Broke & Bent Melling MPR-78 Push Rod in my 390

[AlexS]

Well Ill start off by saying what I have. 405hp 390 with a 270s Comp Cam, solid lifters with melling MPR-78 push rods, stock adjustable rockers and rocker shafts with end stands.
So on saturday I went to take the truck into town like every weekend, got into town, started accelerating around a corner, 1500-2000rpm not getting on it at all, then all the sudden POP POP POP POP through the carb. Thought it was possibly a broken valve spring, so dad pulled me home. Got home pulled the valve covers to find that the exhaust side push rod on cyl 5 had a broken cup and the rocker was sliding along side of the push rod, intake valve on cyl 5 got bent from trying to open with a pressurized cylinder. So we got to looking at it further and It appears that the ball on the stock rocker arms do not sit all the way down in the melling push rod cups. They seem to ride really high up on the sides of the cup instead of sitting down in them causing them to crack. the only two push rods in my motor that are cracked are the two on cyl 5 but all the other ones appear to be riding high on the rod cups as well. Im not exactly sure what is going on, even the ball end of the melling rods do not sit all the way down in the cup ends of the rods, I tried to take a picture of the ball of the melling rod sitting high on the cup of the broken rod. On the broken one it does sit lower just because half the cup is gone but it still sits really high up. Has anyone else had this kind of problem with these rods? I have two replacements already but I don't want to put it all back together with these rods only to have this happen again in an embarrassing environment, I took the intake off and found the broken pieces, but would like to find a good solution to this. The motor doesn't even have 2,500 miles on it and the rev limiter is set at 5,800rpm so it doesn't really get over revved, and its not like I bounce it off limiter, it has hit it a few times but not for very long. Here are some pictures of the broken and bent rods, If you look close you can also see the wear mark on the cups where the ball is riding along with the crack.

[jayb]

Alex, I think you've got the wrong pushrods.  Maybe they came from Melling wrong in the box or something?  The ball on the rocker arm adjuster should fit down into the cup more.  You can see by the wear pattern that the ball is riding way up high at the top of the cup, and nowhere else.  That's not the way they should be.

If the Melling number is the correct, I wouldn't take a chance on another set. You could go to a Comp Cams set, or Smith Brothers.

[cammerfe]

When You talk to Melling, you may find that they are designed that way. When you have a contact 'ring', there's much less contact, therefore less friction. That's good! But you may have a set of pushrods that have the cup end harder than it should be. Brittle perhaps?

KS

[AlexS]

Jay thanks again for the rods, I actually ended up ordering another set of comp cams rods, the number 7530-16 that you gave me was the correct number, only problem was they only had 3 singles and wouldn't be able to get the 4th one to me by the weekend, so I ordered a whole new set of 16.

So here comes the interesting part that I over looked both when I assembled the motor and when I took the rods out.

So I had a brand new box of melling rods when I put that motor together. Tonight I went back out to the garage to compare your comp cam rods to the melling out of my motor. I grabbed a random melling rod out of my organizer/Dr Pepper box and I compared it to your comp cam rod and for some reason they looked identical... Thats not right they were WAY different, so i put it back and grabbed another one, that one was way different. I ended up with 4 rods in my batch of melling rods that look exactly like your comp cam rods. Same diameter, same length, same cup size, same ball I also noticed that most of my melling rods had part numbers on them, a few didnt but they were the melling rods.

So I looked at the 4 oddball rods closer and I find that they have the same MPR-78 Melling number on them as the incorrect melling rods, Melling must have changed their rod design for that part number and Im not sure witch one is the newer one, the four odd ball ones I have are correct and identical to the comp cams rods only they have melling part numbers, the other melling rods I have that came in the same box have the same number but the wrong cup, smaller diameter rod, and a different ball on the end.

Check out the pictures, the one on the far left is the defective MPR-78 Melling rod, the one in the middle is one of my odd ball MPR-78 Melling rods and the one on the far right is the Comp Cam rod.

[jayb]

Looks like you got some wrong pushrods in your original Melling order, Alex.  Its funny that they are marked with the same part number and then they are so obviously different.  Somebody at Melling goofed, that's for sure...

You know, I gave you the 12 Comp cams pushrods, and you have 4 Melling pushrods that look to be correct.  You could probably run that set of 16, and bail on the new set from Comp. 

[AlexS]

I had thought about canceling my comp cam order and using yours and the 4 correct melling rods but Sean said to keep all the melling rods because hes pretty sure we can get our money back. At this point i just want to make sure i have enough of the correct rods here so i can get the motor put back together early this weekend, that and i really dont want to put any of the melling rods correct or not back into my motor.

[AlexS]

Well I got my Comp Cams rods today, They to are different from the rest of the rods here. They dont have a press in ball like the other ones, The cup is also different, the walls on the cup is quite a bit thinner but i dont think that will be an issue being it has the correct cup size and angle. Are there any pros or cons to the cup or tip on these rods?

[jayb]

I don't think you'll see any difference with those, Alex.  They look fine to me; I'd run them - Jay