Engine Knock after an F-Engine rebuild (1 Viewer)

[Swompdog]

I have recently rebuilt and in the process of assembling an F-Engine in a 1964 Fj40. I was successful in restarting the motor and has been running very smooth. I noticed a small leak in the rear of the head gasket and have now replaced it with a second OEM gasket. Now that it is installed and reassembled I am experiencing a very concerning KNOCK. I have checked the timing and removed the oil pan and do not see anything unusual. I am simply at a loss as to what could be causing this after such a smooth initial start up and all that has been done since is remove the head and replace the gasket.

Can anyone help with a suggestion on what could be the culpret.

Thanks

 

[Steamer]

Just to be clear, are you saying you just rebuilt the head and haven't done anything below?

 

[Swompdog]

No. It has been completely rebuilt. Block bored, new Pistons, rings, crank turned, new cam, bearings, etc

 

[shawnfj40]

What is your oil pressure?

 

[Swompdog]

I am not sure, we did not get that far on the second start up before the knock started. What should the oil pressure be? On the initial start up the engine was thoroughly primed and immediately started receiving oil in the rocker arms. Assuming that the engine was thoroughly oiled on the second startup after the head gasket replacement, I did not reprime. I am fearful we spun a rod bearing? I plan to remove the caps and check it out today? It's a head scratcher that it was runnining so well on the initial start up

 

[Fast Eddy]

You started a new engine without an oil pressure gauge?

 

[Swompdog]

Incorrect, I have a oil pressure gauge that during the initial start up was between 25 and 60 psi . Just curious what your thoughts on what the pressure should be is all. I pulled the caps off all the rods, and they look good, #2 looks like it had a little debris in it but nothing troubling that would cause a knock. I was concerned that maybe oil was not getting to #1 and maybe that was the culprit. #1 looked good and well lubed. I am pulling the mains now to see if I can trouble shoot. Any thoughts Fast Eddy from Cali?

 

[JAFO2014]

Are you using plastigage to check the bearing clearances? That is what I have used all my life when I rebuild an engine or install a crank kit. Oil flow is more important than pressure. You want all the oil openings nice and clear, so the oil flows everywhere it should. My old 1940's Caterpillar diesels have very low oil pressure, but lots of volume (flow). I think back in the 30's Caterpillar stopped putting pressure numbers on their gauges and instead just a 'GOOD' zone because the low oil pressure their old engines ran with alarmed people.

You are saying that as soon as the motor starts there is a low knock? Even before oil pressure builds? I think I would prime the engine and see if my oil pressure gauge came up to normal oil pressure. But also, you do want to verify that oil is getting to everywhere it should be.

 

[Swompdog]

Thanks for your thoughts. Yes, I plastigauged all clearances and were within spec during the rebuild. Main cap bearings #2 and #3 look fine.

 

[JAFO2014]

I know this sounds way out there, but could you have left something in one of the cylinders? You have any kind of fiber optic scope you could look through the spark plug holes? Rods and mains knock. What else can knock in an engine? The fact you had the head off makes one think the noise could be related to that work in some way.

 

[Pin_Head]

Check things that you have messed with since it was running fine, like the valve train. Cam and crank thrust can also make a knock, but I presume you didn't fool with this when you did the head gasket.

If you lost oil pressure it is more likely it would be seized rather than knock.

 

[Swompdog]

I had that very thought as well. I took pictures of the block which showed the piston and cylinder which shows nothing In the cylinder.

 

[Splangy]

Check for a loose or bent pushrod, too. They can make a loud knocking noise with a surprisingly slight amount of bend to them.

 

[Swompdog]

Thanks splashy, I'll give them a look

 

[sggoat]

I recently put a rebuilt head on my 77(about 7 months ago) the valves were adjusted hot and running. Have not had the chance to open it up and readjust as is recommended. I've noticed a "noise" in the last month or so that really doesn't sound like a knock--more of a rattle--could this be what you are hearing? Maybe just a valve adjustment could fix this?? Easy enough to do(I should follow my own advice!!!)

 

[Swompdog]

It sounds like a rod knock due to a spun bearing but after today that has been ruled out, I'm wondering if it could be something outside the engine maybe the fly wheel or something

 

[65swb45]

Sam

Did you try putting a pipe, rod, or stethoscope to the motor to localize the sound? I've heard heavy knocks that turned out to be timing gears, fuel pumps, oil pan clearance issues, flywheel etc. knowing where the sound seems the loudest would help. A low speed run with good oil pressure shouldn't hurt anything more than it already might be.

@calico kid got a screaming deal on his 40 because the PO misdiagnosed a crank/pump interference issue as a rod knock. @StaleAle has a horrible knock when his dipstick is fully seated.

I'm subscribed now, so I'll check back on this.

Mark

 

[gator25]

Might check to make sure your dist. tight, they make some racket when a little loose.

 

[Swompdog]

Thanks guys for your insight I will keep you posted

 

[Fast Eddy]

Check things that you have messed with since it was running fine, like the valve train. Cam and crank thrust can also make a knock, but I presume you didn't fool with this when you did the head gasket.

I was thinking about crank thrust as well.

+1 On Mark's idea of a pipe to find the knock.

Does it get worse at higher RPMs?