2F Knocking noise at idle?

[Kilgore]

The motor was just rebuilt a few thousand miles ago. I know cylinder 6 had to be rebuilt and bored over a bit. How could the bearing go bad that quick?

I am going to check my timing as well, just be sure as I haven’t checked this either.

 

[65swb45]

Pull the clutch inspection cover and try tugging front to back on the flywheel as well.

 

[Kilgore]

Pull the clutch inspection cover and try tugging front to back on the flywheel as well.

If there is play fore and aft, that tells you it’s a bearing issue? Or if it is loose in any direction?

 

[65swb45]

If there is play fore and aft, that tells you it’s a bearing issue? Or if it is loose in any direction?

…or the flywheel bolts are backing out. Seen that twice.

 

[crawsfire]

Sounds like a wrist pin issue if you haven't lost oil pressure. Were they replaced during the rebuild?

 

[Chungas Revenge]

Get a 4 foot long dowel and put it against various parts of the engine while it is running (don't stick it in the fan blades!). Put the other end of the dowel up to your ear and you will hear the knock. This is a poor man's stethoscope.

^^^Church...

 

[Kilgore]

No play in the fly wheel, no loose bolts.

 

[Kilgore]

Exhaust is white, smells pretty gassy.

 

[Kilgore]

Here is a video from under passenger seat.

 

[Kilgore]

No play in the fly wheel, no loose bolts. Wrist pins were replaced.

View attachment 2910713

 

[crawsfire]

Pull #6 spark plug and let it idle. It will be loud but you should be able to tell if the knock is still there or got quieter. If thats the case then it's probably wrist pin or piston slap.

 

[65swb45]

Pull #6 spark plug and let it idle. It will be loud but you should be able to tell if the knock is still there or got quieter. If thats the case then it's probably wrist pin or piston slap.

Playing with fire. Drop the pan.

 

[Kilgore]

Pulled the plugs. Here’s spark plug #6

 

[Pighead]

Sometimes, an exhaust leak can make a knock sound. I hope.

 

[Skreddy]

Playing with fire. Drop the pan.

I agree completely with Mark. Worst case is you buy an oil pan gasket and oil for no reason.
Could be any number of things including a lifter sticking, valve sticking, bent pushrod hitting side cover. But I think the worst possibility is a bearing issue on the crank because if it goes……

 

[Kilgore]

It’s not getting louder with revs, but I can hear it the frequency increase with revs until the transmission and engine get louder than the noise. After removing all the plugs, they need a cleaning or replacement. The noise gets softer when the engine is warmed up. Have not gone as far as finding TDC and doing a timing adjustment.

Valves were just adjusted and are good. Pushrods are all new. This noise has been with this engine ever since it was rebuilt, it just seems a little louder on startup now.

Oil pressure by the dash gauge is great, it fluctuates around the 2/3 mark predictable with RPM. I’ll try to get a oil pressure tester gauge on it this week and look for fluctuating on the gauge and low pressure. Will also try to get the oil pan dropped to check the crank. With the oil pressure being high and the knocking noise it would seem to point to a spun bearing. What else in the oil pan might be making noises, loose oil pump, etc?

 

[65swb45]

Pull the clutch inspection cover and try tugging front to back on the flywheel as well.

Case in point, real time. Picked up a core from @bmoonhajjar on Saturday. Just got the trans separated from the engine this morning and dropped the clutch.
When I put my prybar between the flywheel and bellhousing to start the process of separating it from the crank and tugged, the crank came back over 1/8” with the flywheel! I’m already sure the bottom end of this thing is toast. But that’s not what I got it for.

 

[Living in the Past]

…or the flywheel bolts are backing out. Seen that twice.

Only seen that once but that was in fall 1974 on my 68 I bought during the summer. In my case the flywheel wasn't loose just one bolt sliding out and locking the clutch disc to the flywheel. Quite the baptism on working on 40 series. No garage, no floor jack much less a transmission jack and very few tools. That year November was cold in Flagstaff. Once I got it all pulled apart found the three locking plates there but last person there didn't bother to bend the tabs over. Also found the knock it experienced later was a castle nuts on the rod caps were all missing cotter pins. One had come loose after four years owning it.

No play in the fly wheel, no loose bolts.
View attachment 2910713

The bolts Mark is talking about are on the center of the flywheel and used to hold it the crankshaft. Have to pull the transmission and then pressure plate to get at them. Mark was just saying check to see if there was play caused by loose bolts or if the crank might be loose.

 

[crawsfire]

Playing with fire. Drop the pan.

Curious how you would think that this is playing with fire.? This is a tried and true method of relieving pressure on the wrist pin / pistom to eliminate that possibility from the equation.

 

[1911]

Curious how you would think that this is playing with fire.? This is a tried and true method of relieving pressure on the wrist pin / pistom to eliminate that possibility from the equation.

Mark has been a 40-series mechanic for a living for more than 40 years. If there's anything he doesn't know about F-series motors, it's not worth knowing.