kimo1965

Been dealing with a weird issue for two summers now. Have a 67 427/435. Running an offbrand solid lift cam...Elgin...spec card attached. My machine shop thought it was a good cam. I think it is junk and is the root of my problems. I keep finding on either the #3 cylinder, or the #4 cylinder, that the pushrod will push through the rocker on the exhaust and bend the pushrod on the intake valve of the same cylinder. I am absolutely sure that the valves were adjusted properly per the specs. (many times over I should say) Originally, I thought they may be too tight, but what I discovered was that the studs were worn and the nuts were backing off. When they would back off, I thought it was getting a pounding action and causing the pushrods to push through the rocker arms. Therefore, I put all new hardened ARP studs and new factory nuts. It would run fine for a week or so, and then missing etc. Pull the valve covers and same ole issue! This latest time as you can see in the photo, the end actually broke off of the pushrod (thank goodness it was laying in top of the inside of the head and didn't get into the engine!!) and then pushed through the rocker arm. I even pulled the heads and checked the piston/valve clearance. No issue there. I have had several solid lift engines and have never had this problem. Had a stroker with a solid roller cam that would take over 7500 rpms and never and issue like this? Am I nuts? My opinion is that I have a junk cam and that is the root of my problem, but what do you guys think? Thanks, Jim

midyearvette

i think the first thing you want to check is the assembled spring height.....coil bind....wrong springs etc.....it is not the bumpstick as i have used elgin stuff for quite a while without a problem, i know there is a first time for every thing but i really doubt your diagnosis..good luck.......

kimo1965

I have not checked the things you mention. You have a good point. I assumed the machine shop (which is pretty reputable here) matched the correct valve train components, but we all know what assuming gets us sometimes...Will check it out. Thanks, Jim

midyearvette

hey jim..double check with the cam grinder and see if they supplied the correct springs or maybe they got mixed up by the machinest or maybe wrong spring height...you may want to check the lifters also for cracking at the top due to this problem...it takes a lot of force to bend or break a big block valve train!!...again good luck......

kimo1965

I will do that Frank! My Dad said the same thing about breaking a BB valve train. He said they were like workhorses and this should obviously not be happening. It has never happened when I have hammered on the car either. Just happens after a little while of easy driving...Jim

landshark 454

What brand rockers are you using? Are they long slot rockers? Check the front of the rocker slot, which would be up against the stud when at full lift. Is it shiny there? Are there any marks on the stud in the same area? I have run Elgin cams for years in 454s with .550+/.570+ lift with no problems. In my opinion they make a good product. You may want to verify the lift on the lobes that are failing. You could have gotten the wrong cam.

Coil binding, as mentioned earlier, would do the same thing.

I find it interesting that it is always the same cylinder, which suggests an issue in the head with that cylinder. The fact that it is only the exhaust valve makes me wonder about valve stem clearance.

kimo1965

Rich, I just checked the rocker on the latest one to take a crap. It is not shiny on the inside where it might rub on the stud. However, the corresponding stud does have a little bit of shiny wear on it, but doesn't really look abnormal. I am using standard GM replacement rockers (part 10112680). I think the slots are standard. By the way, I didn't mean to disparage Elgin in general. I just thought I may have a bad one. By the way it is not always the same cylinder...it seems to alternate to the 3 or 2 cylinder and I have had both heads off and nothing looked out of synch...but who knows?? Thanks, Jim

65convt

My first thought would have been wrong length pushrods on intake and exhaust, but I see it happened more than once.
I hope you find the Gremlin.

kimo1965

Thanks. Checked those a few times, and they are standard length. The valve geometry appears to be coorect as the tips of the rockers are rubbing exactly where they should on the stems.

Ironcross

Nothing wrong with Elgin products. Tall lift cams are great but have to be in a good environment and normally are not just drop in parts. Something I see missing here is retainer to guide clearances. These go away fast with high lift cams. Rubber umbrella seals over stock guides take up clearances very fast and can cause all the symptoms you described and are hidden out of sight inside the springs, therefore need to be checked before assembly.... Its not the cam...

DansYellow66

I agree it's not the cam - all it does is move the pushrods. Do all the above stuff but if the springs are set up right for the cam and it's a pretty aggressive cam - why not get some good quality roller rocker arms?

I haven't heard of anybody suggesting this but with the oil companies reducing the zinc anti-wear additives - the old stamped GM style rock arms look like a prime candidate for high rubbing wear, especially with high spring pressures.

Dan

66BlkBB

Shouldn't the BB push rods look like this??? Especially if you are using the real high lift cam in the engine? These are the ones I pulled out of my 427/390 when I rebuilt it. The parts store tried to sell me the ones you are using and I declined. I had them order in a set just like what I had. JMT

Ironcross

If you have a real L71 the pushrods will automatically be 3/8 in diameter. Hydraulic cammed engines are 5/16 and super duty`s are 7/16. And some performance P/R`s are hardened at the push rod guide section of the rod.

66BlkBB

It appears his have the hardened ball type on the end of the push rod. The diameter of the push rod is the same as the ball. On the type I have the end is smaller diameter than the main push rod.

Ironcross

thats a good cam, actually the OE grind for a L71-L72 and L78. No reason to bend pushrods it has to be an assembly problem....

kimo1965

[QUOTE=66BlkBB;1570564651]Shouldn't the BB push rods look like this??? Especially if you are using the real high lift cam in the engine? These are the ones I pulled out of my 427/390 when I rebuilt it. The parts store tried to sell me the ones you are using and I declined. I had them order in a set just like what I had. JMT

Thanks. I agree that maybe I should get a set of pushrods like you have pictured, but that doesn't explain that the pushrod will still actually push through the rocker on the exhaust and typically bend the intake pushrod on the same cylinder?? After reading everyone's responses so far, I think I am going to pull a couple of springs and have them checked by the machine shop. Jim

kimo1965

I think you guys (and my Dad) has now convinced me it is not the cam. I suspect the cuplrit is probably a spring issue. I tried to see if I could see an issue with the retainers hitting the guides, but as you say, they are hidden, so I will have to take one off to have it checked. Appearancewise, these springs have a large outer coil, smaller inner coil, and then a flat coil, and look pretty stout. Thanks for your advice. Jim

kimo1965

Just wondering guys, and I misspoke earlier about which cylinders it happens on, it always happens on either the 3 or 4 cylinder....why do you think it only happens on these 2 cylinders??? I would think that if I had the wrong springs, retainers, etc. the problem would tend to hop around to other cylinders wouldn't it?? Thanks, Jim

arw57

When you reassemble the engine take and roll the engine over by hand and listen for a click. The innner spring will break. As the engine turns over you will hear a click. As the spring seats agian it will go back into its unbroken position. Pull the spark plug and look at the cylinder with a bore scope. Look at the spark plug too!!!!!!
If you floated the valves you will kill valve springs. It only takes a few time.

snake321

Get an adjustable pushrod tool and measure your pushrods. Aftermarket anything changes your tolerances.