[AhuraMazda04]

Hey Guys:

New here. Have a 2006 Mazda Tribute with the 3.0 V6 with 120k on the clock that has a knocking/rough idling engine. Engine likely has a bad bearing(s) on the bottom. I'm not looking to keep the vehicle too long. Is it possible to change the rod and/or main bearings from under the vehicle without removing the engine? How difficult would it be to do?

I don't want to replace the motor because the vehicle is used very seldom and just around the block. I don't need it to be ultra reliable, just running properly.

How hard would it be to drop the oil pan and replace those bearings?

Thanks in advance.

Don't assume the worst. Has the engine been maintained? How does the oil look and is there a lot of blow-by? It could be a harmonic balancer or something else.

 

[AhuraMazda04]

shot a video of the engine performance and noises. smooth and slightly noisy at higher rpm (2000-3000) bery rough and noisy idle. thoughts?

https://drive.google.com/file/d/0B5sRAO ... sp=sharing

Sounds like the timing is off. Timing chain might be to blame.

 

[AhuraMazda04]

and here's another video...

https://drive.google.com/file/d/0B5sRAO ... sp=sharing

That doesn't sound like rod knock, more like wrist pin. It's a lighter noise. I still stand with the timing being off too. The ensioners are I believe to be hydraulic, if you ran out of oil that means no pressure; which means no tension; which leads to the possibility of a jumped chain and given that you are getting codes for the camshaft position sensor.... seems plausible.

 

[AhuraMazda04]

The tensioners are expected to last into the 100's of thousands of miles. If you had low oil pressure, it is possible that the tensioner(s) got out of place. They are(I think) designed with mechanical 'steps' such that as they wear, they walk up the step, and take out however much tension, the oil pressure coming along when running, and removing any more 'slack' as needed, and if they wear more, then they will get onto the next 'step', thus keeping the chains mostly taught even with minimal pressure.
That said, I suspect it could happen. I did NOT listen to the noises.

A spun bearing can be perfectly quiet. How it does it, I have no idea. The rearmost main on a Ford 390 spun, no noise, no particular reason, and the rear main seal leaked heavily. No external signal the bearing was spun until I took it apart to replace the rear main seal. The bearing cap weighs 2-3 lbs, and is held in place by bolts about the size of my fingers... and it spun... no symptom except oil leaking... It got all new main bearings, and was just as quiet when done as before.
tom

I understand that it's not common but it's not unheard of with this engine and lack of oil can cause an engine to do strange things. It is the only explanation I could think of linking the camshaft position sensor and the manifold absolute pressure. I doubt that both would randomly fail at the same time. If timing was off it would explain both of these perfectly.

 

[AhuraMazda04]

update...got the car back together and runs smoooooth! thanks to all who helped on here. wanted to post the resolution. no valve damage but definitely feel this engine is interference. guess i got lucky. it was just the tensioner that failed. in particular, the ratcheting mechanism that prevents the piston from falling back failed.

really really really appreciate all who helped here- couldn't have done it without you guys!

Glad it wasn't any damage! I knew it had to be the timing chain...