Bent exhaust pushrods.

M

Maxhawkins28

Well Known Member
That's for sure I was scratching my head going what can I do at this point... I'm very thankful of the knowledge all you have . and yes skipxt4 I was already thinking about getting the guides. And the screw in stud and new rockers.
 
G

Greg Reimer

Well Known Member
The fine folks at the 409 factory kept enhancing the performance on the 409 with the 690 heads.One way was to keep increasing the cam lift. A point was reached where the cam had more lift than the 690 head with stock length valves and springs could comfortably handle without getting close to coil bind. That breaks rocker arms, pulls or breaks rocker studs,bends pushrods, and can flatten a cam real fast. The factory fix was the 583 head, available on 64 and 65 400 horse engines, and the 64 425 horse head. That head had the valve spring seats cut deeper into the head, then a taller spring was used to get the valve train geometry right with proper spring tension. Chevrolet released a TSB on those that had a story about servicing the high performance 409 through 64 and 65. It basically told you not to put the 7735 cam into an earlier engine or coil bind could occur. If you put the 690 cam in the later engine with the 583 heads, no problem. If you put the 7735 cam in any earlier 409, that's where the problem lies. On that 348 with an OEM cam,valves, and pushrods and rockers, that shouldn't be even anywhere near to being a problem. Make sure the cam is installed correctly on the timing marks, no sense having incorrectly timed valves hitting pistons, and make sure your valve springs aren't too tall and binding up. Also, valve spring pressures of 90-100 on the seat and 225-250 at .400" lift would be good to shoot for.Keep us up to speed on this project!
 
wristpin

wristpin

Well Known Member
I have to wonder if the rockerarm nuts weren't over tightened and that is the cause of all this damage. I could see one or two bent pushrods due to lifter issue but not all these bent and studs pulled.
 
skipxt4

skipxt4

Well Seasoned Member
Supporting Member 18
That could be.:dunno When my 64 Conv. was new, I brought it back for the dealer, for warranty work. Oil and Filter, Adjust the valves, and a Tune-up. :clap After about 3 hours, they told me, the car was ready.:applAs soon as I started her up, I new something was wrong.:eek1 Didn't want to stay running.:bang I went around the block, and came back, and complained. They took it, right back in. I watched a different mechanic, take the valve covers off. He readjusted all the rockers, and this time, they were correct.:clap He said the original mechanic thought, the motor had Hydraulic's, and adjusted them, that way.:drop He told me, there were no bent pushrods.:clapEven the Pro's screw up, sometime.:dunno2
 
M

Maxhawkins28

Well Known Member
After I bent the first ones I thought I set the valve lash wrong and then bent some more and yeah not good I just wanted her to start of course that wasn't a good idea of just throwing some more in...
 
Jeffrey Osstyn

Jeffrey Osstyn

Well Known Member
Supporting Member 3
Wow! I thought my engine had a bad valve train setup! You have me beat. I have done lots of work with the SB Chevy and I have never encountered as many valve train issues as I have seen with the 348/409. I am fairly new to this game, but after a few years working on mine I have come to the conclusion, which many of you already know, if you stray from basically stock cam shafts in your build just about every other part will need to be adjusted to accommodate the change. The factory built them to go many miles, as long as you don't mess with their combination. Check everything! Take a break, then do it again! Or..... break/bend parts.
 
GCAMINO

GCAMINO

 
Supporting Member 1
Make sure the those little retaining balls on the rocker arms are the larger ones. Small block chevys are smaller. I had the same problem. Ended up using guide plates. Also look at the push rod holes in the head, and see if they're opened up from wear. Should be a pretty close fit.
 
skipxt4

skipxt4

Well Seasoned Member
Supporting Member 18
Maxhawkins28 said:
That's for sure I was scratching my head going what can I do at this point... I'm very thankful of the knowledge all you have . and yes skipxt4 I was already thinking about getting the guides. And the screw in stud and new rockers.
Click to expand...
When using Guideplates, the Pushrods, are Special, and need to be installed, with the Dot or Arrow pointed Up.:clap
 
You must log in or register to reply here.
Top