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Kindly assist.

My 1GFE engine had a rod knock sound and I replaced all the bearings, oil filter, cleaned the sump & strainer and tolled it with brand new fully synthetic oil.

The engine ran for about two hours and the rod knock sound came back, what could be the cause?

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  • Were the bearings actually bad?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Apr 3, 2016 at 14:39
  • They first and last one were a bit bad the others were not so bad
    – Mompati
    Commented Apr 3, 2016 at 14:44
  • Did you just throw them in there or did you check clearances? Did you look at the mains?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Apr 3, 2016 at 14:49
  • Well I would've assumed the mechanic had checked because after replacing he turned the engine and said they were fine and once we started the engine car was fine till we drove it for about 2 hours, so does this mean the crankshaft has to come off?
    – Mompati
    Commented Apr 3, 2016 at 14:58
  • If you've had bearing issues, you will likely need to remove the crank and have it machined. In the past, I've used some 600+ grit sandpaper on the crank journal to ensure it is smooth (no gouges). Not the best method or correct procedure. Also, how was your oil pressure?
    – rpmerf
    Commented Apr 4, 2016 at 11:08

1 Answer 1

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Rod Knock Causes

Rod knock is when the hydrodynamic layer of oil between a hydrostatic bearing and a journal is being broken during the 4 cycle combustion process. Additionally, rod knock occurs with ball bearings in a connecting rod if there is too much clearance between ball bearings and races.

You can get rod knock frequently in conjunction with the following issues

The following answer explains crankshaft bearings.

What are crankshaft bearings and how are they different from camshaft end bearings?

Another post explaining the results of oil starvation in an ICE

What actually happens when there is not enough oil in a car engine?

  • Low oil pressure - Oil pressure is key to maintaining the hydrodynamic lubrication of hydrostatic bearing.

  • Debris - Debris can clog oil galleyways and filters. As well, a rare filter disintegration can occur which can create an oil starvation scenario by clogging oil feed lines, coolers and oil pickups.

  • Heat - Overheating an ICE can result in the integrity of oil being comprimised thereby creating another situation where lubrication is root cause to a bearing.

Remediation

You stated

I replaced all the bearings, oil filter, cleaned the sump & strainer

I do not see a task in your list associated with cleaning up your prior crank journals. If you were experiencing rod knock prior to rebuild you could have a crank journal that is 'out of round' and allowing oil pressure to escape thereby creating a low lubrication issue.

OR

The out of round crank journal is just not measured into your bearing with the factory clearances and now you are dealing with the issue again.

It's concerning that the journal may not have been machined to a round state during your previous remediation effort. I would see this as a likely cause to what you are experiencing again. Too much clearance on the journal that is unable to maintain hydrostatic lubrication.

Due to excessive clearance you are getting metal to metal contact between the connecting rod hydrostatic bearing and the crank journal which is the sound of the knocking.

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