Knock at low rpm

[mecevans]

i get chatter, which sounds like rod knock, at a low rpm. if the car is idling and i blip it chatters then after 1200rpm it goes away. I am doing an Na-T build within the month and im debating whether to just pull the motor and freshen it up a bit or leave it as is? ill have to wait for an extra check and it will spend more time off the road.

 

[hvyman]

what kind of clutch do you have? push the clutch in and see if it goes away.

 

[mecevans]

Still does it. stock clutch i believe, i have a w58 trans.

 

[Nghty89]

Stethoscope it and see where exactly its coming from.

 

[hvyman]

^agreed. if its a knock it will be rpm dependent and happen all the time.

 

[Nghty89]

Sweet, so I get a cookie right? :naughty:


But seriously, any other things that happen to make you think rod knock? Overheating, eating oil/coolant, other noises?

 

[mecevans]

Sweet, so I get a cookie right? :naughty:


But seriously, any other things that happen to make you think rod knock? Overheating, eating oil/coolant, other noises?

eats about 1 qt of synthetic a month. it just goes clack-clack-clack under 1200rpm and flooring it.

 

[Nghty89]

Up to what point does it stop making the noise? Did the noise get progressively worse over time? Did it just happen out of the blue? Have you had any leaks that you have noticed? Overheating?

 

[hvyman]

if it happens flooring it then it happens when your not flooring it. grab a stethoscope or a long screw driver and put the metal end to the block down about where the rods would be and the other end to your ear and raise the rpms to around 2500. if your hear a loud knock then you need a rebuild.

if you lost a few qts of oil you might have lost enough for the bearings to go.

 

[isnms]

See if your crank bolt is loose.

 

[mecevans]

Up to what point does it stop making the noise? Did the noise get progressively worse over time? Did it just happen out of the blue? Have you had any leaks that you have noticed? Overheating?

say if i rev it to 2k for a launch and drop the clutch, it wont do it. If i where to purposely stall it it does it. also if im in a high gear and below 2k or so and floor it.

the noise has been the same level since i owned the car and the only RPM related noise is from the cams. No leaks, but i had to change the thermostat once. i never let the oil go below 3/4q low.

i will try the screwdriver.

 

[Nghty89]

Does it only happen when you are moving? Or can you reproduce it while sitting still and no load on the engine?

 

[mecevans]

Does it only happen when you are moving? Or can you reproduce it while sitting still and no load on the engine?

YEP and with the clutch in.

 

[Nghty89]

Rebuild time is what it sounds like to me. Just make sure you listen to it with the stethoscope to get a good idea where and what it is. Lower down = rod knock

 

[mecevans]

is it possible to have rod knock from sloppy bearing clearances and/or damaged bearings?

 

[Nghty89]

Yes. that's pretty much what causes rod knock. The reason BHG's cause it is because the coolant mixing with the oil creates a corrosive mixture which eats the softer metal of the bearings, which in turn cause too much damage/clearance between the rod/bearing/crank. Hence: rod knock. It is literally knocking back and forth.

If someone sees a flaw in this info/logic, please let me know so I can correct myself for future use. Thanks!