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Author Topic: 350 making a nasty noise and no power  (Read 2141 times)

Offline SuburbanHunter

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350 making a nasty noise and no power
« on: July 08, 2014, 11:58:43 pm »
My 77 K10 pickup has started to make a nasty noise and has lost a lot of power. The noise is "like" a knock but seems to be ignition/timing related rather than a rod or valve gear. It is not as regular as knock usually is (not in sync to RPM) and sounds like it comes from under the intake manifold. The noise stops at certain RPM ranges. The truck has also started to backfire up through the carburetor when it the engine first starts. This is not the original motor it is a replacement(of unknown origin)with electronic ignition.

I thought about pulling the timing chain cover but A) that is a lot of work for a troubleshooting exercise and B) I read on the internet (so it must be true) that it is virtually impossible for the Chevy small block to "jump" the timing chain. It seems equally unlikely that the distributor somehow "jumped" a tooth but something happened.

Any ideas? Tricks for isolating the issue?

Its only at $1500 beater but my only transportation at the moment. So I want to get it fixed but I an not anxious to drop a new motor in it. I'd more likely start looking for another beater truck if it can't be fixed pretty cheaply.
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Offline bd

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Re: 350 making a nasty noise and no power
« Reply #1 on: July 09, 2014, 12:36:24 am »
It probably has a cam exhaust lobe wearing flat.

What's the oil pressure running?

Does it "pop-pop-pop" back through the carb if you rapidly rack the throttle full open?
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline thefarmboy21

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Re: 350 making a nasty noise and no power
« Reply #2 on: July 10, 2014, 07:58:41 am »
Wiped cam lobe, collapsed lifter, broke rocker, or bent/broke pushrod is my guess. My buddy just had this happen and I told him and told him while he was tearing into everything but the valve train and sure enough, wiped cam and 5-6 lifters had worn anywhere from 1/8-1/2" short....never seen anything like it LOL.

Easiest way is to pull valve covers and watch the rockers move.
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AMSOIL DEALER # 5583011
86 Chevy K20 Custom Deluxe-Grandpa bought it new 11/20/85
77 Chevy K10 Custom Deluxe-Dad's first truck
69 Chevy C30 flatbed-Grandpa's farm truck
1950 International L-112-Grandpa bought it new, parked in 1963

Offline SuburbanHunter

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Re: 350 making a nasty noise and no power
« Reply #3 on: July 11, 2014, 01:22:30 pm »
Thanks! I haven't had much time for troubleshooting but I pulled the valve cover off the driver's side and all the value gear appears to be working: rockers going up and down, the noise is no more specific with the valve cover off, no play in the push rods, springs look ok so far.

I appreciate the advice and will keep digging. Probably pull the other valve cover next.

Thanks,
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