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Old 07-06-2007, 10:30 AM
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wrist pin troubleshooting sbc 350

Good Afternoon

Basic setup:
1984 StepSide Chevy
350 sbc - 4 bolt
Bottom end was apparently done before I got the engine
New cam and lifters installed
Camel Hump heads
Edelbrock Performer Intake
Edelbrock 600 cfm carb

After purchasing a short block (apparently rebuilt) I assembled the rest of the engine. But while running it(first 100 miles), it developed what I thought was a lifter tick. We tried adjusting the hydraulic lifters, but the tick remained. I purchased new hydraulic lifters and installed them. Assuming that I had a bad one in the bunch. After getting it back together again, I still have the tick/knock. I seems to be worse when the engine is slowing down after stepping onthe gas a little (2200 rpm or so). This is with the vehicle parked, not driving onthe street.
I am thinking that this sounds like a wrist pin, but not sure how to identify the problem further.

I have limited engine experience, so please don't assume anything. Any suggestions would be appreciated.

ps.
I am running a automatic trans

Thanks in advance.

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Old 07-06-2007, 12:29 PM
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Quote:
Originally Posted by 1984stepside
Good Afternoon

Basic setup:
1984 StepSide Chevy
350 sbc - 4 bolt
Bottom end was apparently done before I got the engine
New cam and lifters installed
Camel Hump heads
Edelbrock Performer Intake
Edelbrock 600 cfm carb

After purchasing a short block (apparently rebuilt) I assembled the rest of the engine. But while running it(first 100 miles), it developed what I thought was a lifter tick. We tried adjusting the hydraulic lifters, but the tick remained. I purchased new hydraulic lifters and installed them. Assuming that I had a bad one in the bunch. After getting it back together again, I still have the tick/knock. I seems to be worse when the engine is slowing down after stepping onthe gas a little (2200 rpm or so). This is with the vehicle parked, not driving onthe street.
I am thinking that this sounds like a wrist pin, but not sure how to identify the problem further.

I have limited engine experience, so please don't assume anything. Any suggestions would be appreciated.

ps.
I am running a automatic trans

Thanks in advance.
Wrist pin knock, rod knock and piston knock all have the common double tick to them, it takes a familiar ear to pick out which is which.

For what it's worth rod bearings have a heavy double knock as the rod goes from compression to tension at TDC and BDC as it takes up the bearing clearance. It tends to be louder when backing off and as oil pressure falls with RPM.

Pistons have a higher tone double tick if the skirt is cracked as they flop from the major to minor thrust side and back. This tends to get louder with increased power, with a loud snap when suddenly closing the throttle.

Pins also have a lighter tone double tick as the rod or piston take up the clearance at TDC and BDC. This is more like a rod in that it gets louder when suddenly dropping RPM, but doesn't track with oil pressure.

But most of the diagnostics of these is in the ear of the experienced mechanic, suggest you find an old guy to listen to it.

Bogie
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Old 07-06-2007, 12:52 PM
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without spark vs "no" spark plug

If I were to run the engine with out spark to the cylinder with the problem and then remove the spark plug completely (if it will run this way?) What might I expect to change in the sound.

IE.
1. With the spark plug wire removed. If the sound seems to go away, or soften, would this indicate rod / wrist pin?

- if the noice is consistent before and after, what might this indicate.

Sorry if this is a stupid question. Just not very good at troubleshooting this situation.

thanks again
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Old 07-06-2007, 05:30 PM
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Quote:
Originally Posted by 1984stepside
If I were to run the engine with out spark to the cylinder with the problem and then remove the spark plug completely (if it will run this way?) What might I expect to change in the sound.

IE.
1. With the spark plug wire removed. If the sound seems to go away, or soften, would this indicate rod / wrist pin?

- if the noice is consistent before and after, what might this indicate.

Sorry if this is a stupid question. Just not very good at troubleshooting this situation.

thanks again
Not a stupid question at all.

Unfortunately in all the cases I sighted, the click and clack will become quieter if the plug doesn't fire. This will, however, tell you which cylinder is having the problem.

I'd still recommend you seek out an old timer familiar with listening to these sounds. But in the long haul that probably doesn't matter given the fix will require pulling and disassembling the motor, still given the effort, knowing for sure the problem is correctly identified can avoid spending big bucks unnecessarily. Chevy's do like to eat cam lobes and lifters, you'd hate to open up the bottom end only to find it was a lifter/lobe problem.

Bogie
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