2F Engine Knock (1 Viewer)

[Cascade Cruiser]

Please help me diagnose....

I've got a moderate engine knock, noticeable at idle and lower RPM's and all engine temps. It may be around at high RPM's too but there's too much peripheral noise to tell for sure. Poking around with my stethescope leads me to the front bottom portion of the motor. It's not the fuel pump. The knock subsides when I pull #1 and #2 spark plug wires. Here's the compression numbers, #1-6:

140 135 142 139 137 148

The knock appears to be in sync with the timing light, so I'm thinking bottom end bearings. I guess that would be either a main, rod, or wrist pin. I'm thinking/hoping it's a rod bearing due to ease of replacement.

Any help with the diagnosis and pointers for rod bearing replacement are greatly appreciated.

Thanks

 

[Pin_Head]

If the knock is in synch with the strobe, then it is cam related because the crank rotates twice as fast as the cam and distributor.

 

[Cascade Cruiser]

If the knock is in synch with the strobe, then it is cam related because the crank rotates twice as fast as the cam and distributor.

That is a good point about the timing light sync. However, the knock goes away when #1 and #2 aren't firing, which leads me to believe the culprit component is in the load path of the power stroke. This leads me away from the cam. However, I'm inexperienced in engine diagnosis so I could be wrong on this. Is it possible that knock would only occur on the power stroke, which would result in a bearing knock synced w/ the timing light? This is getting more complicated....

 

[bull]

could you have a bad exhaust leak?

 

[Mark W]

With an idle of 600 rpm giving you 5 strobes per second I wouldn't place too much emphasis on the knock seeming to be inm sync.

Cams don't knock, not do valvetrains. They may tick or tap, but not knock.

Most likely rod. Especially since it goes away when the firing cycle is de-energized. If it is a higher pitch sound at a faster rate, then it may be wrist pin or cracked piston. Not nearly as common though.

Pull the pan and expect to find a bad rod bearing. Or since pulling either #1 or #2 spark plug wire affects it, you may be looking at a bad main bearing. Check #1 main first (after the rods).


Mark...

 

[Cascade Cruiser]

could you have a bad exhaust leak?

Funny you ask...I actually do have an exhaust leak that acts up when the motor is under load (I'm thinking it's at the EGR tube/exhaust manifold gasket). However, the "engine knock" is more of a mechanical sound and definitely distinct from the exhuast leak.

 

[Cascade Cruiser]

Most likely rod. Especially since it goes away when the firing cycle is de-energized. If it is a higher pitch sound at a faster rate, then it may be wrist pin or cracked piston. Not nearly as common though.

Pull the pan and expect to find a bad rod bearing. Or since pulling either #1 or #2 spark plug wire affects it, you may be looking at a bad main bearing. Check #1 main first (after the rods).

Thanks for the advice. I think it's narrowed down to #1 rod bearing, #2 rod bearing, and/or #1 main.

I've never worked on the bottom end of a motor before. Is there enough clearance to replace a main bearing w/o removing the crank? Do main bearings need to be replaced as a set (all 4)? I was going to replace all 6 rod bearings if one of them is the culprit.

Thanks

 

[Mark W]

If you have one bad main, it is likely that they're all "not so good".

Realize that there is a good chance that the crank surface will be damaged too.

You can replace the mains without pulling the crank. You have to remove all of the main bearing caps and let the crank hang a little (it doesn't shift much, don't expect to be able to see clearance change). Then you can rotate the bearings around the crank. Tough with the #3 main becuase of the thrust bearing gripping the block. Easy to damage the bearings if you are not careful.

*IF* the main bearing has spun in the journal, then the block can not be repaired without line boreing. Most machine shops can not line bore a 2F due to the length and the different size main bearing journals.


Mark...

 

[Cascade Cruiser]

Thanks for all the information. I'm going to pull the pan this weekend and investigate. I will post back with the results. I'm crossing my fingers that the crank is in OK shape!

 

[Cascade Cruiser]

Ok, I'm stumped.

