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FlyinRed7 "8th Year" Gold Supporting Member Posts 1594 |
04-18-12 02:19 PM - Post#2216575
My 350 SBC w/ new Vortec heads and flattop pistons, Mallory Uniilite, ceramic headers and Edelbrock 600 cfm carb on an air gap type intake is starting to pop and crack at 1500 + RPM. It doesn't seem to have the power it should either and I think it is running too lean. Nothing has been done to the carb since it was last used on this engine before the general overhaul from a basic stock 76' Camaro. The cam was replaced with a Crane 272H @.454 I/E so it's kind of tame but should work well on the street. I am really unhappy with it and have a new set of wires and plugs for it which I'll put on soon but don't think thats the problem. Also my 700R4 tranny vibrates in OD only but smoothes out if I pull it back to direct. What is going on with that? My rear is stock 3:55, perhaps a little too high? It has not been set to lock up the converter FWIW. Any help is much appreciated. Thanks guys.
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Allan In NE Contributor Posts 904 |
04-18-12 02:29 PM - Post#2216582
Nothing wrong with your transmission, it's just reflecting that engine miss. Popping out the carb? You've got troubles with the valve train on an intake valve. "Usually" a flat cam, bent pushrod, broken rocker, broken spring, etc., etc. Allan
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FlyinRed7 "8th Year" Gold Supporting Member Posts 1594 |
04-18-12 02:37 PM - Post#2216584
Pops out the exhaust but it did backfire a couple of times.
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Allan In NE Contributor Posts 904 |
04-18-12 02:49 PM - Post#2216589
Okay, Disregard the "intake" stuff. Find that engine miss. There is absolutely nothing in that tranmission that can "vibrate". Allan
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FlyinRed7 "8th Year" Gold Supporting Member Posts 1594 |
04-18-12 02:54 PM - Post#2216593
The driveline is new and good all the way as is the angle and phasing. Something is damn sure wrong. Is it possible that the converter could be bolted up wrong to the flexplate? I mean does it have to go in a certain position. As you can tell I'm not a tranny guy but I do know drivelines well.
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MikeB Senior Member Posts 9388 
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04-18-12 02:56 PM - Post#2216594
I'd double check valve adjustment. You may have put too much pre-load on one or more lifters. Very easy to do with a new lifter that's not full of oil. I like to tighten the nut very slowly until the pushrod no longer moves up and down, then loosen the nut to double check that you were at zero lash and NOT BEYOND THAT. Then take out the lash again and go down 1/2 turn or whatever Crane recommends. Let us know what you find.
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Allan In NE Contributor Posts 904 |
04-18-12 03:03 PM - Post#2216595
Yes, possible. If the converter is out of lop with the flywheel, it will vibrate in neutral/park just off idle. Still think you have an engine miss, especially so, because it really shows up in overdrive. Like the other gent said, recheck your valve adjustment and do it with the engine hot and running. Allan
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Old_Longboarder Ultra Senior Member Posts 12225 
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04-18-12 03:12 PM - Post#2216602
If the popping, sounds like a machine gun firing as engine RPMs increase, you have an exhaust valve that isn't opening.
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Allan In NE Contributor Posts 904 |
04-18-12 03:15 PM - Post#2216605
Yep, Same as the intake "rat-a-tat-tat".  Allan
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jk56chevy "10th Year" Silver Supporting Member Posts 820 
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04-19-12 09:01 AM - Post#2216875
Just a shot in the dark, don't ask me how I know, if your coil is mounted horizontally, that can cause sounds like that.
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FlyinRed7 "8th Year" Gold Supporting Member Posts 1594 |
04-19-12 11:07 AM - Post#2216923
I'm pretty sure it is a valve adjustment issue because I just had that done by a guy who is supposed to know his apples but I swear it doesn;t run as good as I had it. Could possibly be a lobe wiped but I did run it in for about 20 minutes at 2K when I first got it running. That doesn't guarantee anything I guess so I'm going to check that also. If the guy really tightened the lifters down I guess he could even have bent a pushrod. Thanks for the input everyone and for confirming what I've been thinking. Alan...I'll check the converter/flywheel bolt thing. Thanks. ps..the coil is vertical but thanks for the thought.
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tri5ss "7th Year" Silver Supporting Member Posts 2546 
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04-19-12 11:58 AM - Post#2216934
How about something as simple as a broken/cracked distributor cap or a bad/worn rotor. My old motor did the same thing a couple of days before it actually quit. Fix, new cap and rotor. See if you have any "black" spots on the inside of the cap and look for wear marks on the rotor. You may get lucky and find it's a quick and relatively inexpensive fix. Good luck, Randy
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MikeB Senior Member Posts 9388
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04-19-12 12:05 PM - Post#2216936
There's not necessarily any damage done, but I'd certainly look at all rocker arms and pushrods. Once you find the problem, you can check lobe lift at that pushrod, which for your cam would be .302". Don't try to measure lift at valve unless you have a light test spring, because a regular valve spring will compress the lifter internals when there is no oil pressure. If your lobe lift is OK, I'd say the cam's OK. Lobe wouldn't get damaged unless it was trying to push against a coil bound valve spring. So if your springs are good for, say, .480" lift + .060" safety margin, you might be OK. Then again, if a piston hit a valve... 
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MikeB Senior Member Posts 9388
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04-19-12 12:07 PM - Post#2216937
How about something as simple as a broken/cracked distributor cap or a bad/worn rotor. Good idea. 
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FlyinRed7 "8th Year" Gold Supporting Member Posts 1594 |
04-24-12 03:05 PM - Post#2218727
Rocker arms, springs, pushrods all OK & the cam lift appears equal. Replacing plug wires and loom. Hoping this does it. It does run better but still has a lifter type noise but all are adjusted properly. The noise is not necessarily a clicking but is just noisy almost like mechanical lifters. Any thoughts
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retiredrich Contributor Posts 792 
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04-24-12 05:02 PM - Post#2218763
It does run better but still has a lifter type noise but all are adjusted properly. The noise is not necessarily a clicking but is just noisy almost like mechanical lifters. Any thoughts Try putting a stethoscope down in the fuel pump area and also the push rod for it. |
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FlyinRed7 "8th Year" Gold Supporting Member Posts 1594 |
04-28-12 09:13 AM - Post#2219943
"Try putting a stethoscope down in the fuel pump area and also the push rod for it. " Not a bad idea and I'll try it. Thanks.
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beejay "8th Year" Silver Supporting Member Posts 12550 
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04-28-12 12:01 PM - Post#2219977
Well, I'm gonna go a different route. Try replacing exhaust/header gaskets. They go rat-a-tat-ta, also, and don't asking how many of the wrong ones I changed before getting the right ones installed. I replaced both, one bad, one not so good.
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