350 rocker/push rod problem

77ElkySS · Posted: Wed May 21, 2008 3:07 pm Post subject: 350 rocker/push rod problem

77 El Camino SS, original 350 engine removed, boiled and steamed, bored to 355 and completely rebuilt.

Installed Comp cam 12-210-2 with .454 lift, 2.02 heads, Edelbrock Performer RPM intake, Carter 750cfm carb, HEI distributor, Hedman headers.

When I first got the car after the rebuild I was unhappy with the performance. Sluggish with no response. Took it back to the engine builder after throwing a push rod. Was told the springs were too strong on the heads and they rebuilt them again.

Performance improved but shortly after, the rockers started clacking. I adjusted the valve lash out but after an hour started clacking again. Enough... took it to another performance engine builder, had all the lifters, push rods and rockers replaced again. Engine sounded good, performance was good.

After 1000 miles the rockers started clacking again. Removed the valve cover and noticed the rocker sitting off to the side of the valve stem. Removed the (bent) push rod and replaced it. Adjusted the lash out, again rocker off to the side, bent another push rod. I've inspected the rocker and see no damage at all.

Am I using the wrong lifters, push rods and rockers because their stock? Have I collapsed a lifter? Can I replace just one lifter? Or have I damaged the lobe of the cam? Very frustrating....

dwagner1974 · Posted: Wed May 21, 2008 6:00 pm Post subject: 355 engine help !!

if its the same pushrod everytime then that could mean they installed the valve that is controlled by that pushrod incorrectly .. anytime you install a larger cam and or upgrade valve springs you should never use stock lifters or push rods .. you are gonna have problems almost everytime .. the stock rocker arm usually can be used unless you get really wild with your camshaft but you havent .. its pretty mild .. i would go with replacing the push rods first with some stronger ones and then if that doesnt fix it .. replace the lifters with upgraded lifters and if that doesnt fix it I would take it back to the place that built the engine and heads and ask for some help ... camshafts are pretty tuff usually .. thats where i would start .

good luck
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toms84ss · Posted: Wed May 21, 2008 7:13 pm Post subject:

Couple things to check. Valve retainer to valve guide/seal clearance. Also check rocker arm slot, you may need to step up to a long slot rocker arm. Look for contact between the rocker and rocker stud. I wouldn't think with that small a cam it would be an issue. But it may.
Also, when you say the springs were too stiff originally. What springs were in it and what replaced tham? The cam should have a spring recomendation from the factory. This will include pressures and installed heights. Was this followed? If not and you have a set of budget springs, it may be coil bind. Find out what was put in and why.

77ElkySS · Posted: Thu May 22, 2008 11:24 am Post subject:

The rocker slots are not damaged and no contact with the stud. The first head rebuild had double springs which were replaced with singles, or so I was told. Since it is the same push rod that gets bent I'm going to replace the lifter and push rod this weekend and see if that resolves the problem. Thanks for the suggestions.

77ElkySS · Posted: Wed Jun 11, 2008 3:50 pm Post subject:

Thanks for all the suggestions, here's an update...

The studs are screwed in instead of pressed in as previously thought (had one back out while undoing the nut, different cylinder).

Replaced the lifter and all the push rods with new high energy push rods from Summit. Replaced all the spark plugs and wiring as well. The old lifter showed no wear or marks of any kind, was hydraulic and looked new. Put it all back together with new gaskets.

Fired it up and clack, clack, clack. Removed the valve cover and the rocker was now jammed beside the valve spring instead of just off the valve stem. The new push rod was now bent instead of just bowed.

I can only conclude that there must be a problem with the valve or valve stem and need to remove the head and inspect the valve. Am I missing anything?

toms84ss · Posted: Wed Jun 11, 2008 9:48 pm Post subject:

Are you running guide plates with the screw in studs? Sounds like there is an interference problem. If its the same cylinder all the time and its not the rocker or stud contact. Look for coil bind on the valve spring or retainer to seal/valve guide contact. Something seems to be stopping the movement of the rocker and bending the push rod.

77ElkySS · Posted: Thu Jul 03, 2008 4:04 pm Post subject:

The heads didn't have guide plates, are cast iron and not worth the money to repair. So....

I bought new Edelbrock Performer RPM heads (60739) and Summit aluminum roller rockers (G6905) that match my Edelbrock RPM intake (7104). Also all new Pushrods, Hardened Steel, Heat-Treated, 5/16 in. Diameter, 7.800 in. Length.

Now I'm getting a backfire (on throttle up) through the exhaust. Checked timing, vac lines, new plugs and plug wires, all good. I installed the rockers with a 3/4 turn after 0 lash and thought maybe that was too much, so I backed them off to only 1/2 turn. Engine starts right up and idles fine but any quick throttle and it backfires. Leaned out the mixture screws, played with some distributor rotation, still backfires. Didn't have carb problems before but... could it be this Carter AFB (9755S) 750cfm is just to much?

elcamino74guy · Posted: Thu Jul 03, 2008 6:42 pm Post subject:

Check the timing again and reset the idle mixture screws back to stock settings. Idle mixture is just that, for idle, once you hit part throttle the idle circuit has no effect on fuel delivery. If you're overfueling its time to check float level, jets, metering rods and the like.

Backfire in the exhaust sounds like too rich with too much timing.

Could also be an issue with too much overlap causing the intake valve to stay open too long.

Just some suggestions..

Happy

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74 El Camino Classic - project car #1
96 Camaro - RIP, Traded 10-16-2007

2008 Mustang GT, It ain't a Chevy but at least it's American!

PaPa Johns 77 · Posted: Thu Jul 03, 2008 10:10 pm Post subject:

That is the same cam I'm running. I got the cam/lifter kit. Used the stock rockers pushrods and valve springs with no problems at all. 30,000+ miles and still ggod to go. Cool

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"Still Just Truck'in"
"Johnny"
Bradley, Illinois

mnunn · Posted: Fri Jul 04, 2008 5:45 am Post subject:

Sounds to me like the valves may be hitting the pistons and bending the pushrods.

When the engine was on the bench, did anyone do a piston-to-valve clearance check? Minimum clearance s/b about .050".

Also, because of the new symptom "backfire on throttle up" I'd do a compression check. If there's a clearance issue, you may now have a bent intake valve.

Hope I'm wrong.
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70 Elky (Non-SS) 454CID, TH700-R4
69 Chev C-10 Pickup (recently Upgraded to 454) w/TH400
29 Model A (Recently Sold).

Hansmanbo · Posted: Fri Jul 04, 2008 7:02 am Post subject:

I'm thinking he needs .1 longer pushrods?
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York SC /1979 GMC Caballero / 350 Roller / Alum Heads / 410 posi

77ElkySS · Posted: Sun Jul 13, 2008 12:10 pm Post subject:

Got it fixed!!!!

Reset the timing (with a light this time), reset the mix screws and backed off on the valve settings. Adjusted the floats correctly. My brother came over to take a look and insisted on checking everything one more time... bingo, we found it! As hard as it is to admit, I had a plug wire crossed! I must have checked that 3 or 4 times before but just didn't see it. This just goes to show you how important a second set of eyes can be. I want to thank everyone on this site for your suggestions which forced me to adjust and check things I normally wouldn't have. It runs like a bear now! Thanks!

toms84ss · Posted: Sun Jul 13, 2008 12:47 pm Post subject:

Glad you got it fixed! I know a second set of eyes have seen things I missed right in front of me. Enjoy your ride.