JD 4040 knocking noise

[rdhRDH]

I am looking at a 4040 of a neighbors that sounds like it has a extra knock in the engine. It run and has good power but has this knock. Have taken everything loose from engine and still does it. it did it when they bought it used and has had new pistons and liners and head redone. Seems to me it is putting compression out the air cleaner when filters are out and it will blow the little rubber dust cup off of bottom of air cleaner. I think it is a valve letting compression by, but they say there is no difference in sound when they break injectors. I want to see all the valves working or take the intake off and see if any compression out intake ports. Anybody have any suggestions or seen this before????????

 

[WTW]

If its got a distinct thump in the air cleaner check for crushed push rod or broken rocker arm or broken rocker arm hold down clamp. If valve is not actuated the intake valve can be sucked open and dropped shut causing a distinct thump in air cleaner. I would look there first. DW

 

[David G]

Agreed, more than likely exhaust valve not opening.

 

[centash]

Exactly what my 2120 was doing...fwoop fwoop noise at idle. I thought a valve was out, but inspection revealed the locknut on one rocker arm had backed off. New nut and rocker, runs like new again.

Ben