Engine tapping noise, comes and goes, OldsDiesel 4.3V6

turbokinetic

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Hey folks. I'm new here, and have a very unique project going on. I chose the 6.2 forum because it seems the closest to the type of engine I have. If there's a better place, it won't hurt my feelings if the admins move it.

I'm working on a 1984 Oldsmobile Cutlass Ciera with the 4.3L Olds Diesel V6 engine. The car belongs to a friend, and it has sentimental value to him. His mom (who has passed) had one when he was younger. This is a labor of love project, so please understand the reason for repairing this car.

This engine is an indirect injected engine using a Stanadyne DB2 injection pump, and glowplug system very similar to the 6.2 IDI.

The engine was in terrible shape when I got it. These 4.3V6 diesels were not known for a long life; although this one lasted more than 30 years. The previous owner had apparently run it very hot and both of the aluminum heads were cracked beyond repair. A local machine shop actually had a spare set of core heads! They rebuilt the cores they had.

The engine is obsolete, and it's very difficult to get parts for it. Pistons are completely unavailable and gaskets are very very difficult to obtain.

During the engine repairs, I found a couple of cracked pistons (skirt cracking) and replaced them with used pistons from another engine I had here. The pistons are letter-coded as to bore size, and I matched the letters.

The Olds 4.3V6 diesel is a roller-lifter engine. All the lifters were in serviceable shape as far as galling on the rollers, scoring on the lifter body etc.

After putting the engine together, it runs very well and starts easily. There's not any significant smoke from the exhaust. There is not any bupping or chuffing from the intake or exhaust.

The only problem is a very loud tapping noise. The tapping noise is strange in that it fades in and out. When the engine is started cold, the timing advance causes it to be clattery as expected, but I can hear the tapping on top of the fuel combustion sound. As the engine warms up, it runs smooth. There is no missing or any sign of a problem; other than the tapping.

When the engine is run on the road, the tapping is very noticeable in the car. After coming to a stop, the tapping is still just as loud as it was going down the road. If I let the engine idle, after about 5 minutes, the tapping will gradually fade away. If I revv the engine, the tapping comes back then takes a little while to fade away again at idle.

If I shutdown the engine while it's fully warmed up, then re-start it after a few minutes - the tapping will be gone until the engine has been revved up again.

During the engine repairs, I changed all bearings (the old ones were not destroyed and all were standard).

In troubleshooting this, I have done the following:

- Turn off the ignition while the car is moving, thereby cutting off the fuel. The tapping continues as long as the engine is rotating and the car is coasting in gear.
- Disconnect fuel injection lines one at a time trying to change or eliminate the tapping. Can not change the noise, and the engine runs the same way for each line disconnected. In other words, all cylinders working.

The above make me think it's a mechanical problem; and not a fuel combustion knock.

I further did the following:
-Remove valvecovers. Run the engine and observe the motion of the rocker arms. They all appear (by eyeball) to be moving the same distance.
-Press down on the rocker at the pushrod end and the valvestem end, with engine running. I used a piece of 5/8" heater hose to do this. I was not able to "Feel" any difference in the movement of any valve. I also noticed NO change in the engine sound when pressing down on any valvetrain component.

The engine has 40 PSI oil pressure when going down the road. It has 15 or 20 at idle.

The sound appears to be coming from the "middle" of the engine. I just don't know what it could be and I am hoping for any insight. The problem is the gaskets are very hard to get. So I need to minimize the number of times I dismantle the engine.

Here is a video where I am testing an electronic part I built. If you go to the end of the video, you can hear the tapping noise gone after I re-start it. That point is about at 7:30 in the video.
https://www.youtube.com/watch?v=qb7FcNfRbLc

Here is a thread concerning the car and its engine, with engine build pictures:
http://www.a-body.net/forums/showth...s-Ciera-Diesel-Engine-repairs-and-restoration

Thanks in advance for any insight.
Sincerely,
David
 

whitehorse

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I have no idea on this engine but we had one in school when I took diesel mechanics. It's still there today in Oxford alabama just pushed to the side....
 

turbokinetic

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I have no idea on this engine but we had one in school when I took diesel mechanics. It's still there today in Oxford alabama just pushed to the side....

