Knock at idle

D

Don S

Senior Member
My engine has a knock that is very noticeable at idle. Engine has bearing shells
with less than 20000 miles on them. All engine internals were balanced as per standard practices ,has counterweighted crankshaft,Stype touring cam,and Brumfield 5.9 head. I removed the fan belt,but knock persists. Drained oil,plug has magnet installed, but no pieces of engine stuck to it,just the graphite sort of crud on the magnet. The engine has been running great until the other day after a 60 mile run. I checked the timing,and points all good. Any ideas that you may have will be appreciated

Don S
 
Don,

FYI FWIW.

Sometimes an exhaust manifold gasket leak can make a sound similar to a ticking or clicking sound.

More of a clicking than a knock depending on how large the leak is.

Of course exhaust port number 4 is most likely as this is where a drooping manifold problem shows up first.

A 3 foot piece of 1/4 inch rubber hose held up to your ear makes a good tool to locate these leaks.
 
Thanks for your input. The main pulley is a two piece,but can’t see any cracks or missing pieces. The exhaust manifold and intake were machined as a pair , no leaks at this point. I used a 4 foot 1/2 inch wood dowel for checking for noises , the noise is loudest at the front main bearing bolt. I may have to drop the pan, but at 87 it will be a chore.
Don S
 
Thanks for your input. The main pulley is a two piece,but can’t see any cracks or missing pieces. The exhaust manifold and intake were machined as a pair , no leaks at this point. I used a 4 foot 1/2 inch wood dowel for checking for noises , the noise is loudest at the front main bearing bolt. I may have to drop the pan, but at 87 it will be a chore.
Don S
 
Guten Tag Don,


6000 km after the engine overhaul, a low, not very strong knocking noise gradually became audible when idling cold and when climbing hills with a lot of gas. The problem was the 3rd main bearing seat on the crankshaft. It had been running rough.
 
Have an knock in #3, pulled the head and I figured out that the idiot who rebuilt the engine DIDN'T put in the connecting rod (piston) pin keeper so the pin slid against the cylinder wall and scored it badly. LRF
 
Werner, the noise is very loud at full retard idle,and although when driving at speed I can’t hear the noise ,it is still there as my son was helping today. It really sounds like metal scraping against each other,inside the pan. I think the pan has to come off to get any further . Something in the rotating mass is touching where it shouldn’t ?Herb , I did not mention that I have a bronze timing gear that is still performing as expected.
When I get any info to add I will add a note onto this thread .
Don S
 
lrf said:
Have an knock in #3, pulled the head and I figured out that the idiot who rebuilt the engine DIDN'T put in the connecting rod (piston) pin keeper so the pin slid against the cylinder wall and scored it badly. LRF
Click to expand...

I am amazed at how often that is done. here are a lot of incompetent engine "assemblers" about.
 
As others have mentioned, the knock can come from several places. High on the list is the cam thrust bearing. It will knock at idle and not at higher rpm. This is the trust bearing that is pushed in by a spring and is contained by the front cam gear cover. The usual fix is to add some kind of spacer behind the spring, like one or more washers or a nut. Some people have modified the front cover by drilling and tapping a hole so that a bolt can be used to push on the spring. The advantage in that system is that the spring can be adjusted externally.
 
Hello, To post 8 that must have been the same engine I had , or one just like it , had to bore and sleeve it , piston pin did great grooving job !How many incompetent people out there?
 
Nkaminar, I have the pan off ,nothing obvious ,or loose. I will check for any for/ aft movement of the cam gear before I remove the cam gear housing. If no movement ,spring is doing its job ? We did check for knock at higher rpm,s , my Son said he could still hear a knock using dowel,but the sound is drowned out at that point. In the cab the engine sounds good, but knock is definitely there at idle ,and much worse at full retard.
Thanks for your suggestions
Don S
 
Problem solved. Cam nut was loose enough to turn with fingers. Bronze cam gear and crank gear appear ok, so will do a cleanup, make new gaskets and put her back together.
Thanks to all for your input,
Don S
 
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