Engine knock at low rpms only

[Meadows]

I am open for suggestions...knocks only at idle, as rpms are increased, it goes away. I've had the rig for about 8 years and it has sounded this way ever since. Engine has had a rebuild by the previous owner or his mechanic, but the milage since is unknown. Rod bearings were replaced 5-10k due to oil pump failure...noise still there. Noise is loudest from the rear main cap/flywheel pressure plate area with dust cover off.

I have used search and found exact match for this problem but the thread just died. I pm'ed to find the rig was sold before locating the problem.

Anyone experienced this or have suggestions???

 

[Pin_Head]

It might be a bearing with a little excess clearance, but if it has been that way for 8 years, I wouldn't worry about it.

 

[Meadows]

Here are pics of bearings..No.2 is the one with the nut out of line...Pic 2 is the number 2 bearing from the rod side. Could the rod bore be egg shaped?

 

[mikeob1]

With the oil pan down, can you take a photo of the ends of the bolts holding the oil pump on? Inspect them and see if there are any signs of rod contacting either of the two bolts holding the oil pump to the block.

 

[Pin_Head]

Check the bearing clearance with plastigauge and mike the journals to see if they are round. The knock could also be piston slap or a bad piston wrist pin. The bearings look scored from junk in the oiling system and worn unevenly. Might as well replace them while you are in there if the crank is OK. Might as well check the mains too.

Personally, I wouldn't worry about a knock that you can only hear at idle. Run it until it drops and then get a new engine.

 

[Morse_FJ40]

My low-end knock came from my fuel pump on the cam.

 

[FJforty]

X2`on the fuel pump. Those bearing dont look too bad. I would polish the crank and put in a new set if you have the money. I wonder what the PO did to get that much junk in the oil.

 

[Cruiserdrew]

That's about what my rod bearings looked like on my FJ40. I replaced them all since they are cheap, and they plastigaged to spec.

I agree with Pinhead. Replace and run it. It likely has another 10 years in it.

 

[Meadows]

Pic of rod clearance at the oil pump. (Straight shiny part at the blot threads is the bottom of the rod) These do not make contact when rotating by hand, but there cant be many .001's there at all.

Is this normal??

Let me know what you think.

 

[splitshot]

The knock could also be piston slap or a bad piston wrist pin. The bearings look scored from junk in the oiling system and worn unevenly. Might as well replace them while you are in there if the crank is OK. Might as well check the mains too.

Personally, I wouldn't worry about a knock that you can only hear at idle. Run it until it drops and then get a new engine.

I agree with Pin_Head....

If it helps, I've been running a f engine with a cracked block for about 10 years now. I've got a 2f in the shop to replace it with, but why do it now,the old one still runs like a champ..

 

[Poser]

Those bearing dont look too bad. I would polish the crank and put in a new set if you have the money. I wonder what the PO did to get that much junk in the oil.

Really.


That #2 bearing pictured is showing wear indicative of a big end of the rod being out of round, and or, mismatched connecting rod caps. I wonder where the noise is being generated from....






But what do I know...

 

[Meadows]

Really.


That #2 bearing pictured is showing wear indicative of a big end of the rod being out of round, and or, mismatched connecting rod caps. I wonder where the noise is being generated from....






But what do I know...

I feel like you and others here know alot more than I do about these 40's...I've dabbled with them for about 15 years and still alot of learning to do...


Can I get that rod out from the bottom?...It looks like there would not be enough clearance for the pin. Looks like it will hit the block on one side and a crank throw on the other side...Maybe trun piston and rod 90 degrees?...Maybe cant come out the bottom at all.


Still looking for the source of the noise...harmonic balancer does have a little wobble to it?...Cant rule out a wrist pin without the head off, (although I have inspected each from the bottom and all seem tight with no up and down slop). Could be piston slap...
All the piston skirts look good from bottom... Hmmm

I can move the crank back and forth about a half inch and I can hear a little noise but I am thinking that could be crank and cam gear lash.

 

[Pin_Head]

I can move the crank back and forth about a half inch and I can hear a little noise but I am thinking that could be crank and cam gear lash.

Whaddaya mean? Rotational? Axial front to back thrust? Either way, a half inch sounds excessive. I still say if it runs fine, run it until it drops and then find a new one.

 

[Meadows]

Whaddaya mean? Rotational? Axial front to back thrust? Either way, a half inch sounds excessive. I still say if it runs fine, run it until it drops and then find a new one.

Rotational only...simulating the up and down forces on the rods and wrist pins etc.

Crank thrust is ok. I checked with feeler gages. I also checked the rod thrust on the crank...only one measured as high as .012" (#5).The rest were under. (#2 was almost none).

I think I am going to put in new rod bearings and button it up and run it for a while.

I just want to do all I can without a rebuild for now.

Still interested in knowing if a rod can be removed from the bottom, anyone attempted this?


Thanks!

 

[Cruiserdrew]

Still interested in knowing if a rod can be removed from the bottom, anyone attempted this?


Thanks!

It can come out the bottom if you remove the crank. Otherwise, out the top.

 

[mikeob1]

Pic of rod clearance at the oil pump. (Straight shiny part at the blot threads is the bottom of the rod) These do not make contact when rotating by hand, but there cant be many .001's there at all.

Is this normal??

Let me know what you think.

Thanks for taking that picture. I was curious to know if there was contact because a 2f motor I inspected recently did have obvious contact at that oil pump bolt.

I was more interested in seeing if you potentially have a crankshaft wobbling, with push rods wobbling, which might causes those couple .001 to allow the rod to hit the oil pump bolt and chip it off

I wasn't suggesting it is the contact that causes your specific low end noise.

I think the more experienced eyes on the main bearings you have displayed suggest the most likely root cause.

Thanks again for the picture.

Best Regards,

Mike

 

[FJforty]

Just to make something clear. Mechanical fuel pumps can knock at idle because of a defect in the fuel pump having nothing to do with the engine. Often the return spring breaks or the idler shaft wears out.