rejection and a return to proper MOPAR DNA (as in remotoring with a proper LA motor with shaft mounted rockers, 273,318,340,360) should cure them.
The Jalopy Journal
