Clunking/knocking sound from -48 320

W

wacker

Member
Hi,
I have some problems with my -48 320 engine.
It makes a clunking/knocking sound when driving faster than 35 MPH. Its louder when having part throttle (or at least easier to hear).
Its gets worse when the engine is hot.

At first I thought the timing was wrong and it was knocking because of that. I changed the initial to 0 degrees and the sound was almost gone.
I changed it more and now when its on -5 degrees I dont hear it at all.
To me this indicates that its not the timing that is the issue but the stress on the engine is less and therefore I dont hear it.

The engine was renovated about 10 years ago and I dont think it has been driven that much since then.
Maybe its the main bearings? I feel a bit bad about tearing it apart since it has been renovated but I guess I dont have a choice.
Can they be changed without removing the engine? Seems a bit tight under there.
Any suggestions from the experts here?
Thanks in advance!
//Stefan
 
Sounds like a rodbearing .... drop the oil pan and check it,before you damage your motor completly.
I think you can drop it while the motor is in the bay. On 248 and 263 It works.

Wish you much luck that the crank isnt damage.
 
I missed to write that I have been driving with this for about two years and it haven't changed to the worse yet. The oil pressure is ok.
Can anyone verify what can be done without taking the engine out?

Regards
Stefan
 
you said 35 mph. so what does it do at no load? is it rpm related? yes check valve lash. if one is out of spec, make sure the valve is not sticking. pull rocker shaft and pop each stem with a plastic hammer and note protrusion.
 
I cant hear it when standing still and revving the engine.
Feels like its time to tear all of it apart and do everything from scratch. Then I know how everything has been done.
Now I know about the renovation but not exactly what was done etc.
I will drive with the car during the summer in condition it is right now. It has been like this a long time and hopefully it will not break during the summer. I know that the best would be to do it now but just getting the right parts would probably take around a month (delivery to sweden).
Thanks for the responses. I will update when I know what is was.
 
wacker said:
I cant hear it when standing still and revving the engine.
< snip >
I will drive with the car during the summer in condition it is right now..
Click to expand...
You are risking far more damage and far more expense when it does fail completely. It will fail. Check the items as suggested above.
 
Stefan dont risk it !!
I know,in sweden is summer now ,
but like 1939 Buick said, you risk a damage of your complete motor and then you have a much longer and expenciver break like only the rest of this year.
 
Im now rebuilding the engine and it turned out that it was the connection rod bearing for cylinder one that was causing the sound. After some investigation I found out that the previous owner had it "metal sprayed" at that cylinder because the Journal was in bad shape when he bought it.
I talked to a friend who works with rebuilding engines and he said that he dont trust metal spraying at all and that I should find a new crankshaft.
There is no one that got a spare crank fitting a 320 48-52 with dynaflow?
If I cant locate one I can get a complete 1950 engine from a friend but that would cost me around 3500 USD.
The last way to go is if its possible to machine a manual crank to fit a dynaflow. I need to investigate if there is enought metal for that. Do anyone know if the rest of the crank are the same.

Regards
Stefan
 
I was finally able to locate a crank in Sweden. It costed me around 800 dollar but at least its less than buying a whole engine.
I will hopefully be able to buy connecting rods from the same guy, the surface are in bad shape on one of them.

While rebuilding the engine im thinking about dipping it in acid to get rid of all the rust in the cooling passages. Do this this I must remove the camshaft bearings. Is that something that is wise to do or will I have trouble with getting them installed again? As I understand installing new ones will be much work since they need to be reamed.
 
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