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Chevy 350 knock

Posted by sneaker12345 (My Page) on
Sat, Sep 12, 09 at 0:09

It sounds like a rod bearing. It gets loud like one. But,it don't knock at idle and when I tack the RPMs up quick it doesn't knock. It knocks only when I ease the gas on and starts a bit after it . This is in park also as it happens. It is diffently in the engine. Could it be the knock sensor or timing got to far advanced from a friend tinkering with it to get it to run smother? Also the temp gauge isn't hooked up because wrong sending unit?
It does idle pretty well now but a slight miss you can hear.

This is a donor 350 engine out of a 1990 4X4 suburban
The engine is now at rest in a 1997 CK1500 4x4(it had a 305 I believe)
The engine ran strong and without any knocks before it got transfered.

Follow-Up Postings:

RE: Chevy 350 knock

Have you checked for sensor compatibility of the older (1990) with the newer (1997) engine contoller. There were many changes happening in engine management during those years across all brands. For example, I swapped in a 1996 6 cyl Jeep engine into a 1992 6 cyl model. The engine ignition controls had radically changed. Both engines took timing signals off holes in the flex plate (on flywheel), but the newer engine had a diferent number of holes in the flex plate. The injectors were different also. We took the easy solution and converted the 1996 engine to 1992 by putting putting the old flywheel and intake manifold (with injectors) on the newer engine. That way, no changes were required in the wiring harness or engine contoller (computer). The control of the electric fan was compatible between models.

The engine mapping in the controller must be compatible with the engine cams and characterestics of the transmission. I think you may have a 1997 controller on a 1990 engine and the two may not mix. It has to be checked out. And you need to get the temperature gage working. Are you sure the electric fan control is working?

Unfortunatley, this may not be the source of your knock.

Since you have swapped in an older engine into a newer model, you probably will have to convert the 1990 engine to 1997 (sensor and control wise) to become compatible to the engine controller and wiring harness.

RE: Chevy 350 knock

All sensors from the 97 was placed on the 90 engine.
TBI was also changed from the 97 to the 90 engine. Neither of the vehicles had an electric fan. I wouldn't think the temp gauge would have anything to do with the knock though.(yes I need to get it replaced though) These Chevy engines don't have crank triggers as the jeeps.

RE: Chevy 350 knock

Here are some of the things that you have to do when you work on those 97 CK pickups. A friend down at the body shop just had the engine replace in his 97. They worked on it for about a month before I gave them this info.


"CASE" means: crankshaft angle sensor error. A crankshaft variation relearn must be performed if:

A diagnostic trouble code of P1336 is present.
The computer has been replaced or re-programmed.
The crankshaft position sensor has been replaced.
The engine, harmonic balancer, clutch, or flywheel have been: disassembled, removed, or replaced.
The crankshaft position variation learning feature enables the computer to compensate for part manufacturing tolerances. This allows the computer to accurately detect an engine misfire throughout the engine RPM range. The learning process is stored in the computers memory and does not have to be repeated unless one or more of the above conditions are present.

To perform the relearn, proceed as follows:

Connect a scan tool to make sure there are no trouble codes stored in the computers memory. If there is any power train trouble code other than P1336 (Crankshaft Position Variation not learned), the computer will disable the relearn function until the problem that aused the code has been eliminated. Also, make sure that the engine coolant (check it when the engine is cold) and oil levels are at an acceptable level.

1. Set the parking brake and block the drive wheels. Make sure that the hood is closed.
2. Start the engine and make sure that the engine coolant temperature is at least 158 degrees F. (70 degrees C.)
3. Turn the engine off for at least 10 seconds.
4. Select the crankshaft position variation learn procedure (CASE Learn)on your scan tool.
5. Make sure that the transmission is in Park. Start the engine.
6. Apply the brakes and hold the pedal firmly.
7. Follow the scan tool instructions.

Remember: That you are going to increase the engine speed to approximately 3000 RPM, 4000 RPM, or 5150 RPM. Thats the variation learn fuel cutoff RPM (depending upon the engine), and that its important to release the throttle when the engine RPM starts to decrease as a result of the fuel cutoff going into effect. Failure to do such will result in over revving of the engine, causing possible engine damage.

8. Once the engine has returned to idle, check the status of Diagnostic trouble code P1336. If the scan tool indicates that the CASE has been learned, the relearn procedure is now complete. If CASE has not been learned, check for the presence of other power train codes. If any exist, correct the problem, then repeat this procedure.