I tore down the bottom end and found a few surpises. Rod bearings and journals were in good shape and oil clearance was within spec. Main bearings and journals were in good shape as well, although oil clearance was a little out of spec but did not exceed the "limit" specified in the FSM. I'm not sure how accurate the main bearing measurements were considering there was still oil in the block side of the bearing. All bearings were .050 mm undersize so I guess this bottom end was re-worked at some point. The cam lobes looked fine.

I lubed everything and put her back together with original bearings (didn't have .050 bearings available otherwise I would have put new ones in). Runs exactly the way it did before. I also realized that it DOES knock when #1 and #2 spark plug wires are disconnected. My mistake earlier, I was wrong in previous posts when I said the knock went away when pulling #1 and #2.

More poking around with the stethescope led me to the cam side of the bottom end, right near the fuel pump. So maybe it is the fuel pump after all. However, the proper spacer appears to be installed between the pump and the block, and I don't know how a fuel pump could be knocking so loud for so many miles without disintegrating. I guess it could be a pushrod?

So once again, any suggestions are greatly appreciated.

Thanks,

 

[Mark W]

If the mount for the oil pump (the one bolted to the side of the block from the inside) was unbolted during the rebuild, it has almost certainly be reinstalled slightly off from the original positioning. This will cause a knock from the oilpump/distributor.

About the only way to remedy this would be to SLIGHTLY loosen these two bolts and use the bolts themselves to attempt to shift the mount.

While the engine is running.

Hopefully you can achieve the original alignment and eliminate the knock.


Mark...

 

[Pin_Head]

Other possible noise sources could be the cam thrust washer/retainer and the timing gears.

 

[Cascade Cruiser]

Thanks for the additional suggestions. I'm going to take a closer look at the fuel pump and distributor because they are the easiest to access. Since the knock is coming from the front of the motor, the fuel pump is my number one suspect.

 

[Cascade Cruiser]

Ok, so it's not the fuel pump because I swapped pumps w/ my roommate's FJ60 and the knock was still there. Also the noise is concentrated at the front of the motor, away from the distributor.

It looks like Pin Head may be right all along w/ his cam theory. I'm thinking cam bearings, lifters, pushrods, timing gear.....is there anything else that could be making noise? Are the cam/lifters inspectable via the side cover that runs along the cam side of the block? I'm starting to get a little frustrated w/ major tear downs to chase this noise, but it sounds like one of these weekends I'll have to remove the radiator and pull the timing cover and take a look in there.

Thanks again for all the tips.

 

[Mark W]

A "knock" produced by the cam is usually going to come from the cam/crank gear. Damage to one to the teeth The rest of the valvetrain makes a higher pitch noise when it makes any noise. Tapping, not knocking.

A bad cam bearing would probably make this sort of noise too. But I've never encountered a failed or even seriously deteriorated cam bearing that was not accompanied by really really trashed rod/main bearings.


Mark...

 

[bigbrowndog]

When you had the conrod bearing caps off could you feel any excess movement in the gudgeon pin [conrod to piston connection, not sure what you blokes call it]?Did you check for this on all cylinders? cheers

 

[Buckwheat]

Wrist pin, mate, but I think you would get that noise on the top, when the piston reverses direction.

 

[bigbrowndog]

Wrist pin, mate, but I think you would get that noise on the top, when the piston reverses direction.

Fair enough, cheers
I thought the mains made more of a rumble sound.
The big ends made a deeper metallic clack or knock.
And the worn gudgeon pins made a lighter metallic clack at the end of each stroke.
If the spark plug wire is pulled off the gudgeon clack/knock will be reduced to a single softer clack when the piston is returning from the bottom of its stroke.

 

[bigbrowndog]

Guess I should have added not to over rev the motor with a spark plug wire off as when the piston returns from the exhaust stroke to the power stroke this is when the conrod is most venerable due to no downward pressure of the power stroke and with no spark this happens twice in the one cycle. Removing the plug wire will not reduce the big end knock if that is the noise.

 

[mtb_rider]

The main bearings do make more of a deep, pounding type knock, where rod knock is more of a clacking type of knock. However, worn wrist pins should make noise at the bottom and top of the stroke. I might be leaning towards a wrist pin or cracked piston skirt, especially if you find nothing in the valve train/cam/timing gears.