Hi, my son has a 2003 Mazda 6S (6cyl) that just developed what I think is rod knock. At idle there is no knock and oil pressure looks ok. When rpms increase a loud knocking develops.
I am going to drop the pan and inspect the bearings etc. if the bearing do show damage and the journals look to be in good condition I am going to change the bearings while the motor is in the car. I know this is not the “right” way to fix this but if it works it is better than spending a few thousand on a motor.
my question is, normally I would always change the rod cap bolts when I do this but the local parts shops have said that rod bolts are not available. Does anyone have a source or should I put it back together using the old bolts?

thanks
mark

 

Just saw this post. How did the bearing replacement go?

 

Hi Bones.
The long story
There was a rod knock in cyl #1. The good news is that you can drop the pan with minimal work. Upon inspection the rod bearing show some damage. There was very light scratches on the crank journal but the rod looked ok. I measured the journal and tried to sand and polish the crank while measuring frequently to ensure that it was staying round and making sure I didnt take too much material off. I used plastigage for the final measurement. The clearance was on the high side of the tolerance so I didnt want to go any further. I reassembled and it ran great for about 4 weeks. Then the knock started coming back. I knew it was a gamble since the crank journal was not perfect.

Short story is it failed....

 

Ok thanks for the info. Yeah judging by the sound I am hearing I'm guessing my crank is toast. Did you scrap the car or get another engine or what?

 

Bones,
Have you verified that it is a rod knock?

We have been driven daily with the rod knock. It doesnt seem to be getting worse but who knows. We add a quart of Lucas at every oil change to change the viscosity a bit.

Used motors with low mileage are about $1600 (plus) so I may pull the motor and just replace the crank and bearings as this would only be about $500.

 

I don't know how to verify it for sure. Afraid to even start it. The noise is really bad and I'm afraid it will throw a rod thru the case and ruin the whole motor??? It's a heavy thud thud thud. I'm thinking if I could yank the motor myself and replace the crank and bearings it would be worth doing.

 

It sounds like the motor is already toast. At this point the best/cheapest/fastest solution is to buy a used motor and drop it in. Keep us posted.

 

Yeah the problem is finding the time to do it plus I've never worked on these type of engines before. If I had the time I'd like to do a total rebuild on it and trick it out. Otherwise I like the car.

 

Shipo is right. The correct course of action is either get a used engine or have yours rebuilt. Depending on the year of your car, replacing the motor may cost more than the car is worth.

Good luck and keep us updated.

 

The thing about replacing the motor costing more than the car is worth. While that in many cases may be true, that in no way means it isn't an economically viable solution. By this I mean, if the salvage value of a car with a bad motor (and/or transmission) is say, $500, and the cost of putting a used motor in is say, $2,000, then can you buy something at least as nice as the existing car for that $2,500? If the car is in otherwise good condition, and if comparable cars cost more than $2,500, then spending the $2,000 on the new engine is a bargain.