#2 1997 Chevrolet C Pickup 5.0L, 5.7L, and 7.4L Timing

Below is the text from GM Service manual for 1997 Chevrolet C Pickup 5.0L, 5.7L, and 7.4L
Accordind to this you don't set the timing but the timing offset.
You need a "Scan Tool" that plugs into the truck and can read the data from the trucks computer.
Besides from that, it looks like a normal timing procedure.
You might be able to borrow a scan tool from a parts store, or at least use their tool and do it in their parking lot.

Setting Timing
Camshaft Retard Offset Test
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

With the ignition OFF, install a scan tool to the DLC.
Start the engine and bring to normal operating temperature.

Cam Retard Offset reading will not be accurate below 1000 RPM

Increase engine speed to 1000 RPM.
Monitor the Cam Retard Offset.
If the Cam Retard indicates a value of 0 2, the distributor is properly adjusted.
If the Cam Retard does not indicate 0 2, the distributor must be adjusted.
Adjusting Camshaft Retard Offset

With the engine OFF, slightly loosen the distributor hold down bolt.
Important: Cam Retard Offset reading will not be accurate below 1000 RPM

Start the engine and raise engine speed to 1000 RPM.
Using a scan tool monitor Cam Retard Offset.
Rotate the distributor as follows:
To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
To compensate for a positive reading, rotate the distributor in the clockwise direction.
Repeat step 4 until 0 2 is obtained.
Turn the ignition OFF.
Tighten the distributor hold-down bolt to 3Nm(25 lb. ft.).
Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset.


RE: Chevy 350 knock

Oh my bad you all. It's a 1994 CK1500 not a 97. Don't rubber hose whip me. It has been a long week for me.

RE: Chevy 350 knock

Reading your description of the knock the first thing that comes to mind is the flywheel to converter bolts might not be tight.

Beyond that, the "transplant" was something I would not advise someone attempt to do anymore. Sure some people get away with doing this and don't encounter significant problems. But when it comes to emissions testing (which also pulls the VIN to make sure that it matches) software issues arise because of the potential variation in displacement which causes problems with both the base fuel schedule, as well as the timing map. FYI the software is VIN dependent, so if you had a 305 and you replaced it with a 350, the initial base fuel calculation will be short, which fuel trim will need to correct.

There are so many potential traps, and you cannot go to a book for help once you start down this path.

RE: Chevy 350 knock

It is without a doubt a rod bearing sound. The flexplate is original from the 305 along with the converter.Bolts are cranked down with loctite. The only emission testing we have here is to see if the cat is installed. There is no other tests at all.
Would fuel shortage be the cause of the knock though John?
I hit the gas hard there is no hesitation and no knocking sound. The engine is very strong. Tomorro I will play with the timing a bit and maybe replace the cap and rotor and see what gives. Maybe I did spin a bearing but not that bad though. 20$ I can get a new set and throw them in quite easy. I will get back to you all when I figure this out. Thank you all for your replies. Dan

RE: Chevy 350 knock


You appear to be sure this is a rod bearing knock. Why then did you write this?

Quote "It sounds like a rod bearing. It gets loud like one. But,it don't knock at idle and when I tack the RPMs up quick it doesn't knock. It knocks only when I ease the gas on and starts a bit after it." Quote

You did everything that you could to convince a reader that the sound is almost anything except for a connecting rod noise.

Are you in fact attempting to describe carbon on top of one or more pistons causing a knock? The carbon if built high enough actually contacts the head and it will hammer like crazy at times.

Changing the cap and rotor would be a waste of effort IMO. You could cancel cylinders to see if you can identify the source of the sound to single cylinder. This comes in handy for diagnosis of wrist pin, or piston skirt issues.

As far as just throwing a set of bearings in it, if a bearing spun, then the rod should be resized, the crankshaft should be polished, the clearance of the bearing measured in case an oversize is required, and you cannot complete this correctly in chassis.

RE: Chevy 350 knock

Been reading along this thread and was confused too. Started out talking about a rod knock sound but kind of asking if it could be timing which would generate a spark knock sound. Those sounds have always been totally different to my ears.

If it is a hard knocking type sound, and if it didn't do it before this transfer, a carbon knock like john g suggested would be a pretty good guess imo and easy to fix. Get a can of carbon blaster, top engine cleaner, whatever you want to call it, and follow the instructions. I've used the stuff several times over the years for carbon knock and it worked every time. Carbon knock sounds a lot like a very bad rod or wrist pin to me.

RE: Chevy 350 knock

You have a rod knock. End of discussion.

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