Cool, that's neat that they used that engine as a teaching aid. We still have a couple oldies at our shop, too. They have an old 3208 and a couple D399's.
 

turbokinetic

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Lifters might be shot not sure maybe a or all pushrods bent???

It could be one bent pushrod, possibly. I was able to rotate each pushrod by hand and could not detect any bend. The problem with that test is, there is only a small amount of pushrod visible at the top without removing the intake manifold.

Depending on the time I have today, I may pull the manifold and investigate further.
 

Eli

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I know the Olds 4.3 is the olds 350/5.7 Diesel with two cylinders chopped off. I also know there were thousands of leftover NOS engines around at one time, most of which went to scrap but they do pop up in quantity from time to time.

Eli
 

turbokinetic

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I know the Olds 4.3 is the olds 350/5.7 Diesel with two cylinders chopped off. I also know there were thousands of leftover NOS engines around at one time, most of which went to scrap but they do pop up in quantity from time to time.

Eli

Thanks for the response! Interestingly, the 4.3V6 Olds Diesel shares almost nothing in common with the 5.7 V8. The V6 was designed as a diesel from day-one and was longer lived than the V8. If I remember, the only significant internal parts that interchange are the piston rings. The bearings, wrist pins, timing arrangement, and other parts are completely different. It was still a very far cry from modern diesels; but it did incorporate some lessons learned from the V8.

Very interesting about there being spares available. I haven't seen one in a long time and would be interested; assuming the price was right. It seems people who have these are under the impression they are worth huge money because there aren't many left.
 

towcat

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just by a quick glance, i'm suspecting a lifter bleeding down or oil flow problem.
iirc the lifters should be the same as 5.7 but not 100% sure need to do research.
 

turbokinetic

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just by a quick glance, i'm suspecting a lifter bleeding down or oil flow problem.
iirc the lifters should be the same as 5.7 but not 100% sure need to do research.

Thanks for the insight. I was thinking the same thing about a lifter. Can't think of any other part of the engine that can ever "change" like that - one minute it taps, the next it's quiet.

I had some other things to do today and didn't get to work on it. Will work on it more and hope to have some findings to show.
 

opusd2

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Just curious as to whether or not this was figured out...
 

turbokinetic

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Just curious as to whether or not this was figured out...

Thanks for the followup.

I did make some progress with it. Upon advice of another IDI expert; I re-did the test where one fuel injection line at a time is loosened. I found one cylinder which, when loosened, would stop the idle tapping noise.

So, I installed a different fuel nozzle in that cylinder. This stopped the tapping at idle, however it is still present at higher RPM's but it is much less noticeable.

The fuel nozzle I installed was a used part from a similar engine, but I am not sure it is completely good or is correct part. The engine doesn't idle as smooth as it did before.

So, bottom line is this. The engine tapping noise does appear to be fuel related, and possibly all the nozzles need to be replaced with a matched set.

Seeing how this is a 30 years old, obsolete engine - there is a good chance the nozzles have been changed out one or two at a time in the past and they may be at all different stages of wear and tear.

After getting to this stage, I had a work assignment come up. Now I have some training classes coming up. So it may be a while before I can get back on it.

Sincerely,
David
 

79jasper

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You may talk with Mel at Conestoga. He could probably clean those up.
It seems you can use the 5.7 injectors also.

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turbokinetic

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You may talk with Mel at Conestoga. He could probably clean those up.
It seems you can use the 5.7 injectors also.

Thanks, I will contact him when I return home.

I am not sure the engine has a matched set of nozzles. There is one I installed from another year of engine and it should be same part but I am not sure. The others were in the engine when I got it. Engine did not run correctly beforehand because of badly blown headgaskets - so I don't know how it had been running before the overheating incident took it off the road.

I bet Mel can test and determine exactly if they are matched.
 

79jasper

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Yes.
I read that the 5.7 injectors are supposed to gain you 15hp. Rather I believe that, I don't know.

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